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4 , O c t . 1 9 8 0, p p . 3 7 1 - 3 8 4
Ap proaches to the D esign
t P . F o r t i n o 1
of H opp er Dredges
T h r e e n e w h o p p e r d r e d g e s o f d i ff e r e n t s i z e s a n d m i s s io n
p e r fo r m a n c e a r e c u r r e n t l y u n d e r c o n s t r u c t i o n f o r
t h e
U . S . A r my C o r p s o f En g i n e e r s . T h i s
p a p e r d e s c r i b e s t h e
p a r t i c u l a r f e a tu r e s o f
t h e d r e d g e s t h a t c o n s t i -
t u t e
a d v a n c e s i n
t h e s t a t e o f t h e
ar t , and
re v ie w s t he ph i los oph y be h ind t he i r de s ign . In a dd i tion , t he
a u th o r
d e m o n s t r a t e s h o w t h i s n e w d r e d g e f l e e t , th o u g h
sm al le r than ear l i e r f lee ts , w i l l
i m p r o v e t h e
C o r p s ' c a p a b i l i-
ty , fo r bo th c i v i l i an and mi l i ta ry
p u r p o s e s , t o
main ta in a l l U . S .
c o a s t a l w a t e r w a y s
a s w e l l a s l o c a t i o n s o v e r -
s e a s t h a t a r e o f
in t e re s t t o t he Un i t e d S t a t e s .
F i n a ll y , d a ma g e s ta b i l it y r e q u i r e me n ts a n d n o i s e a b a te m e n t
s p e c i f ic a t i o n s a r e t r e a t e d i n s e p a r a t e a p p e n d i c e s .
I n t r o d u c t i o n
T a b l e 1 T h r e e n e w h o p p e r d r e d g e s - - g e n e r a l d a t a
I N JU N E O F 1 97 6, t h e U . S . A r m y C o r p s o f E n g i n e e r s e m b a r k e d
t o d e s i g n th r e e n e w h o p p e r d r e d g e s a s a fi r s t s t e p
n t h e e s t a b l i s h m e n t o f a r e d u c e d b u t m o d e r n s t a t e - o f - t h e - a r t
o p p e r d r e d g e f l e e t. T h e f l e et r e d u c t i o n i s i n c o n f o r m a n c e w i t h
e c e n t l y e n a c t e d l e g i s l a ti o n ( P L 9 5 -2 6 9 ) w h i c h i n d i c a t e s t h a t a n
i n c r e a s in g s h a r e o f t h e n a t i o n a l d r e d g i n g w o r k i s t o b e p e r f o r m e d
b y c o m m e r c i a l l y o w n e d p l a n t , w h i c h i s t h e r e a s o n w h y c o n t r a c -
t o r s a r e n o w b u i l d i n g h o p p e r d r e d g e s .
T h e t h r e e n e w d r e d g e s w h ic h h a v e b e e n d e s i g n e d a n d a r e n o w
u n d e r c o n s t r u c t i o n f o r t h e C o r p s a r e o u t l i n e d i n T a b l e 1 , a n d
p r e l i m i n a r y d e s i g n p r o f i l e s a r e s h o w n i n F i g s . 1, 2 a n d 3 .
T h e p h i l o s o p h y g o v e r n i n g th e r e d u c e d f l e e t is th a t t h e n e w
d e s i g n s w i l l b e c a p a b l e o f o p e r a t i n g o n a l l c o a s t s a n d w i l l b e
a v a i l a b l e o n s h o r t n o t i c e f o r n a t i o n a l d e f e n s e n e e d s o r f o r m i l i t a r y
o r c i v il e m e r g e n c i e s a n y w h e r e i n t h e U n i t e d S t a t e s o r i n a n y o f
i t s o v e r s e a s i n t e r e s t s . I n t h e a b s e n c e o f s u c h e m e r g e n c i e s , t h e
d r e d g e s w i l l b e k e p t i n r e a d i n e s s b y c o n t i n u o u s o p e r a t i o n i n
r e g u l a r d r e d g i n g a s s i g n m e n t s . N e v e r t h e l e ss , s o m e s p e c i a l c a p a -
b i l i ti e s m a y b e p r o v i d e d . T h e
Yaquina
i s d e s i g n e d t o b e e s p e c i a l l y
s u i t a b l e f o r o p e r a t i o n a t s h a l l o w d r a f t i n s u c h i n l e t s as a r e f o u n d
o n t h e W e s t C o a s t. T h e l a r g e -c l a s s h o p p e r d r e d g e ( L C H D ) i s
i n t e n d e d t o h a v e e n o u g h p o w e r t o o p e r a t e a l l f o u r o f i t s d r e d g e
p u m p s s i m u l t a n e o u s l y . I t h a s th e u s u a l t w o s i d e d r a g a r m s , e a c h
c a r r y i n g a s u b m e r g e d d r e d g e p u m p , a n d , i n a d d i t i o n , a t h i r d
d r a g a r m i n a c e n t e rw e l l c a p a b l e o f fe e d i n g t w o d r e d g e p u m p s .
W i t h a l l fo u r p u m p s o p e r a t i n g , th e d r e d g e c a n b e e s p e c i a ll y e f -
f e c t i v e w h e n w o r k i n g i n t h e a g i t a t i o n m o d e , t h a t i s , s i m p l y o v -
e r fl o w i n g fr o m t h e h o p p e r s c o n t i n u o u s l y , a l l o w in g th e m a t e r i a l
t o b e b r o a d c a s t o v e r th e w a t e r o n b o t h s i d e s o f t h e d r e d g e a n d
l e t t i n g t h e c u r r e n t c a r r y t h e s o l i d s t o b e d e p o s i t e d o u t s i d e o f t h e
c h a n n e l b o u n d a r i e s . T h i s d r e d g e i s e x p e c t e d t o b e p a r t i c u l a r l y
e f f e c t i v e i n d e a l i n g w i t h t h e s h o a l i n g w h i c h o c c u r s i n t h e M i s -
s i s s ip p i R i v e r p a s s e s , w h i c h o c c a s i o n a l ly h a s r e q u i r e d a t t a c k b y
a s i z e a b l e d r e d g i n g f l e et .
T h e m e d i u m - c l a s s h o p p e r d r e d g e (M C H D ) c a n be co n s i d e r e d
a g e n e r a l - p u r p o s e d r e d g e , d e s i g n e d t o b e e f f i c ie n t a n d e f f e c t iv e
i n a ll a s s i g n m e n t s . I t s d i m e n s i o n s a r e a v e r a g e , a n d i t s l o a d e d
d r a f t c a n b e t o l e r a t e d b y t h e m a j o r i t y o f a u t h o r i z e d d r e d g i n g
p r o j e c t s .
T h e a u t h o r h a s b e e n c o n t i n u o u s l y i n v o lv e d w i th t h e d e s i g n ,
1 Chief, M ar ine D es ign Divis ion (Ret . ) , Phi lad elph ia Dis t r i c t , U . S.
A r m y C or ps o f Eng i ne e r s .
Presented a t the December 7 , 1979 meet ing of the P hi ladelphia Sect ion
of TH E SOCIETY OF NAVALARCHITECTS AND MARINE ENGINEERS.
The op i n i ons e xp r e s s e d he r e in a r e t he v i ew s o f the a u t ho r a nd no t
necessar i ly those of the U. S. Arm y Corps of Engine ers or the U. S. Army
at l a rge .
Yaquina M C H D L C H D
Len gth OA, f t 200 350 409
Len gth BP, f t 193 333 384
Beam , mo lded, f t 58 68 78
De pth amid ships , mo lded, f t 17 35 39
H o p p e r v o lu m e , y d~ 825 6000 8400
H op pe r c a pa c i t y , s a nd ( m i n . ) , yd 3 650 4818 6000
Prop uls ion power, shp 2 1125 2 3500 2 5200
Design draf t , loaded (es t .) , f t 12 27 29.5
Displa cem ent a t loade d draf t , LT 2963 13 950 19 000
Speed , loade d (es t . ), knots 10 13.4 14.5
D r e dge Pum ps , i nboa r d :
num be r 2 2 2
discharge dia , in . 16 26 30
bhp , each 565 3000 3600
D r e dge pum ps , d r a ga r m - m oun t e d :
num b e r 0 2 2
d i s c ha r ge d i a m e t e r . . . 26" 26 /
Bh p, each . 1450 1600
M axim um dredgin g dep th , f t "4'5 80 80
No. in crew 28 38 40
t e s t in g , o p e r a t i o n a n d m a i n t e n a n c e o f C o r p s o f E n g i n e e r s h o p p e r
d r e d g e s s i n c e 1 9 3 9 . D u r i n g t h a t p e r i o d h e h a s o b s e r v e d a n d
c o n t r i b u t e d t o c h a n g e s t a k i n g p l a c e t h a t c o u l d b e c a ll e d k e e p i n g
u p w i t h t h e s t a t e o f t h e a r t , a n d i n a fe w i n s t a n c e s e v e n p u s h i n g
t h e s t a t e o f t h e a r t . T h e C o r p s c a n r i g h t f u l l y t a k e c r e d i t f o r p i -
o n e e r i n g t h e f o ll o w i n g f e a t u r e s o n h o p p e r d r e d g e s :
( a ) P i l o t h o u s e c o n t r o l o f p r o p u l s i o n , w i th t h e i n t r o d u c t i o n
o f e l e c t r ic a l l y p r o p e l l e d d r e d g e s i n 1 9 2 4 o n t h e f o u r Kingman-
class d r e d g e s .
( b ) A u t o m a t i c c o n t r o l o f p r o p u l s i o n h o r s e p o w e r , f i r st i n t ro -
d u c e d o n t h e d r e d g e
Goethals
i n 1 93 7, a n d l a t e r i m p r o v e d o n t h e
Comber c l a s s , Essayons a n d Markham. T h i s f e a t u r e e n a b l e s t h e
v e s s e l s t o a d j u s t p r o p u l s i o n m o t o r r p m a u t o m a t i c a l l y so t h a t 1 0 0
p e r c e n t p r o p u l s i o n p o w e r is u s e d w h e n r e t u r n i n g l i g h t f r o m , a s
w e l l a s w h e n p r o c e e d i n g l o a d e d t o , t h e d i s p o s a l a re a .
