Wouter,

Thanks for the extensive analysis. What you say makes perfect sense. I think we can summarize in one question:

What drag/weight ratio is more efficient - displacement with narrow beam hulls (cat) or hydrofoils?

I am sure that low weight multihulls with supercavitating hydrofoils are faster then beach cats - but this is no news.

I also believe that the Catri will be faster then beach cats, but only marginally, because of its more conventional hydrofoils and stabilization system - they are very practical but not so suitable for airborne sailing. The size itself will play a role in it, too.

(by the way, Playstation looks like a beach cat to me - this pushes the displacement speed limit to over 40 knots...)

Unfortunately I do not have enough knowledge to write about the Catri, but I am sure that itsi design has more smart features then it seems at first sight. A real specialist in multihulls told it to me after a thorough analysis.

Now some details I feel able to talk about, and that might interest:

1) The original Catri 26, the US Catri 27 and the Brazilian Catri 27 are the same hull but for cosmetic details. The US 27 has a different **** with longer transom and the Brazilian 27 has a rear seat and increased **** size (at the expense of rear cabin volume). The last is partly due to my request - I like ample ****...

2) The rear outrigger foils have a very interesting geometry, that is hard to see in the drawings, but can be seen in the pictures. There is a narrow triangular section under the outriggers supporting the rear foils and locating them slightly under the bottom curve. This feature and their angled down position, enable them to effectively lift the outrigger's transom out of the water - but for the triangular support.

3) As can be seen in the drawings, the outrigger itself is inclined forward, relative to the mainhull waterline. When the boat heels, this causes the bow to lift - and the rear foils to enter the water. The modified pitch attitude creates the initial angle of attack.

4) When the bruce foils are working, when the lift exceeds the needs, the foils themselves are raised out of the water. This has two effects: the Bruce foil's span is reduced and the angle of attack is increased - for all foils, in this last case. If the Bruce foils raise too high, since there is a limit for the angle of attack, the reduced span reduces the lift so it sinks a bit, and reduces the angle of attack. For me this seems to be a stable equilibrium situation. If we look at the rear foils, when the bruce foils are up, the rear ones start working with greater angle of attack, so they will lift the transom higher. This reduces the angle of attack. I have not analyzed it deeply, but both systems seem to be in stable equilibrium, especially when seen together.

The few informations I could get from the designer are that this kind of analysis is plain vanila and wave interaction is the real secret.

5) Eliptical x square extremities - the truth is that I have no clue why the designer prefers eliptical shapes both for sails and for foils.
My best guess is that in that side of the world they are not using equations that take infinite span as an initial condition (like we do) and found means to analyze the actual behaviour of the extremities in variable wave/wind conditions, as in the real world.

I don't understand completely how the Catri system works (and can not discuss all the parts I understand), but the reports from the guys who sailed it are amazing. One said something like "...yes, I know we can surpass 30, but after sailing at 25 I don't know if I really want to"

Anyway, I will learn more about it when the boat is ready...

Can't wait!
Cheers,