900 Wharves and Moorings

AbstractSection 900 introduces basic layout and design considerations, including design load calculations, for tanker wharves and offshore moorings. The guidelines are written for entry-level engineers or experienced engineers working outside their discipline or area of expertise. These guidelines can also be used for barge facili-ties. This section does not cover the design of piping and other facilities such as vapor recovery systems.

Engineers can use this section to define the number of berths and layout of a tanker wharf for given condi-tions, make preliminary estimates of breasting and mooring loads, make preliminary decisions on construction materials, specify wharf loading arms, and initially size a single point mooring buoy and its mooring system.

Contents Page

910 Background and Basic Data 900-3911 Industry Codes and Practices912 Environmental Considerations920 Tanker Wharves 900-5921 Required Design Information922 Wharf Location and Layout923 Types of Construction

924 Breasting System Design925 Mooring System926 Loading Platform and Loading Gear

927 Utilities and Other Facilities930 Offshore Moorings 900-35931 Mooring Types

932 Basic DataChevron Corporation 900-1 December 1993

933 Mooring Forces934 Chain and Anchorage Design

900 Wharves and Moorings Civil and Structural Manual935 Ship-to-Buoy Attachment936 Underbuoy and Floating Hoses937 Miscellaneous Design Considerations

938 Installation and Operation940 Corrosion Protection 900-68941 Cathodic Protection

942 Coatings950 Glossary of Terms 900-69960 Model Specifications and Standard Drawings 900-71961 Model Specifications962 Standard Drawings970 References 900-71971 Terminals and Wharves972 Single Point MooringsDecember 1993 900-2 Chevron Corporation

Civil and Structural Manual 900 Wharves and Moorings910 Background and Basic DataThis section lists pertinent industry codes and practices, and reviews the major considerations in wharf and offshore mooring design.

911 Industry Codes and PracticesThis section lists the applicable codes used for design of steel and concrete tanker wharf structures and offshore moorings.

Manual of Steel ConstructionAmerican Institute of Steel Construction (AISC). Includes: AISC Specification for the Design, Fabrication and Erection of Structural Steel for Buildings.Structural Welding CodeAWS D1.1 American Welding Society (AWS).Building Code Requirements for Reinforced Concrete. American Concrete Institute (ACI 318, Latest Edition).Oil Companies International Marine Forum (OCIMF) Guidelines and Recommendations for Safe Mooring of Large Ships at Piers

and Sea Islands

Design and Construction Specification for Marine Loading Arms Guide to Purchasing, Manufacturing and Testing of Loading and Discharge

Hoses for Offshore Moorings Mooring Equipment Guidelines

Hawser Guidelines

SPM Hose Ancillary Equipment Guide

Buoy Mooring Forum Hose Guide

Recommendations for Equipment Employed in the Mooring of Ships at Single Point Moorings

Single Point Mooring Maintenance and Operations Guide

U.S. Coast Guard, Department of Transportation. (Applicable publications that address local requirements for marine transport, terminals, and navigation.)API RP-2P, Analysis of Spread Mooring System for Floating Drilling Units.

ABS, Rules for Building and Classing Single Point Moorings.

API RP-FP1, Recommended Practice for Design, Analysis, Maintenance of Moor-ings for Floating Production Systems.Chevron Corporation 900-3 December 1993

900 Wharves and Moorings Civil and Structural Manual912 Environmental Considerations

DesignDesign decisions for tanker wharves and offshore moorings must be made while bearing in mind the importance of protecting the environment. The potential for accidental discharge of hydrocarbons into the marine environment is always present by the very nature of a tanker terminal. The fact that significant accidental discharge occurs so rarely attests to the efficacy both of operational procedures and the designs of the Company marine terminals. Proposed new facilities should draw heavily on the successful experience of the Company both for operations and design.

The following agency or operational-related concerns and requirements may impact terminal designs, but a detailed discussion is not within the scope of this guideline.

U.S. Army Corps of Engineers Coast Guard regulations Spill contingency plans Deck drainage and waste handling Tanker emissions Support and maintenance craft impacts Testing of terminal lines

The potential environmental areas and concerns that frequently have to be addressed as a part of a wharf or mooring design are listed below for dredging and construction operations.

Dredging Operations The actual dredging operation will disturb marine life within a localized area

around the work.

Bottom sediments to be dredged may contain metals or other chemical compounds. The dredging operation disturbs these materials and a portion of the sediments will be resuspended in the surrounding waters. The actual impacts on marine life are not well understood and are very controversial. Studies report such extremes as growth stimulation by nutrients released to the surrounding water to toxicity from poisons.

Getting approval on the disposal of dredged spoils can be difficult and adequate lead time must be scheduled.

Offshore disposal. The concerns mentioned above regarding disruption to marine life (loss of feeding grounds) and possible undesirable material in the spoils applies to disposal.

Onshore disposal. Even with a dedicated dredge spoils disposal area, there are a number of concerns to be addressed. These primarily relate to getting sufficient settlement time for the spoils material so that the specified limi-tations on suspended solids in the final runoff are met.December 1993 900-4 Chevron Corporation

Civil and Structural Manual 900 Wharves and Moorings Permits are typically required for both dredging and disposal operations.

Construction Operations Air emissions that are produced by construction equipment must be addressed.

Noise emissions, particularly from pile driving operations, may be a problem if the facility is close to residential areas. Certain activities may need to be limited to specific work hours.

Fuel transfers to equipment can be of major concern. In some cases special impounding is required to contractors floating equipment in order to refuel at the site.

Accidental or deliberate discharge of prohibited materials into the surrounding waters must be prevented. These materials include hydrocarbon spills, restricted vessel discharge, construction-type materials, or rubbish. Strict rules governing the contractors activities must be issued and enforced.

920 Tanker WharvesThis section outlines design information needed and tells how to select a site and lay out a wharf. It describes the choice of materials for wharf construction and gives design details for breasting and mooring systems, loading platform, loading gear, and utilities. Figure 900-1 describes six Company tanker wharves with associ-ated construction costs.

For information on completing a tanker berthing impact analysis, see Appendix D of this manual.Chevron Corporation 900-5 December 1993

900 Wharves and Moorings Civil and Structural ManualFig. 900-1 Six Company Wharf Structures for TankersDecember 1993 900-6 Chevron Corporation

Civil and Structural Manual 900 Wharves and Moorings921 Required Design InformationThe following items are presented as a checklist of information that should be obtained or developed during the course of a wharf design project. The extent of information required for a particular item varies from case to case.

Functional Requirements1. Number of berths.

2. Range of tanker sizes for each berth. (Obtain such tanker dimensions as overall length, parallel mid-body length vs. draft, position of manifold flanges, in addi-tion to tanker displacements.)

3. Water depth requirements.

4. Mooring and breasting dolphin arrangements.

Product Requirements1. Types of products to be handled and their fluid properties.

2. Design loading and/or unloading rates.

3. Ballast handling requirements.

Meteorological Data1. Wind conditions.

a. Wind roses (frequency of occurrence by velocity and direction) for each month.

b. Maximum wind velocity and directionannual basis and also 50- or 100-year return period.

2. Extreme temperatures.

3. Visibility conditions for each month.

Oceanographic Data1. Wave conditions

a. Wave roses (frequency of occurrence by height and direction) for each month. Also swell conditions by height and period (by months).

b. Maximum wave height with direction and period for 50- or 100-year return period.

2. Astronomical tide ranges for neaps and springs. Class of tidediurnal, semi-diurnal.

3. Storm surge or tide in feet.Chevron Corporation 900-7 December 1993

900 Wharves and Moorings Civil and Structural Manual4. Current velocities and directions. Field measurements are typically required. A survey of the local current behavior is helpfultide rips, eddies, shear lines, for example.

5. Harbor oscillation or seiche action if any. Again, field measurements may be required.

6. Sand movement if any.

7. Ice conditions including strength, thickness, and approach direction.

Sea Bottom Conditions1. Soil borings and soil tests. Extent of coverage and nature of tests will vary with

type of structure proposed and also with type of soils encountered. The poten-tial for scour or filling in should be checked. With this data, design criteria for anchors and piles or other foundations can be developed.

2. Obstruction surveys. A wire-drag survey to locate hidden navigation obstruc-tions, rock out-crops and coral heads, for example. Side-scan sonar surveys are also very helpful in assessing bottom conditions.

3. Acoustic sub-bottom profiling to extend range of soil survey.

Earthquake Design Requirements1. Earthquake zone for site.

2. Potential for tsunami action at site.

Operational Requirements/Permit Requirements1. Cargo loading systemhose versus arm.

2. Mooring gear requirementshooks, posts, and/or pulleys.

3. Utility system requirements.

4. Means of personnel access.

5. Communication system requirements.

6. Office, warehouse, washroom needs.

7. Tugboat and mooring launch needs.

8. Safety equipment requirementslife rings, Jacobs ladders, etc.

9. Fire protection and emergency evacuation.

10. Oil spill clean-up requirements, spill booms, etc.

11. On-deck spill containment facilities.

12. Navigation aids (Ref.: U.S. Coast Guard).13. Drainage needs.December 1993 900-8 Chevron Corporation

Civil and Structural Manual 900 Wharves and Moorings14. Cargo hose handling and storage.

