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.

[Doug Lord]

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.
----------------
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]

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.

[lewisboats]

Tru, 6 kts may have been a little optimistic. I DO consistantly read of small boats exceeding their 'theoretical' hull speed by 30 to 50% in winds up around 16-20mph. There is much debate (at least in my own mind) over whether the 1.34 x sq rt DWL shouldn't be bumped up a bit. Even so, DWL is about 9.2 ft...Giving about 4.1 kts 'theoretical' hull speed. If I take liberties and add 30%, I get 5.4 kts. Close enough to say "around 6 kts" I think. I'm not real worried if I never see it tho.

Steve

[lewisboats]

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.

I have been tossing around the idea a lot and have pretty much decided it is too complicated to mess with. The keel would have been two flaps of 1/2" thick steel plate tho, pretty tuff stuff. You would crank it up as you coasted in then hop out and beach it. I have been considering twin leeboards and simply beaching on the hull. There isn't that much Vee in it, so it wouldn't list too much when grounded. Will probably have ballast inboard, in the form of painted blocks of steel or cast iron. That way I can chuck 'em overboard if necessary. What do you think of a keel that is an inverted Y?

Steve

[gonzo]

I was refering to the 9' LOA. Small boats that reach high speeds have hulls with straight buttock lines so they can plane. Your design has rounded, tucked in lines. The longer hull, with the same type of shape, may do 1.2 x sq.rt. WL.

[lewisboats]

Ah...good! Now I have even more incentive to build the thing. Gotta see how fast it'll go. Gonna have to beg, borrow or (yeowch) buy a GPS. I have been procrastinating on my building, mainly because I had a bad epoxy experience glassing the joints on the side panels. The epoxy didn't have enough hardener...so...Sticky Goop. I peeled the tape off and kinda threw everything aside in disgust. I haven't touched in a month. Today is my day off, so I'll try to get to it after I get some sleep.

Steve

[Leo Lazauskas]

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

Why would it need to plane?

Regards,
Leo.

[gonzo]

When you exceed theretical hull speed by more than 40% or so, the exact limit is debatable, the hull is planing. That is, it is overcoming its bow wave and has a large amount of dynamic lift.

[PAR]

At quick glance you have several things restricting this little hull from speeds over a 1.3 speed length ratio (you'll need 1.5 speed/length to plane)

As has been pointed out, the run has too much sweep, the buttock angle to steep to effectively permit planning.

The entry is quite bluff, though the forefoot may produce some dynamic lift, it will carry a large wave train along with her, further limiting her ability to overcome the theoretical hull speed.

I'm not sure how much sail area you intend for this little craft, but it would seem you have a lot more lateral area in her appendage then would be necessary for craft of similar size and/or sail area. This excess wetted surface will do no good for the speed/length ratio you need.

The hull shape looks rather burdened, not at all conducive to going fast. This shape will carry a load, but not quickly.

There is a great amount of windage to the topsides structures, again not helpful in the go fast areas.

The "butterfly" appendage is clever, but restrictive. The struts will generate much more drag then you've estimated and the slot or gap between the appendage halves will also cause turbulence, all of which will need be dragged along with her, until enough power is provided to get the boat over 1.5.

A ballasted craft with such a short LWL designed to move at 6 knots is a very tall order to fill. Unballasted it's a tough nut to crack.

Weight, shape and resistance must be reduced dramatically or you'll be well pressed to do anything close to 4 knots.

Have a look at some of the successful small planning sailboat figures and note how far off your numbers are in comparison. Then try to shape your numbers (and hull) to get close enough to have a chance at increasing the speed/length ratio. Over canvassing isn't the answer, you'll just get knocked down when the wind strength is high enough to provide the power necessary to overcome this design's short falls.

[lewisboats]

OK...OK!!! Short, Fat and SLOW... Sounds like ME! ;) ... so it should suit! :D
I'm still building it, even if it DOES sink! :rolleyes:

BTW, the hull is a separate entity (as opposed to having the cabin attached) and has very good load carrying capacity as a tender/playing-around-sailor.

Steve

[SamSam]

If it set down on some of the slimey, mucky bottoms here, a bunch would stick to it and hinder it from closing all the way, which would seem to double the surface area subject to some sort of drag, plus our muck isn't very streamlined anyway. Sam

[lewisboats]

Got a good cure going today, so I'll probably take it 3D tomorrow. I'm looking to get the bottom, sides and transom connected together (Stitch and glue). Actually, from that point you can build it as a dinghy or continue to add the cabin on. In dinghy form it can be used to sail or row, perhaps as a tender. It should easily handle 650 lbs gross weight. If the boat runs 110 or so, thats 540 lbs net load with a nice waterline. 770 lbs would be max gross weight you would want to run, with a bit of the transom dragging. I am hoping the cabin will be light, using 1/8" and 1/4" ply. Looking to come in at around 75 lbs or so. Cabin furniture will run another 35lbs for about 110lbs. anticipating the hull to run 60 lbs bare, this makes 170 lbs. Add 80 lbs of ballast somewhere for a dry weight of 250 lbs. With my 200 lbs this means I can stock around 200 lbs of supplies and 'stuff' and still have a decent waterline. Add a few gallons of water and other liquid consumables that will go over the side via the kindney pump, I can approach the 770 gross wt with enough supplies for a couple weeks at least.

Steve

[lewisboats]

When you exceed theretical hull speed by more than 40% or so, the exact limit is debatable, the hull is planing. That is, it is overcoming its bow wave and has a large amount of dynamic lift.

Ya think I could add hydroplanes to lift the derrier end and get it to plane?

Facetiously
Steve
PS: it would also make a 3 point landing system for beaching.

[lewisboats]

Got a good cure going today, so I'll probably take it 3D tomorrow. I'm looking to get the bottom, sides and transom connected together (Stitch and glue).



Got sides and bottom together. Lotsa stitches! Chipped a bit in the front bottom...not from the stitches but hit it on something.


Steve

[safewalrus]

:) hey lewisboats

Never mind the experts - go build your boat and ENJOY shape looks like it WILL work one way or another, who cares as long as you enjoy it (and don't kill yourself in the process) But keep us posted we're all interested!