Kenneth Cooperstein wrote: > As to Craig Olsen's assertion that wood and water ballast *will* affect > boat buoyancy, we are talking about different things. I am concerned > about buoyancy when swamped. If you add lead ballast to your kayak and > it fills with water, it could sink, whereas before the lead was added it > might float -- unless you provided additional floatation. If you add > water or wood ballast, then you don't have to increase floatation > because both are neutral or buoyant in a swamped boat. But they're less dense, and so you need *more* to get equivalent stability, as lead will be carried much lower in the boat, being 11.34x as dense. Water ballast has a problem in that being neutrally bouyant it doesn't add any resistence to heeling until it's actually out of the water. Sailboats that use water ballast have to carry a *lot* of it, usually either side of the keel. Water ballast is handy for trailerable boats, or if you're backpacking your kayak as well, I suppose. > For example, if you added 64 lbs of lead to a boat, you would need to > add a 1 cu. ft. air bag to float that lead it if you swamped. It is > just simpler to forget the lead and instead add a 1 cu. ft. water bag to > get the same 64 lbs. of ballast. That's assuming you're totally swamped, of course; but if your boat is packed well with air bags taking up most of the spare space that won't happen. More likely is that you're talking about a situation where you have water and air (in the form of a partially inflated bag) or water and lead filling an area. Given a hypothetical kayak of 10 ft^3 volume, we could get 64 lbs of ballast from 0.133 ft^3 of water or .012 ft^3 of lead. Assuming the rest of the space is air filled, the boat has the same displacement in either case, but a greater resistance to heeling with the lead. -- Michael Edelman http://www.mich.com/~mje Telescope guide: http://www.mich.com/~mje/scope.html Folding Kayaks: http://www.mich.com/~mje/kayak.html Airguns: http://www.mich.com/~mje/airguns.html *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net ***************************************************************************Received on Fri Feb 13 1998 - 10:35:02 PST
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