( c) P r o c e s s in s t r u m e n t a t i o n , i n c l u d i n g t h e d e v e l o p m e n t o f
t e c h n i q u e s f o r t h e d i r e c t m e a s u r e m e n t , d i s p l a y a n d r e c o r d i n g
o f h o p p e r l o a d , f l o w v e l o c i t y a n d d e n s i t y , a n d s o l i d s f lo w r a t e ,
d u r i n g t h e d e c a d e o f t h e 1 9 5 0 's .
( d ) S e l f - u n lo a d i n g o f h o p p e r d r e d g e s b y d i r e c t p u m p o u t , f i rs t
t o a r e h a n d l i n g v e s s e l (1 9 54 ) a n d l a t e r d i r e c t l y t h r o u g h l o n g
p i p e l i n e s t o s h o r e d i s p o s a l a r e a s , b e g u n i n 1 9 63 .
( e ) C o n t r o l l a b l e - p i t c h p r o p e l l e r s , f i r s t i n s t a l l e d d u r i n g r e -
p o w e r i n g o f th e d r e d g e Harding i n 1958 .
( f) B o w t h r u s t e r s , f i r s t i n t r o d u c e d o n t h e d r e d g e
Markham
i n 1 95 9. T h e s e i m p r o v e d r e d g e c o n t r o l a t s lo w d r e d g i n g speeds
O C T O B E R 1 9 8 0
0 0 2 5 3 3 1 6 1 8 0 1 1 7 0 4 0 3 7 1 5 0 0 . 5 3 10
3 7 1
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, . . . . . . . . . . " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . o : '
I I Y '
Fig. 1 Hoppe r dredge,
Yaquina
200 by 58 by 17 ft
and greatly facili tate docking, especially for dredges engaged in
direct pumpout operation which are required to moor, without
assistance, to a disposal facility perhaps a half-dozen times each
24-hour (h) period.
(g) Waste management systems for shipboard use, first pro-
vided on the dredge M a r k h a m in 1959.
(h) Semi-automatic operation of the dragarms, a feature de-
signed into the dredge M c F a r l a n d in 1965. At the touch of a
button each dragarm can be deployed out to the dredging position
from its stowed position on deck, and vice versa.
(i) Acoustic habitability. First steps in this direction were
taken in 1955 after conversion of the old steam hopper dredge
N e w O r le a n s to a diesel-powered sump rehandler. As a result of
this experience, specifications for the dredge M c F a r l a n d con-
tained stringent requirements for acoustic engineering and
testing.
Other innovations and improvements have been incorporated
on existing dredges as a result of research and development work
done by the Corps or observation of European practice.
A number of new features or departures from previous practice
mark the design of the three new dredges. The rest of this paper
is devoted to a description of these features.
Dam age s tabi li ty
Heretofore, the U. S. Coast Guard has had no rules enforcing
the subdivision of cargo ship hulls. The Load Line Regulations
make provision for the assignment of lesser freeboards to vessels
if they are designed to "remain afloat in a satisfactory condition
of equilibrium after flooding" of any single or any adjacent pair
of damaged compartments. However, such subdivision is not
mandatory. In the absence of any such regulation the Corps long
ago, commencing with dredges built in the 1930's, adopted a
policy that all dredge hulls would, where practicable, be designed
to survive flooding of any two adjacent compartments. An ex-
ception was made for small dredges like the H a i n s class and the
Paci f ic , which were designed to a one-compartment standard of
subdivision. The rules followed in implement ing this policy were
the Rules and Regulations for Passenger Vessels, Part 73, Wa-
tertight Subdivision, and Part 74, Stability. Since the Corps
hitherto has been the only builder of hopper dredges in the
United States it did in effect thus set a standard for design of
dredge hulls, thereby relieving the Coast Guard of having to es-
tablish a regulation.
With the e ntry of commercial firms into hopper dredging, this
picture has changed. Since non-Government-owned hopper
dredges would be operating in harbor channels, with the atten-
dant risk of collision due to traffic and bad weather, the Coast
Guard had to become concerned. In Washington, D. C.~ in De-
cember 1975 Corps personnel had a preliminary meeting with
Coast Guard marine safety representatives. In the 2 August 1976
issue of the F e d e r a l R e g i s t e r there appeared an Advance Notice
of Proposed Rule Making issued by the U. S. Coast Guard enti-
tled "Damage Stability Standards for Hopper Dredges." The
Corps responded to this proposal with a documentation of its
experience record and with the recommendation that "as a
minimum, a one-compartment subdivision standard under
maximum draft loaded condition be established as the rule
governing damage stability standard for hopper dredges."
In the meantime, both private industry and the Government
were rapidly developing plans for the design of new dredges, and,
in due course, designers and prospective owners began applying
to the Coast Guard for consideration of reduced "working free-
boards" such as permitted by Bureau Veritas for Europea n de-
signs. The Coast Guard's reply was that it had no authority to
deviate from the Load Line Regulations. Nevertheless, as the
Coast Guard further considered this problem, it developed a set
of conditions under which it could agree that a "working free-
board up to one-half the tabular B-100 freeboard may be au-
thorized .. . . "T hes e conditions appear in a letter dated 23 June
1977 from the U. S. Coast Guard to the C. F. Bean Corporation
and are reproduced here as Appendix 1.
3 7 2 M A R I N E T E C H N O L O G Y
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o o o o o o o o
r , ; j l
, , i . . . . ~ ~ . . . . . : 7 ~ : . . . . . . . . , ~ . . . . . . , " . . . . . , ;o : : '~ - : - - : ,~ : - - x '
c c ~ s a , ~ E ~ S
U S AR M Y
Fig, 2
,2 _)"
Hopper dredge, medium class, 34 4 by 68 by 35 f t
At the time that the U. S. Coast Guard made this letter public,
the Corps had virtually completed the design of the shallow-draft
dredge Yaquina to a one-compartment standard. Considerable
redesign was necessary to meet the two-compar tment subdivision
required by the conditions of Appendix 1, including an increase
in beam from 56 to 58 ft and the introduction of some longitudinal
subdivision and cross-flooding provisions.
Examina tion of the conditions set forth in Appendix 1 reveals
two interesting points:
(a) A length of damage is specified, namely, 0.495L2/3. In some
areas of a hull, this length may very well span three compart-
ments.
(b) There is no reference to a margin line as the limit of sub-
mergence. Thus the decks may very well be awash. It is simply
required that an equilibrium position be established with the
final angle of heel not exceeding 30 deg, with positive righting arm
of at least 4 in. over a range at least 20 deg beyond equilib-
rium.
As the Yaquina hull was recalculated in accordance with Ap-
pendix 1, it further developed that advantage could be taken of
the spillage which occurs from the hoppers as the vessel heel in-
creases. This represents an appreciable help because the hoppers
are considered to be loaded with a fluid having a specific gravity
of 2.0. This is a penalizing factor when figuring free-surface effect
in calculations of intact stability, but it helps in calculations of
damage stability.
S upers truc tures
A major change from previous practice is the location of the
_2
, , a . . . . . , . . . . , [ /
- : :. . . . . . . . : : : : : : i . . . . . . : . . . . . . . . . . . . . . . . .
- . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .
J,
: : , . . .
F ig .
3 Hopper dredge, large class, 409 by 78 by 39 f t
O C T O B E R 1 9 8 0 3 7 3
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Tab le 2 L igh t t r im data
Es t i m a t e d L i gh t Tr im , f t
Vessel LBP, f t @ 0% B ur nou t @ 90% B ur nou t
Yaquina 193 2.86 5.33
M CH D 333 10.12 13.93
LC HD 384 9.33 9.67
e n t i re s u p e r s t r u c t u r e a f t. W i t h t w o e x c e p t io n s , b o t h d a t i n g b a c k
t o t h e l a t e t h i r t i e s , it h a d b e e n g e n e r a l C o r p s p r a c t i c e t o h a v e a
s u p e r s t r u c t u r e a n d p i l o t h o u s e fo r w a r d a n d a n o t h e r s u p e r s t r u c -
t u r e a f t , w i t h t h e h o p p e r s p a c e b e t w e e n s u p e r s t r u c t u r e s .
T h e p r o v i s i o n o f t w o s u p e r s t r u c t u r e s m a d e i t e a s i e r t o a c -
c o m m o d a t e t h e l a r g e r c r ew s , w h ic h f o r t h e o l d e r d r e d g e s n u m -
b e r e d b e t w e e n 5 0 a n d 1 1 0 p e r s o n s . T h e y a l s o m a d e i t a l it t l e
e a s ie r t o m a i n t a i n r e a s o n a b l e t r i m f r o m t h e f u l ly lo a d e d ( e v e n
k e e l) t o t h e l i g h t (9 0 p e r c e n t b u r n o u t w i t h h o p p e r s e m p t y ) c o n -
d i t i o n .
T h e n e w d r e d g e s w i l i h a v e r e d u c e d c r ew s o f b e tw e e n 2 8 a n d
4 2 p e r so n s , s o t h a t a s in g l e s u p e r s t r u c t u r e a f t c a n a c c o m m o d a t e
a l l c r e w s a n d t h e n e c e s s a r y f a c i l it i e s . B y c a r e f u l l y s p o t t i n g t h e
h o p p e r l o a d a n d f o r w a r d t a n k s , a n a c c e p t a b l e li g h t t r i m c o n d i t i o n
c a n b e e s t a b l i s h e d . T h e d r e d g e s a r e d e s i g n e d t o b e a t e v e n k e e l
w i t h a f u l l l o a d o f w e t s a n d i n t h e h o p p e r s a n d w i t h a l l t a n k s f u ll .