922 Wharf Location and LayoutWhen planning a Company wharf, it is important to have the counsel of Chevron Shipping from the outset. Agreement as to the design range for tanker displace-ments and dimensions, design wind, current and wave forces, critical water depths, clearances, operating limitations and mooring arrangement is vital.

Site SelectionThe location selected for a tanker wharf should be based on the following:

1. Accessibility to point of need, e.g., refinery, oil field or terminal.

2. Protection from open-sea exposure.

3. Required water depth.

4. Tanker maneuvering room.

5. Prevailing wind, wave, current and ice conditions.

6. Construction problems presented by soil and oceanographic conditions.

Where an otherwise attractive wharf site is exposed to wave action, thereby limiting the period for safe tanker operation, the use of offshore moorings (conventional spread moorings and single-point moorings) should be considered as well as the possibility of breakwater construction.

Wharf LayoutA tanker wharf must be laid out in a manner that permits the mooring lines to hold the tanker in the correct position with respect to the loading platform. Mooring points should be located as nearly as possible symmetrically about the center line of the wharf. Mooring line arrangements should be such that the mooring lines range from 115 to 165 feet in length, with parallel lines as close as possible to the same length.

The overall length of the wharf is controlled by the maximum length of tanker to be handled. This distance should be such that the bow and stern mooring lines make an angle no less than 45 degrees with the axis of the wharf for the maximum size tanker.

Guidelines and recommendations for mooring large ships at fixed structures are presented in the Oil Companies International Marine Forum (OCIMF) publication, Guidelines and Recommendations for the Safe Mooring of Large Ships at Piers and Sea Islands, (Reference 8). This reference represents the industry standard and should be continuously reviewed during design of a tanker wharf.

The major components of a wharf are: 1) mooring structures, 2) breasting struc-tures, 3) loading platform, 4) pipeway/causeway, and 5) connecting walkways. Figure 900-2 shows a typical wharf layout. A mooring structure is any element that Chevron Corporation 900-9 December 1993

900 Wharves and Moorings Civil and Structural Manualholds the ships mooring lines to restrain the ship. Such a structure can be as elabo-rate as a framed steel platform or as simple as an anchored buoy. A breasting element is a structure that resists the motion of the tanker normal to the axis of the wharf. These elements are usually designed to withstand the impact of a tanker during docking. The loading platform supports the cargo transfer piping plus the gear necessary to make the connection to the tanker manifold. Finally, the pipeway/causeway connects the wharf to the shore facilities, and the connecting walkways provide access from the loading platform to the mooring and breasting structures. Where the wharf is well offshore and no solid cargo is to be handled, it can be economical to use submarine pipelines in place of the pipeway/causeway. Without a causeway, however, rough sea conditions can restrict access to the loading platform and lead to operational problems.

The first three of these components can be combined in a wide variety of ways to suit a particular location. For example, a single, quay-like structure that combines all components in one unit could be used in relatively shallow water, whereas a multi-element structure may be preferred in deeper water.

The wharf should be oriented to minimize mooring loads. Typically this means aligning the wharf axis with the direction of the current. In some areas with very weak currents, it may be advisable to set the wharf parallel to the prevailing wind direction. In harbor basins known to be subject to surging, it may be possible to locate the wharf at a spot where surge action is minimal.

923 Types of ConstructionTanker wharves have been constructed of timber, concrete and steel or a combina-tion of these materials. Economics and service requirements determine the best material.

Fig. 900-2 Typical Wharf LayoutDecember 1993 900-10 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsTimber ConstructionTimber has proven successful in light-duty wharves. The term light-duty, of course, is relative and must reflect tanker size, berth occupancy, and wharf expo-sure. For example, the Point Orient Wharf at Richmond, before its modification in 1985, was all-timber and handled four to five tankers per month ranging in size up to 29,000 DWT. In 1985, a steel-and-concrete fender system and mooring dolphins were added to increase the wharfs capacity to 40,000 DWT.

Timber construction can also be used for the loading platform portion of heavier-duty structures if the mooring forces and tanker impact loads are handled by other structures.

Timber elements should be pressure treated with wood preservative to provide some resistance to marine borers, insects, and decay fungi. Pressure treatment should conform to American Wood Preservers Association (AWPA) Standard C18, Standard for Pressure-Treated Material in Marine Construction. Handling require-ments and field treatment of cuts and holes should be in accordance with AWPA Standard M4, Standard for the Care of Preservative-Treated Wood Products.To stop attack of marine borers, concrete jackets (or PVC wrap) have been applied successfully from below the mudline to above the tidal range.

Timber has other uses in wharf construction. Mooring dolphins can be constructed out of a cluster of 3, 7 or 9 individual piles strapped together by cable-windings. The strength of such dolphins depends on the water depth and soil conditions, but they are generally limited to design mooring line pulls of less than 20 kips. At the Empire Terminal, creosoted Southern Yellow Pine is used as a rubbing surface on the loading platform fender designed for barges. Tropical hardwoods such as Green-hart and Azobe have been used in this service at the BORCO wharves to improve service life. The use of these hardwoods is limited, however, because they are expensive and difficult to work.

Timber design, in the absence of any governing local code, should conform to the National Design Specification for Stress-Grade Lumber and its Fastenings, published by the National Forest Products Association.

Steel ConstructionSteel is most often used for the primary members in major tanker wharves. These wharves can be of open-construction (tubular jacket structures supported on steel pipe piles), or they can be solid, quay wall-like structures using sheet-pile cells. This latter type of construction is more suited to freight handling wharves and is less frequently used where the wharf is strictly for tankers.

The four sea island berths at the BORCO refinery are examples of steel construc-tion in deep water. In this design, the mooring dolphins are rigidly trussed towers; the breasting dolphins are flexible elements using high-strength steel; while the loading platforms are special jack-up type barges. Catwalks supported on light, tubular trusses provide access to the various elements. Sub-sea pipelines connect the wharves to the refinery tankage.Chevron Corporation 900-11 December 1993

900 Wharves and Moorings Civil and Structural ManualSteel design, in the absence of any governing local code, should conform to the Specification for the Design, Fabrication and Erection of Structural Steel for Build-ings, published by the American Institute of Steel Construction. To prevent mois-ture penetration, all pipe, plate, and structural shape intersections should be completely seal welded. Structural steel members which can retain water should be avoided or provided with adequate drainage to minimize corrosion.

The construction of new large tanker wharves often involves the use of tubular steel members. Tubular design and pile design should conform to the American Petro-leum Institutes Recommended Practice (RP 2A) for Planning, Designing, and Constructing Fixed Offshore Platforms, (Reference 10).Direct connections between tubular members require special design consideration to insure proper behavior. Two problems are especially important. First, where a tube of smaller diameter is connected to the outside of a larger diameter tube (with no stiffeners or gussets), it is important to be sure the wall thickness of the larger tube is thick enough to resist the very high local stresses that will be induced. Second, in earthquake areas, it is important to detail the connection so it can carry high strains (strains several times greater than those at nominal yield in the joint). The design of tubular joints should be in accordance with API RP 2A.Steel piles are often used for wharf structures because they are resilient, light to handle, capable of being driven hard to deep penetration and readily cut off or extended in the field if required. Tubular piles are preferable to H-Section because they induce smaller drag forces. Tubular piles may be driven closed-ended to develop end bearing resistance over the pile base area. For hard driving conditions (e.g., gravelly soil lenses), open-ended piles should be used. For easy to moderately easy driving conditions, no shoes or other strengthening devices at the pile toe are required. Where open-ended piles must be driven through resistant layers to obtain deeper penetration, or where they must be driven into rock, the toes can be strength-ened by welding on a steel ring. Alternatively, cast alloy cutting shoes are available. Associated Pile and Fitting Corporation, for example, markets a variety of shoes for both tubular and H piles. Internal rings (or inside flange cutting shoes) should be used where necessary to develop the full frictional resistance of the pile shaft.

Concrete ConstructionConcrete has wide application in marine construction because of its durability and cost advantages. In wharf construction, concrete is often precast (piling and deck panels, for example) to simplify handling by marine equipment.In situations where a large deck area is desired and where the water depth is in the 30- to 50-foot range, precast, prestressed concrete piles can be used economically. Because these structures are rigid, special fenders are needed to handle ship impact loads. The Berth 4 addition to the Richmond Long Wharf is an example of this type of construction.

In the absence of any local governing code, concrete design should conform to the American Concrete Institutes Building Code Requirements for Reinforced Concrete (ACI 318) and its Guide for the Design and Construction of Fixed Offshore Concrete Structures (ACI 357R).December 1993 900-12 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsPrestressed concrete pile design should conform to the Prestressed Concrete Insti-tutes Recommended Practice for Design, Manufacture, and Installation of Prestressed Concrete Piling.

