Re: [bolger] Re: Plywood thickness for lapstrake hull
- On Sun, Mar 7, 2010 at 4:37 AM, Andrew <a.c.l.yen@...> wrote:--- In email@example.com, "daschultz2000" <daschultz8275@...> wrote:In my calculations I assumed that the stiffness of the hull will be related to the stiffness of the planks in bending. As we know, the round boat shapes increase stiffness considerably over flat planks stiffness - but I still think that if you double the stiffness of the planks then you will - more or less - double the stiffness of the boat.
Stiffness is related to the square of the depth of a beam, so doubling planking thickness would quadruple stiffness. In calculating the scantling number, the product is directly related to the product of length, width and depth. In the case of the rowing gig in relation to the 25 foot Chebaco, the length is 7 feet longer, but width and depth are much less, so its scantling number is lower. It also doesn't have to carry the loads imposed by the mast and sail. Clinker built gigs are skin stressed, monocoque boats that don't need framing except to add some marginal stiffness and shape retention under stress. A carvel built gig would need substantial framing.