I received this email from my friend Dirk and I'm happy to publish.
I 've always been trying to make a board that sails more like a surfboard instead of a windsurfboard "shorter turns, easier to go under the lip more speed of the top,...." The boards I made at Richard Green 's place worked really well for me in the bottom turn (you can always ask Glenn this), but in top turns I was always wrong in timing, came out with no speed,... anyway I always missed the next section because of my bad top turns.So my answer to this was to make something more like a surfboard.
Windsurf shapers tried the thruster set-up but there was still one fin (also too big) in the middle that gave a lot of drag. Then Kauli came out with the twin fin set-up, here we go something new, lets check it out!
I continued my research on surfboarddesign putting some more energy towards twinfins
Let’s look at a small part of the short board history. Shapers started with making shortboards with a single fin set-up, this was not working well enough and they came up with the idea of using 2 "smaller" fins. This already made a big improvement on the performance of the boards but there was still a lot of room for improvement.
In the early 80's shapers came up with the idea of a quadfin, but the first quad fins where very similar in feel to the twin fins and so the thruster setup -what gave a nicer balance between single and twin fin- took over. Quad fins where put aside, and only a few devoted shapers continued the research.
Recently a lot of shapers have reevaluated the quad design and are trying it out on modern shapes and designs.
So mainly what are the strong points of a quad in comparison to a single or twin fin:
from Kimo Greene:
Why Do Quads Work Better?
Quads are way faster than standard thrusters or even twin fins. Most would think, how can they be faster with an extra fin…wouldn’t that create more drag? Actually, because both sets of fins are working together on the rail, there’s nothing to slow you down like the center fin of a thruster. Quads are a lot more efficient with speed.
Quads are much more responsive than twin fins or thrusters. The reason is that the fins are set further up the board which essentially puts the fins directly under your back foot. The end result is an ultra responsive board that goes where you want it to go and fast.
Four fins boast an extraordinary amount of holding power in larger surf. A large number of the world’s best big wave surfers use quads in giant surf at Jaws and Mavericks. Many of them claim that a quad fin board has better holding power and speed in giant surf. If it works well at Jaws, imagine what it could do at your local beach break?
From Bruce Mckee:
1. A faster board with all turns having an added boost
2. More security taking a higher line, so pulling out of a close out section is easier, also running high and getting speed or sitting high and deep in the tube
3. also slamming a bottom turn without fear of spinning out "No more 'nursing' a turn"
4. Much more control in floaters
5. Drive of the top instead of a stall.
6. rail to rail turning
7. Also what you will notice when the waves are bigger (with the same small wave board) is that you will have absolutely no 'nursing' the board trough a high speed bottom turn
Anyway You will be slamming or putting all you weight into everything. Not because you need to, but because you can!
For me this was enough info to convince me in trying out the quad fin setup instead of making boards that everybody was going to make, (this was about 3-4 years ago). So I called Alex Mussolini asked if he was interested in trying a few quad fins (at that time I was making his boards so it was easy to get him to try this out). I redesigned the outline (opposite from the trend of wider and rounder outlines), the bottom shape ( a little bit more v of the back,..) and the rocker, and off course instead of a single a quad fin setup.
He used it in Chili and loved, at the same time I made myself a couple of Quad fins and I was blown away with the result. The only thing that was left for me to do now is to get the twinfin master himself "Kauli" to try a quad fin out, so let's see what he thinks of his board.
For me it does all what is stated above (apart from the tube off course) and in terms of normal sailing I can add that it gets on a plane super fast, also very good upwind performance and even in choppy water I have no problems controlling the board "knowing that I only use 4'5 inch fins, about 11,4 cm in depth".
PS. Wonderful photos of epic California surf here. Sequence 23 is truly incredible.