W i t h h o p p e r s e m p t y a n d c o n s u m a b l e s 0 a n d 9 0 p e r c e n t b u r n e d
o u t , t h e p r e s e n t l y e s t i m a t e d t r i m s b y t h e s t e r n a r e a s g i v en i n
T a b l e 2 . R e t e n t i o n o f t h e i n b o a r d d r e d g e p u m p s i n a c o m p a r t -
m e n t j u s t f o r w a r d o f t h e h o p p e r s p l a c e s so m e h e a v y m a c h i n e r y
a n d p i p i n g f o r w a r d , a n d t h i s h e l p s to m a k e t o l e r a b l e th e c h a n g e
i n t r im f r o m t h e l o a d e d t o t h e l i g h t c o n d i t i o n .
T h e s u p e r s t r u c t u r e , i n e a c h i n s ta n c e , i s l o c a t e d o v e r t h e m a -
c h i n e r y s p a c e , w h i c h h o u s e s a l l o f t h e d i e s e l e n g i n e s f o r p r o p u l -
s i o n , p u m p i n g a n d s h i p s e r v i c e p o w e r , a s w e l l a s o t h e r n o i s e
g e n e r a t o r s l ik e h y d r a u l i c p u m p s a n d c o n t r o l li n e s. T h i s h a s g i v e n
a d d e d i m p o r t a n c e t o c o n s i d e r a t i o n s r e l a ti v e to a c o u s t ic h a b i t a -
b i l i t y . S p e c i f i c a t i o n s f ir s t d e v e l o p e d i n 1 9 6 5 f o r t h e d r e d g e
M c F a r l a n d h a v e b e e n f u r t h e r r e f i n e d a n d i n c l u d e d w i t h t h e r e -
q u i r e m e n t s f o r th e t h r e e n e w h o p p e r d r e d g e s . A s a n e x a m p l e ,
A p p e n d i x 2 p r e s e n t s t h e n o i se a t t e n u a t i o n r e q u i r e m e n t s e x -
c e r p t e d f r o m t h e M C H D s p e c i fi c a ti o n s . N o t e p a r t i c u l a r l y t h e
r e q u i r e m e n t f o r p r e c o n s t r u c t i o n e n g i n e e r i n g a n d p o s t c o n -
s t r u c t i o n t e s t i n g .
A u t o m a t i o n a n d r e d u c e d c r e w s
A n o b j e c t iv e o f t h e n e w d r e d g e d e s i g n s h a s b e e n t o r e d u c e
o p e r a t i n g c o s t s , w h i c h , o f c o u r s e , b e c a m e t r a n s l a t e d i n t o d e -
s i g n in g d r e d g e s r e q u i r in g f e w e r o p e r a t i n g p e r s o n n e l . T h i s o b -
j e c t i v e c o u l d b e r e a c h e d b y t r a v e l i n g e a c h o f s e v e r a l ro u t e s :
( a ) A d o p t n e w o p e r a t i n g p h i l o s o p h i e s , s u c h a s c o m b i n i n g
d u t i e s a n d e l i m i n a t i n g c l a s s if i c a t i o n s , a n d r e d u c i n g c o s m e t i c
m a i n t e n a n c e l ik e c le a n i n g , c h i p p i n g a n d p a i n t i n g .
T a b l e 3 S u c t i o n /d i s c h a r g e v a l ve s e t u p s w i t c h L C H D )
Pos i t i on Pum ps D i s c ha r ge
N o . Func t i on U s e d D e s t i na t i on
1 d r e dg i ng ove r s ide hopp e r l oa d i ng
2 d r e dg i ng i nboa r d hopp e r l oa d i ng
3 un l oa d i ng i nboa r d po r t d i s c ha r ge
to shore
4 un l oa d i ng i nboa r d s t a r boa r d d i s c ha r ge
to shore
5 d r e dg i ng i nboa r d ove r boa r d
( a g i ta t i on ) ove r s i de t o hoppe r s
and overflows
6 d r e dg i ng i nboa r d t o hoppe r s
ove r s i de t o hoppe r s
7 d r e dg i ng i nboa r d ove r boa r d
(agi ta t ion) overs ide overboard
( b ) C h a n g e f r o m t h e t r a d i t i o n a l 4 -h w a t c h e s t o o th e r d u t y
c y c l e s , w i t h s o m e s c h e d u l e d o v e r t i m e .
( c) I n t r o d u c e e x t e n s i v e a u t o m a t i o n i n t o o p e r a t i o n o f b o t h t h e
s h i p a n d t h e d r e d g i n g m a c h i n e r y .
T h e d e s i g n s h a v e a c c o m p l i s h e d t h is b y a c o m b i n a t i o n o f a ll
t h r e e m e t h o d s . T h e r e s u l ts a r e i n d i c a t e d b y t h e f o l lo w i n g c o m -
CLASS VESSE L CREW SIZE
La r ge Essayons 110
La r ge LC H D 42
M e d i u m Comber 90
M e d i u m M C H D 3 8
Sm a l l Pacific 42
Sm a l l Yaquina 28
p a r i s o n :
T h e c o m p a r i s o n s i n th e l a r g e a n d m e d i u m c l a s s e s a r e n o t t o t a l l y
f a i r , a s t h e E s s a y o n s a n d C o m b e r a r e s t e a m t u r b i n e - e l e c t r i c
v e s s el s w i th f i r e m e n , w a t e r t e n d e r s a n d e l e c t ri c i a n s i n t h e i r w a t c h
c o m p l e m e n t s , w h e r e a s t h e n e w d r e d g e s a r e d i e s e l - p r o p e l le d . '
A n a p p r e c i a b l e p a r t o f t h e c r e w r e d u c t i o n i s a t t r i b u t a b l e t o t h e
d e c i s i o n t o i n t r o d u c e e x t e n s i v e a u t o m a t i o n . A d d i t i o n a l l y , i t w a s
d e c i d e d t o b u i l d i n t o t h e s e v e s s e ls t h e c a p a b i l i t y fo r u n a t t e n d e d
e n g i n e r o o m o p e r a t i o n , f o ll o w i n g t h e p r e c e p t s o f U . S . C o a s t
G u a r d N a v i g a t i o n a n d I n s p e c t i o n C i r c u l a r N o . 1 -6 9 d a t e d 8
J a n u a r y 1 96 9. T o t h i s e n d , t h e v e s s e l s a r e to b e i n s p e c t e d a n d
c l a s s e d b y t h e A m e r i c a n B u r e a u o f S h i p p i n g ( A B S ) w i t h M a l t e s e
C r o s s A C C U 2 c e r ti f ic a t io n . H o w e v e r , i t i s n o t i n t e n d e d t o o p e r a t e
i m m e d i a t e l y w i t h o u t e n g i n e r o o m w a t c h p e r s o n n e l , a n d t h e f ig -
u r e s t a b u l a t e d i n t h e p r e c e d i n g d o n o t r e f le c t su c h p o s s i b l e f u r-
t h e r p e r s o n n e l r e d u c t i o n s .
E x t e n s iv e a u t o m a t i o n o f d r e d g in g m a c h i n e r y a n d e q u i p m e n t
o p e r a t i o n i s sp e c i f ie d . T o b e g i n w i t h , a p r o c e s s w i ll b e d i a l e d , b e
i t h o p p e r l o a d in g , a g i ta t i o n , d ir e c t p u m p o u t , e t c. F o r e x a m p l e ,
T a b l e 3 o u t l i n e s t h e p r o c e s s e s w h i c h c a n b e s e l e c t e d o n t h e
L C H D . U p o n d i a l in g a n d p r e ss i n g t h e " e x e c u t e " b u t t o n , t h e
p r o p e r v a l v e s w i ll b e a u t o m a t i c a l l y o p e n e d a n d c l o se d , a n d l i g h ts
o n a m i m i c d i a g r a m w i ll s h o w t h e s t a t u s o f ea c h v a l v e a n d t h e
f l ow p a t h .
I n a d d i t i o n , p o w e r f o r th e d r e d g e p u m p s i s d e r i v a b l e fr o m m o r e
t h a n o n e s o u rc e . A g a i n u s i n g th e L C H D a s a n e x a m p l e , F i g . 4 ( a )
s h o w s t h e m a i n p u m p p o w e r s y s t e m d i a g r a m a n d F i g . 4 ( b ) th e
p o w e r r o u t e s t h a t c a n b e s e l e c te d . T h e p r o p e r c i r c u i t b r e a k e r s
w i ll b e o p e n e d o r c l o se d u p o n s e l e ct i o n a n d e x e c u t i o n o f p o w e r
p a t h s , a n d l i g h t s w i l l s h o w t h e s t a t u s o f e a c h c i r c u i t b r e a k e r .
A d r e d g e c o n t r o l o f f i c e r ( D C O ) o n t h e b r i d g e w i l l m a k e a l l
p r o c e s s d e c is i o n s a n d o p e r a t e t h e d r e d g i n g s y s t em . D u r i n g a c t u a l
d r e d g i n g h e w i l l b e s e a t e d a t a c o n s o l e h o u s e d i n a g la s s b l is t e r ,
" f r o n t " a n d c e n t e r o f t h e p i l o t h o u s e , a t a l o w e r l e v e l s o a s n o t t o
i n t e r f e r e w i t h t h e h e l m s m a n ' s v i s io n . B e f o r e i n i t i a t i n g d r e d g i n g
t h e D C O w i ll f i rs t n o t e a t h i s c o n so l e w h e t h e r t h e p u m p i n g p o w e r
e n g i n e s a r e w a r m . I f s o, a n d i f t h e y a r e n o t r u n n i n g , h e c a n r e s t a r t
t h e m a t t h e c o n s o le . If t h e y a r e n o t w a r m , t h e y m u s t b e s t a r t e d
b y t h e e n g i n e e r .