The steel reinforcing in concrete wharf structures must be protected from corrosion by proper construction details and construction practice. Reinforcement in regions exposed to salt water or salt spray should be given special concrete cover: 3 or 4 inches for cast-in-place concrete and 2-1/2 inches for precast concrete. Adequate steel should be provided for the control of temperature and shrinkage cracking. Most important of all is to use a good, sound, durable concrete mix. Minimum strength should not be less than 4,000 psi at 28 days and air-entrainment should be provided. ASTM Type II cement should be used. The use of epoxy-coated rein-forcing steel should also be considered.

924 Breasting System DesignThe basis of fender design is the energy which the fender system must be able to absorb during the berthing operation. The breasting structure is designed for the reaction force that exists when the energy absorbing elements are deformed to the extent that their stored potential energy equals the design kinetic energy. The struc-ture must be able to resist wave forces as well, but in virtually all cases, tanker breasting forces will control design.

The two most commonly used methods of determining the design kinetic energy are the kinetic method and the statistical method.

Kinetic MethodThe kinetic approach is based on theoretical consideration of the ships kinetic energy. The kinetic energy of the berthing ship, assuming the ship moves in pure translation, is:

(KE)ship = m (v)2(Eq. 900-1)

where:m = mass of the ship

v = approach velocity

The energy to be absorbed by the fender system is based on the ships energy, but the calculation is complicated by other considerations including the inertia of the water moving with the ship and the partial energy dissipation/absorption by elements other than the fender system. This approach is discussed in more detail in Appendix D of this manual.

The kinetic approach, although widely used, has a number of shortcomings (e.g., the large number of assumptions involved in establishing design velocity and energy modification coefficients). Accurate evaluation of the tanker approach velocity is especially important because the design energy is proportional to the square of velocity. For most locations, proper mooring practice calls for the tanker Chevron Corporation 900-13 December 1993

900 Wharves and Moorings Civil and Structural Manualto be brought to a complete stop at some distance off the face of the wharf and then to be pushed sideways (athwartship) by tugs until it comes against the breasting elements. Normally one of the breasting structures is contacted before the other. Fender damage occurs when tankers approach with accidentally high velocities. The design of breasting elements from an economic standpoint must assume that tankers will have a controlled velocity at the time of contact. It is not practical to design for abnormally high approach velocities. The design velocity should vary with the degree of exposure and the amount of current at the wharf. If the wharf is to handle barges as well as tankers, a higher velocity for the barges should be considered because of their unwieldy nature.

Statistical MethodThe statistical method is based on measurements of energies actually absorbed in fenders at existing terminals. Therefore, it automatically includes the effects of the energy modification coefficients listed above. The statistical method even includes the human factor, which contributes to the variability of tanker approach veloci-ties.

Information collected to date indicates that the most important parameters affecting fender energy are ship size and current conditions. The data analyses, therefore, concentrate on variation of the impact energies with these two parameters. Figures 900-3, 900-4, and 900-5 present the recommended design normalized energy to be used for fender design of three types of harbors. The graphs are based on analysis of accumulated data presented in Reference 4 of Section 971. Statistics used in the analysis of the three types of harbors included in Reference 4 follow.

Fig. 900-3 Design Energy Coefficient, Harbor Type ADecember 1993 900-14 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsFig. 900-4 Design Energy Coefficient, Harbor Type B

Fig. 900-5 Design Energy Coefficient, Harbor Type CChevron Corporation 900-15 December 1993

900 Wharves and Moorings Civil and Structural ManualHarbor Type A. Well protected against waves, no current, sufficient tugboat running assistance available.

Harbor Type B. Well protected against waves but exposed to moderate (2-4 knots) current parallel to berth.

Harbor Type C. Well protected against waves, but exposed to currents running in directions significantly different from the orientation of berth.

The recommended design kinetic energy for each primary breasting element is:

(KE)Design = Ceff(W)(Eq. 900-2)

where:(KE)Design = design Kinetic Energy, ft-lb/1000

W = tanker displacement at time of mooring, long tons/1000

Ceff = statistical energy coefficient, kip feet per 1000 long tons (2240 pounds per long ton). The coefficient will depend on wharf expo-sure, ship displacement, and desired reliability.

For a receiving wharf, the design displacement W will usually be for full tanker displacement. For a shipping wharf, the displacement may be for a ballasted tanker. However, shipping wharves which are used for topping off should be designed for the highest vessel displacement expected to berth.

It should be emphasized that the energy coefficient design graphs are based on limited berthing data from a limited number of locations for fully loaded vessels. Until more measurements are incorporated in the design graphs, considerable judg-ment will be needed to select an appropriate design energy. This is especially true for designs in very exposed locations (Type C Harbors) for which little data are available.

Rotterdam, British Petroleum Berth 1 461 ArrivalsRotterdam, British Petroleum Berth 2 526 ArrivalsEsso Berth Kalundborg, Denmark 166 ArrivalsTorshamnen, Gotenburg, Sweden 1916 ArrivalsTotal Data Type A: 3069 Arrivals

Gulfhavn Stignaes, Denmark 149 ArrivalsBritish Petroleum Berth, Finnart, UK 270 ArrivalsWilhemshafen, NWO Berth 659 ArrivalsTotal Data Type B: 1078 Arrivals

British Petroleum Berth, Kent, UK 578 ArrivalsTotal Data, Type C: 578 ArrivalsDecember 1993 900-16 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsReference 4 cautions that due to the lack of a strong data base, statistically derived energies should be compared with those predicted by the kinetic method. Reference 4 also presents a more rigorous statistical procedure for determining risk and the statistical distribution of fender energies based on an assumed distribution of ship sizes. The extent of analysis appropriate for a particular design should be evaluated by the designer.

Because of their increased freeboard, partly laden vessels are more easily influ-enced by wind load, thereby making them more difficult to control. However, the scarce published data for partly laden vessels do not show appreciable differences in design energy for partly laden and fully laden vessels at design risk levels (Refer-ence 11 of Section 971).

RiskThe statistical behavior of fender impact energies requires that the designer explic-itly consider the probability (risk) that the selected fender energy will be exceeded. The assignment of acceptable risk is ultimately the responsibility of the owner of the facility, based on advice from the designer. The following should be considered:

1. The number of berthings expected during the life of the fender.

2. Economic consequences of a shutdown due to damage. A one-berth facility may require a lower risk level than a multi-berth facility.

3. The expense of performing repairs compared to the initial investments involved in increasing the capacity of the fender to an energy value with a small risk.

For comparison, past Company practice has labeled design values with an exceedence probability of 1 in 500 berthings (0.2%) as Low Risk and 1 in 100 berthings (1%) as Moderate Risk.

Frictional ForcesIn addition to forces perpendicular to the fender panel, the fender system must be designed to resist frictional forces in the plane of the panel. Frictional forces should be obtained from Equation 900-3 and applied in any direction in the plane of the panel that creates maximum stresses in the structural components.

Ff = (N)(Eq. 900-3)

where:Ff = design frictional force, lb.

= coefficient of friction between the ships hull and the fender panel (Typically, 0.3 < < 0.4)

N = maximum horizontal normal force on the fender panel, lb.Chevron Corporation 900-17 December 1993

900 Wharves and Moorings Civil and Structural ManualFender Design: GeneralThe design kinetic energy from Equation 900-2 is taken by the breasting elements, which usually transfer this energy of movement into stored potential energy. This fender structure must, therefore, be designed to carry a potential energy equal to the design kinetic energy as follows:

(PE) Fender = (KE) Design(Eq. 900-4)

The amount of stored energy in a structure is equal to the area under the load-deflec-tion curve of the structure. In a linear, elastic system, potential energy is given by:

PE = 1/2 (K) (X)2(Eq. 900-5)

where:PE = potential energy, kip-ft.

K = spring constant of the system, kip-ft.

X = deflection of the fender, ft.

Fender Types and Breasting Dolphin DesignThe primary design problem for a wharf fender, therefore, is to maximize deflec-tion without overstressing any of the structural members. Current practice for wharves designed to handle tankers over 40,000 DWT is to insert special rubber units in the structure between the fender panel and the primary support structure or breasting dolphins. Figure 900-6 shows some common rubber fender units. The average service life of rubber fenders is about 25 years. The size and type of rubber units should depend upon the rigidity of the structural system to which they are attached.

It is critical in fender selection that the fender absorb a large amount of energy while transmitting a relatively small reaction to the wharf structure. The fender manufacturers have different hardnesses of rubber available in various fender sizes. Mid-range rubber hardness is desirable; the harder rubbers, while absorbing more energy, transmit a larger reaction to the wharf structure, and the softer fenders have not been as durable.

The rated deflection of rubber fenders more commonly used today ranges from 45 to 55% of the fender length in the direction of loading. The maximum reaction load, however, does not often occur at the rated deflection. Therefore, when deter-mining the load for which to design the structure, the entire performance curve for the fender should be observed. Often, a high load reaction occurs at approximately 20% deflection. Figure 900-7 shows a typical performance curve for a rubber fender unit.

