Looking for sharpie plans

Several things about flat bottom boats don't appeal to my engineering sense. One is the tendency to pound in chop but everyone knows about that although some do seem to discount it. Another is the difficulty of attaining a strong, inflexible bottom structure. Some do it with very thick bottom scantlings and Bolger did it with his box keel. I know of one that had a 1 1/2" bottom that still flexed. I prefer a simple V bottom to greatly improve performance of both issues. A V is just not much more difficult to build than the flat bottom and if a builder is influenced by that small difference, they are going to be flummoxed by other more difficult tasks.

About 1/4 mile down the creek from my dock sits a 36' or so Carolina Core Sounder, built from the hull of a local old working boat. It looks much like Flossie and the builder did a good job. Core Sounders, like all local boats have a modified forefoot that is fairly sharp to deal with serious local shallow water chop . Trouble is, all that top hamper must have come to haunt the proud builder because, other than one trip to Florida, the boat has never moved in over 10 years. I would be very wary of taking that boat out on our coastal NC rivers and sounds on other than calm conditions.

Working sharpies were built to have very little cabin above decks and ALL of the traditional ones will look like that. They also did best when loaded with a hold of fish or oysters. Sure, they are pretty but before you get too enamored with the type, just know what has to be done to make them a good all round boat. Just raising the topsides is not going to make them much more seaworthy. Few powerboat are tested very much for righting moment although for sailboats that is almost always done. Narrow sharpies with high cabins should certainly have that as the first order of design business.

 

Agreed. By the time you've widened a sharpie's beam enough to handle a lot of top hamper, and/or increased the draft for the same reason, you don't really have a sharpie anymore.

I'm obviously not even close to being a designer. But I think the best approach for a cruiser, if you want to keep that classic sharpie look and narrow beam, would be a V-bottom with ballast -- a la Thomas Clapham's Nonpareil sharpies. As you said...

 

If the sharpie is large enough, you can make the whole bottom the lower portion of a box beam, which does make it stiff enough for use and offers some shallow storage space as well. A V bottom does complicate the build a little, but well designed, not much more of a challenge, as Tom points out. Top hamper on sharpies can't be over emphasized enough. A skiff hull form is a different matter and if using this hull shape, the V bottom becomes more desirable, because you have enough initial stability to offset loses from the V.

 

There is only a loss of stability in a shallow vee hull if you take no advantage of the lower keel. For instance, if two hulls sections have identical girth sheer to sheer and both have a CG at the waterline, then the max RM when heeled to the sheer will be slightly higher for the flat bottomed boat, but it only takes a very small reduction in CG in the vee bottom boat to cancel this out and make it a wash. And this assumes each are at their optimum displacements. The vee bottom optimises at a heavier load. If the flat bottom boat is overloaded, There is a vee bottom that will have a higher RM.

Attached are four snippets from a spreadsheet I wrote.

1. Particulars for an optimum flat-bottomed section. Max RM at sheer submersion. CG at waterline.

2. Same for a vee bottom with 15 degrees deadrise. CG at waterline. RM is less. Displacement is more.

3. Same vee hull with the CG lowered to match the RM of the flat bottomed section. CG lowered about 40% of the draft difference between the two sections. Same displacement as in 2.

4. The flat bottomed section loaded to the displacement of the vee bottom section. The proportions of the section were tweaked to gain max RM with this load. RM is about 10 percent less than the vee bottom for the CG=waterline cases.