W i t h e n g i n e s r u n n in g , a n d w i t h d r a g h o i s t m o t o r - g e n e r a t o r s e t s
r u n n i n g , t h e D C O n o w p r e ss e s a b u t t o n t o i n i t ia t e d r e d g i n g - -
a c t u a l ly , a b u t t o n f o r e a ch d r a g a r m . T h i s d e p l o y s t h e d r a g a r m ,
l i f t in g i t f r o m i t s s t o w e d p o s i t i o n o n t h e d e c k , b r e a s t i n g i t o u t -
b o a r d , t h e n l o w e r i n g i t d o w n t h e s h i p ' s s i d e t o a h o r i z o n t a l r e f -
e r e n c e p o s i ti o n , w i th t h e t r u n n i o n p r o p e r l y s e a t e d i n t h e o p e r -
a t i n g p o s i t io n . T h e m e c h a n i s m s w i ll s t o p a t t h i s p o i n t a n d a l i g h t
w i l l a d v i s e t h e D C O t h a t a l l is r e a d y f o r d r e d g i n g .
N e x t t h e D C O w i ll p r e s s a " l o w e r " b u t t o n . T h e d r a g a r m w i ll
n o w p i v o t a r o u n d t h e t r u n n i o n , t h e r e b y l o w e r i n g t h e d r a g h e a d
t o d r e d g i n g d e p t h . W h e n t h e l a t t e r to u c h e s b o t t o m , t h e s w e ll
c o m p e n s a t o r w i l l a s s u m e c o n t ro l , s t o p p i n g t h e l o w e ri n g a c t io n .
T h e s w e l l c o m p e n s a t o r w i l l a u t o m a t i c a l l y k e e p t h e d r a g h e a d i n
p r o p e r c o n t a c t w i t h t h e b o t t o m , a n a d j u s t m e n t h a v i n g b e e n
2 Pa r a g r a p h 41 .7 o f A B S r u l e s de f ine s t h i s s ym bo l a s " A u t om a t i c
C on t r o l Sys t e m fo r U na t t e nde d E ng i ne R oom C e r t i f i e d . "
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p r e s e t t o d e t e r m i n e h o w b i g a " b i t e " t h e h e a d w i ll t a k e , t h a t i s,
t h e d e g r e e o f e m b e d m e n t i n t o t h e b o t t o m m a t e r i a l . T h i s a d -
j u s t m e n t e s t a b l i sh e s w h a t p o r t i o n o f t h e d r a g h e a d w e i g h t is
s u p p o r t e d b y t h e h o i s t i n g c a b l e s a n d w h a t p o r t i o n b y t h e c h a n n e l
b o t t o m . T h e s w e l l c o m p e n s a t o r i s a h y d r a u l i c c y l i n d e r w i t h a
s t r o k e o f 1 2 f t, o r 4 - 6 f t a b o v e a n d b e l o w a m e d i a n . T h i s p e r m i t s
t h e d r a g h e a d t o f o l lo w u n e v e n n e s s o f t h e c h a n n e l b e d w i t h i n
t h e s e l i m i t s w i t h o u t o p e r a t i o n o f t h e d r a g h o i s t w i n c h e s . I f a l a r g e
h o l e o r h i ll is e n c o u n t e r e d , t h e h y d r a u l i c r a m w i l l t r a v e l t o o n e
o r t h e o t h e r e n d o f t h e s t r o k e a n d a u t o m a t i c a l l y s t a r t th e w i n c h e s
t o h o i s t o r l o w e r t h e d r a g h e a d u n t i l t h e r a m r e t u r n s t o t h e m e d i a n
p o i n t .
O t h e r a u t o m a t i c d r a g a r m d e v i c e s k e e p t h e d r a g h e a d f r o m
d r i f t i n g u n d e r t h e s h i p ' s h u l l .
A t c o m p l e t i o n o f d r e d g i n g , t h e s a m e a u t o m a t i c f e a t u r e s p r e -
v a i l, a s n e e d e d , i n t h e r e v e r s e d i r e c t i o n f o r s to w i n g t h e d r a g a r m s .
O r , i f t h e d r e d g e i s t o b e t u r n e d 1 8 0 d e g f o r a r e v e r s e c u t, r a i s i n g
t h e d r a g a r m s o u t o f t h e w a t e r i s a l so a p u s h b u t t o n o p e r a t i o n .
S t i l l o t h e r a u t o m a t i c d e v i c e s w il l g o v e r n t h e l o a d i n g i n t h e
h o p p e r s a n d r a i s i n g a n d l o w e r i n g o v e r f lo w le v e l s f o r w a r d o r a f t ,
p o r t o r s t a r b o a r d , i n r e s p o n s e t o p r e s e t i n s t r u c t i o n s a n d t o v e s s e l
t r i m o r l i s t ,
W h e n t h e v e s s e l i s d u m p i n g , a u t o m a t i c c o n t r o l s w il l o p e n t h e
d o o r s i n t i m e d s e q u e n c e i n a c c o r d a n c e w i t h p r e s e t i n s t r u c t io n s ,
a u t o m a t i c a l l y i n t e r r u p t i n g t h e d u m p i n g o p e r a t i o n a n d a d v i s i n g
t h e D C O i f t h e s h i p s t a r ts t o t a k e a n i m p r o p e r a t t i t u d e o r i f s o m e
o t h e r f a u l t o c c u r s .
I f t h e v e s s e l i s u n l o a d i n g i t s h o p p e r s b y d i r e c t p u m p o u t , t h e
a u t o m a t i c s a r e d e s i g n e d t o p r e v e n t l i n e p lu g g i n g , a s w e l l a s t o
e f f e c t u n l o a d i n g c o n t r o l .
T h e D C O i s p r o v i d e d w i t h r e m o t e c o n t r o l s a t h i s s t a t i o n o r in
t h e b r i d g e f o r a ll d e t a il s o f t h e d r e d g i n g , lo a d i n g a n d u n l o a d i n g
o p e r a t i o n s . T h e r e i s a l s o a w e a l t h o f i n s t r u m e n t a t i o n t o t e l l h i m
w h a t i s g o i ng o n a n d h o w w e l l h i s e q u i p m e n t a n d s y s t e m s a r e
f u n c t io n i n g . T h e h o p p e r l o a d i s c o n t i n u o u s l y d i s p l a y e d , a n d s o
i s t h e l o a d i n g ra t e , s o th a t h e c a n q u i c k l y d e d u c e w h e n h e h a s
a c h i e v e d a n " e c o n o m i c l o a d " i n th e h o p p e r s . P o s i t i o n i n d i c a t o r s
a n d r e c o r d e rs v e ri f y t h a t t h e s h i p a n d t h e d r a g h e a d s a r e a c t u a l ly
w o r k i n g e x a c t l y w h e r e d e s i r e d o n t h e s h o a l e d a r e a s. A t t h e m a t e ' s
D.C. SWITCHING I 2 3 4 5 6 7
1 DRED GING RECTIFIER NO 1 X O 0 O X 0 X
2 DREDGING RECTIFIER NO 2 0 0 0 X 0 X X
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I DREDGING--PORT GENERATOR TO OVERSIDE PUMP S
2 DRED GIN G-ST BO G ENERATO R TO OVERSIDE PUMPS
3 AGITATION DREDGING
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5 DREDGING-STBO GENERA TOR TO INBOARD PUM PS
CA)T HROUG H RECTIFIER NO l
(B) THRO UGH RECTIFIER NO 2
6 DREDGING-PORTGENERATOR TO INBO ARD PUMPS
CA)THROUGH RECTIFIER N O1
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o p t i o n , c o u rs e c o r r e c t io n i n f o r m a t i o n c a n b e f e d t o t h e a u t o m a t i c
p i l o t to h o l d t h e d r e d g e o n t h e c u t .
B e c a u s e o f t h e p l a n e v e n t u a l l y t o o p e r a t e o n t h e b a s i s o f a n
u n a t t e n d e d e n g in e r o o m , m u c h a u t o m a t i o n h a s b e e n i n t r o d u c e d
i n t h e a r e a o f p ro p u l s i o n a n d a u x i l i a r y m a c h i a e r y o p e r a t i o n . D u e
t o l i m i t a t i o n s o f s p ac e , h o w e v e r, t h i s p a r t i c u l a r a u t o m a t i o n
c a n n o t b e d i s c u s s e d h e r e . A s a f i n a l n o t e o n t h i s m a t t e r , h o w e v e r ,
r e c o g n i t i o n s h o u l d b e g i v e n to t h e p r o v i s i o n o f s o m e d e g r e e o f
a u t o m a t i o n i n k e e p i n g t h e s h i p ' s lo g . I n t h e p i l o t h o u s e t h e o p -
e r a t o r w i ll h a v e a v a i l a b l e a n a u t o m a t i c e v e n t l o g g e r , h a v i n g a
k e y b o a r d , a p r i n t e r a n d a c lo c k m e c h a n i s m . B y s t r i k i n g t h e a p -
p r o p r i a t e l y n u m b e r e d k e y , h e c a n c a u s e t o b e p r i n t e d t h e i d e n t i t y
a n d t h e t i m e o f o c c u r re n c e o f s u c h e v e n t s a s s t a r t i n g a n d s t o p p i n g
o f d r e d g e p u m p s , g o i n g t o a n d r e t u r n i n g f r o m t h e d u m p , i n t e r -
r u p t i o n a n d r e s u m p t i o n o f o p e r a t i o n , a n d a n y o t h e r e v e n t s t h a t
t h e d r e d g e m a s t e r m i g h t c a r e t o h a v e a u t o m a t i c a l l y r e c o r d e d .
C e n t e r w e l l d r a g a r m
T h e l a r g e -c l a s s h o p p e r d r e d g e w i l l b e p a r t i c u l a r l y d i s t i n -
g u i s h e d b y a t h i r d d r a g a r m l o c a t e d i n a c e n t e r w e l l d e s i g n e d i n t o
t h e h u l l i n t h e h o p p e r a r e a a l o n g t h e c e n t e r li n e . T h e d r a g a r m i s
r a i s e d a n d l o w e r e d a n d p e r m a n e n t l y l o c a t e d i n t h is w e ll .
