Benjamin, 

This is a great question! While there are folks on this forum much better qualified to answer your question than I, here are a few thoughts. You generally want the the boat to have neutral or some weather helm. That is, the sail's center of effort(CE) near or slightly aft of the the hull's center of lateral resistance(CLR). So if you keep all else equal, moving the sail forward will tend to move the CE forward in relation to the CLR,  increasing lee helm, which is not desireable. But, from your post, it sounds like you will be moving the akas forward, which I'm assuming then that the leeboards are going forward as well. That will move the boat's CLR forward as well. So the question is if you still have the sail's CE near or slightly aft of the CLR. It seems to me that if the kayak, without sailrig, has neutral or some weather helm, then it would not be that critical where the forward akas and mast are located. You could try it and if there is too much lee helm, increase the area of your leeboards a bit or even add a retractable skeg forward on the hull. You could even reduce the area of your rudder, though that's probably not the best idea. This subject can get as complex as you want and people have written detailed articles on the subject. I'd suggest doing a google search on "center of effort". You'll find a number of basic articles on the subject of balancing the sail boat's helm and basic design recommendations. I'm about to build a sail rig too, and would like to come up with a rough estimate of the hull's CLR. The calculation for an estimate of the sail's center of effort is pretty easy. Hope this helps and do post what your ultimate plans are and how the build turns out. Hopefully, someone with more sailing experience and first hand experience with the sail rig might pipe in. Dave

Thanks Dave!

Good points, practicly Ithink I´ll start by pulling the aka positions apart, getting the center of bouyancy aft a bit Ideally i should have extended the amas as well but being unexperinced builder I won´t make it to complicated. maybe on the next one! 

Another thought is to give the mast some extra rake to move sail center aft as well. I havent decided on the rig yet. the easiest for me to try with is testing with different windsurfing masts and sails. there are plenty of models and sizes around.

There is a hobie version that can be furled (no battens) but it seems to be a bit small, and i havent checked out the construction on the furling wich I imagine will be the tricky bit to solve.

I´d be happy to hear from anyone who got experiences in the matter.

Benjamin

I am building a MKII sail rig and will try to fit it to a CLC 18 and also make it compatable with the double that my SO paddles with me. This will mean spreading the akas further apart because the standard 48 inch distance between them would put the akas in the middle of the forward cockpit. I called tech support and was told that making the akas about 18 inches further apart would not have much effect. Consequently my plan is to make the amas with two aka attachment points, one for the CLC 18 and one for the Wilderness System fiberglass double.

The entire center of effort issue is a little easier to handle, it seems to me, by the sort of generic attachment system of the MKII rig. You can basically just move the entire set of amas and akas forwards and backwards, and although I don't like to cut too many holes in my boats, I suppose that you could make a second mast step to adjust CE forward or backwards if some obvious lee or weather helm develops. A quick and dirty way to determine CE in a double kayak would be nice if anybody knows how to get a rough estimate without getting too involved.

As I found sailing my clc triple w/ sailrig alone, its necessary to play around with strategically placed ballast to get the right balance. The sailrig design itself - leeboard and sail placement - work fine. If you were to use a different sail configuration that moved the Center of Effort (CE) on the sail much fore or aft of the leeboard's Center of Resistance, you might need to tweak things a bit.   leeboard has some adjustment in it as you can raise it slightly, which angles the part of the board in the water slightly aft. a little jib up front could balance things out if needed.

Again, I have found that shifting ballast around boat was the quickest, easist, cheapest way to adjust balance.