sailing skiff help

[fishmonger]

I want to build a hard chine plywood sailing skiff, but I’ve got a couple questions.

1) I’m mostly going to be sailing in sheltered bays, but I’ve heard that a flat iron skiff doesn’t do well in any kind of chop. Would chining out the bottom from the middle frame help? I was thinking of dropping the middle of the boat about 6 inches, and tapering it to zero at the bow, stern, and sides. My hope is this would solve some of the pounding problems. Additionally, I don’t mind if I loose some of the initial stability, because I think the skiff would sail better on a heel with a slightly sloped bottom. Am I correct in my thinking? Would this work at all?

2) There are a multitude of designs for flat irons out there. Some look better than others. I want a skiff that’s 12 feet long and 4/4.5 feet wide. Is there anything wrong with coming up with the design myself? I’ve modeled the skiff in Hulls, and it seems to work well. My next step is to build a paper model. Basically I want to build the middle frame and transom, wrap the sides around it and clamp on the bottom. A lot of the designs I’ve seen are based on straight cuts along the top to make the gunwales, and rockered bottoms. I would want to do the same thing, but add a slight rocker to the bow and stern as well.

Any suggestions would be much appreciated. I’ve been reading a ton, but I'm very new to this. If I’m way off coarse please don’t be shy about telling me. Alternatively, if you know any great V bottom skiff plans I'd love to take a look at them. THANKS!

[Tim B]

There are a couple of ways of going about a skiff design. And indeed, 'skiff' is sometimes assumed to mean different things. However, I generally assume that a skiff is a fast, wind driven sailing craft.

The problem of slamming is really secondary to manouvrebility and stability. If you try to reduce the slamming, by narrowing the bow, then the boat will tend to 'nose-dive', conversely, adding more rocker will make the boat less stable both longitudinally and laterally. Therefore, my advice is to keep the bow sections fine, but not to get carried away.

There is a tutorial on 'Hulls' at http://home.clara.net/gmatkin/hullstut.htm
and it may be useful to have a look at this page.

There is no particular problem with designing the boat yourself, but you must make sure it is stable I would suggest that you try to find some stability curves (from manufacturers) for small dinghies, or conduct tests on a few boats yourself. An inclining experiment should be easy and there should be plenty of info on the web as to how to conduct one, if not, e-mail me and I'll find the method for you.

I have attached two diagrams of two hulls. The surfaces are NURBS surfaces and what is interesting is that the surface points are in exactly the same place. The difference though is in the weight of the points (obviously the ones at the chine). It may be worth considering this method, as the whole boat can be treated as a solid (easily) and then hydrostatic data can be developed purely from geometry, which is nice and easy.

Anyway, best of luck,

Tim B.