D e s p i t e t h e p r e s e n c e o f t h e c e n t e r w e l l , t h e h u l l m o d e l t e s t s
i n d i c a t e t h a t a f u l l -p o w e r l o a d e d d r a f t s p e e d o f a b o u t 1 4 k n o t s
m a y b e e x p e c t e d . T h e m o d e l t e s t in g r e v e a l e d t h a t t h e c e n t er w e l l
a d d s a b o u t 2 1 p e r c e n t r e s i s t a n c e a t s p e e d s o f 12 k n o t s a n d h i g h e r.
T w o o t h e r i n t e r e s t i n g p o i n t s w e r e e v i d e n c e d b y t h e m o d e l t e s t s :
( 1) I t i s b e t t e r t o k e e p t h e d r a g a r m l o w i n t h e c e n t e r w e l l , f o r m i n g
a s o r t o f r o u g h c l o s u r e o f t h e w e l l w h e n t h e s h i p i s u n d e r w a y . T h i s
p r e v e n t s o s c i l l a t i o n o f t h e w a t e r l e v e l i n t h e w e l l , w h i c h i f a l l o w e d
w o u l d r e p r e s e n t a d d e d r e s i s t a n c e a n d a d i s s i p a t i o n o f e n e r g y . ( 2)
B y e l i m i n a t i n g tr a n s v e r s e k e e l s o n s b e t w e e n t h e h o p p e r b o t t o m
d o o r s , h i th e r t o u s e d t o f o r m i n d i v i d u a l h o p p e r d o o r w e l l s, o r
r e c e s s e s , t h e h u l l r e s i s t a n c e w a s d e c r e a s e d a b o u t 1 3 p e r c e n t a t
s p e e d s o f 12 k n o t s a n d h i g h e r . T h u s , a n e w f e a t u r e fo r t h e L C H D
a n d M C H D w i ll b e a s i ng l e h o p p e r d o o r t r o u g h o n e a c h s i d e , i n -
s t e a d o f i n d i v i d u a l d o o r r e c e s s e s .
T h e c e n t e r w e l l d r a g a r m w i ll f e e d t h e t w o i n b o a r d d r e d g e
O C T O B E R 1 9 8 0 3 7 5
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6/14
o
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o
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EXISTING ELONGATED
DRAGARM DRAGARM
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4 0 5 0 6 0 7 0 8 0 9 0 ] 0 0
DREDGING DEPTH-FT
F i g . 5 C a l c u l a te d p u mp p e r fo r ma n c e o f d r e d g e
Essayons
wi th ex i s t i ng
36- in . - i ns ide-d iamete r d ragarms and w i th added p ipe leng ths hypo thes i zed
fo r dep ths g re a te r than 60 f t )
p u m p s . E a c h o f t h e s e p u m p s h a s a d i s c h a rg e d i a m e t e r o f 30 in .
T h e d i a m e t e r o f t h e d r a g a r m s u c t i o n p i p e i s 4 2 i n. , w h i c h i s j u s t
1/2 i n . s h y o f t h e d i a m e t e r r e q u i r e d t o p r o v i d e a c r o s s s e c t i o n e q u a l
t o t h a t o f t w o 3 0 - i n . s e c t i o n s . T h i s s u c t i o n s o u r c e t o g e t h e r w i t h
t h e t w o s i d e d r a g a r m s w i l l p e r m i t s i m u l t a n e o u s o p e r a t i o n o f al l
f o u r d r e d g e p u m p s . T h e p o w e r s e t u p i s s u c h t h a t t h i s c a n b e d o n e
w i t h o n e d r e d g e p u m p g e n e r a t o r p o w e r i n g t h e t w o o v e r s id e p u m p
m o t o r s a n d t h e o t h e r g e n e r a t o r p o w e ri n g th e t w o i n b o a r d p u m p
m o t o r s .
A s p r e v i o u s l y s t a t e d , n o r m a l d r e d g i n g c a n b e c a r r i e d o n w i t h
t h e i n b o a r d p u m p s i f t h e o v e r s i d e p u m p s a r e d i sa b l e d . H o w e v e r,
a p r i n c i p a l r e a s o n f o r p r o v i d i n g c e n t e r w e l l s u c t i o n i s t o a l l o w t h i s
d r e d g e t o b e e s p e c i a l l y e f f e c t i v e i n a g i t a t i o n d r e d g i n g . I n t h i s t y p e
o f d re d g i n g , p u m p i n g t a k e s p l a c e c o n ti n u o u s l y , a n d t h e e x c a v a t e d
m a t e r i a l s a r e b r o a d c a s t o v e r a w i d e a r e a o f t h e o u t s i d e w a t e r
s u r f ac e . T h e s o l i d s a r e o f s u c h f i n e g r a i n a s to r e m a i n s u s p e n d e d
l o n g e n o u g h f o r t h e c u r r e n t s t o c a r r y t h e m e i t h e r to d e e p w a t e r
o r o u t s i d e o f t h e c h a n n e l . I n t h i s m o d e o f d r e d g i n g , t h e l a r g e- c l a ss
d r e d g e w i ll h a v e a b o u t t w i c e t h e c a p a b i l i t y o f th e d r e d g e Goe-
thals, w h i c h i s p r e s e n t l y t h e s e c o n d l a r g e s t d r e d g e i n t h e C o r p s
f l e e t .
T h e a d d e d c e n t e r w e l l s u c t io n c a n b e u s e d a d v a n t a g e o u s l y f o r
c u t t i n g d o w n t h e t i m e t o l o a d t h e h o p p e r s a l s o . O r d i n a r i l y , it
t a k e s a b o u t 1 5 m i n o n m o s t d r e d g e s f o r th e i n i t i a l f i ll i n g o f t h e
h o p p e r s b e f o r e o v e r fl o w co m m e n c e s . W i t h t w i c e th e u s u a l
n u m b e r o f p u m p s i n o p e r a t i o n th e t i m e c a n b e c u t i n h a lf . T h i s
r e d u c t i o n c a n b e s i g n i f i c a n t . I f , f o r e x a m p l e , t h e d r e d g e i s w o r k i n g
o n a 3 - h ( 1 8 0 m i n ) c y c l e, s u c h a s 1 h p u m p i n g a n d 2 h g o i n g to a n d
f r o m t h e d u m p , a r e d u c t i o n o f 71/,2 m i n i n a 1 8 0 - m i n c y c l e g i v e s
a t h e o r e t i c a l p r o d u c t i o n g a i n o f 4. 3 p e r c e n t . ( O f c o u r s e , a s s o o n
a s t h e h o p p e r s a r e i n i t i a l l y f i l le d , t w o o f th e f o u r p u m p s w i l l b e
s h u t d o w n ; o t h e rw i s e , t h e t o t a l f l o w w i ll o v e r w h e l m t h e h o p p e r
a r e a a n d p r e v e n t s e t t l i n g o f s o li d s , a n a l o g o u s t o t r y i n g t o f i ll a
s m a l l b u c k e t w i t h a f i r e h o s e . )
J u s t a s t h e t w o s i d e d r a g a r m s a r e d e s i g n e d t o b e r a is e d e n t i r e l y
a n d s t o w e d o n d ec k , w h e r e m a i n t e n a n c e c a n b e p e r f o r m e d , t h e
c e n t e r w e l l d r a g a r m c a n b e s i m i l a r l y r a i s e d a n d l o w e r e d . A l a d d e r
s t r u c t u r e a r o u n d t h e s u c t i o n p i p e a n d g u i d e s i n th e c e n t e r w e l l
s t r u c t u r e w i ll r e s t r a i n l a t e ra l m o v e m e n t o f t h e d r a g a r m w i t h i n
t h e c o n f i n e s o f t h e w e l l .
O v e r s i d e p u m p s
T w o o f t h e t h r e e n e w h o p p e r d r e d g e s w il l h a v e d r e d g e p u m p s
m o u n t e d o n t h e d r a g a r m s , so th a t d u r i n g d r e d g in g t h e se p u m p s
w i l l b e w e l l s u b m e r g e d . T h i s , o f c o u rs e , g r e a t l y i n c r e a s e s t h e
w e i g h t o f e a c h d r a g a r m a n d m a k e s f o r i n c r e a s e d d r a g a r m h a n -
d l i n g p r o b l e m s , s u c h a s w i n c h p o w e r , w i r e r o p e s i z e s a n d s u p -
p o r t i n g d a v i t s t r u c t u r e . H o w e v e r , t h e y a r e e s s e n t i a l, fo r d e e p
d r e d g i n g p r o j e c t s w h i c h a r e p l a n n e d f o r t h e f u t u r e , a n d t h e i r
i n c r e a s e d e f f e c t i v e n e s s is u s a b l e o n p r o j e c t s a t c u r r e n t d e p t h s .
T h e p e r f o r m a n c e o f c e n tr i f u g a l p u m p s i s l i m i t e d b y s u c ti o n
l i f t c o n s i d e r a t i o n s . H e r e t o f o r e , d r e d g e p u m p s o n h o p p e r d r e d g e s
h a v e b e e n i n s t a l l e d in b o a r d . T h e p u m p s h a v e b e e n s o i n s t a l l e d
a s t o p l a c e t h e s u c t i o n s a s lo w i n th e h u l l a s h u l l s t r u c t u r a l c o n -
s i d e r a t i o n s w o u l d p e r m i t . E v e n s o , w h e n d r e d g i n g a t , s ay , 4 0 - f t
d e p t h a n d p u l l i n g in a s o l i d s / w a t e r m i x t u r e o f p e r h a p s 1 .2 a v e r a g e
s p e c i f i c g r a v i t y , t h e p u m p w i l l p u l l a v a c u u m i n t h e r a n g e o f 22
t o 2 8 in H g , r e g a r d l e s s o f t h e f a c t t h a t t h e p u m p c e n t e r l in e m a y
a c t u a l l y b e s e v e r a l fe e t b e l o w t h e o u t s i d e w a t e r s u r f a c e .
