Stability And Trim, United States Coast Guard / National Maritime Center Merchant Mariner Exam Test Question Pool.

Established in 1996. SeaSources.net, Training for Mariners is a registered trademark. Follow @SeaSourcesnet

The First with Online Study for the Maritime Industry.

Multiple Choice Quizzes with Illustrations for United States Coast Guard Exam Preparation Assistance.

Home Page Exam Question Downloads Download TesTTaker Software Free Sample Downloads Maritime Links Member Comments Contact SeaSources Boat Jobs Available

Click Here to Register and Begin Preparing For Your Exam with SeaSources Online Study.

Download Illustrations

Practice Final Exams

Downeast Maritime, Inc.

SeaSources Group Testing Service

SeaSources Celestial Navigation Training Videos

The subjects listed below are currently available for testing in the new online study room and are available for download to your computer. Click on subject below for details.

Vessel Nomenclature New

Engineering Examination Questions

All Engine Room Questions

Engine Room Electrical

Deck Examination Questions

Master 25/50/100 Ton

Operator Uninspected Passenger Vessel

All Deck Questions

Able Seaman Questions

Advanced Subjects, Unlimited Oceans Master, Mate

Rules of the Road

Aids to Navigation Glossary Included

Breathing Apparatus

Cargo Equipment

Cargo Stowage

Charts and Publications

Fire Fighting Glossary Included

Instruments and Accessories

Lifesaving

Lifeboatman

Liquid Cargo and Bunkering

Marine Radio Operator

Meteorology "Glossary Included"

Mobile Offshore Drilling Unit

New Revised Questions

Celestial Navigation

Navigational Procedures

Pollution Control and Prevention

Rules and Regulations

Plotting/Navigational Problems

QMED

Survival Craft

Seamanship Glossary Included

Sailing Vessels

Ship Handling

Ships Construction Glossary Included

Ships Business

Signaling

Stability and Trim Glossary Included

Tankerman

Tides and Currents Glossary Included

View Screenshots of "TesTTaker" Software

Download or Upgrade "TesTTaker" Exam Software

View Screenshots/Tutorial of Online Study

View comments from SeaSources Members

For details on license requirements, application forms, licensing fees, and testing locations, visit the United States Coast Guard / National Maritime Centers web site and look under Mariner's information center. The questions used in the online study are once again available to the public in PDF format from the NMC link above. The illustrations are not yet available for some of these questions.

MARYLAND NAUTICAL Great source for practice charts and study guides

NAVIGATION COURSE

National Oceanic & Atmospheric Administration (NOAA)

The Navigation Center

Chart No. 1 Nautical Chart Symbols Abbreviations and Terms

Bluewater Books and Charts

Search CFR'S Online

Additional Online Testing Services for School Administrators

Required Subjects for all Deck Licenses

Required Subjects for all Engineering Licenses

Required Subjects for Mobile Offshore Drilling Units, MODU.

Sea Service Requirements for Coast Guard Licenses

Vessel Delivery Service

Stability and Trim

Click here to review the new question databank from the NMC.

Click here to see detailed video instructions on using SeaSources.net online license preparation.

(See Glossary Below)

STABILITY DATA REFERENCE BOOK, information on the cargo ship S.S. AMERICAN MARINER or the tank ship S.S. NORTHLAND to determine the correct answer.

Download Blue pages Download White pages Download Salmon pages

Adobe Reader Required To View These Downloads

See sample solution for free surface correction problem SS American Mariner.

See sample solution for righting moment problem

Sample solution for Vertical Center of Gravity (VCG) problem M.V. Surveyor.