The relationship between energy absorption and fender reaction of the buckling fenders is non-linear. That is, the reaction may be increasing faster or slower than the fenders ability to absorb energy. Because of this non-linear relationship, consid-December 1993 900-18 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsFig. 900-6 Rubber Fenders

Fig. 900-7 Typical Rubber Fender Performance CurveChevron Corporation 900-19 December 1993

900 Wharves and Moorings Civil and Structural Manualeration should be given to compatibility of safety factors for the structure and fender. This issue is discussed in detail in Section 2.2.6 of Reference 4 (Section 971). The possibility of providing extra energy absorption capacity in the fender should be considered as part of the overall assessment of safety factors in design loads and allowable stresses.

The performance of these fenders will be altered depending on the angular approach of the tanker on the fender. Fender manufacturers offer methods to analyze fender systems for different angles of approach. The fender connection details as well as the breasting structure must be able to handle approach angles (included angles between tanker side and fender panel surface) of at least 10 degrees. This angle may be smaller for ULCCs and VLCCs.

Another common practice is to use flexible tubular piles of high strength steel (steel monopiles) cantilevering from the bottom as fenders. Rubber fender units are usually attached near the top of the monopile, between the pile and the dock struc-ture, to increase the energy absorbing capacity of the fender system. The use of high strength steel increases the importance of considering weldability and suscepti-bility to local buckling.

The performance of flexible dolphins has been generally good, except for several cases of localized buckling prior to attainment of the steel yield strength. This should be considered when selecting allowable stresses.

In case of accidental overload, the monopile should be designed to maintain its capacity through concentrated inelastic deformation. Portions of the piles where inelastic deformation is possible should be designed to compact section require-ments of API RP-2A (D/t < 1300/Fy, ksi). Other portions of the pile should be sized to preclude local buckling (D/t < 60).Spacing of Breasting Dolphins. The spacing of breasting dolphins, where isolated units are used, should be about one-third the overall length (LOA) of the largest tanker to be handled. To ensure contact with the parallel sides of the vessels to be moored, however, the spacing limits are generally set a minimum of .25 LOA and a maximum of .4 LOA for the largest vessel. If a wide range of tanker sizes is expected, then intermediate breasting dolphins must be spotted between the end dolphins. The parallel mid-body length of the smallest size tanker will control the spacing of these intermediate dolphins.

End Breasting Dolphins. Experience has shown that the most frequently damaged fenders are the end or corner breasting dolphins. Because of their critical exposure, an increase in design energy for these fenders may be justified.Fender Panel Design. Most fender systems include fender panels, frameworks that receive the ships impact and distribute the impact force over a large enough hull area so that no damage is done to the ship. The area of the fender panel must be large enough to hold the peak pressure on the vessel hull under 5000 psf and prefer-ably under 4000 psf. The fender panel should also be wide enough to span between the transverse frames in the tanker, if possible. For a 270,000 DWT tanker, this spacing can approach 20 feet.December 1993 900-20 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsThe contact surface of the fender panel must be covered with a material which offers a low coefficient of friction in order to reduce friction loads between the ships hull and the fender panel. Synthetic resins, high density polyethylenes, and other engineering plastics are commonly used for this purpose. Corrosion resistance should be considered when selecting materials for all hardware, including the fasteners which attach the wear pads to the fender panel. The preferred material for performance in immersion service is Monel; however, economics and availability issues often dictate use of alternate materials. Due to susceptibility to pitting of stainless steels and rapid depletion of zinc coating (galvanizing) in salt water, these materials are not recommended for immersion service. Company materials special-ists should be consulted when specifying materials for severe service environments.

It is important to specify beveled edges on the fender panel to prevent protruding plates in the vessel hull from hanging up on the panel and overstressing the fender. Fender panels should also be detailed to prevent mooring lines from catching on or running underneath the panel. If barges are expected to use the wharf, the panel design should prevent them from getting beneath the panel under all sea conditions.

When rubber fender units are used, it is usually necessary to install fender panel chains to transfer the shear and tension forces from the panel to the support struc-ture. Chain assemblies should be designed with a weak-link component (e.g., shackle) which will fail before structural damage occurs. Each assembly should also include a turnbuckle to facilitate length adjustments during construction and service life. The chains function as follows:

1. Tension Chainsresist rotation of the fender panel in a vertical plane caused by impact from a vessel at the bottom of the panel.

2. Load Chainssupport the dead load of the fender panels.

3. Shear Chainstransfer frictional forces in the plane of the fender panel.

Allowable Stresses. The maximum allowable stress under impact conditions for structural steel members in wharf construction should typically be limited to 1.33 times the basic design stress given in the AISC Specification for the Design, Fabri-cation and Erection of Structural Steel for Buildings. This factor is generally used for extreme environmental loading conditions. Fendering units which impart near maximum reaction forces with little deflection regularly subject structures to high forces (see Figure 900-7). The potential energy stored in a deflected structure also varies as the square of the bending stress. Therefore, using a very high allowable stress drastically reduces the amount of overload capacity or safety factor before reaching the ultimate bending capacity. This factor should be carefully considered when setting the allowable stress for design of breasting dolphins.

Rated Approach Velocity. When Equation 900-2 is used to determine the design kinetic energy, approach velocity is not explicitly considered. If the wharfs opera-tors require a design approach velocity, Equation 900-1 can be solved for V using the statistically based design energy. A typical maximum velocity is 0.4 to 0.5 feet per second. A higher or lower value may be appropriate depending on wharf expo-sure and operational requirements.Chevron Corporation 900-21 December 1993

900 Wharves and Moorings Civil and Structural Manual925 Mooring System

Mooring LayoutWharves must be laid out to provide proper orientation of mooring lines. Proper location of mooring structures is critical in optimizing the range of environmental conditions under which a vessel can be safely held at the berth. Typically, there are three functional classifications for mooring lines used to hold a tanker alongside a wharf (See Figure 900-8):1. Bow and stern lines.

2. Spring lines.

3. Breasting lines.

Reference 8 in Section 971 discusses recommended mooring principles and should be consulted when designing a mooring arrangement.

If adequate mooring facilities are made available for good breasting and spring line arrangement, a ship can be moored most efficiently virtually within its own length. Bow and stern lines, due to their long length and poor orientation, are usually not very efficient in holding a vessel at berth. The vertical angle of mooring lines should be kept to a minimum and always less than 25 degrees. Horizontally applied loads are more efficiently resisted as the mooring line gets flatter.

The spring lines hold the tanker in position longitudinally along the wharf and act as shock absorbing elements. The breasting lines hold the tanker from drifting away from the face of the wharf.

Mooring elements must be positioned to handle the expected range of tanker sizes. This often means that additional mooring dolphins must be spotted between the ones on the extreme ends of the wharf. It may be desirable to have the breasting dolphins also double as mooring dolphins to handle spring lines. Where practicalfor example, at wharves where berthing is only on one sidethe mooring dolphins should be set back from the breasting face of the wharf by as much as 100 to 150

Fig. 900-8 Mooring Line ArrangementDecember 1993 900-22 Chevron Corporation

Civil and Structural Manual 900 Wharves and Mooringsfeet, to limit the upward component of the mooring pull (tanker light) and also to reduce the navigational hazards.

In locations subject to large waves or seiches, the mooring system must be analyzed to ensure that it has enough elasticity to accommodate expected tanker displace-ments.

Design Mooring ForcesTheoretical mooring forces are calculated from the locations design wind, wave, and current that would act on the largest tanker for which the wharf is designed. These calculated (theoretical) forces are used to optimize the layout of mooring structures. Generally, calculated mooring line forces should be restricted to about 55 percent of the minimum breaking load (MBL) of the weakest line in the system.Figure 900-9 lists typical breaking strengths of typical mooring line components. The strengths of these components will vary slightly from one manufacturer to another.

(1) Hawsers commonly carried on Chevron Shipping vessels.

The theoretical mooring forces can be calculated as the sum of the current, wave/surge, and wind forces, in various tide and vessel draft conditions. CPTC (San

Fig. 900-9 Typical Breaking Strength of Mooring Line Components, Kips

Size (inches) Diam. Circum. Manila Polyester (Double Braid)

1 3 9 28.4

1-5/16 4 15 49

2 6 31 106

3 9(1) 64 229

4 12 105 396

5 15 606

Size (inches)

6x24 wire rope Galvanized Plow Steel

6x37 wire rope Galvanized Plow Steel

Cast Steel Stud Link Chain Die Lock Chain

1 57 64 84.5 129

1-1/2 126 142(1) 185 280

1-5/8 220(1)

2 220 248 322 488

2-1/2 492 744

3 693 1045

3-1/2 922 1383

4 1176 Chevron Corporation 900-23 December 1993

900 Wharves and Moorings Civil and Structural ManualRamon) maintains state-of-the-art analysis capabilities for the prediction of design mooring forces.

The design force for a mooring dolphin should be calculated according to the following equation:

PD = 0.55 N(S) PT(Eq. 900-6)

where:N = number of hawsers that may be run to the dolphin (consult

Chevron Shipping Co.)S = breaking strength of each hawser, kips

PD = design mooring force on the dolphin, kips

PT = theoretical mooring force on the dolphin in kips, calculated by subjecting the design tanker to the wind, current, and wave forces.