T h e o r e t i c a l l y , if t h e p u m p w e r e t o b e p l a c e d a t t h e c h a n n e l
b o t t o m , t h e p u m p s u c t i o n w o u l d a lw a y s b e u n d e r a h i g h st a t i c
h e a d a n d t h e p u m p w o u l d n e v e r p u ll a v a cu u m . T h e l i m i t a t i o n
o n p u m p p e r f o r m a n c e t h e n w o u l d b e t h e a v a i l a b l e p o w e r f o r
p u s h i n g t h e s o l i d s / w a t e r m i x t u r e u p t h e d r a g a r m p i p i n g a n d i n t o
t h e h o p p e r s .
O n e d r e d g e w a s b u i l t i n E u r o p e w i t h t h e d r e d g e p u m p a c t u a l l y
p l a c e d a t t h e d r a g h e a d o n t h e c h a n n e l b o t t o m . D r e d g e s b u i l t l a t e r
t h a n t h i s on e p l a c e d th e d r e d g e p u m p a b o u t h a l f w a y u p t h e
d r a g a r m , a p p a r e n t l y t o r e d u c e h a n d l i n g p r o b l e m s a n d p r o b le m s -
a r i s in g f r o m s e n d i n g h y d r a u l i c o r e l e c tr i c p o w e r d o w n t h e d r a -
g a r m t o s u c h d e p t h s . O n t h e C o r p s ' m e d i u m - a n d l a r g e - c l a s s
d r e d g e s t h e p u m p s a r e p l a c e d a b o u t h a l f w a y u p e a c h d r a g a r m .
F i g u r e 5 d e m o n s t r a t e s t h e n e e d f o r t h e s u b m e r g e d d r e d g e
p u m p s f o r d e e p d r e d g i n g . I t sh o w s t h e c a l c u l a t e d p u m p p e r f o r -
m a n c e o n t h e d r e d g e
E ssay ons
( p r e s e n t l y t h e C o r p s ' l a r g e s t
d r e d g e ) a t v a r i o u s d r e d g i n g d e p t h s , w i t h e x t e n d e d s u c t io n p i p e
h y p o t h e s i z e d to r e a c h t h e g r e a t e r d e p t h s . T h e p u m p s a r e p la c e d
i n b o a r d o n t h i s d r e d g e a n d t h u s a r e l im i t e d i n p e r f o r m a n c e b y
t h e i n c r e a s e d v a c u u m e x e r t e d a t g r e a t e r d e p t h s . P e r f o r m a n c e
i s s e e n t o b e a c c e p t a b l e u p t o a b o u t 6 0 - t o 6 5 -f t d e p t h , b u t a s h a r p
d r o p - o f f i n p e r f o r m a n c e i s s e e n t o s t a r t a t a b o u t 7 0 f t.
T h e m e d i u m - a n d l a r g e- c l as s h o p p e r d r e d g e s w i ll h a v e i n b o a r d
d r e d g e p u m p s i n a d d i t i o n t o th e d r a g a r m - m o u n t e d p u m p s . T h e s e
a r e n e e d e d p r i m a r i l y f o r d i r e c t p u m p o u t o p e r a t i o n s o t h a t t h e
d r e d g e s c a n u n l o a d t h e m s e l v e s i n t o a sh o r e d i s p o s a l ar e a . H o w -
e v e r, p i p i n g c o n n e c t i o n s a r e s u c h t h a t e i t h e r o r b o t h o f t h e i n -
b o a r d p u m p s c a n a l s o b e u s e d f o r d r e d g i n g i n t h e e v e n t t h e o v -
e r s i d e p u m p s a r e d o w n f o r r e p a i r s. I n s u c h a c a se , th e p u m p /
m o t o r m o d u l e o f t h e d r a g a r m i s r e p l a c e d b y a l e n g t h o f p ip e , o n
t h e m e d i u m - c l a s s d r e d g e . O n t h e l a r g e - c l a s s d r e d g e , t h e i n b o a r d
p u m p s w i ll t a k e s u c t i o n f r o m t h e c e n t e r w e l l d r ag , a n d t h e s i d e
d r a g a r m s w i l l b e s t o w e d o u t o f s e r v ic e :
T h e p u m p s a n d m o t o r s o f t h e d r a g a r m - m o u n t e d u n i ts w i ll b e
c l o s e -c o u p l e d . T h e p u m p s w i ll h a v e 2 8 - in . i n s i d e d i a m e t e r s u c t i o n
a n d 2 6 - in . i n si d e d i a m e t e r d i s c h a r g e . T h e m o t o r s w i l l b e 3 - p h a s e
s q u i r r e l - c a g e i n d u c t i o n t y p e , o p e r a t i n g a t 2 4 0 0 V a n d o i l -c o o l e d .
E n c l o s u r e s a n d s e a ls w i ll b e s p e c i a ll y d e s i g n e d f o r s u b m e r g e d
o p e r a t i o n .
M o t o r s p e e d i s c o n t r o l l e d b y c o n t r o l o f e n g i n e s p e e d , t h a t i s ,
b y c o n t r o l o f a c f re q u e n c y p r o d u c e d b y t h e g e n e r a t o r . S p e e d
c o n t r o l is a u t o m a t i c , b u t t h e o p e r a t o r c a n c h a n g e o v e r to m a n u a l
c o n t r o l i f t h e s i t u a t i o n s o r e q u i r e s .
P u m p p o w e r
C a r e f u l c o n s i d e r a t i o n h a s b e e n g i v e n t o t h e d r e d g e p u m p
3 7 6 M A R I N E T E C H N O L O G Y
8/10/2019 Fortino E P.new Approaches to Th.oct.1980.MT (1)
7/14
T a b l e 4 C o m p a r i s o n o f h o p p e r d o o r s i z e s
D r e dge A r e a o f ba y , f t2 V o l um e o f B a y , yd 3 Area of Door , f t2 A r e a o f D oor % o f a r e a A r e a o f D oor % o f V o lum e C
Comber
class 300 255 19.5 6.5 7.6
Essayons
450 345 23.86 5.3 6.9
Goethals
369 401 23.43 6.3 5.8
Lyman
clas s 196 115 13.77 7.0 12.0
Harding
368 340 21.0 5.7 6.2
McFarland
286 262 18.0 a 6-3a 6.8
Markham 433 340 20.2a 4.7 a 5.9
Pacific
304 125 16.0 5.3 12.8
W es t Co ast 315 150 24.0 7.6 16.0
La rge class b 404 to 644 516 to 743 66.0 16.3 to 10.2 12.8 to 8.9
M ed ium class 425 502 64.0 15.0 12.8
a The se are p rojec ted areas , ha l f of ac tua l . Doors are on a s lope of 60 deg.
b N O TE: H op pe r ba ys no t un i f o r m due t o ho ppe r a r r a nge m e n t . D a t a r e p r e s e n t s pa n o f c ha r a c t e ri s t ic s .
c Square footage of hopp er do or area p er 100 yd 3 .
p o w e r r e q u i r e m e n t s , e s p e c i a ll y f o r d r e d g in g . T h e r e w a s a t i m e
w h e n i t w a s t h o u g h t t h a t t h e m o r e p o w e r o n e c o u l d a p p l y t o a
p u m p , t h e b e t t e r t h e o p e r a t i o n . T h i s t h i n k i n g w a s ju s t i f i e d w h e n
p u m p s d r i v e n b y l a rg e l o w - p r e s s u re r e c i p r o c a ti n g s te a m e n g i n e s
w e r e a c t u a ll y u n d e r p o w e r e d . T h e a d v e n t o f t h e c o m p a c t e l e c tr i c
m o t o r d r i v e e n c o u r a g e d t h e u s e o f h i g h e r p u m p p o w e r , a n d
e v e n t u a l l y so m e d r e d g e s w e r e b u i l t w i th t o o m u c h p u m p p o w e r.
T h i s r e s u l t e d i n f l u i d b e i n g d i s c h a r g e d i n t o t h e h o p p e r s o f a s t a s
t o c r e a t e a d e g r e e o f t u r b u l e n c e t h a t i n h i b i t e d t h e s e t t l i n g o f
s o l id s i n t h e h o p p e r s . U n d e r t h e s e c o n d i t i o n s , s o li d s w e r e b e i n g
w a s h e d p a s t t h e o v e r f lo w s a t a r a p i d r a t e . T h e p u m p s h a d t o b e
s l o w e d d o w n i n o r d e r to i m p r o v e t h e h o p p e r r e t e n t io n r a t e , t h a t
i s, t h e s e t t l i n g r a t e o f s o li d s in t h e h o p p e r s .
A n a n a l y s i s o f t h i s s i t u a t i o n r e v e a l e d t h a t t h e r e i s a n o p t i m u m
a v e r a g e d i s c h a r g e r a t e f r o m t h e p u m p s i n t o t h e h o p p e r s a n d t h a t
t h i s r a t e is p r o p o r t i o n a l n o t t o t h e h o p p e r v o l u m e b u t t o t h e
h o p p e r s u r f ac e a r e a . M a t h e m a t i c a l l y , t h i s is e x p r e s s e d a s
Q = KA
I f A i s t h e h o p p e r a r e a i n s q u a r e f e e t, Q w i l l b e t h e t o t a l d i s c h a rg e
r a t e i n t o t h e h o p p e r s , i n c u b i c fe e t p e r s e c o n d . K i s a f a c t o r h a v i n g
t h e d i m e n s i o n c u b i c f e e t p e r s e c o n d p e r s q u a r e f o o t o f h o p p e r
a r e a . T h e a n a l y s i s , b a s e d o n a s t u d y o f e x p e r i e n c e w i t h a l l
C o r p s - o w n e d h o p p e r d r e d g e s, s o m e b e t t e r t h a n o t h e rs , i n d i c a te s
t h a t t h i s f a c to r s h o u l d n o t e x c e e d 2 . 5 t o a s s u r e a n a c c e p t a b l e
s o l id s s e t tl i n g r a te . T h i s i s k n o w n a s t h e " p o n d i n g r a t i o . " W i t h
t h e a i d o f t h i s f ig u r e , a n d a c a l c u l a t i o n o f t h e t o t a l p u m p h e a d
w h e n f lo w i s t a k i n g p l a c e a t d e s i g n v e l o c i t y a n d d e n s i t y ( u s u a l l y
2 4 fp s a t t h e p u m p d i s c h a r g e a n d 1 .2 s p e c if i c g r a v i t y o f m i x t u r e ) ,
t h e p u m p p o w e r is o b t a i n e d f r o m t h e w e l l - k n o w n f o r m u l a
b h p = QWH/550 E
w h e r e W i s th e m i x t u r e d e n s i t y i n p o u n d s p e r c u b i c f o o t, H i s t h e
t o t a l p u m p h e a d , i n f ee t o f f l u id , a n d E i s t h e a s s u m e d p u m p
e f f i c i e n c y .
