Monohull dinghy with amas above waterline just for stability

Hello Everybody!

I have an idea of desinging a small halfdecked sailboat (lets call this vessel a dinghy) for daysailing as well as inland and coastal camp-cruising. This dinghy would have very shoal draft (with CB) and most probably a scow bow. I have been thinking about short folding outriggers (amas) not touching the water (I assume they would be some 2 ft above the water line or something like that in the open position) just for stability purpose (I mean stability in rough conditions while the hull would be a typicall mono) so I would get a pretty fat hull which would be light (because of no ballast) but sea capable.

What do You think about such idea? Maybe You know already existed designs like the one I'm thinking of?

Good winds!

 

The EPOH dinghy , with stabilisers above the water, seems close to your idea :What is the ePoh ? EPOH TRANSSONIQUE NEW DRIVER MADE IN FRANCE http://epoh.eu/en/what-is-the-epoh/#innovant

 

Thanks! It's almost exactly what I'm thinking of except in this case the wings/amas aren't foldable I suppose. Do You know why this solution isn't common?

 

Cost, weight, strength, complexity. Think economics and liability, these are mass produced commodities. No need or market and higher risk.... every single nut and bolt is part of the equation.

 

Let us suppose that the amas extend two feet outside the sheerline of the dinghy. Suppose the dinghy is rather narrow at 4 feet overall width. that puts the ama at four feet off center and is two feet above the waterline. The heel angle will be something north of 25 degrees when the amas begin to contribute to righting moment. Few dinghy sailors are comfortable with heel angles of more than 10 degrees. Not only that, the boat itself does not like to heel excessively and if it does there is a serious drag penalty. Sailors with even a rudimentary set of skills, do not need or want outriggers.

Trimarans are a whole different ball game. The amas do contribute a major influence about keeping the boat somewhere near upright. The layout of the tri, lets the amas just kiss the water in light to moderate airs and the heel angle is very small. Trimarans typically have a narrow main hull and will need some help to stay upright. Thus, outriggers. Dinghys usually have length beam ratios of three plus or minus. . They do not need extra righting moment when sailed by a reasonably competent skipper.

 

This idea is sometimes used in Moth dinghies, especially for training

regards

krzys

 

Back around 1997 I built a boat something like a larger version of the Moth above, but with a wider hull and wings with buoyancy in the ends. I documented the project here. ++ PlusPlus ++ Home Page ++ http://www.devboats.co.uk/sailing/plusplus/
Note though this was a high performance racing craft, and not your recreational cruising craft, but maybe some of the experience might be relevant.

The main issue for you is perhaps that when the float hits the water it provides a big increase in drag way off the centreline which tends to steer the boat in the direction of the float. You can get round this to an extent with careful design so that the floats contact the water progressively without a sudden increase in drag, but its surely always going to be a factor. If you are going to be sailing your boat in open water with serious waves its perhaps going to be rather more than an issue, because it will be hard not to be somewhat randomly battered by waves hitting one float or the other. With a trimaran or catamaran the hulls are more consistently in the water so I imagine the behaviour is more predictable.

 

The bigger question is... Why?
Seriously, Why?

 

Thanks for the information about Your project and the comments. So, yes, it's a factor I didn't think about. Maybe a good way is to make the amas higher. My intention is to have a fat main hull which would act like just a typicall mono. The amas are only to be equivalent of heavy ballast to prevent capsize in true critical situation.

 

As I've mentioned - to prevent capsize in critical situation without having heavy ballast. Is there something wrong in my way of thinking?

 

Actually, it lacks preliminary outlines of your project to be able to debate consistently about the safety issue re. the capsize risk and the stability at large.
A sailing « dinghy » with a small cabin for camping purpose, can be something like the Maraudeur ? (L 4,83 m x B 1,71 m x Draught 0,31/1,13 m x Light weight 325 kg (inc. lead ballast 70 kg + steel centerbooard 17,5 kg. Or similar sizes but without the lead ballast ? with more beam ? Or more length ? more or less weight ?
Maraudeur CI – François Vivier Architecte Naval https://www.vivierboats.com/en/product/maraudeur-ci-en/

 

Are you new to sailing?

 

No, maybe just to dinghy sailing. Why?

 

Before you try to reinvent dinghies, I suggest you learn how to sail them.

 

OK but, please, write something more. Do You think I see a problem which doesn't exist in everyday life or something like that? As far as know the problem with sailing a dinghy on the sea waters or a big lake is such a vessel doesn't have balast (to be relatively light) and isn't self righted. I know that RIB vessels, for example ones used by coastgouard, also don't have balast but they are equipped with an inflatable float on a frame which can be filled with compressed air after capsize. Why similar solution can't be applied on a dinghy? I proposed a bit simplier solution without compressed air - just permament amas.