The stresses caused by this design force are at a working stress level (i.e., they are to be compared with soil or material allowable stresses).Figure 900-10 lists design mooring forces used for selected Company facilities.

Wind Forces. The design wind velocity should be the maximum velocity expected at the wharf site when a tanker is at berth. The design wind velocity should not, in normal circumstances, exceed 60 knots, because in practice the tanker must move off the wharf when a severe storm approaches.

Current Forces. In the preliminary design phase, studies should be made to deter-mine current velocities and direction. Where large currents are present, studies to determine primary current direction and variability may be justified. It is desirable to locate and orient the wharf so that the wharf face is within 2 to 3 degrees of the primary current direction. Mooring line forces are extremely sensitive to vessels moored at an angle to current direction.

Other Forces. Three other types of design forces should be mentioned: surge forces, ice forces, and wave forces Surge forces can arise in several ways; for example, in harbors with narrow channels, passing ships can cause oscillation in turning basins with resulting surging of moored ships. This happens along the Houston Ship Channel. A second type of surging occurs in harbors subject to seiching. Seiching is a long period (2 minutes to 10 minutes, typically) resonant oscillation of a bay, inlet or lake. Monterey Bay in California experiences seiching. For surging, the best solution (if the wharf cannot be relocated) is to run additional mooring lines and keep them snugged-up. The breaking strength of these extra lines, of course, adds to the mooring forces to be considered in design.

Ice forces can be a design factor in many areas of the world. Typically, broken, floating sheets of ice move down rivers or tidal estuaries and exert force against the tanker. A possible design condition is where an ice floe becomes trapped between the tanker and the wharf resulting in large form-drag forces being developed. December 1993 900-24 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsDesigners must rely on their judgment to determine if such a situation is a practical operating condition.

The structure should also be checked for wave forces, but tanker-induced forces almost always control.

(1) At BORCO, bow and stern dolphins handle both inside and outside berths.(2) At NIKISKI, ice forces plus very high currents control design. Spring lines run to combined breasting-

loading platform.

Fig. 900-10 Design Mooring Forces

Empire (1982)

150,000 DWT - Bow 550 kips/dolphin

- Breast and Stern 440 kips/dolphin

- Spring 440 kips/dolphin

Pascagoula - Berth 7 (1982)

100,000 DWT - Bow and Stern 250 kips/dolphin

- Breast 250 kips/dolphin

- Spring 160 kips/dolphin

Oak Point (1978)

40,000 DWT - Bow and Stern 400 kips/dolphin

- Spring 350 kips/dolphin

Borco - Berth 9 and 10 Jetty (1970)

Berth 10 (Outer Berth)

(400,000 DWT) - Bow and Stern 600 kips/dolphin (1)

- Spring (Outer) 350 kips/dolphin

(Inner) 185 kips/dolphin

- Breast (Outer) 650 kips/dolphin

(Inner) 350 kips/dolphin

Berth 9 (Inner Berth)

(120,000 DWT) - Bow and Stern 600 kips/dolphin (1)

- Spring 185 kips/dolphin

- Breast 385 kips/dolphin

Nikiski (1969)

80,000 DWT - Bow and Stern 230 kips/dolphin (2)Chevron Corporation 900-25 December 1993

900 Wharves and Moorings Civil and Structural ManualMooring EquipmentMooring hooks, bitts, bollards, and similar mooring equipment must be provided to hold the mooring lines. For major facilities, quick-release hooks are furnished to reduce the manpower needed to castoff a tanker.

These hooks should be proof tested to 150% of their design load. The hooks and their anchorages, depending on their configuration, may allow 180-degree hook rotation in the horizontal plane, but it is usually not practical to design for the 180-degree rotation. The variety of mooring line arrangements normally encountered at a tanker wharf does not subject these hooks to such rotation. In addition, the hooks should be able to handle loads acting at an angle of 30 degrees up from the hori-zontal. The trip mechanism must be able to release under full load and slack line conditions. Figure 900-11 shows some typical hooks.

Manufacturer catalogs should be consulted for the rotation and combined rotations available. Common suppliers of mooring equipment are Seebeck, Sugita and Wash-ington Chain and Supply. Coating of steel mooring equipment should be specified after consulting the Companys Coatings Manual. Good protection has been obtained with polyamide epoxy over inorganic zinc. An additional coat of aliphatic polyurethane is sometimes recommended for additional protection.

Fig. 900-11 Mooring EquipmentDecember 1993 900-26 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsTo simplify running of lines during mooring, motor-driven capstans should be spotted near the hooks or integral with them. These capstans should have a 12- to 15-inch diameter barrel and a minimum loaded pulling capacity of 1 to 3 tons with a motor geared to give a pull rate of 60 to 80 feet per minute. The capstan height (center line of hawser on capstan) should be 30 inches to 40 inches above the deck. Capstans should be provided with a mechanism which prevents free-wheeling of the drum if power is interrupted. All electrical equipment and motor enclosures must meet requirements of the applicable area classification.

Mooring pulleys should be considered for use on tanker wharves where a number of line limited ships (ships having an inadequate number of mooring lines) are expected to berth. These pulleys allow single mooring lines to be doubled up in order to adequately restrain the vessel at its berth. A typical quick-releasing pulley is shown in Figure 900-11.

926 Loading Platform and Loading Gear

Loading PlatformsThe loading platform supports the cargo transfer piping and is usually the opera-tions center for the wharf. In some installationsNikiski, for examplethe loading platform is also the primary breasting structure. More recently, the practice has been to provide separate breasting structures to isolate the loading platform from any tanker forces. The BORCO wharf is an example of this arrangement.

When the loading platform is designed as an isolated unit, wave and current forces (or ice) control the structural design. In designing to resist wave forces, it is vital to provide sufficient clearance between the crest of the design wave and the deck of the platform. For wharves in exposed locations, a design wave having a 50-year or a 100-year return period should be selected. The level of acceptable risk, as discussed in Section 924, should be considered when determining the design wave. For wharves in protected waters, the wave height is limited by the available fetch. This maximum wave is then the design wave. CPTC (La Habra) can assist with develop-ment of design environmental conditions.

The loading platform should provide sufficient work surface area to support all wharf operations other than mooring. Components may include the following:

1. Piping manifolds

2. Loading arms or hose mast plus hose storage room

3. Metering facilities

4. Operations office, washroom

5. Storage space

6. Fire protection equipment

7. Boat landingChevron Corporation 900-27 December 1993

900 Wharves and Moorings Civil and Structural Manual8. Gangway access to vessel

9. Oil spill collection equipment (spill booms)10. Vehicle access

11. Safety Equipment

If submarine pipelines are used to tie the wharf to the onshore tankage, the design and construction details for the pipeline risers are most important. Risers have proven to be the weak-link in too many installations. It is necessary to provide some positive means of support at the base of the riser as well as adequate attach-ments between riser and platform. In no case, however, should there be a support-clip welded directly to a fluid-carrying pipe. Always provide some form of rein-forcement pad designed to minimize stress concentrations.

The potential for scour around the base of the risers as well as around all other parts of the wharf should be considered. Scour is particularly troublesome on sand bottoms but can occur on any bottom. At the Nikiski wharf, which is founded on a coarse sand and cobble bottom, scour developed some years after initial construc-tion. The most practical solution to scour problems is to place a layered or graded filter-blanket of properly sized stone around the structure. This prevents currents from washing out the finer material.

For more information on submarine pipelines, see the Pipeline Manual. For pipe-line coatings, see the Coatings Manual.

Loading GearThe connection to transfer crude or products between the tankers manifold and the wharf piping is made with either cargo hoses or articulated metal arms. The choice here depends on the type of product, design load rate, tanker size, and berth occu-pancy. For crude loading, the maximum rates shown in Figure 900-12 are recom-mended.

Fig. 900-12 Recommended Maximum Load Rates, by Vessel Class

Vessel Class Maximum Load Rate

29,000 DWT 40,000 BPH

44,000 50,000

53,000 60,000

66,000 75,000

73,000 75,000

150,000 150,000

212,000 150,000

216,000 150,000

251,000 180,000

261,000 180,000December 1993 900-28 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsThese rates are based on the venting capacity of the various tankers. For tanker unloading, the peak rates are lower as they are governed by the ships pumps. Typical rates are 75,000 BPH maximum for 200,000 DWTs and 100,000 BPH maximum for 250,000 DWTs. For products transfer, the economical loading rate is usually lower than for crude. Typical product rates are in the 5,000 to 25,000 BPH range.

Marine Loading Arms. If it is economically attractive to design the marine terminal for the maximum rates shown in Figure 900-12, fully-articulated, swing-joint arms are justified. These arms are readily available in sizes up to 16 inches. Loading arms as large as 24 inches have been installed, but overall, their use is limited. In selecting loading arm size, caution should be used if flow velocities in excess of 30 feet per second are required. High flow velocities may cause cavita-tion, which can result in erosion damage, severe vibration, or fatigue failure in the loading arm.