Sample solution for Vertical Center of Gravity (VCG) problem M.V. Hudson

Join the thousands of members who have successfully and affordably prepared for their Coast Guard Exam with SeaSources.net. If you do not see what you are looking for here go to the online study. When using the service we recommend using either Mozilla Firefox, Google Chrome, or the latest version of IE as a browser. Listed below is a table of contents of the questions on this subject as they appear in the new online study. If you arrived on this page by doing an internet search on this subject then you need to proceed to the Enter Online Testing Site link above and Register to create an account and get the full benefits of using this site. The latest multiple choice questions on this topic can be downloaded and installed to your computer by creating an account in the online study and installing the latest version of the "Betabox Software".

The subject of Stability and Trim consists of 884 question. 586 on working problems and 298 questions on stability general which can be taken as 20 question quizzes, all at once, or randomized. We also have the ability for you to configure and assign your own practice final exams in the online study as well as in the installed stand alone software. There are 177 illustrations associated with this subject. If you are studying for your United States Coast Guard Deck License exam you should continue working through all of these quizzes until you are scoring 70% or better on all of them.

If you are currently a user of the New Online Study, any downloads and purchases made through your old online study account can be rolled over to the new software based on the New Online Study Database.

UNDER DECK EXAMINATION QUESTIONS

STABILITY AND TRIM

DEFINITIONS

DRAFT AND DENSITY

DRAFT/DISPLACEMENT

FREE SURFACE - DEF, MISC

GM/KG/KM-DEF,MISC

LIST

MISCELLANEOUS

EVALUATION

DAMAGE STABILITY

PROBLEMS

AVAILABLE GM MARINER CLASS

CHANGE OF DRAFT FROM TRIM TABLE MARINER CLASS

DAMAGE STABILITY

DB TKGE FOR 1 CMPT STD

BALL FOR REQD GM/MIN REG GM

DETERMINE DRAFTS MARINER CLASS

DRAFT AND DENSITY

DRAFT/DISPLACEMENT

FLOODABLE LENGTH - CURVES OF FORM

FREE SURFACE CORRECTION MARINER CLASS

FS, FC REDUCTION OF GM

INCLINING EXPERIMENT

KG OF CARGO OR LIQUID LOAD MARINER CLASS

LCG OF CARGO OR LIQUID LOAD MARINER CLASS

LIST

GM

ROLLING PERIOD

TRIM

USE OF TABLES

DETERMINE DRAFT IN FRESH WATER

DETERMINE KM

DETERMINE MT1

DETERMINE DISPLACEMENT FRESH WATER

DETERMINE DISPLACEMENT SALT WATER

Glossary of Stability and Trim Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Added Weight Method: A method of solving for damage stability where the water which enters the vessel is considered as an added weight.

Anti-rolling Devices: These include the bilge keel, or rolling chocks, anti-rolling tanks, gyro stabilizer, and stabilizing fins.

Return to top

B

B - Symbol for center of buoyancy.

Beam-draft Ratio: Ratio of beam to draft. This ratio has an important bearing on the height and movement of M.

Block Coefficient: A coefficient of fineness which expresses the relationship between the volume of displacement and a block having the length, breadth, and draft of the vessel.

BM: Symbols for metacentric radius; distance between B and M.

Buoyancy: The upward vertical support supplied by the liquid in which a vessel is floating.

Return to top

C

Capacity Calculator: A device which calculates quickly the capacity of a hold at any point in the loading of the hold.

Capsize: To "turn turtle" due to loss of transverse stability.

Center of Buoyancy: That point at which all the vertically upward forces of buoyancy are considered to be concentrated; the center of volume of the immersed portion of the vessel.

Center of Flotation: The center of gravity of the waterplane; the point around which a vessel trims.

Center of Gravity: That point at which all the vertically downward forces of weight are considered to be concentrated; the center of the mass of the vessel.

Change of Trim: The algebraic sum of the initial trim and the trim after weight has been shifted, loaded, or discharged.

Compartment Standard: The number of compartments in any location which can be flooded up to the margin line without causing the vessel to sink. Based on certain permeability, usually 63 percent for cargo spaces and 80 percent for machinery space.

Couple Moment: Created by two equal forces exerted in opposite directions and along parallel lines. In stability, the forces through G and B.

