canoemaran/kayakamaran - best compromise in hull shapes

[thedutchtouch]

one of the ongoing projects thats been bouncing around for a while in my head/notebook is a canoemaran or kayakamaran, my main question or point of concern is the hull shapes i want to design them so they can perform "well" as both a catamaran and as separate canoes. catamaran would be a sail/OB and canoes as paddle only (although i may hook up my 3hp to one just to see what happens). i'd weight use at probably 6-=75% catamaran, 25-40% canoe. from my research longer slender hulls will be best for the cat, however there has to be a minimum beam for each hull in order to have a functional canoe.

another option i'd be ok with is using 2 single-ender hulls, styled similarly to rowing wherries but with a less dramatic skeg. anyone have opinions/suggestions? lets shoot for max LOA in the 15 foot range, plus or minus a foot or so. hope that's enough information to start some discussion. please note this is a recreational use craft and i wholly emphasize fun and ease of use over squeezing out every possible knot, so am willing to compromise sailing speed, but not maneuverability.

[Petros]

I have doodled a similar idea, but your premise is impossible: you can not use the same hull design for a canoe/kayak with a catamaran. Cats have very narrow hulls (high fineness ratio), tall to give a dry ride, with round bottoms (least wetted area), canoes have fairly flat bottoms with fairly large beam to be stable when full of cargo. Kayaks better finess ratios than canoes, but must also have a fairly flat bottomed hull compared to a catamaran hull or you could not stay upright in them. Both are also low to the water surface (little free board) to allow paddling closer to the surface of the water.

Since you only have single person muscle power in a kayak, I would design for an optimum kayak design; 17 ft LOA, about 21" beam (or less if you are skilled enough), and than just live with the performance they give assembled as a catamaran. Since you would presumably have a sail driving the assembly, the "extra" drag of the less than optimum hulls will not really harm you, you will just not get max speed possible.

Realize also there will be limited cargo capacity in the kayaks, so you would have to pack light. To solve that I have also thought of another arrangement: two light kayaks with a large cargo canoe in the middle to form a trimaran. will give you much more cargo capacity, and once you get to your destination and you set up camp, two single kayaks and a canoe to use to explore the area. You will also only need one rudder and lee board or dagger board in the center canoe.

Either way I would build them as light skin-on-frame kayaks, and use hollow cross beams that are attached with bungie cords (light and simple, easy to field repair) and a trampoline deck between them. this should all fold up to fit easy on a compact car roof.

[Stevo]

Any progress? While not roof topable, I built this in a weekend (not the rig)..
note leeboard angle...toed in too..
http://www.youtube.com/watch?v=s0xTZH3nYAw

[Squidly-Diddly]

Why leeboards toed in?

Wouldn't be be better to have single big swing board in the center?

How about adding oar locks on the gunnels and a center seat for rowing.

With 'plain' straight oars you could then use oars as leeboards.

[guzzis3]

Actually I've often thought multihull hulls would benifit a lot from canoe design. We tend to think about them moving directly forward through the water but apart from running they "crab" just like a canoe does with it's asymetrical drive (paddling one side then the other)

While the low freeboard is not ideal the wide flat hulls will just slow it down a bit. It wont scare any nacras or tornados but it should work fine.

Towed leeboards are probably slightly more efficient than a mid mounted single board but there probably isn't that much in it. If you want the hulls for paddling the weight/space penalty of a centerboard or daggerboard case is probably too much.

[Manfred.pech]

http://www.ebay.de/itm/Kajakat-Kajak...item3a745a7582

Normal Canoes are drawn for speeds between 3-5kn, where resistance is low. For speeds above this resistance is increasing rapidly. Kayaks are better because they are more slender.

The cat above - Kajakat - sails good in light airs, but very wet in choppy water.
For transport one hull can be stowed into the other.

[Stevo]

This is a 11 knot boat so far. She starts to hydrofoil at 9. I did have one centerboard at first but I wanted her higher and drier. The video link has no toe in/it's the old model. The picture has the old leeboards on a new beam. Raked under at 45 deg and toed in 4 that gives me 2 up and 2 in....liftoff! There are two rudders depicted here as well...thing of the past. One T-foil coming up.
Search Crazy Canoe Cat on this site for more pictures/dialog....with the leeboards and rudder(s) retracted the draft is only 5" at best with kids, dogs and ice chest! paddling solo requires the center opening. The mast requires an extra eye when paddling in close. She could be lighter at 225ish unladen. hope this helps Mr. DutchTouch -Stevo