Swing-joint arms should be designed with counter-balances or controls that limit the reaction force applied to the tanker manifold. This factor becomes increasingly important for large tankers because their great draft necessitates very long and, therefore, very heavy loading arms. The use of hydraulic control should be consid-ered on these larger arms. Figure 900-13 shows a typical loading arm. Company Specification CIV-MS-4074, Marine Loading Arms, and OCIMF Specification Design and Construction Specification for Marine Loading Arms should be consulted when preparing a specification for loading arms to be installed at a tanker wharf.

Hoses. For small, light-duty wharves, hoses can be used to make the piping connec-tion between tanker, or barge, and wharf. Hose cranes should be furnished to help lift and handle the hose sections. Hose for this application in conjunction with tankers should conform to the Companys Specification PIM-MS-2923. Hose obtained for use in connection between barges and wharves should conform to Specification PIM-MS-3133. These hose specifications will be in the Companys Piping Manual.

The hose handling areas, including the hose connection manifolds, should be provided with spill containment (concrete or sheet metal) deck and curbs and a collection tank or sump.

Arcing during Connection and Disconnection. To provide protection against arcing during connection and disconnection, metal marine loading arms and cargo hose strings should be fitted with an insulating flange or joint or a single length of non-conducting hose. This will ensure electrical discontinuity between the ship and shore. Cargo hose strings can be insulated with an insulating flange on the dock piping riser. All metal on the seaward side of the insulating section should be elec-trically continuous to the ship; that on the landward side should be electrically continuous to the jettys earthing system.Critical Dimensions. When specifying marine loading arms, it is necessary to record on the OCIMF data sheet (4.3 and 4.4) some critical dimensions relating to the berth and tankers. Figure 900-14 summarizes dimensional data used for existing Chevron Corporation 900-29 December 1993

900 Wharves and Moorings Civil and Structural ManualCompany terminals. These data can guide you in specifying these dimensions. The numbered items correspond to dimensional designations given in the OCIMF speci-fication.

For a new or modified terminal it is necessary to get a representative slate of vessels that could reasonably be expected to use the facility. This effort should also consider what type/size of vessels might be used in the future. The agreed slate of vessels is usually developed jointly with Chevron Shipping (Ports & Navigation) and the facility operators.

Defining the Marine Loading Arm Envelope. Prior to filling out the data sheets to specify the marine loading arms, an initial planning study should be made to define the required marine loading arm envelope as shown in Figure 2 and 3 of Reference 9 in Section 971.

The plot of vertical and horizontal tanker manifold positions with respect to the loading platform should identify the extreme envelope conditions, vessels at full draft at low tide, and vessels at light draft at high tide. With this plot completed, the following items can be considered:

Dimensional checks on the proposed geometry of the loading platform

Deck height Set-back from the berthing line

Fig. 900-13 Typical Marine Loading ArmDecember 1993 900-30 Chevron Corporation

Civil and Structural Manual 900 Wharves and Moorings(1) Value for surge fore and aft is combined with spotting allowance fore and aft of marine arm center line.(2) Heave not separately identified. In protected waters heave is generally judged to be small, and normal arm envelopes can accommo-

date it.

Distance from center line of the marine arm risers to the face of the loading platform

Spacing between loading arms

Identification of the extreme tanker manifold positions that will govern the geometry of the loading arms. Generally, the majority of tanker manifold posi-tions will conveniently fall within a reasonable envelope. However, careful consideration should be given to the few instances where a tanker manifold is positioned well outside the normal envelope. The additional cost to provide marine arms to meet an unusual, extreme case may not be justified. For such situations take into account the following:

What is the expected frequency of this vessel at this terminal, and is this expected to continue for a significant number of years?

Fig. 900-14 Dimensional Data for Selected Company Wharves

ItemOCIMF Reference

Richmond Berth 3

Richmond Berth 4

Pascagoula Berth 4

Pascagoula Berth 7 Empire

Tanker Sizes(DWT)

To 50,000 75-150,000 30-100,000 30-100,000 To 150,000

Arms (qty-size)

2-8", 4-12" 2-12", 3-16" 1-8", 1-10" 2-12", 2-16" 1-10", 2-16"

PrimaryService

Products Crude Products Crude Crude

Surge(1)

Fore & Aft4.3 d. & e. 7' & 7' 7' & 7' 7' & 7' 7'6" & 7'-6" Not avail.

Sway 4.3f 7' 7' 3'-0" Not avail. Not avail.

Heave atmanifold

4.3g.&h. (2) (2) (2) (2) (2)

Top ofplatform to LLW

4.4.a Approx 16' Approx 25' 12'-6" 18'-6" Approx 15'-10"

Loading plat-form face to berthing line

4.4b 8'-0" 7'-7-1/2" 3'-6" 5'-0" 5'

Loading plat-form face to center line of risers

4.4c 9'-0" 10'-0" 7'-6" 8'-0" 7'-6"

Distance between center line of risers

4.4d 8'-8" 10'-0" Approx 8' 10'-0" 10'-0"Chevron Corporation 900-31 December 1993

900 Wharves and Moorings Civil and Structural Manual What is the frequency of the extreme tidal conditions that cause the problem?

Are there operational changes that can be made to the loading procedures to mitigate the extreme draft conditions for the vessel?

If the tanker handrail located outside the manifold causes an interference problem, is it removable?

Another recommended step prior to filling out the OCIMF marine loading arm data sheet is to review the loading arm envelope with the marine arm suppliers. The two largest manufacturers of arms are:

LTV Energy Products(Continental Emsco)DuraTech ProductsP.O. Box 461388Garland, TX 75046

FMCPetroleum Equipment Group (Chiksan)1803 Gears Rd., P.O. Box 3091Houston, TX 77001(713) 591-4000

Representatives from these manufacturers can provide valuable input regarding the loading arm geometry. Items to be considered include:

Optimum height of trunnion swivel

Optimum lengths for inboard and outboard arms

Arm interferences with lateral sluing. The large triple swivel assemblies at the outer end of the arms can cause interference problems at the extreme lateral travel positions.

A commonly employed layout alternative reverses the hand of one or more loading arms. The position of the trunnion swivel can be specified for either the right or left hand side of the riser. Making one-half the bank of arms the reverse hand of the other half sometimes allows greater flexibility in connecting the arms to ship manifolds.

927 Utilities and Other FacilitiesThis section briefly covers utilities and the other facilities required for a functioning wharf. The degree to which these supplemental facilities are required depends on the intended duty of the particular wharf.

Electric PowerPower is required for lighting, impressed current cathodic protection systems, and equipment such as loading arms, gangways, capstans, fire-water pumps, and reels for oil spill boom equipment. Special outlets for welding are provided at some installations.December 1993 900-32 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsBuildingsAs a minimum, an operators shack with office, toilet facilities, and storage space is usually provided. A major installation could well include a full operations-office building, locker room facilities, bulk-cargo warehouses, shops, and a bunk house.

Navigation AidsNavigation aids, such as lights and fog horns, must be provided in accordance with the particular governing regulations. In the United States, the Coast Guard is in charge and will outline their requirements when the Corps of Engineers permit is filed.

Personnel SafetyAdequate personnel safety provisions are mandatory. There should be a minimum of two escape stairways or ladders leading to boat landings. In addition, jacobs ladders should be provided for all remote dolphins. Life jackets and life rings should be provided as required by local regulating authority.

Fire Protection and Emergency EvacuationA fire protection system is required for the loading platform area of a wharf. The intent of the system is to limit damage to the wharf, not to save a moored ship. Design guidance can be obtained from the Companys Fire Protection Manual and from CRTCs Health, Environment, and Safety Group.

Current fire prevention requirements include:

1. A firewater system connecting to hydrants, monitors, and fire-aid hose reels. If justified, foam capability should be considered.

2. A one-hour firewater supply of 500-1000 gpm for single berth docks, or a four-hour firewater supply of 2000-4000 gpm for multi-berth docks.

3. A sufficient number of International Ship-to-Shore Connections to deliver the required firewater supply for a single berth dock. A drawing of the connection is shown in an appendix of the International Safety Guide for Oil Tankers and Terminals.

4. Drainage should flow away from loading pipes, arms, and shut-off valves.

5. Consideration should be given to the use of remote controlled fire monitor protection over the platform loading area.

These guidelines are minimum requirements and may not always be sufficient. Some foreign governments, for example, require much more elaborate fire protec-tion and evacuation systems. Therefore, it is necessary to confirm requirements with the specific government agencies issuing permits to the facility. It should be noted that the Oil Companies International Marine Forum (OCIMF) is compiling a summary of recommended guidelines for fire protection and emergency evacuation.Chevron Corporation 900-33 December 1993

900 Wharves and Moorings Civil and Structural ManualCommunicationsThe operations center on the loading platform must be furnished with a variety of communications links. A telephone line should connect the wharf to the shore facili-ties. A radio system is needed to communicate with arriving tankers. Portable radio sets are very useful in the mooring operation. Horns and buzzers can be used to signal the operators when they are away from the office.

