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Old 10-14-2008, 12:11 AM
Bushwacker Bushwacker is offline
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Join Date: Feb 2007
Location: N. Palm Beach, Fl.
Posts: 2,456
Default Re: What about this???

You're right Chuck - SeaCraft never built them like that!

Just noticed that axial "step" at the chine! The idea of an axial step is to create a flow separation and trap air much like the lateral steps on the VDH. I have a book by a famous British guy named Uffa Fox, who built some racing hulls with a series of axial steps and wedges in the 1920's. The hulls had about 3 equally spaced steps along the bottom, giving them a "saw tooth" appearance when viewed from the side. The concept was that when a wave forced the forward section of the hull out of the water, the increasing "angle of attack" on the rear section of the hull would create extra lift and force the bow back down, much like a trim tab. I believe the concept worked fairly well and created a very flat running angle.

The problem with this one is that they didn't do it right! You need a sharp 90 degree step in the surface to cause flow separation, not 45 degrees like this one. I suspect the water won't separate, but will just follow the surface and blow right up thru the scupper, especially at low speed! Looks like someone tried to add a wedge to the aft end of the outer panel as well (the hook that Chuck mentions) because the lateral step is gone in that area. That feature will also increase the pressure in the area forward of the wedge, further aggravating the problem of blowing water up thru the scupper! The other small wedge just forward of the scupper is also not original - hard to tell w/o a scale in the photo, but it looks MUCH thicker than the one Potter used on the 20's, which were less than a 1/4" thick.

If you carefully sight down the chine of a 20' hull from forward looking aft, you can see where Moesly DID build in a slight wedge or hook in the outer panel but it's very subtle - the chine drops down maybe a 1/2 inch over the aft 8-10' of the hull. This panel is almost clear of the water at about 40 mph, so this wedge would have no effect at high speed; I suspect it's purpose is to improve with low speed planing and load carrying ability. It may be there on the 19 also. Haven't looked at the 21 or 23.

Bottom line is, Chuck is right, the only way to fix that thing is to rebuild that section of the hull to original configuration which is well proven! I'd also move the scuppers to the transom and maybe cross them also, the way Moesly used to do it.
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