Three diagrams necessary for lecture 3:
Trim...Keeping it simple
What you see above is a profile to of the Victory Ship SS Harvard. The profile important to the conceptual understanding of the concept "Trim"
First notice the outer line… this measures the vessel's overall length. The inner line measures the waterline length, or sometimes called, length between perpendiculars.
Secondly, notice that the vessel is profiled on and even keel. Draft FWD equals draft AFT.
In profile, if she is cargo laden, what we have is this: the cargo moments (deadweight) FWD equals the cargo moments (deadweight) AFT..
So the question raised is this: FWD or AFT of what point...…What is the pivot point? Answer: Center of Flotation…CFL.
The Center of Flotation is to be found somewhere proximate to the centers of the two aforementioned lines.. When the moments AFT exceed the moments FWD… the vessel is "trimmed by the stern"…. meaning the draft AFT exceeds the draft FWD. Of course if this was the case the vessel would no longer be on an even keel…A condition normal to any voyage.
Analyzing this relationship, and solving load problems through equations, is the basis of the lecture and the problems encountered on the C.G. Exam.
My suggestion would be, read over all the problems first, allowing intuitive theory to sink in. If you feel deficient in theory read over John La Dage; nevertheless, I feel you have enough theory to solve the problems.
Historical Note:There were 534 Victory Ships built. 150 of these ships were named after American Colleges and Universities. The pictures of the SS Harvard have been provided greatfully by the U.S. Merchant Marine Organization whose link you will find in the Reference Library.
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