Crank Ship: A vessel with small metacentric height; top-heavy.

Criterion of Service Numeral: A number (usually between 23 and 123) based on the dimensions and service in which the vessel is engaged, which is used to obtain the subdivision requirements for a vessel.

Cross Curves of Stability: Curves for various angles of inclination up to 90 degrees. The ordinates are displacements. Intersections of ordinates with curves produce the abscissas (righting arms).

Curves of Form: See Hydrostatic Curves.

Curves of Statical Stability: See Statical Stability Curves.

Return to top

D

Damage Stability: Stability of a vessel after flooding.

Dead Rise: The distance the bottom rises in one half the beam.

Deadweight Scale: A scale of values of TPI, MT1, displacement, and deadweight, for all drafts.

Deep Tank: A tank usually used for carrying sea-water ballast, but also used for carriage of fuel oil and cargo.

Deflection: Distance along the batten that the inclining experiment pendulum moves in a horizontal direction after inclination.

Degree of Subdivision: A relative term expressing the relation of actual subdivision to required compartment standard.

Density: The density of any given material is the weight of that material that occupies a given volume (i.e., weight per unit volume). Therefore, density may be expressed as the weight per gallon or weight per cubic foot or weight per other unit of volume of any liquid or bulk (solid) material. Using a common example: fresh water has a density of 62.4 lbs. per cubic foot This means that a cube of fresh water, one foot on each side, weighs 62.4 lbs. Salt water is more dense than fresh water with a density of 64.0 lbs. per cubic foot.

Displacement: The weight of water displaced by a floating object. Equal to the weight of the object.

Draft: The linear distance from the bottom of the keel to the waterline.

Dynamical Stability: The energy which a vessel possesses to right herself due to the work performed in inclining her.

Dynamic: Referring to movement.

Return to top

E

Equilibrium: Vessel is in a state where there is no movement; G must be in the same vertical line with B.

Even Keel: A condition when the draft forward is the same as the draft aft.

Expansion Trunk: Narrow upper part of tank on an oil tanker, used as an allowance for expansion of oil at high temperatures.

Return to top

F

Factor of Subdivision: A number less than 1 obtained from curves of factor of subdivision which, when multiplied by floodable length produces permissible length of compartment. It is the reciprocal of the compartment standard.

Flare: The outward curvature of a ship's side.

Floodable Length: At any point of a ship, the length of the space having its center at that point, which can be flooded without causing the ship to sink.

Founder: To sink due to loss of reserve buoyancy.

Freeboard: The distance from the waterline to the upper deck.

Free Surface: Condition existing when a liquid is free to move in the tank or compartment of a vessel. Causes a virtual rise of the ship's center of gravity.

FSC (free surface correction)

FSM (free surface moment)

Return to top

G

G: Symbol for center of gravity.

GG: Distance that the center of gravity moves due to weight movement or free surface of liquid.

GM: Metacentric height; distance from the center of gravity to the metacenter.

GZ: Righting arm or lever. Distance between lines of force through G and B.

Return to top

H

Heel: The transverse angle of inclination of a vessel.

Heeling Moment: The moment tending to heel the vessel. Opposed by the righting moment.

Heterogeneous Cargo: Cargo of a varied nature; general cargo.

Homogeneous Cargo: Cargo of the same density throughout.

Hydrostatic Curves: Curves based on the form of the immersed portions of a vessel. They include:

Coefficients of fineness,

TPI,

displacement in salt and fresh water,

MT1,

Height of B and M above the keel,

Increase of displacement for one foot trim by the stern.

Hold: The large, bottom space of a cargo compartment of a vessel.

Return to top

I

I: Symbol for moment of inertia.

Initial Stability: Stability of a vessel for small angles of inclination (up to 15 degrees).

Inner Bottom: Tank tops over double bottom tanks, forming an inner skin for the vessel.

