New boat and sail plan

[David Urban]

Hi all. I have slowly been building a Kipawa (John Winters/ Green Valley) and have been thinking about adding a sail plan. I of course have Todd' s book and have been using it while planning things out. The hull is done, gunwales on, and I now that it is frozen in Chicago (building in unheated garage), I am starting to work on caneing the seats, and building a foredeck and afterdeck in my basement shop

I have attached a jpeg of what I am thinking of doing. The forsail would be about 50 sqft and the mizzen about 15 sq ft. I really like the look of the sailing canoes with the large foresail mounted almost at the bow- and I understand the concept of actually keeping the CE of the sails ahead of the CE of the hulll, so that when one heels- rudder effort all balances out- But when I do some rough calculations (the large vertical line is where the CE of the sails end up) it seems very far forward of the CE of the hull- Does this look right to you?

I plan on paddling in the rivers around Chicago, and sailing off the beach on Lake Michigan.

Anything else I should let you know for youall to respond?

Thanks,

Dave Urban

 

[Todd Bradshaw]

Dave, Your C.E. for the combined sailplan is in the correct spot with relation to the sails shown. The only things that struck me as strange were that the daggerboard (or centerboard or whatever it will be) is too far forward and awfully small. Typically it would be back in a position nearer the combined CE (right under it wouldn't be a bad place to start) about twice as big (fore-and-aft) than shown and most likely a bit deeper as well. If you want to get it even closer to the middle of the canoe, you can move the mizzen aft (leaving the mainsail where it is). This will move the combined CE aft as well, though not drastically since most of the sail area is in the main. It would also allow you to step the mizzen through the aft deck, which might be easier than adding some sort of other thwart. It's pretty common on boats with similar twin rigs to see a good portion of the mizzen hanging off in space behind the stern. It works fine.

As long as the CE/CLP relationship is in the ballpark you should be OK. Keep in mind that in addition to the centerboard's position, two other big-time contributors to the helm balance and steering are fore-and-aft trim and sail trim (the amount of wind power you're trimming into each of the two sails as they pull and push on their respective ends of the boat). These two variables create both a rather large "fudge factor", in terms of how closely the "on water" version has to match the profile drawing version and still work, and they also give you a lot of adjustability of the true working CE and CLP when you're actually sailing.

 

[David Urban]

Todd: Thanks- the boards will be leeboards mounted on a moveable thwart- I was just moving them around in the drawing to see where the CE of the underwater areas would be to create a point of equivalence for th CE of the sails (moment arms and all that) - it was moving way to forward - thus the orginal post. Obivously actual testing on water will determine where the leeboards go, and weather, and where I sit, and, and....

I was thinking that a high aspect ratio (depth to width) leedboard would work kind of like a high aspect sail, therefore I want to design one deeper but narrower. I also found Cedar fencing at HD which is about 6 inches wide and 6 or so feet tall. I was thinking (and actually have shaped) of using this as a leeboard- properly shaped and covered in fiberglass/epoxy.

If I need to go bigger I will.

The rudder is the same- but 2 boards thick with glass/ epoxy to bond them. I am finishing shaping it this week also. It glasses into a nice color also.

 

[Todd Bradshaw]

High-aspect leeboards can work. They tend to have more leverage on the bracket, so it needs to be sturdy. My impression from the drawing was that the underwater portion of the board would only be about 18"-24" by about 6", which wouldn't be very effective. I made a single leeboard rig once that had a board about 5' by about 10" and it seemed to work decently, though there were times when shallower draft would have been nice.

 

[David Urban]

Thanks for the advice. I am going to re think the leeboard, I am after all going to be launching from a beach into Lake Michigan and I know about 50 feet out there is a sandbar.

Oh- and thanks for writing the book!