3318 Rear Hull Shape

06-16-2008, 11:15 AM

Doug Fir | 3318 Rear Hull Shape

John, Bud or any of you water pros out there. I was curious to why the rear hull of the SeaWind has a 2 1/2 in flat step and is not rounded at the bottom outer edge? Was it an ease of construction choice or an hydro-dynamic efficiency issue? Doug

06-19-2008, 11:17 AM

Jim Small | 3327

Doug,

I read an article recently that touched on this issue. I believe what you refer to is our afterbody deadrise angle. We need flat surfaces to be efficient as a planing hull. The deadrise angle allows the hull to "partially slice through the waves" as opposed to slamming into them with a single flat surface. In other words, it reduces landing loads. There was a lot of work done on these hulls by NACA and others in the 1930's and 1940's. The article I read said that a modern book still in print that discusses seaplane design is: Design for Flying, 2nd Edition, Thurston, David, Tab Books, 1995. You might also try a Google search on deadrise angle or round bottom hull.

Jim

06-20-2008, 11:18 AM

Doug Fir | 3334

Jim, Thanks for the suggestion. I took your advise and found some info on the web.. Like Dean I am planning to modify the last five feet of the rear hull and increase the longitudial angle,not the dead angle per se). This means the transom would be a few inches more shallow. This in theory allows more room before tail strike. The job of course means cutting and removing and rebonding material. Because of this modification Dean`s rudder protrudes a few inches into the slip stream when retracted. It is streamlined in this profile and doesn`t appear to affect the planes drag. I`m studying the possibility of making a new type of rudder that doesn`t need to be extended, as well only ENGAGED. I believe Scott was thinking about this alternative as well. Doug