1 BOATS AND THEIR BITS STABILITY


This is a complicated subject but the basics are very simple. Firstly, at low angles of heel a boat with a wide beam will be more stable than a narrower one. Look at the two crates shown here as A and B. Assuming they weigh the same, it’s easy to appreciate why B − the wider one − is the more stable. Now let’s compare B with C. They are both of the same size and in the same position but C weighs twice as much and would obviously be the most difficult to turn over − ie, the most stable. So weight is as important as width − basically, the more you have the better. Is that the end of it? Not quite. Now look at D and E. The crates are the same size and weight but their contents are concentrated at different heights. No prizes for guessing that the one with its contents at floor level (E) runs less risk of being knocked over than top heavy D. That’s simply because E’s Centre of Gravity (C of G) is lower.


Of course, boats float in a fluid rather than stand on solid surfaces but the principles are similar. Beamy boats with lots of weight stowed low will always be more stable than lighter, skinnier ones with their gear carried high.


A


A


B


B


C C


D D Fig 1:11


Before we leave this subject, it shouldn’t be assumed that lots of stability is always a good thing. Exceptionally stable boats − the proper term is ‘stiff’ and the opposite is ‘tender’ − will snap upright with a speed that can shake your teeth loose. The ideal boat will be stiff enough to keep her feet while rolling gently so the crew doesn’t suffer whiplash. To achieve the perfect compromise is one of a designer’s greatest challenges.


10


E


E


RYA Seamanship for Sea Anglers


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