Intact Buoyancy: Intact space below the surface of a flooded area.

Inclining Experiment: Experiment, which by inclining a vessel a few degrees, produces with the aid of a formula the metacentric height (GM) and the position of the center of gravity of a vessel.

Return to top

J

K

K - Symbol for keel.

KB - Linear distance from the keel to the center of buoyancy. (When vessel is upright.)

KG: Height of center of gravity above keel.

KM: Height of metacenter above keel.

Return to top

L

Light Displacement: Weight in long tons of vessel in a light condition.

List: Transverse angle of inclination of a vessel.

Load Displacement: Weight of vessel in long tons when fully loaded.

Longitudinal Center of Gravity (abbreviated LCG) is a term that may be applied to your vessel as a whole or to any individual tank or compartment within your vessel. When applied to the vessel as a whole, LCG refers to the longitudinal position of the center of gravity or the location of the vessel's center of gravity in relation to the bow and stern. When applied to a tank or compartment, LCG refers to the longitudinal distance of a point within that tank or compartment from the vessel's tipping center.

Longitudinal Stability: Tendency of a vessel to return to its original longitudinal position. Longitudinal stability terms:

Longitudinal metacenter,

GML,

BML,

Center of buoyancy,

Center of gravity.

Return to top

M

M: Symbol for metacenter.

Mean Draft: That draft midway between the draft forward and draft aft.

Metacenter: The highest point to which G may rise and still permit the vessel to have positive stability. Found at the intersection of the line of action of B when the ship is erect with the line of action of B when the ship is given a small inclination.

Metacentric Height: Distance between G and M. Used as a measure of initial stability.

Metacentric Radius: Distance between B and M.

Moment: Created by a force or weight moved through a distance.

MT1: The moment necessary to change the trim of the vessel one inch.

Return to top

N

Negative Stability: Exists when G is above M, that is, when there exists a negative GM or GZ.

Neutral Equilibrium: Exists when G coincides with M. The vessel does not tend to return to an upright position if inclined, nor to continue its inclination if the inclining force is removed.

Return to top

O

P

Parallel Sinkage: Vessel increases her draft so that the drafts forward and aft are increased by the same amount; increase of draft without change of trim.

Permeability: The percentage of the volume of a compartment which can be occupied by water if flooded.

Permeability of Surface: The percentage of the surface of a flooded compartment which is occupied by water.

Peak: Found at the ends of the vessel are the fore peak and after peak spaces.

Permissible Length: Maximum length permitted between main, transverse bulkheads. Found by multiplying factor of subdivision by floodable length.

Plimsoll Mark: The load line which is stenciled in and painted amidships on the side plating.

Return to top

Q

R

Ralston Stability and Trim Indicator: A device for calculating the stability and trim of a vessel by adding or removing representative weights on a metal profile of the vessel.

Range of Stability: The end of the range of stability is reached at an angle of inclination when the righting arm is equal to zero. Practically, the range of stability is ended shortly after deck edge immersion in most vessels.

Reserve Buoyancy: The volume of all intact space above the waterline.

Righting Arm: The distance between the line of force through B and the line of force through G, when there is positive stability.

Righting Moment: The product of the weight of the vessel (displacement) and the righting arm (GZ).

Rolling Period: The time it takes a vessel to make a complete roll, that is, from port to starboard and back to port again.

Return to top

S

Settlers: Tanks used for "settling" fuel oil before using.

Slack Tank: Tank which is not completely filled or empty.

Specific Gravity of a body (which may be a solid, liquid or gas) is the ratio (i.e., a comparison) of its density to the density of pure fresh water at a temperature of 4° Celsius. The temperature of 4° Celsius is specified because water is at its most dense state at that particular temperature. You can determine specific gravity by dividing the weight of salt water or any other liquid or solid by the weight of an equal volume (i.e., the same number of gallons) of fresh water.

Sponsons: Bulges on the upper sides of canoes and other small boats which add breadth when the boat inclines.