Gangway SystemMost tanker wharves built today require the installation of fixed gangway facilities for vessel access. On the most recent wharf projects, the gangways have been two-piece systems, an inboard section and an outboard section. The stair treads for each section should be self-leveling or curved fixed treads that are relatively easy to walk on in most operating positions. An envelope drawing of the tanker showing its maximum limits of drift away from the berth and the maximum and minimum deck elevations should be prepared to insure the gangway will satisfy all operating condi-tions.

A tower structure is typically required to support the gangway and its associated control equipment. A motorized gear winch is commonly used to provide control of the gangway. At Richmond Berth 1, the gangway has powered control in the vertical plane, but the horizontal position is controlled by a swinging mechanism. The gangway at Empire has powered control in the vertical and horizontal direc-tions.

Washington Aluminum has manufactured the gangways installed at a number of recently constructed tanker berths.

Oil Spill Containment SystemIn case of accidental oil spill, the facility must have access to equipment for containing the spill until it can be skimmed off. This need is usually met by providing the wharf with floating barriers called oil booms or spill booms. Often, a combination of permanent booms and deployable booms are provided which are usually connected together in use. Permanent booms, which are used to protect areas which would be difficult to protect with a deployable boom, are affixed to float continuously on sliding connections that allow movement up and down with the tides. They require substantial maintenance due to wear of the sliding connection and accumulation of marine growth. Deployable booms are stored out of the water and towed by boat into position when the need arises.

As with most contingency plans, spill containment system design is generally a compromise between budget and desire to provide for most likely accident scenarios. Scenarios should be prepared for various combinations of wind and current direction and spill location. Instead of completely surrounding the spill, often it is possible to contain the spill by partially enclosing it in the direction of the driving wind and current forces. In some areas, the regulatory agencies must be involved in the decisions on spill containment system design.

Choice of boom type should consider available storage space, available deployment manpower, and harbor conditions (wave height and current) as well as cost and December 1993 900-34 Chevron Corporation

Civil and Structural Manual 900 Wharves and Mooringsdurability. The wharves at Richmond, for example, are provided with compactable, self-inflating/self-deflating booms stored on wharf-mounted hydraulic/electric or pneumatic powered reels. The reel assemblies minimize required storage area and deployment manpower. These deployable booms are connected in an emergency to permanent booms located under the wharves.

Government regulations in the United States are not very specific regarding spill containment. The Code of Federal Regulations Section 33CFR154 contains general oil pollution prevention regulations that must be followed for marine oil transfer facilities capable of transferring oil from vessels of 250 barrels or greater capacity. The Coast Guard reviews equipment and procedures in order to judge compliance with this regulation. The facility must have access to enough equipment (boom, towing vessels, etc.) and personnel to deploy the boom and contain the spill in what the Coast Guard considers a reasonable time period. Of course, the facility must also have access to a means of removing the spill once contained.

Many company facilities belong to local cooperatives that purchase and maintain spill clean-up equipment. The extent of equipment required at a particular wharf will depend upon what equipment would be available from the cooperative, if one exists.

Drainage SystemThe loading platform requires a drainage system to collect, contain, and dispose of spilled hydrocarbons in all areas where spills may occur. Typically, the spills are collected in sumps on the wharf. The oil may then be disposed of by pumping it into a ballast line if one exists. Some facilities rely on a vacuum truck to periodi-cally empty the sumps.

Other SystemsThe following systems may be required or desirable depending on particular condi-tions:

1. Fresh Water or Potable Water

2. AirUtility or Instrument

3. Sanitary Sewage

930 Offshore Moorings

931 Mooring TypesThis section provides information to assist in choosing, evaluating, or designing single point mooring (SPM) terminals for loading or offloading crude tankers. Cate-nary Anchor Leg Moorings (CALM), which are the most common type of SPM terminal, are specifically addressed. This section primarily contains general infor-mation. A complete set of references is contained in Section 970.Chevron Corporation 900-35 December 1993

900 Wharves and Moorings Civil and Structural ManualCategories of MooringThree general categories of mooring types are used for mooring tankers offshore:

Fixed Jetty or Sea Island. The vessel is tied up to fixed point mooring structures and breasting against fenders on a fixed structure. A loading platform is usually located at the center. This type of mooring is limited to shallow water and sheltered locations or mild environments. The structures are fixed in location so the vessel cannot be re-oriented to minimize wind, current, and wave forces if the weather direction changes. Tankers must be handled by tugs, and very large tankers cannot be accommodated because of their water depth requirements. Capital cost outlay can be significantly larger than for a single point mooring. Still, this type of mooring facilitates quick, clean, and simple loading or offloading when the location is suitable. (See Section 920: Tanker Wharves.)Spread Mooring. The vessel is held with ropes to buoys secured by anchors or mooring dolphins from several points around the vessel circumference. This system fixes the orientation of the vessel; the vessel generally cannot be re-oriented to mini-mize wind, current, and wave forces if the weather direction changes. Therefore, although the mooring lines allow compliance to wave motions, spread moorings are limited to mild environments. Moreover, connecting mooring ropes to several points around the vessel is more time consuming and requires more maneuvering than connecting to a single point.

Single Point Mooring. Single point moorings (SPMs) are preferred over conven-tional spread moorings when the moored vessel needs to be able to easily change its heading in response to changes in wind, wave, and current directions. Because a single point mooring restrains a vessel through a single point or axis, the vessel is free to weathervane and find its heading of least resistance to the weather. Another reason for restraining the vessel through a single point is to facilitate quick and easy connection to, and cast-off from the mooring. SPMs are well suited for use as loading terminals for both of these reasons.

Types of Single Point Moorings (SPMs)Several different single point mooring systems are available. The most common categories are described below:

HawserCALM. This is the most common type of tanker loading terminal and the main subject of this section. CALM stands for Catenary Anchor Leg Mooring. The vessel is connected to a buoy by one or more synthetic fiber hawsers. The buoy is fixed in orientation to the sea floor by catenary anchor legs, but has a turntable arrangement to allow the hawser attachment point to rotate. The hawsers are typically tied to the vessel at the forecastle on the bow. A vessel moored by hawser CALM needs propulsion or tug assistance to avoid risk of colli-sion with the buoy when the weather changes.

Rigid YokeCALM. This mooring is similar to the hawser-CALM up to the buoy turntable, but instead of a hawser connecting the vessel to the buoy, a rigid yoke structure spans the space between the buoy and the bow or stern of the vessel. Generally, the yoke is hinged at both ends to decouple the buoy from the vessels heaving and pitching motions, but the buoy does roll with the vessel. Rigid yoke December 1993 900-36 Chevron Corporation

Civil and Structural Manual 900 Wharves and MooringsCALMs do not lend themselves to quick connect or disconnect, so they are not suit-able as loading terminals. They are typically used to permanently moor storage or production and storage tankers, with lightering tankers loading in tandem or along-side. The rigid yoke is stronger and more durable than a hawser, and prevents colli-sions between vessel and buoy.

Soft YokeCALM. This mooring differs physically from the rigid yoke CALM only in the connection of the rigid yoke to the vessel. Instead of hinges at the bow or stern, a soft connection is made at the vessel. The vessel end of the rigid yoke is connected to two pendulums suspended from the port and starboard sides of the bow or stern. The pendulums are chains, weighted at their ends with a heavy rod passing under the vessel and suspended from both chains. In this configuration, vessel motions cause less loading on the anchor legs, but vessel to mooring connect and disconnect is still not routine.

SALM. SALM stands for Single Anchor Leg Mooring; it is described here but not specifically addressed by this section. As with the CALM type, the SALM is suitable for use as an export terminal with hawsers between the vessel and SALM, or as a permanent mooring with some kind of structural yoke between the vessel and mooring. SALMs differ from CALMs in that the buoy on a SALM is anchored to the sea floor by a single tensioned anchor leg rather than several catenary anchor legs. The single anchor leg is often a rigid tubular structure, but always articulated near the sea floor, where the base is held down by piles. Sometimes more articula-tions are employed along the anchor leg. The top of the anchor leg is buoyant, providing the restoring mechanism, which is analogous to that of a pendulum, but inverted and provided by buoyancy instead of gravity.

In addition to the hawser option, two types of structural yoke are commonly used to fix the vessel to the buoy. Rigid yokes similar to those used for CALMs are common. Another type, called a buoyant yoke, is unique to the SALM type. Here the buoyancy that tensions the SALM is not in the top of the anchor leg but rather on a submerged part of the yoke truss. This design is also referred to as a SALS, for Single Anchor Leg Storage. Buoyant yoke SALMs are known to cause stress and wear in the yoke-to-vessel hinge, with at least one catastrophic failure on record.

Turret. A turret is similar to a CALM, except that the turret uses the vessels buoy-ancy to support the weight of the anchor legs. Consequently, no yoke or hawser is required to attach the mooring to the vessel; the turret is either cantilevered off the bow or stern, or built into the vessels hull. Turrets are not suitable for export termi-nals, because the tanker is permanently attached to the mooring.

