If a vessel is sagging, what kind of stress is placed on the sheer strake?
A. Compression
B. Tension
C. Thrust
D. Racking
A. Compression
B. Tension
C. Thrust
D. Racking
Daily License Questions about Ship Stability and Trim: I just think people need to have some knowledge in their heads, professional or otherwise. After 2007 our world has changed due to the advent of Smart Phones. Retaining knowledge is like being able to play a musical instrument, if you do not use it you will lose it! The questions I post with will hopefully help you keep what you already know or remind you of what you should know. William E. George
LETER A
ReplyDeleteSagging ocurs when there is more weight concentrated in the mid ship due to uneven cargo distribution or when there is excessive buyonce at the ends.
Also, sheer strake is usually thicker and stronger than other strakes. The reason why sheer strakes are thicker and stronger is because this strake can have lots of physical damages during the ship's lifetime
The ship's hull can be thought of as an I-Beam in terms of hull strength. The shear strake, stringer strake, bilge strake and keel strake all provide extra steel to build up this equivalent I-Beam when you consider longitudinal hull strength. Normally any doubled plating is for strength reasons in the vessel's original design unless it has been done as a repair.
DeleteThe main deck stress is compression. A.
ReplyDeleteThe best answer is A.
ReplyDeleteA strake is defined as a Nautical term: "a continuous course of planks or plates on a ship forming a hull shell, deck, etc." The Sheer Strake runs along the side of the hull at the main deck. The Stringer Strake runs on the outboard side of the deck. On older ships these strakes were actually continuous doubler plates for strength. So to answer this question you need to know where the Sheer Strake is.
We have already discussed hogging and sagging stresses. The question states the vessel is sagging therefore the deck is in compression and the bottom plating is in tension. So the best answer is A instead of B.
What about Choice C. Thrust? Well you get thrust from the propeller. The Thrust Bearing transfers this thrust to the hull. Without a Thrust Bearing the propeller and shaft would damage the reduction gear or the prime mover. This choice normally has nothing to do with hogging or sagging unless maybe you are on an ore boat in the Great Lakes where propeller shaft design problems can be a problem due to springing.
What about Choice D. Racking? Is not caused by hog or sag. Racking is the torsional twisting of the hull which can be caused do to uneven distribution of weights or buoyancy transversely on a vessel. Racking
(Uneven water pressure caused by wave action leads to distortion of the structure as shown and is resisted by the Shear Stresses in the structure including most significantly the Transverse bulkheads and framing. Racking stresses are highest at the corners of the box section and thus the corner brackets are specially inspected.)
For more information go to:
http://www.marineengineering.org.uk/page82.html
Alpha; the sheer strake is in compression
Delete