: Hi Carl,

: Nice exploration in the genre.

: Couple of things.

: 1. There is a small program you can use to determine the amount of wave
: interference between the hulls, contributing drag. It's called Michlet
: (with its companion Godzilla) Michlet is a free download on the Internet
: and was developed, principally, by Leo Lazauskas, with help from many
: experts in the field, notably... famed canoe and kayak design legend, John
: Winters. Michlet and Godzilla will also look at the optimal hull shape for
: efficiency under human power if you configure it to do that.

: 2. As you know, you have given away wetted surface drag for enhanced
: stability by splitting the kayak hull in two. Then, you lost some of the
: gained stability by raising the paddlers COG to a higher point than one
: would see in the typical sea kayak. The raised and out of the boat
: position, though, has given the paddler lots of freedom for wet exit and
: reentry possibilities. In short... you've met, head-on, the business of
: design compromise faced by boat designers the world over.

: 3. About that forward foil... There are several schools of thought on the use
: of an anti-dive plane for a cat-hulled vessel. Sailing craft designers
: face this issue regularly if they work in the field of multihulls.

: One approach is as stated already, where the forward hull connector is shaped
: in a lifting foil configuration and whenever it is immersed, it will tend
: to lift the bows and prevent a pitchpoling exercise.

: The other major approach is to reduce the forward component as much as
: possible to reduce the area of the surfaces that might contribute to the
: same effect of pitchpoling. You see this in cats that have forward
: trampoline, or net surfaces, that can quickly shed water, should the bows
: become immersed, allowing the designed buoyancy to pull the boat back to
: the surface.

: A forward foil is a dandy idea if the following comes into play: The forward
: speed of the boat (and also the speed of the water over the foil) must be
: within the designed lifting mode of the chosen foil profile, or it will
: not create lift. If it is not creating lift, then it is creating drag.
: With an enhanced horizontal surface area beyond what you'd experience with
: a simple round section, you could be increasing the likelihood of a
: pitchpole and not reducing same.

: If the boat is operating, consistently in the envelope of the foils lift and
: it is mounted properly for an optimal angle of attack, then you really
: have something going for you. A reduced aero profile for the frontal area,
: a lifting device to help the buoyancy of the bows and a structural member
: all in one element. That's a big design win.

: Caveat: It's tricky to determine the settings for all those elements.

: The biggest design decision would be to determine at what speeds and in what
: conditions will the foil serve you to its optimal benefit. This will put
: you in the ballpark of foil section to use, angle of attack for the
: mounting and overall chord for the foil for most benefit... at the least
: amount of weight.

: Fun, huh?

: My personal take... you'll almost never see a suitable foiled member benefit
: for this boat unless you regularly surf the boat at speeds at the higher
: end of the design envelope for a paddled craft. Use the smallest tubular
: solution for the bow of the boat. You can revisit this particular issue
: later. Focus on all the basic design issues you will face to arrive at an
: optimal design of hull shape and spacing. You are working on a very
: interesting paddling solution which has all kinds of primary, as well as
: secondary benefits.

: I'm excited to see how this goes for you.

Hi Chris,

The comparison of these boats should probably be to existing surf skis, that are very narrow and long sit on tops. If anything these cats should have greater stability than the existing skis which are barely able to stay upright without an assist from a paddler. These cat's certainly won't have the stability of sea kayaks with the paddler sitting virtually on the bottom.

Bill H.