transom shape

[Ryon Macey]

I am currently experimenting with a hull that has a round transom. when the hull is run, one side seems to suck down into the water and the hull runs sideways a little. Is this the effect of the round end of the running surface.

Thanks in advance for any assistance. Ryon Macey

[Stephen Ditmore]

I'm going to start with the simple principle: anywhere water has to flow around convex curvature, suction can develop, and this can cause control problems at high speed. It could happen at the transom, but the way you describe the problem I wonder if it might be happening somewhere else as well. Donald Blount <http://www.dlba-inc.com/> and Lou Codega wrote a good paper on control problems such as this, which SNAME <www.sname.org> published, and which was republished in Professional BoatBuilder Magazine.

[Stephen Ditmore]

Citation:

Blount, Donald L. & Codega, Louis T.; "Dynamic Stability of Planing Boats," Marine Technology (a publication of SNAME), Jan 1992, p. 4

For information on how to shape a bottom so these problems don't occur, see my posts at http://boatdesign.net/forums/showthr...p?threadid=261 and follow the link to Harry Schoell's Delta-Conic patent.

Also, fore and aft center of gravity can be part of the issue. Try moving weight aft and see if it helps.

[Evolution Yacht]

It sounds like a weight issue. What is the deadrise at the transom, at what speed does this happen, are there any other problems like bowsteering or porposing.

[Ryon Macey]

The deadrise at the transom is 10 degrees. The problem occurs at between 10 and 20 miles per hour and will not allow the hull to plane. If the hull gets on plane, there is no porposing and no bow steering. One thing I should mension is that the hull utilizes a pocket drive.

Thanks in advance for your suggestions.