Kayak sailing

Minimalist trimaran

Once upon a time, my brother built a stitch and glue kayak. After several years of happy paddling he decided to sail it.

The attached pictures are on the town lake in Tempe, Arizona but he has also sailed it on some reasonably big water in the Sea of Cortez, Sonora Mexico.

The kayak is 21 inches wide, 20 feet long, and ways about 50 pounds. The ama's are 1 foot wide, 12 feet long and weigh about 10 pounds each. The aka's are 2X4s ripped 1/4" thick 16' long with a layer of fiberglass cloth between each of 8 pieces and weigh about 8 pounds each. The mast is 20 feet long and weighs about 10 pounds. The aluminum piece that ties the lee boards to the mast weighs about 15 pounds. Total, about 101 pounds, and my brother weighs about 190 pounds.

He reports that it accelerates like a rocket and tracks like a slot car. His guess is that he's gotten 15 mph out of it in a decent breeze in Mexico. The aka's are flexible enough that they provide lift but each ama tends to react to its own wave set (Gonzo). Apparently the balance is such that it doesn't nosedive but it settles under load. Planing is out of the question.

He likes the rig he has developed but he wants to plane so we're talking about replacing the kayak and ama's with planing forms. He's thinking about creating a higher plumb stem for the hull and both amas, moving the bow of the amas slightly forward of the hull to help keep the front end up and to allow shuttling the headsail from one ama to the other. We're talking about moving him back for obvious reasons. We're planning to retain the kayak length and rocker, make it a little broader a little sooner and only tapering it slightly from its broadest point to the stern.

Any thoughts (other than that my brother should lose some weight)?

Doug Carlson

 

I'm not sure planing form hulls will buy you anything. I'd go with rounded sections, with the area distribution tailored to put the center of buoyancy where you want it. Possibly making the stern sections more elliptical with the major axis horizontal and the forward sections with the major axis vertical. The rocker will fall out from that.

You might take a look at successful trimarans in the size range, such as the Windrider 16.

 

Tom,

Thanks for the reference. Interesting boats. Will the 16 plane with that molded keel?

As soon as i get time I'll model some elliptical forms and post them for critique.

I'm assuming the ellipses share the same center line and rocker is created by varying the vertical axis?

Doug Carlson