Fixed Structure SPM. This type of single point mooring is used in shallow water. A jacket or column structure is piled into the sea floor and the vessel is attached to this structure by a hawser or by a soft yoke or wishbone yoke arrangement similar to the one described for the soft yoke CALM. The top of the structure is fitted with a turntable for weathervaning, and in the case of a hawser connection, the structure is protected from vessel collisions with an impact energy absorbing fender. Hawser-fixed structure SPMs are suitable as loading terminals.Chevron Corporation 900-37 December 1993

900 Wharves and Moorings Civil and Structural ManualOther types of single point moorings include the Counterweight Articulated Mooring (CAM), and Spar buoy. The CAM is intended for deep water and derives its restoring properties from a long structural riser, weighted at the bottom and attached to the sea floor with catenary anchor legs near the bottom end. The Spar is similar to a CALM, but with a buoy large enough for storage of crude oil and equip-ment.

Hawser-CALM InstallationsHawser-CALMs (sometimes called SPM buoys), are manufactured by several firms and used throughout the world. In mild environments and moderate water depths, CALMs are inexpensive and familiar. Many components can be purchased from stock. Tankers do not normally require tugs for assistance during mooring, although a launch is required to handle mooring hawsers and crude transfer hoses. Moreover, CALMs have been designed to handle up to 5 separate products through multiple pass swivels capable of accommodating transfer rates beyond 60,000 barrels of oil per hour. This section focuses on hawser-CALMs because they are the most commonly used type of single point mooring for loading terminals, but some of the information contained here, such as on chains, anchors, and hoses can be applied to other types of moorings.

Description. A typical hawser CALM installation (Figure 900-15) consists of (1) a submarine pipeline or pipelines from shore or offshore production facility to the buoy site, (2) a pipeline end manifold (PLEM), (3) underbuoy hoses connecting the PLEM to the buoy, (4) the CALM buoy, including turntable and product swivel assembly, (5) hoses (usually floating) connecting the CALM to the tanker, (6) mooring chains and anchorage for the buoy, and (7) hawsers from the tanker to the buoy.

The underbuoy hoses are connected to the stationary buoy body, which is restrained from rotating relative to the seafloor. The floating hoses are connected to a section of the buoy called the rotating cargo manifold or turntable, which is free to rotate. The tanker is moored to the turntable and is therefore free to assume a position of least drag due to wind, waves, and current.

The CALM-type SPM was developed and patented by the Shell Development Company, and the buoys are manufactured under license to Shell.

Manufacturers. At the present time, CALM systems are manufactured by the following firms:

Single Buoy Moorings (SBM) SOFEC Inc. IMODCO Bluewater Mitsubishi Heavy Industries

A computer database containing information on almost 300 CALM installations contracted since 1959 can be accessed through CPTC (San Ramon). Since a prece-dent may already exist for any given design problem, this database is well worth looking into before embarking on a design. Literature on existing installations and December 1993 900-38 Chevron Corporation

Civil and Structural Manual 900 Wharves and Mooringscurrent design features is readily available from the manufacturers. Some manufac-turers, keep a sizable inventory of CALM components on hand for immediate delivery and installation.

932 Basic DataThe following items are intended to provide a checklist for use in SPM terminal design. Some of the data will be required by the buoy supplier in order to properly design the buoy, mooring system, and underbuoy hose layout. These items include the following.

Vessel DataFigure 900-32 lists general characteristics of tankers ranging in size from 16,500 to 500,000 L.T. DWT. Also, Chevron Shipping publishes a volume called Vessel Profile Sheets, which is useful for compiling specific or generic data about the vessels (Reference 10 of Section 972).1. Maximum anticipated size of vessel, expressed in deadweight

(DWT long tons).2. Dimensions of largest anticipated:

Length overall Beam

Fig. 900-15 Typical Hawser-CALM InstallationChevron Corporation 900-39 December 1993

900 Wharves and Moorings Civil and Structural Manual Depth Maximum loaded draft Minimum loaded draft

3. Location of cargo manifolds (usually approximately amidship, port and star-board).

4. Capacity of ships derricks for lifting hoses.

5. Anticipated tanker usage frequency.

Fluid Flow1. Number of products to be handled.

2. Products to be handled simultaneously.

3. Loading or discharging? Both?

4. Product data:

Pumping pressure Anticipated loading and/or discharge rate Fluid temperature Viscosity Gravity

Pumping pressure for a discharging tanker is normally 150 psi at pumps and about 120 psi at the ships rail. Loading rates are limited by the tank venting system; refer to the approximate maximum rates shown in Figure 900-12. Average loading rates will be about 85% of maximum due to starting up and topping off operations.

5. Size, number, and distance of pipelines from shore or offshore production facility.

6. Number and size (I.D.) of hoses between buoy and ship.7. Number and size (I.D.) of hoses between pipeline and buoy.8. Is a specific hose manufacturer preferred?

9. Are float/sink hoses required by local regulation? (Normally, Japan only)

Environmental ConditionsInformation on environmental conditions for any location is available from CPTC (La Habra).1. Safety area around and under the buoy. Tankers require a certain amount of

safety area around the buoy to maneuver. The necessary safety area will vary with each location and the size of the largest tanker anticipated. Tankers must normally approach the buoy into the current or wind, whichever controls. The safety area can be as little as two ship lengths to as much as four ship lengths, December 1993 900-40 Chevron Corporation

Civil and Structural Manual 900 Wharves and Mooringsdepending on the direction and intensity of the prevailing winds and currents. Three thousand feet is considered a desirable minimum distance to shoal water (minimum depth). Adjacent CALMs should be separated by at least three (pref-erably more) ship lengths. Buoys should be separated from nearby structures such as platforms or floating production systems by at least 1.5 miles.

Sufficient water depth is required for the fully loaded tanker to clear any pipe-lines at low tide with a 10% margin. Also consider whether the anchor chains can become an obstacle to the tanker. Tankers have been known to catch on anchor chains with their bulbous bows.

Preliminary layout can usually be made from U.S. Coast and Geodetic Survey charts. In locations where water depth changes sharply, CALM buoy may not be the suitable choice for a marine berth.

2. Tidal conditions:

Minimum low water, spring tides Maximum high water, spring tides

3. Minimum significant wave height. Significant wave height refers to the average of the one-third highest waves. The design wave height may be based on a 10-year storm for design loads and on a 100-year storm for buoy survival loads. A rule of thumb for selecting the survival storm return period is to use five times the design life.

4. Maximum storm tide or storm surge. Based on 100-year storm. Will be more severe in areas with extensive shallow water.

5. Maximum wind velocity:

That may occur in vicinity during a 100 year storm. Maximum to which tanker will be subjected. Tankers will not normally

remain at the buoy when extreme winds are expected, such as typhoons or hurricanes. However, if located in an area where sudden squalls or freak winds are not uncommon, the mooring system should be designed with these in mind, since the tanker may not have adequate warning to vacate.

One minute sustained wind velocity at an elevation of 33 feet above the sea surface should be used for the return interval selected.

6. Normal prevailing wind direction. Normally shown on wind rose charts by season or month.

7. Maximum current. If tidal, give for both ebb and flood.

Velocity at sea surface Direction

Also consider current velocity and direction versus depth below sea surface.Chevron Corporation 900-41 December 1993

900 Wharves and Moorings Civil and Structural Manual8. Normal current:

Velocity Direction

9. Cause of current (i.e., tidal or littoral). If tidal, check patterns for rips or shear lines which could cause problems with tanker motion around the buoy.

10. Water temperature:

Minimum Maximum

11. Worst weather periods during year.

12. Bottom characteristics at site. If unknown, a soils survey is mandatory.

Type of soil (mud, sand, clay, shale, rock, coral, etc.) Analysis of bottom (i.e., depth of mud.)

13. Underwater visibility; distance. Poor visibility will normally increase installa-tion costs due to reduced diver efficiency.

14. Underwater obstructions. Plan on performing a side scan sonar survey of the installation area and consider a wire rope drag survey.

15. Ambient temperatures:

Maximum Minimum

16. Is ice build-up on buoy anticipated? If enough to cause problems, a heated canopy may be required.

Terminal and Site Information1. Proposed distance offshore (see above, No. 1 of Environmental Conditions).2. Navigation light:

Required? (Check Coast Guard or Government agency outside U.S.) Range of visibility desired Characteristics desired (i.e., number of flashes per min.) Color of lens desired Specific manufacturer and model?

3. Fog horn:

Required? (Check Coast Guard or Government agency outside U.S.) Characteristics desired (i.e., number of blasts per min.) Specific manufacturer and model?

4. Is power required on the buoy? Normally not required or desirable.December 1993 900-42 Chevron Corporation

Civil and Structural Manual 900 Wharves and Moorings5. Will telephone cables be attached to buoy? Normally, radio communications used.

6. Any other specific requirements?

7. Mooring launches. If at present no terminal launch exists, but will be provided later, consideration should be given to providing a launch with twin screws as they are much more maneuverable than single screw launches. Also, t