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  #16  
Old 02-08-2008, 03:52 PM
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BlackSnow BlackSnow is offline
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Location: Iowa
We buillt one

My friend and I built a canoe catamaran last spring. We used two Nice Canoes from bateau.com, which we had built a few years back. A flagpole was used for the mast and a white polytarp for the sail.

I used a 1/2" piece of plywood for a leeboard. Unfortunately, the mounting was not satisfactory and it broke under use. We tried to make some repairs using "local" materials. My advice: use a very large/strong bearing on the leeboard.

It was fun to sail but would not point worth a damn. Possibly with a better leeboard design/placement it would have worked somewhat better.

We were able to carry a ton of camping gear. Attached are some pics of us on the Turtle Flambeau Flowage in northern Wisconsin.

There is a book on canoe sail design that I found very helpful. I can't find the title right now, but will try to post later.

Let me know if I can help out with your project. I am a mechanical engineer as well.

Cheers!

Greg
Attached Thumbnails
Canoe Catamaran-boys-trip-2006-035.jpg  Canoe Catamaran-boys-trip-2006-064.jpg  Canoe Catamaran-boys-trip-2006-066.jpg  

Canoe Catamaran-boys-trip-2006-080.jpg  Canoe Catamaran-boys-trip-2006-086.jpg  Canoe Catamaran-boys-trip-2006-055.jpg  

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  #17  
Old 02-08-2008, 06:06 PM
Petros Petros is offline
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what a great set up! Keep it simple and have fun with it.

I ran across a simplifying design assumption that has worked pretty well for small boats. Assume that at max condition you will get about 1 pound per square foot of sail area of lateral force. With this you can design the mast and rigging, and the loads on the lee or dagger board. It have found it conservative for recreational sail boats and yet does not over design it. It is also simple to work up the forces on the rigging and hull using this design rule of thumb. You do not have to do a lot of calculations to determine the rigging loads.

If you intend to use it in higher winds (about 15 knots) you might add a 1.5 safety factor on top of this.

If you better understood the forces on the lee board you would have known it was not attached to the hulls good enough for the forces you were generating.
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  #18  
Old 02-12-2008, 09:51 AM
kmeastman kmeastman is offline
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I have done some drag calculations and it is within acceptable limits, which is good because I never intended to change the canoe hull very much. I know there are probably better hull shapes but I am most interested in the cargo capacity of the canoes so that is a compromise I'm willing to make.

to Rwatson, The technique for finding the center off lateral resistance that you mention is in one of the books I have been looking at. Don't know if anyone uses it, I didn't. After modeling the canoe in SolidWorks, I was able to cut a section down the middle and make solidworks create the projected area and centroid of that area. The Center of Buoyancy, LWL, and volume displaced at various levels in the water were found similarly.

I am still having difficulty determining if a centerboard is necessary or not. I assume there is some reccomendation based on the lateral projected area vs. sail size but I have yet to find one. How do I know if I need one and if so, how big do I make it.

Thanks for your help
Kevin
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  #19  
Old 02-12-2008, 10:12 AM
kmeastman kmeastman is offline
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Greg,

I am very interested in your design. It seems very similar to mine. Here are a few of the differences though, tell me what you think of them.

I was intending to buy aluminum canoes, It looks like you made your own out of plywood and fiberglass. Any idea what the weight of the canoe by itself is? Any idea of the weight capacity of the total boat is?

I was kind of worried about using a fiberglass canoe because it might flex and crack near where the brackets are attached, is that really a problem? Also, it was difficult to tell from your pictures how the bracing was attached to the canoes. The reason I ask is that I also intend to make the bracing in a way that can be quickly disconnected to portage between lakes if needed. I was thinking of A permanant bracket on the canoes that would be a hollow tube that the bracing would slide into and then line up two holes and pin it with a trailer hitch pin.


I also intended mine to be much wider, possibly up to 6' between canoes for a hammock area between to put people or cargo.

My sail area to displacement ratio will probably be pretty low when fully loaded. Was yours also low, did it sail well in low/moderate wind and did it make that much difference whether it was loaded up or not?

Thanks for your help
Kevin

How did you go about sizing the leeboard, and what do you think made the boat so unsteerable?
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  #20  
Old 11-22-2013, 09:28 PM
runinan runinan is offline
 
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Cat with Solar power

Hi, Kevin,

I am interested to work it out with you, build a cat with solar power to replace traditional boats in Bangladesh. Can you mail me?

Quote:
Originally Posted by kmeastman View Post
I am a Mechanical Engineering student at the University of Nebraska-Lincoln. For my senior design semester project I would like to design a catamaran that is sail powered and uses two canoes as its two hulls. I have never designed a boat so I was hoping that more experienced people could help me out.

The purpose of using canoes is mostly because the cargo/people capacity would be much greater than with most catamarans. I realize that this would make the boat slower than the average catamaran but I am ok with that.

I was thinking along the lines of using 17' aluminum canoes, which usually come with two seats (each canoe), but a third would likely be added. It would likely be built to the maximum trailerable width of 8'6". I was thinking of having only one mainsail and probably adding a captain's seat between the two canoes toward the rear.

I have done some preliminary research and here are the problems I forsee:

1. Since I am going to buy the canoes instead of building them, I can't get very good estimates of factors like wetted area and lateral plane area. I think I could figure them out if I had a canoe to take measurements on and then model it in a 3D CAD program. The problem is that I don't want to buy one and then find out that I need a larger or smaller one to make this work.

2. The major difference between a canoe hull and a catamaran hull is its width at the water level. Since the canoe is much flatter, it will have a large wetted area compared to its lateral plane area. I'm not sure how big of a problem this could be. I could increase the lateral plane area with the use of a center board but I would definitely have more overall wetted area and drag than an average catamaran. Again, I am not overly concerned about the speed I can get out of it, but it will hardly be worth putting a sail on it if its going to be too slow.

3. Catamarans that I have seen have similar L/B ratios to what I am talking about here. However, because a canoe is much wider than a catamaran hull, the center to center distance between the canoes would be much smaller than the center to center distance on a catamaran given the same L/B ratio. Is this a problem?

4. I was thinking that the boom of the sail would be mounted high enough that it would clear the head of the person in the middle seat (much lower than the other two seats) and the boom would not be long enough to reach the person in the back seat. In order for it not to hit the person in the front seat the rotation of the sail would have to be limited. Since the pivot of the sail and the front seat will likely be at about the longitudinal placement, this is about 180 degrees of rotation. From sailing books I have read, you should never need your sail to be rotated more than this but is there any reason why limiting its travel would be a problem?

Any help is appriciated. If you have any advice on these problems or can think of any other possible problems I would love to hear what you think.

Thanks
Kevin
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  #21  
Old 11-23-2013, 03:42 AM
pbmaise pbmaise is offline
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I hope you are using the correct name.

It is a wa'a wa'a.

The cross members attaching the two wa'a are called aka.

No s exists so never use akas or amas.
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  #22  
Old 11-23-2013, 04:44 AM
latestarter latestarter is offline
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kmeastman has not logged on to this site since 14 April 2008
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  #23  
Old 11-23-2013, 08:13 PM
messabout messabout is offline
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I suspect that you could build two, considerably more appropriate hulls for less money than buying two aluminum canoes. The structural implication would also be less challenging if you design the boats at the outset.
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