Nesting, planing, sailing, rowing dinghy

[sailhand]

You can do all three, but not all particularly well. You can focus more on planing and still sail relatively well. Look at racing skiff hulls for inspiration, flat run aft and very little to no rocker. Beamy hull for form stability under sail. Rowing this type of dinghy is far superior to an inflatable but not as efficient as what you have. A saving grace for this size dinghy is the easy movement of ballast, thats you, to help the transom clear the water aft and reduce drag. I can attest to the efficiency of this technique in standard aluminium planing hulls in Australia. Relocation of ballast to trim the transom clear allows a planing dinghy to row far better. Too far forward and directional stability suffers. Whatever you build clamp your rowlocks to the hull and move them fore and aft until you find the correct trim for solo rowing as well as loaded. Only then fix them in place. A minimal to zero rocker hull is what you need to do 20 knots without handling problems like porpoising. Good luck! Always good to see others push the envelope a little more. Fair winds.

 

[rnlock]

I know from experience that an O'Day Sprite can plane under sail. Presumably that means it would plane under power as well. My guess is that it would row more slowly than a pure rowing boat, but that hull shape might be worth investigating, even though it is slowed down by chop. I recently saw listings for a free 420 and a free Hobie Cat. Those might be good for experiments before building anything. There are quite a few planing dinghies out there. I wonder if hard chine dinghies, such as Windmills, plane more easily. It may help to leave the corners sharp rather than rounding them. I'd guess that any planing hull would be harder to row than a good displacement hull. I guess a multihull that folds up might be difficult. V shaped hulls might give a soft ride but might be heavier and have more wetted surface, which would be bad for rowing.

I've seen listings for plans for DIY hydrofoil boats. My guess is that you could go pretty fast on a very small motor, and keep a good shape for rowing and sailing. Might be a bit tricky to develop unless someone has already worked out something suitable, though I guess an 8 knot hydrofoil might be much easier to design than a 20 or 30 knot hydrofoil. I suspect that you could just carve and glass a wood plank. A fairly thick shape might work ok for a submerged foil, but maybe not for a surface piercer. In that case, a "supercritical" foil, or at least one with the maximum thickness and camber relatively far back, might be best.

However, i think it might be far easier to just attach a properly oriented planing surface to the bottom of your boat. It probably doesn't need to be very sophisticated. There is a famous picture of a guy planing his kitchen table upside down, with a small outboard motor. You could remove the surface when rowing or sailing. I imagine it could be a lot smaller than a kitchen table.

There is a rule of thumb that, for planing, you need one horsepower for each 50 lbs. I suspect this is pessimistic.

 

[HelmutSheina]

This one may be worth a look.

https://forum.woodenboat.com/forum/designs-plans/9549945-speed-pram

 

[rnlock]

This one may be worth a look.

https://forum.woodenboat.com/forum/designs-plans/9549945-speed-pram

As long as you can get a strong athlete to row it for you. It's just a powerboat and probably rows like one.

 

[HelmutSheina]

Usage I guess, I've rowed soft bottomed inflatables and pressed aluminium dinghies when the distance hasn't been terrible and the wind was suitable.

The only way I know of to maintain a reasonable performance under sail, oar & outboard in the same boat is via an outrigger canoe. If I recall correctly, Gary Dierking built the original Wa'apa proa as a tender for his cruising trimaran.

 

[sailhand]

Have you considered just building a new rear part of your current boat for planing and keeping the existing two halves. This would give you the best of both worlds with minimal effort and expense. If you build it slightly longer than the existing rear part you may be able to nest all three parts.

 

[BobbingAboutBob]

Have you considered just building a new rear part of your current boat for planing and keeping the existing two halves. This would give you the best of both worlds with minimal effort and expense. If you build it slightly longer than the existing rear part you may be able to nest all three parts.

Yes, that's exactly what my son suggested.

I've been wondering about building an aft section that bolts on, which gives extra planing surface and would be buoyant enough to support the outboard. The idea being that I could simply leave it floating when I wanted to go for a sail.

 

[BoatBuildLog]

if you do not end up modifying the hull, I would be curious to see how the rowing performance compares before and after. that seems like the tricky tradeoff here.