I t i s e m p h a s i z e d t h a t t h e p u m p p o w e r s o d e r i v e d s er v e s w e l l
t h e a v e r a g e s i t u a t i o n . T h e r e a r e s i t u a t i o n s w h e r e t h i s p o w e r
c a l c u l a t io n i s n o t b i n d i n g . F o r e x a m p l e , i f a d r e d g e i s p u m p i n g
f i n e s i lt , w h i c h d o e s n o t s e t t l e a t a l l i n t h e h o p p e r s , i t h a s b e e n
f o u n d t h a t t h e m o s t e c o n o m i c a l m o d e o f o p e r a t i o n i s s i m p l y t o
f il l t h e h o p p e r s a s r a p i d l y a s p o s s i b l e t o t h e p o i n t o f o ve r fl o w , a n d
t h e n s t o p p u m p i n g a n d t a k e t h e l o a d to t h e d i s p o s a l a r ea . A t t h e
o t h e r e x t r e m e , s e t t l i n g ta k e s p l a c e v e r y r a p i d l y w h e n p u m p i n g
v e r y c o a r s e g r a i n s a n d o r g r a v e k I n e i t h e r o f th e s e s i t u a t i o n s , a l l
a v a i l a b l e p o w e r w i ll b e u s e d . L i k e w i s e , w i t h a s u b m e r g e d p u m p ,
w h i c h c a n b r i n g u p h e a v i e r d e n s i ti e s u n l i m i t e d b y v a c u u m c o n -
s i d e r a t i o n s , p o w e r i s l i m i t e d o n l y b y m e c h a n i c a l a n d g e o m e t r i c
c o n s i d e r a ti o n s a n d b y h o w d e n s e a m i x t u r e c a n e c o n o m i c a l ly b e
" p u s h e d " u p t h e d r a g a r m b y t h e p u m p .
S o m e c o n s i d e r a t i o n m u s t a l so b e g i v en t o t h e p o w e r r e q u i r e -
m e n t s f o r d i r e c t p u m p o u t o p e r a t i o n ( D P O ) . H o w e v e r , t h e r e -
q u i r e d p o w e r m a y v a r y w i t h l in e l e n g t h , t h e d i s c h a r g e h e a d t o b e
d e v e l o p e d a n d t h e d e n s i t y o f t h e m i x t u r e t r a n s p o r t e d t o sh o r e .
T h e p o w e r l e v e l c a n b e e s t a b l i s h e d s o m e w h a t a r b i t r a r i l y , f r o m
p r a c t i c a l m a c h i n e r y c o n s i d e r a t i o n s , b u t i t is i m p o r t a n t t o c o n -
s i d e r th e h e a d t o b e d e v e l o p e d f o r t h e l a r g e s t c o m b i n a t i o n o f l i n e
l e n g t h a n d d i s c h a r g e e l e v a t i o n , a s t h i s w i l l i n f l u e n c e t h e i m p e l l e r
d i a m e t e r a n d r p m . S i n c e i t w i ll b e d e s i r e d t o p u m p o u t w i t h f u l l
p o w e r o n s h o r t l i n e s a s w e ll a s in t e r m e d i a t e a n d l o n g l in e s , a r a n g e
o f r p m w i t h 1 00 p e r c e n t p o w e r c a p a b i l i t y m u s t b e p r o v i d e d . I t
i s f o r t h i s r e a s o n t h a t d c m o t o r s w i ll d r i v e th e i n b o a r d d r e d g e
p u m p s o f b o t h th e M C H D a n d t h e L C H D .
H o p p e r d o o r a r e a s
A s i g n i f ic a n t c h a n g e i n h o p p e r d o o r s i z in g h a s b e e n a c c o m -
p l i s h e d i n t h e t h r e e n e w d r e d g e s , to m a k e t h e m f a s t e r d u m p e r s ,
a g a i n t o c h o p a m i n u t e o r tw o o f f t h e c y c l e t i m e . A s t e p t a k e n o n
t w o p r e c e d i n g d r e d g e s t o s p e e d u p d u m p i n g w a s t h e e s t a b l i s h -
m e n t o f u n s y m m e t r i c a l h o p p e r s l o p e s, t o p r e v e n t a r c h i n g o f
m a t e r i a l , p a r t i c u l a r l y s a n d , in t h e h o p p e r s . T h e n e x t l o g i ca l
c o u r s e w as t o in c r e a s e th e d o o r si ze to t h e m a x i m u m p e r m i t t e d
b y s t r u c t u r a l d e s i g n .
T a b l e 4 s h o w s s t a t i s t i c s f o r th e h o p p e r d o o r s o f e x is t in g d r e d g e s
a n d o f t h e t h r e e n e w d r e d g e s . T h e i m p r o v e m e n t i n th e l a t t e r i s
e v i d e n t .
T h e s iz e a n d n u m b e r o f h o p p e r d o o r o p e n i n g s i n th e t h r e e n e w
d r e d g e s a r e a s f o ll o w s :
NO. OF DOOR SIZE OF OPEN INGS
DR E DGE OPE NING S L W
Yaquina
6 6 f t 9 in. 3 f t 8 in.
MC HD 12 8 f t 0 in . x 8 f t 3 in .
LC HD 14 8 f t 0 in . X 8 f t 3 in .
A p o s s i b i l it y c o n s i d e r e d , in t h e i n t e r e s t o f s p e e d i n g u p t h e
d u m p i n g p r o c e s s, w a s t o d e s i g n t h e d r e d g e s a s s p l i t - h u l l t y p e s ,
d e s i g n s f a v o r e d b y c o n t r a c t o r s n o w b u i l d i n g h o p p e r d r e d g e s i n
t h e U n i t e d S t a t e s p a t t e r n e d a f t e r E u r o p e a n d e s ig n s . I n t h is
m a t t e r , a s w e l l a s i n o t h e r a s p e c t s o f d e s i g n , t o p - l e v e l o p e r a t i n g
p e r s o n n e l o f t h e C o r p s w e r e c o n s u l t e d p r i o r t o c o m m e n c i n g t h e
d r e d g e d e s i g n s , a n d a c o n s e n s u s w a s o b t a i n e d t h a t f o r t h e s e
p a r t i c u l a r t h r e e d r e d g e s a d o p t i o n o f a s p li t - h u l l d e s i g n w a s n o t
a p r a c t i c a l a p p r o a c h . T h i s d e c i s io n w a s n o t r e a c h e d l ig h t ly , a n d
n o t w i t h o u t e x p e r ie n c e . T h e C o r p s o w n s a n d o p e r a t e s o n e s m a l l
s p l i t - h u l l h o p p e r d r e d g e ( th e
Currituck
W i l m i n g t o n D i s t r i c t ,
i n N o r t h C a r o l i n a ) a s w e l l a s a n u m b e r o f s p l i t - h u l l h o p p e r
b a r g e s , a n d t h e C o r p s m a y v e r y w e ll i n t h e f u t u r e d e s i g n a n d
c o n s t r u c t a n o t h e r s p l i t- h u l l t y p e o f h o p p e r d r e d g e . F o r t h e t h r e e
n e w d r e d g e s , h o w e v e r , t h e r e a s o n s f o r d e f e r r a l o f t h e s p l i t h u l l
a p p r o a c h w e r e c o m p e l l in g . T h e s e i n c l u d e d t h e r e q u i r e d v e r s a -
t i l it y o f t h e d r e d g es . I n p a r t ic u l a r , d i r e c t p u m p o u t t h r o u g h l o n g
l i n e s , t o d i s t a n c e s o f a t l e a s t 2 m i l e s , w i t h o u t a s s i s t a n c e b y e x -
t e r n a l b o o s t e r s t a t i o n s , is a c u r r e n t n e e d a n d o n e w h i c h i s c e r t a i n
O C T O B E R 1 9 8 0 3 7 7
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of wider application. This requires provision of large high-pres-
sure high-power pumping plants forward, not easily accommo-
dated in the half hulls of the split-hull design. The split hull might
have been adopted for the small dredge Yaquina which is not
equipped for direct pumpout capability, but this dredge is re-
quired to operate at shallow draft with a 300-yd load as well as
at 12- and t3-ft drafts with heavier loads. Special problems would
have been encountered designing split hulls with provision for
the self-opening and self-closing capability at several drafts,
which is normally expected of this type vessel at a single draft.
C o n t r o l l a b l e - p i t c h
p r o p e l l e r s
The application of controllable-pitch (CP) propellers for a
hopper dredge is no longer new, since the Corps began this on the
dredge Harding in 1958 and again on the dredge McFarland
completed in 1967. The Harding wheels were each 2000 hp and
those on the McFarland3000 shp. The dredge Pacific repowered
in 1977, was fitted with two CP wheels, each absorbing 1050 shp.
For the large-class dredge each wheel will absorb 5000 shp, and
on the medium-class dredge 3350 shp. On the small dredge Ya-
quina each propeller will absorb about 1050 hp.
