Monday, January 4, 2016


Illustration by: Cmglee Creative Commons Attribution-Share Alike 3.0 Unported license.
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Editor's note: This post is a permanent feature in our Merchant Marine Interest Section collection of Officer Candidate Training Videos.

STABILITY IN A NUTSHELL is the art and science of managing a ship's trim in such a manner that the hull's center of gravity and center of buoyancy are in close enough proximity to avoid having the hull become "tippy", that is "unstable". The same mathematical principles apply whether you are attempting to predict the behavior of a small sailing dingy, or a super tanker. However, for professional licenses for deck officers on vessels over 100 gross tons there are usually professional exam questions requiring the candidate to demonstrate an understanding of this concept and the mathematical skills to predict the stability of vessels under various conditions of load.  In the offshore oil and mineral industry ratings such as "Ballast Controlmen" must also demonstrate these stability predictive skills. The mathematical equations depicted in these training videos are designed to help the deck officer achieve and maintain stability by such means as adjusting ballast and planning for crgo loading and discharge, and in voyage planning in anticipating changes to stability as the result of burning fuel, consuming stores, changes in waterway salinity, etc. Books help, but we like to provide our visitors with links to free training videos on merchant mariner professional exam subjects whenever we can because everyone has difficulty achieving a 10% retention factor with written materials but nearly everyone has a 50% retention factor on what we see and hear. The resources below found on You Tube are not an exhaustive treatment of the subject, but it appears new videos are being posted on this subject and they are generally found in close proximity to the linked videos below. Good luck! 


Stability Unit, Part 1: Introduction to Stability (Part 2, Changes in Center of Gravity, Part 3 Free Surface Effect, Part 4 Initial vs Ultimate Stability, Part 5 Waves follows immediately,

Maritime Training: Ship Stability: Learn Basic Definitions   An excellent video illustrating basic naval architectural terminology needed to understand subjects such as stability and trim. 

The Plimsoll Mark: The basic mark assigned by the classification society which indicates safe levels of free board for various conditions of load and sea route.

Draft Survey _ Basic Concepts Part 1 , 2, 3, & 4   Note: The Indian narrator in this training video uses the term "Center of Flotation" ,this seems to be an alternative term for the more commonly used "Center of Buoyancy" in other training videos on stability. You may encounter both terms in this collection of training videos. This is the basic course in computing a ship's basic draft survey, which should be undertaken before leaving port after taking on cargo, or fuel and stores. Following Basic Concepts 1 through 4 this same link continues with trim calculations. Some of the trim calculations video lessons may be a bit redundant with some simpler versions listed below. 

Ship Stability_ Definition of Dock Water Allowance ( DWA )

Ship Stability List Formula

 The introduction of Equivalent Design Waves (EDW) marks a significant change in the way dynamic loads are calculated in the DNV GL rules. The new advanced load concept is a major step towards a more realistic representation of the environmental loads.

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