Wild Hair

[lewisboats]

Mission: to try to come up with a suitable amount of ballast, low enough down, while also coming up with a beachable hull and still keeping the interior of the boat without large intrusions. This is for a very unlikely pair (or more) of boats called Guppy and GuppyII. I am currently building GuppyII. They are both one person VERY micro-cruisers, one at 9 ft loa and the other at 11.5 ft loa. What I came up with is something I call a ButterFly Keel... When sailing, it has a full keel (though not foil shaped), and when beaching, the keel splits and makes a kind of landing pad. Still working on the mechanism tho it probably will be cable operated of some kind. The arms that stick out from the wings have small pads on the ends which rest on pads on the hull, allowing the keel "wings" to fully support the weight of the hull as it sits on hard ground. The wings are of a suitable thickness of Stainless to provide about 170 lbs of ballast, which should be strong enough to support the weight of the boat (about 210 lbs). The arms will of course add turbulence and drag, but will only knock a few .10's of a knot off of the overall speed. This is not a racer by any means and should only top out at about 6 kts or so in a good stiff breeze. Here are some pictures of the boat and the proposed keel. I am looking for opinions from the learned folks here, tho I don't promise not to be pig headed and go with it anyways.

Steve

[mackid068]

That is quite the cute little vessel! It's great looking and is probably fun to sail. Make it a motor vessel and it'll serve admirably as a tender/lifeboat.

[lewisboats]

Yes...Thank you. While it hardly fits the bill as "seaworthy" (6:1 ratio, curve of areas, etc) I have tried to compensate with ballast, high freeboard and full length cabin. Cons include high windage, low L:W ratio, low speed and a low aspect ratio rig. Transom is wide enough for a 5 hp motor which is more than enough to push it to beyond hull speed, tho not much beyond. Still...the question is:...what do you think of the keel thingy???

[lewisboats]

I had originally considered bilge keels, but don't want to work out the hydrodynamics, toe in, etc. I would probably need to tank test to get it right. Plus there is the increased surface area to consider and I think the lateral resistance will be more with the single (deeper) keel vs multiple (shallower) keels.

Steve

[mackid068]

Me? I really like the little keel. On such a small boat, you're going to need as much resistance (lateral) as you can get.

[lewisboats]

OK...so do you see any problems splitting the keel, hinging it and using it as a single foot(0r pad) for beaching?

Steve

[Skippy]

There will be a LOT of stress on the fulcrum struts when beached. And probably at least as much drag as the bilge keels while under weigh. Not to mention the complexity of a mechanism to control them. Another intresting aspect of bilge keels is that if you heel over enough, the weather keel comes out of the water, increasing its effective net weight and decreasing its drag. With bulbs, hopefully the ballast will be fairly low.

[D'ARTOIS]

The Jongert Shipyard is already using (and patented) such a keeldesign, we call it the "Wybertjes" keel. It is a diamond shaped keel that can be hydraulically retracted, giving large sailinyachts access to shallow moorings.

I think it is interesting but probably pretty expensive to do right. Have you considered something like an endplate/keel wing that would be flat enough to support the boat? Could possibly have struts fold down from the sides of the boat for extra stability so there was no extra drag...
I think in my recent research I ran across a patent on something like that-if I find it I'll post the number..
You know, if you're contemplating manufacturing or selling the plans you might consider doing a patent search(around $700) just to make sure you don't get yourself into a mess with an inadvertant infringement-and your idea may be patentable in it's own right.
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edit: Note that the upside down "T" endplate/winged keel not only has the potential of allowing the boat to sit upright but probably gets the ballast lower than any other concept that's been mentioned in addition to having no moving parts. I mentioned struts above but they wouldn't be necessary if the "winged" part was extended wider-just at the back end.

[lewisboats]

Originally Posted by D'ARTOIS

The Jongert Shipyard is already using (and patented) such a keeldesign, we call it the "Wybertjes" keel. It is a diamond shaped keel that can be hydraulically retracted, giving large sailinyachts access to shallow moorings.

These do not retract, rather the keel splits in half, then each half folds outward to create a "foot" on which the boat grounds itself when beached.

Steve

[chandler]

Steve,
I always thought about a wing type centerboard for a sunfish. We sail our sunfifish in very shallow water. Very often it is hard to get it off the beach in a headwind due to the shallow water..I'm talking 2' of water for 100 yds. without the centerboard a sunfish has very little longitudinal stability. Maybe a wing type centerboard would be the answer...What do you think??

[safewalrus]

Sounds complicated to me! complicated things break! normally at the wrong time! What about leeboards? YOU are the main ballast in a boat of this size - lee boards give you the depth, give you room in the boat (don't leak, unlike centreboard casings) they also have other uses (table at yer barbie?). and have been tried and tested. That's important in a seaway!

[lewisboats]

I am building it now, but still haven't decided on the foil design yet. Hoping for divine inspiration. all the conventional stuff just doesn't seem 'right', but I suppose I'll have to pick one or 'tother.

Steve

[JonathanCole]

Steve,

I think some of the readers are not realizing that your "butterfly keel" is two halves which are closed while underway to form a normally shaped keel, and only open for use as a stand when on land.

I think an important consideration is how and when the butterfly wings are opened. Although the boat is only 200 lbs, how do you deploy the stand once it is on land, or do you deploy while afloat and drag it onto the beach? Either way represents considerable stress to such a structure which could damage it or the boat.

At the very least you probably need skids on the keel edge, something more dent, bend and abrasion resistant than your stainless steel keel sides. Or maybe even small rollers.

Also, there will be lots of mechanical stress on the hinge mechanism where it attaches to the hull. Maybe you need to extend the metal portion of the device well into the hull surface to provide added robustness. It might also make sense to have it deploy on land without using a cable mechanism which could be a source of leakage. You could have fold down struts hold the boat off the ground and then open the stand.

[gonzo]

There is no way that boat will do 6Kt. The hull speed will be about 3Kt. It would have to plane to do 6.