Stability: The tendency of a vessel to return to an erect position after being inclined by an exterior force.

Stability Tables: Tables which show the proper and improper distribution of weights and their effect on the GM and rolling period of a vessel.

Stabilogauge: A device which automatically calculates GM when actuators indicating weights loaded or discharged are turned.

Statical Stability Curves: Curves for various displacements up to and past load displacement. The ordinates are angles of inclination. Intersection of ordinates with curves produces -the abscissas (righting arms).

Stable Equilibrium: Exists when M is above G. A vessel will tend to return to an erect position if inclined to a small angle.

Stiff Ship: Vessel with low center of gravity and large metacentric height.

Swash Bulkhead: Longitudinal bulkhead, with or without lightening holes, installed for the purpose of reducing free surface effects.

Synchronous Rolling: Occurs when the rolling period of the vessel is the same as the wave period; a condition to be avoided.

Return to top

T

Table of Stability: See Stability Tables.

Tender Ship: See Crank Ship.

TIPPING CENTER OR LONGITUDINAL CENTER OF FLOTATION (LCF) These two terms are essentially the same and refer to the point around which a vessel "trims". Trim is defined as the difference between the draft forward and the draft aft. One practical and well-known method of "trimming" an offshore supply vessel, for example, is to pump seawater into either her forepeak or afterpeak (i.e., "wraparound") ballast tanks.

TPI: Number of tons necessary to change the mean draft of a vessel one inch; varies with draft.

Transverse Metacenter: See Metacenter.

Transverse Center of Gravity is referenced in the transverse (athwartships) direction from the centerline of the ship and is labeled TCG.

Trim: Difference between the drafts forward and aft.

Trim Calculator: A device which calculates quickly the trim of a vessel after loading or discharging.

Trimming Tables: Tables which calculate change of mean draft and change of trim after loading, discharging, or shifting of weights.

Trimming Tanks: The forward and after peak tanks.

Tumble Home: The inward curvature of a vessel's sides.

Return to top

U

Unstable Equilibrium: Exists when G is above M. Vessel does not tend to return to an erect position after being inclined but, for small angles, tends to continue inclination.

Return to top

V

Vertical Center of Gravity (VCG): The vertical height of the center of gravity of a compartment above its bottom, or of the center of gravity of a vessel above its keel. Vertical Center of Gravity is a term that may be applied to your entire vessel. The term may also be applied to any individual tank, compartment or weight on or within your vessel.Consequently, VCG may be given a dual definition as the 1) vertical height of the center of gravity of the contents of any tank or compartment above its bottom, or 2) the vertical height of the center of gravity of the entire vessel above its keel.

Virtual Rise of G: Caused by the "swinging" motion of water in a slack tank.

Volume of Displacement: The volume of water displaced by a floating object; weight of this volume of water is equal to the weight of the object.

Return to top

W

Waterplane: The plane defined by the intersection of the water in which a vessel is floating with the vessel sides.

Waterplane Coefficient: A coefficient of fineness which expresses the relationship between the area of the water plane and a rectangle having the length and breadth of the vessel at that waterplane.

Wing Ballast Tank: Tank, usually located in the upper 'tween deck on either side of the engine room casing, which is especially valuable in raising the center of gravity of a light ship. These tanks also serve to dampen the period of roll of a vessel. Any weights" winged out" increase the" mass moment of inertia" of a vessel, thus dampening rolling.

Return to top

X

Y

Z

No pop ups, Banners, Spam, Garbage, Advertisements, Hidden Gimmicks or any proverbial "Fine Print" to deal with. What you see is what you get. Just down-to-earth information and this site is dedicated to keeping it that way.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of SeaSources.net.

Copyright 2000 by SeaSources.net. All rights reserved.
Revised: 29 May 2013 17:33:29 -0500

Contact Phone: 207-629-7004
Skypename: seasources.net

Return to top