17 foot boat - sail & keel weight - how much?

I've made a sailboat hull with these dimensions: 17 feet long, 2.5 feet wide, 2 feet from top to bottom.

I've made a swing keel which -- when extended -- hangs 3 feet below the bottom of the boat.

What I've been trying to figure out is how to determine the keel weight to sail ratio, and how much sail/weight to put on the thing, considering its dimensions.

Feedback from an experienced designer would be welcome.

Thanks,
Sam

 

That's a slim boat

 

True.

Any ideas about the keel and sail? =)

 

firsttimer,
We are going to need more info....
What will this whole boat weigh when finished (guess)? How fast do you want to go? How much do you and your crew (if any) weigh? Are you hiking out or on a trapeze or on wings/racks?
You see the problem? Unless we know what you want to do with this beast, we are pretty much helpless
Steve

 

Or we can guess that you have 30 to 40 square feet of wetted surface and that you need 60 to 120 square feet of sail to make this boat fun to sail...
Try with the rig and sail you can get and then see how much ballast you need

 

more description - also a pic

The thing would probably weigh 300-350 lbs with a full compliment of supplies. I'm going to put a cabin on the front, and it will extend almost fully to the back. I've been guessing that the keel would be 100 lbs or less.

The crew is me and possibly a second person some times. Averaging 150 lbs per person.

I put this boat together as something to sail the coastline with, and pull onto a beach as needed. (The swing keel can be removed - it's held onto a stub keel with bolts and wing nuts.) I didn't have speed in mind, so much as stability and beachability. It will be the first boat I've ever sailed.

Pardon me, I dont know what you mean with the hiking out on trapeze or wings/racks question.

Perhaps I should mention that I'm in the California area and the coastal winds are pretty strong.

The 60 - 120 sq ft estimate sounds reasonable to me. But I'd be nervous to sail it with no keel weight.

 

Have you considered outriggers, making a triamaran?
You will have almost no stability in this hull, that's why Steve is asking if you hike out to let your body weight satbilize the boat.
With a small keel and 100lbs of lead in the bottom of the keel, try a second hand optimist rig or a small windsurfer sail and see how it feels.
If you want more sail I think you need outriggers or a very deep narrow fin with a bulb in the bottom.

 

but its a swing keel - new pic

Outriggers - yes I've considered them. I could still make them but I've run overbudget so it would delay the project. I didnt like the idea primarily due to drag, but also due to bulk (in overland transport).

You mention a weighted fin, and I have to point to the swing design. The 2x4 is on a hinge -- and since I took the photo I replaced that one with a longer one. When it's extended it's going to hang 3 feet (1 meter - see attachment) below the boat. When it's pulled in, it hangs 1 foot beneath the bottom. When it's removed it doesnt hang at all beneath the bottom.

In theory I could replace that with an even longer one, although that would put the keel weight almost fully at the back of the boat when the keel was pulled in.

Does that modify your opinion about the recommended sail size?

 

just keeping the thread alive, steve

Hi Steve,

Since i replied to you and raggi in the same post i am refreshing your attention to the thread, since you seemed to have an idea. Answers are in the thread.

Sam

 

I still think you should try with a very small rig at first with this little beam.
You should also try to find a low aspect sail, that is one that is not very high, so the heeling moment is small.

 

Born to tri?

Dear firsttimer:

My guess is between 50 and 60sft. This is with the assumtion that your wieght in the boat will be kept very low. You would need a platform no wider than hips to sit on. Because of its rounded 'V' cross section, your boat won't have much initial stability, meaning it will heel over quickly. Then at about 30deg, she'll start stiffening up. She'll behave kind of like a sailing kayak except she'll pound less. You will probably have to go with two masts or a very low aspect ratio boomed lateen sail to get the Cener of Area (CA) low enough to be workable. I, in severe risk of being labeled a heretic, would also recommend a flat cut sail(s) so it can be feathered into the wind quickly and effectively. That may be your only chance of avoiding a quick swim in a sudden gust. I sailed my beloved Super Snark that was like that in a 25kt wind with no reef points and came out of it with a dry shirt.

There are two problems I can see with this scheme.

One is that you will have to sit in the middle of the hull. You will be no where near the tiller so you will need some kind of remote control which could be anything from a continuous rope and pulleys connected to a short tiller, to a full fledged steering system with a wheel and a quadrant to steer the boat.

Two is that this boat would be under canvased for light winds. Some sort of auxiliary propulsion system will be called for. I would have suggested oars except that you would be sitting too low to use them comfortably. I would suggest using a very low thrust trolling moter powered by a battery that would sit deep in the hull. The bracket for the trolling motor would be very close to where you sit. It would be deployed over the side rather than over the transom. The battery, I hope, would also act as ballast.

Moving about on this boat will be difficult. It will be very initially tippy. The sail or sails will have to be able to be set and struck from pretty much where you sit which in itself brings up intersting problems. If it were done up the right way, it would be a good training boat. It would move about majesticly and come about reliably. Just don't race anybody.

I agree with Raggi Thor. This hull was pratically born to be a multihull. Its 7 to 1 Length/Beam ratio is almost perfect. If you went to the trouble of making her trimaran or double outrigger (submersable floats), she would be able to carry at least 50% more sail area.

Besides, the keel (presumably iron or steel) is going to have to be cut and milled or cast to an air foil like section. This should add considerably to your construction cost.

If you went with the trimaran/ double out rigger approach, the keel would not be neccessary. It could be replaced with a much cheaper leeboard. The boat would be easier to beach too. With the double outrigger approach, your crossbeams could be nothing but 8ft 2x4's set on edge.

Best of luck,

Bob

 

Holy lack of beam, Batman! IMHO, the boat's too unstable. You should either have outriggers of some sort (proa, perhaps?) or a centerboard. Trolling motor, that's a gpood idea.

 

ok lets assume i make a trimaran of it

OK, lets assume that I add 2 nicely shaped pontoons.

How wide to space them? How big to make them? How deep do they go, relative to the bottom of the hull?

And is there any reason to keep the keel then? Wouldn't it still add some benefit? Or would it jsut be more trouble than its worth at that point?

And with trimaran, then, 90 sq ft of sail?

Just a refresher, I plan to put a cabin on the front of this boat to close the hull and provide a minimal shelter.

 

ok raggi, considering pontoons then

(see above)

 

The volume of each pontoon should be as large as the total displacement of the boat when it's loaded.
Make the outriggers as long, the boat as wide, as you find practical.
The bottom of the pontoons should just tuch the water when the boat is at rest.
When you sail and heel a little, the windward pontoon is out of the water.
You can sit very comfortable on som cloth between the outriggers, with your feet in the main hull, I guess.
Look at some pictures
At google, for example,
http://images.google.com/images?svnum=10&hl=en&c2coff=1&safe=off&q=trimaran&spell=1
One picture you'll find,
http://www.hydrosails.com/images/home/afbeeldingen/10homepageg.jpg