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Intro to using Mo Boards

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Intro to Relative Motion

Learning Objectives:

Comprehend theory of relative motionvs. true motion

Understand the difference betweenrelative and true bearings

Develop a basic understanding formaneuvering board concepts

Begin basic plotting techniques Bring plotting tools and blue

maneuvering board workbook to classdaily

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Motion

Motion - movement of anobject from one point toanother point

p1

p2

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Motion

measure movementin termsof

p2

p1

1. Direction and distance

2. Direction and speed of object

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Relative Movement

All objects move relative tosomething else

Relative movement - motionmeasured with respect to anarbitrarily selected object(which may or may not havemovement)

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Relative Movement

Must have reference withrespect to which motion canbe describedSHIP VS. SHIP

Key - all motion is relativeto some reference

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Relative Movement

Represented on maneuveringboardConsider yourself onboard ship

monitoring actions of other ships

Find actual course and speedrequired to bring about desiredchange in relative position inmaneuvering a ship at sea

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True/Actual Movement

True movement - motionmeasured with respect to theearthExamples

COG/SOG for shipcar driving 70 mph

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Bearings

Bearings - direction of an objectfrom an observer expressed in

terms of degreesstated in degrees using three

digits from 000 degrees

clockwise through 360 degreesLine of sight - straight line

between observer and object

being observed

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Line of Sight

Each line of sight has twodirections which differ by180 degrees

Heading of either ship does

not affect the LOS

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Bearings

True Bearing - bearingmeasured clockwise from true

north in degrees to line of sightheading of ship does not

affect bearing

reference line true northremains same regardless ofmovement

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Bearings

Relative Bearing - measuredin degrees from shipsheading (course) clockwiseto the observed objectRemember - course of reference

ship will always affect relativebearing because it is referenceline for relative bearing

000 R

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Ships course =

045T

135T

?

N

EW

S

RELATIVE BEARINGS

?

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Ships course =

045T

135T

180R

N

EW

S

RELATIVE BEARINGS

000R

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Relative Bearings

Identify relative bearingswith cardinal/internalcardinal points as they arerelative to the heading of theship (pg.2-5)

Identify with degrees to theright/left of ships heading

max 180 R

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Bearing Formula

Equation to convert Relativeto True

TB = SH + RBExample - Your ship is on

course 090 T. Ship Y bears

180R from you.TB = 090 T + 180 R

TB = 270 T

SH 090 T

RB - 180 R

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Bearings

Direction of bearings btwntwo ships can be expressedtwo waysFROM A SHIP

TO A SHIP

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FROM A SHIP (from A)

B A

Bearing of B is 270 T from A

B bears 270 T from A

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TO A SHIP (to A)

B A

A is bearing 090 T from B

A bears 090 T from B

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The Maneuvering Board

Use - to analyze relativemotion

Determine if risk of collisionexits - CPA

Determine exact Course & Speed

of other shipSolve for precise maneuveringrecommendations for own ship

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Mo Board

Looks just like a Radar Screen

Information being plotted(bearing and ranges to surfacecontacts) is coming from shipsradar

New Radar systems do Mo Boardfor you!

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Mo Board

1:1 measured from center ofplot

2:1, 3:1, 4:1, and 5:1 on left &right marginsYards vs. nautical miles

5:1 usually used for speed scale

Always label which scales youare using with S for speedand D for distance.

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Example

How to plot a bearing:Contact bearing 020 T at 12,000

yds

How to plot a course and

speed:Reference ships course is 090 Tand speed 20 knots

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Mo Board

3-Scale Nomogram at bottom Time(min), Speed (kts), Distance(yds

or nm). If you know 2 of the 3, you can solve

for the third by drawing a linethrough the nomogram

or you can use a calculator or yourhead.

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Mo Board

Plotting techniquesPlot only true bearings on board

(convert relative to true prior toplotting)

plot reference ship in center R

course/speed knowncourse/speed expected to

remain constant throughoutmaneuver

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Mo Board

plot all other ships M inproper relation to R shipM for maneuvering ship

M1 first observation, M2 nextobservation etc....

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Example

At time 0800, ship M bears090 T from your ship at a

distance of 4,000 yds.

Ten minutes later, ship M

bears 100 T from your shipat 3,500 yds

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Maneuvering BoardTechniques

Read carefully andunderstand problem

Work each problem step bystep

Measure and plot correctlyUnderstand basic

fundamentals of MOBOARD

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Maneuvering BoardTechniques

Know the difference btwncourseand bearing

Use sharp pencil

Practice to become proficient

Mo Board tutorial onlineChecklist of Maneuvering

Board Work Habits 2-14

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Homework Terms

Skunk

OTC

CC

Own ship vs. Guide ship

Collision course - CBDR

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Sample problem

You are on a DD on course255 T. Your lookout reports

a contact bearing 085 R.What is the true bearing ofthe contact from you?

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Answer

340 T

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Same problemdifferentquestion

You are on a DD on course255 T. Your lookout reports

a contact bearing 085 R.What is your true bearingfrom the contact?

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Answer

160 T

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Sample problem

At 0800, CIC reports acontact bearing 160 T at

14,000 yards. Ten minuteslater the contact bears 155 Tat 10,000 yards.

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Answer

160 T, 14,000yds

155 T, 10,000yds

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Sample problem

The guide ship is on course250 T. You sight the guide

bearing 230 T at 5,000 yards.You are ordered to takeposition 070 T, 7,000 yards

from the guide.

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Answer

050 T, 5,000 yds

070 T, 7,000 yds

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Student Sample problem

The guide ship is on course300 T. You sight the guide

bearing 330 T at 6,000 yards.You are ordered to takeposition 110 T, 6,500 yards

from the guide.

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Answer

150 T, 6,000yds

110 T, 6,500yds

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Sample problem

Own ships course is 210 Tat speed 15 knots. Skunk

A bears 160 T at 7 miles at1600. At 1610, Skunk Abears 155 T at 10,000 yards.

Will skunk pass ahead orastern of you?

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Answer

Astern

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Homework

Homework problems: 2.2,2.3, 2.6a-d, 2.8, 2.11-2.13, 2.15,

2.20, 2.22, 2.23, 2.25Read blue Maneuvering

Board Wkbk Cpt. 3