This will bring to six the total number of Corps dredges fitted
with CP propellers, constituting evidence of the eminent suit-
ability of such propellers for dredge service. This is so because
dredges operate basically in three propulsion modes: (1) While
dredging, the vessel is in a towing mode, "towing" its dragarms
gainst the resistance of the channel bot tom; (2) when loaded,
t is in a free-running mode at deep draft, going to the dump; and
(3) when light, it is in the free-running mode at light draft with
by the stern, returning to the dredging area. For maximum
ropulsion power in each of these conditions. With a fixed-pitch
em this is not possible. With a control lable-pitch
at 100 percent speed and the pi tch can be adjusted to allow
Prior to the advent of CP propellers, the Corps used dc electric
propulsion with fixed-pitch wheels. Automatic controls
he propeller
for the free-running conditions, so that full horsepower is
The availability of full power under any operating mode can
here and a minute there off the dredging
off this cycle time represents better
is lighter and less costly than the equiva-
by the CP propulsion control mechanisms are some-
offset by the elimination of propulsion generator and motor
H o p p e r c a p a c i t i e s
A hoppe r dredge is nominally designed to carry, say, 6000 yd 3
long tons (LT) per cubic yard
without exceeding the designloaded draft o f the hull when all fuel
and water tanks are full. As the consumables are expended, the
vessel can obviously carry more sand load without exceeding the
permissible loaded draft . If, for example, the vessel carries 1170
LT of fuel and water, then, at the 90 percent bur nout point, the
hoppers could contain an additional 702 yd 3 of sand without
exceeding the loaded draft, provided, of course, that the hopper
volume is sufficient to hold the extra sand.
But the dredges do not operate exclusively in sand. Frequent ly,
they dredge much lighter bottoms, in some cases encountering
bottom material densities as light as 75 lb/ft s, or about 0.9 LT/
yd 3. It would take 11 170 yd3 of this light material to have a
weight equal to 6702 yd 3 of wet sand A commonly encountered
mud has a density of about 1.2 LT/yd3; 8378 yd 3 of this material
is equal in weight to 6702 yd 3 of wet sand.
It is not practical to design a hopper dredge with hoppers of
such depth as to accommodate the entire spectrum of bottom
densities in sufficient volume always to load the hull to its de-
signed draft. A limit is reached when the center of gravity of the
load in the hoppers gets so high as to affect adversely the vessel
stability. Contributing to this effect is the fact that the weights
of the hopper distribution piping, valves, hopper structure and
all other appurtenances over the hopper area are also moving
upward as the hopper coamings are raised in the effort to enclose
more hopper volume.
Nevertheless, within this limitation the effort should be made
to a ccommodate a reasonably wide range of densities. With the
three new dredges it has been found that this could be done.
Figure 6 is a chart showing the capabilit ies in this respect of the
LCHD. This dredge is intended to carry 6000 yd3 of wet sand at
29.5-ft draf t with all tanks full. At 90 percent burnout it will carry
about 6700 yd 3 of sand. The maximum hopper volume was set
at 8400 yd3. Depending on the specific gravity of the hopper load,
the volume of material that can be carried at any condition of
burnout at 29.5-ft draft is shown in Fig. 6.
A similar chart for the MCHD, designed to car ry 4800 yd 3 of
wet sand (1.5 LT/ydU), would show the volumes of lighter den-
sities that can be carried at its loaded draft of 27 ft, up to its
maximum hopper volume of 6000 yd3.
H o p p e r o v e r f l o w l e v e l
A dredge can fill its hoppers only to the level of its overflow
weirs. At this point the hopper fluid spills over the weirs and is
conducted via overflow troughs and ducts to the sea, or sur-
rounding water. Most dredges operate with one or more fixed
overflow levels, selected by opening or closing louver-type
structures in the hopper coaming or sides. The location of the
overflow level is now determined with some regard for promoting
the maximum production capability of the dredge during the
burnout cycle. This is best illustrated by example.
One requirement of the small shallow-draft dredge Yaquina
is that it must be capable of carrying 300 yd3 of wet sand at a draft
not in excess of 10 ft when all fuel and water tanks are full. Since
there had to be provided enough consumables for 12 days of op-
eration, the tank contents, 180 LT, constitute a respectable
percentage relative to the hopper load. In this p~lrticular instance,
the sand used in design computa tions had a wet density of 1.35
LT/yd 3. Thus the weight of a 300-yd load is 405 LT. At the 90
percent burnout point, therefore, the dredge theoretically could
carry 567 LT or 420 yd3 of sand.
Consider, now, the two extremes: (1) If the overflow level is set
at 300 yd3, then the dredge can initially load up to 300 yd, but as
fuel and water are consumed it will be unable to hold any more
than 300 yd. Thus, as burnout occurs, the ship will not be loaded
to design draft. (2) At the other extreme, suppose the overflow
level is set at 420 yd. Initially, then, the hoppers mus t be limited
to that weight of sand plus water above the sand such that to-
gether the total weight of hopper contents does not exceed 405
M A R I N E T E C H N O L O G Y
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d )
123
rr
130
c h
g
85OO
M A X H O P P E R V O L U M E : 8 4 0 0 C U Y D S
. . . . -~Z . . . .
_ _ ~ ~'3_2~ ~ ~ ~
j . - / ~ / /
6 5 0 C ~ /
60C0 IO 20 30 40 50 60 70 80 90
PERCENT BURNOUT
F i g . 6 L C H D h o p p e r c a p a c i t y . C a r r y in g c a p a c i t y o f v e s s e l a t 2 9 .5 - ft d r a f t, b a s e d o n
p r e l i m i n a r y d e s i g n t r i m a n d s ta b i l i ty c o n d i t i o n s a s a f f e c te d b y ma te r i a l d e n s i t y . Bu r n o u t
i n c l u d e s p o ta b l e a n d f re s h w a te r s , f u e l o i l a n d d o me s t i c s to r e s
A s i m p l e a l g e b r a i c c a l c u l a t io n w i l l s h o w t h a t t h e i n i t i a l s a n d
b i l i t y is a b o u t 1 4 0 y d S . A t 9 0 p e r c e n t b u r n o u t , w h e n 1 62 L T
c o n s u m a b l e s h a v e b e e n e x p e n d e d , t h e p e r m i s s i b l e w e i g h t o f
p e r c o n t e n t s i s 5 67 L T , s o t h a t t h e d r e d g e c a n , a t t h i s u l t i m a t e
t i n t h e p r o v i s i o n i n g c y c l e , c a r r y 4 2 0 y d ~ o f s a n d . A s t r a i g h t
c a n b e d r a w n b e t w e e n t h e s e t w o s a n d c a p a c i t i e s t o s h o w h o w
s a n d w i ll b e c a r ri e d a t i n t e r m e d i a t e b u r n o u t p e r c e n t -
I t i s s e e n f r o m F i g . 7 t h a t A l t e r n a t i v e 1 n e v e r p e r m i t s t h e s a n d
r i s e a b o v e i t s i n i t i a l 3 0 0 - y d l e v e l . A l t e r n a t i v e 2 s t a r t s w i t h
n d a t t h e 1 4 0 - y d l e v el , b u t t h e s a n d l e v e l r i s e s p r o g r e s s i v e l y
u t u n t i l i t r e a c h e s th e m a x i m u m p e r m i s s i b l e 4 2 0 - y d
. O v e r t h e e n t i r e p r o v i s i o n i n g c y c l e , w h i c h l e v e l r e s u l t s i n
a r r y i n g t h e m o s t s a n d ? I s t h e r e a n i n t e r m e d i a t e o v e r f l o w l e v e l,
es s t h a n 4 2 0 y d b u t m o r e t h a n 3 00 y d , w h i c h o v e r th e p r o v i -
i o n in g c y c l e w i ll p e r m i t c a r r y i n g a m a x i m u m a m o u n t o f
a n d ?
T h e a n s w e r is y e s , a n d r e a d e r s w i t h a n y f o n d n e s s f o r m a t h e -
m a t i c s c a n d o w h a t t h e a u t h o r d i d a n d s e t t h i s u p a s a c a l c u lu s
p r o b l e m t o f i n d t h a t v a l u e o f o v e r fl o w le v e l w h i c h , w h e n i n t e -
g r a t i n g t h e t o t a l p r o d u c t i o n u n d e r t h e c u r v e b e t w e e n t h e 0 a n d
9 0 p e r c e n t b u r n o u t l i m i t s , r e s u l t s in m a x i m u m p r o d u c t i o n .
T h e r e s u l t is
Ss
- -
Sw Tb
C = Y , 4
Ss Ss
w h e r e C i s t h e c u b i c y a r d s a t t h e o p t i m u m o v e r f l o w l e v e l, Yn t h e
n o m i n a l d e s i g n s a n d l o a d w i t h a l l t a n k s f u l l ( 3 0 0 y d 3 i n t h e
f o r e g o in g e x a m p l e ) , Ss a n d S w t h e d e n s i t y o f s a n d a n d w a t e r
r e s p e c t i v e l y , i n lo n g t o n s p e r c u b i c y a r d , a n d Tb t h e l o n g t o n s o f
c o n s u m a b l e s e x p e n d e d a t t h e e n d o f t h e b u r n o u t p e r i o d .
A p p l y i n g th i s r e s u l t to t h e c h o s e n e x a m p l e
1 . 3 5 - 0 .7 7 1 1 62
C = 300 4 = 351
1 .35 1 .35
A c c o r d i n g l y , a f i x e d o v e r f l o w l e v e l f o r t h e
Yaquina
w o r k i n g a t
1 0 - f t d r a f t w o u l d b e p l a c e d a t 3 5 0 c u b i c y a r d s . T h i s v e s s e l is a ls o
p r o v i d e d w i t h h i g h e r o v e r fl o w l e v el s fo r w o r k i n g a t d r a f t s u p t o
1 2 f t .
I f a c o m p a r i s o n i s m a d e o f t h e t o t a l a r e a s u n d e r t h e c u r v e s o f
F i g . 7, i t w i l l b e f o u n d t h a t t h e y a r e i n t h e r a t i o o f a b o u t 1 01 t o
1 0 8 t o 1 1 7 . I t i s s e e n t h a t t h e o p t i m u m o v e r f l o w le v e l p e r m i t s a
s i z e a b le p e r c e n t a g e i n c r e a s e i n p r o d u c t i o n o v e r t h e e x t r e m e a l -
t e r n a t i v e s .
4 0 0
u ~
3oo
u
a