You are welcome, Matt...

The whole question of foiling revolves around the weight that needs to be lifted in order to take advantage of the extreme reduction in wetted surface that takes place once the hull is lifted. If the boat, the load and the crew are to be lifted, then the formula depends on sufficient foil size for the required lifting surfaces AND enough power to drive the boat at a speed that will bring the foil lift potential into play.
Clearly, it's a juggling act.

There are examples of lifting foil-equipped trimarans, such as you suggest for your very slender kayak hull. Take a look at the Windrider Rave and the Hobie Trifoiler. Both boats can carry two, though they are limited in potential for load once you get beyond that reality (especially if the crew are fairly stout people) Look at the amount of sail area they need to provide the opwer to weight ration needed for the foils to do their job. Truthfully, that isn't very practical for a sea kayak... well, if the kayak in question is to retain much of its kayak heritage and purpose, that is.

There is also a "fiddle factor" for any foil borne craft, as the foils need to be tunable for angle of attack in order to present the optimal lift in a wide variety of sea states. This requires a floating wand mechanism which tells the foils how to adjust themselves for optimal lift in any condition. Additoinally, the foils themselves, need to be deployable in such a manner that allows the boat to take to very shallow water while reducing the potential for damage to the foils.

Another issue is maintenance of the various moving parts, as well as the still unresolved issue of how to avoid the miscellaneous crap in the water at most seaside locations. Any weed, plastic bags, hamburger wrappers, flotsam, etc. that collects on the lifting surfaces will virtually destroy the lift coefficient of the foil surface and drop you back to what is called, sea-hugger, status.

Not a bad thing for a kayak that is already at home in the water when paddled. The problem is that once the boat is immersed in displacment mode again, it has excessive drag from the foil surfaces and it will be quite slow... with ugly handling as well.

For my $.02, the foilborne thing is for controlled conditions, those that have a serious and unbridled need for speed and for the guy(s) that can accept the added maintenance that goes with the additional moving parts. Oh, did I say it costs a lot to build and replace the foils, as they are typically, full carbon laminates built in female molds with vacuum bags to keep the epoxy/cloth ratio to the absolute lowest levels of resin for max strength to weight?

If you are up for all this, then true lifting foils could be in your future.

There is, however, a mid point of foil applications that is well within reach, though it does not give full flying, like the above mentioned boats and their possibilities.

You can build, what are commonly referred to as Bruce foils, for a whole lot less in money, expertise and structure. They will slightly lift the boat, reducing wetted surface and allowing greater speeds than pure displacement sailing/paddling. They can be built from more common materials, are easily deployed from the cockpit and do not have the high level of "fiddle factor" associated with true lifting foils. You also don't need to fly a nasty/spendy, high performance rig in order to take advantage of the potential... simplifying the boat even further. Google Bruce Foils for an idea as to what is going on with the design approach.

For my money, though, a well designed rig setup that is portable, easily struck and able to deliver real power to such a light and skinny boat is best employed with a trad trimaran setup that is simple and easy to construct. The whole boat is much easier to understand, as there are not a mountain of issues to keep dialed-in in order to experience the full blast of its potential.

You can see from the video clip that the XCR is very capable of speeds that would quickly leave a paddled kayak in its wake when going upwind. Offwind, it's not even close. This performance is not gained by sacrificing the paddling potential of the canoe. While you will not likely get the same performance from your double kayak (unless the hull has an optimization bias for sailing) you will still see much greater speeds than any paddled boat. You also have very serious speed advantages over fast singles, simply by having a longer, usable waterline.

This sailing option can be achieved with a rig that is fully stowable in your boat, offering you the option, at any point in a kayak adventure, to haul out the rig and turn your boat into a vessel that can truly take advantage of the prevailing conditions. What a treat to make a long, open passage in a quick and grand style, while reducing your exposure to the elements.

What you will probably do is engage in two types of applications. There will be the trips in which you principally sail, while occasionally paddling with the rig up when the wind dies or you need to maneuver in close quarters. The other type of trip will most likely be regular, paddled adventures with no hint of the sailing rig in the entire journey. The nice part is that you get to decide which type to do and then enjoy them for what they allow you to experience.

Chris