Theory aside, what's your personal experience with the tail cutaways. Do they really work?
re: And whats the theory behind what they do? I thought they were handles? Got one with and 2 without.
Plan sooner, faster ...""reducing drag, wilst retaining surface", etc...but do they work?
I put some in an old board and ruined the board, its trim became all wrong and the ride very harsh in chop, but it was a narrow board to begin with a 55cm slalom board. So it certainly makes a difference, in a before and after project.
I would say that's a valuable (though paradoxical) practical first hand information.
If you have a narrow board with the cutaways, it should work better if you fill them in.
My startboard go has cutaways, but don't really notice it making me plane faster, maybe its becuase its the size of an aircraft carrier!
well everyone knows that the only thing more important then how fast you can sail is how cool you look doing it.
and cutaways are COOOL!
well you dont see many speed boards with cut outs any more, no need i dont think with such a small water surface area once going.
Geez I've got 4 boards with Cutouts but no chick has shown interest in me? Maybe its because I'm an old fat ugly bastard
plus I don't have any cutaways on my boards anyway, this is entirely theoretical. I figure, if your board has cutaways it looks like a transformer, and megan fox was in transformers, hence the connection between looking cool and cutaways.
i'll let you know if the girls dig pink boards as much as pink polo shirts with popped up collars HAHA 
I deleted my reply so not to offend ayone, but it was picked up too quickly
So even the coolness of the cutaway board has turned to a theoretical discussion...
The conclusion is:
Cutaways are a marketing plot to get us to upgrade and attract more chicks.
I get worried over the depth of my thoughts sometimes.
there's no doubt in my mind they work. not only do they reduce drag on wide tailed boards but when combined with cutaways also make board better to gybe.
on narrow tailed board i think there is less to gain and they are not as effective.
Hardie, you need the cutaways in your torso, the chicks don't seem to dig love-handles anymore 
I learnt that one from experience too
I learnt that one from experience too
Yes they do work. They are a trimming device.
I used to sail an Exo Turbo Boost - kitsch and cool. It had a gigantic cut out that went right around the fin. It came with an infill plate to fill in the cut out. It was called the "upwind kit". It was called that because the fin without the hull as end plating had to be 50 to 70 mm longer to achieve the same lift as the fin required when the infill plate was installed. With the plate in it was back foot heavy. Without the plate it trimmed beautifully. I sailed it without the plate nearly all the time.
High aspect foils are more efficient (more lift per unit area) than low aspect. If you want a high aspect planing surface (short and wide) then you have to pull the back edge forward if you want comfortable trim. Although the planing surface is more efficient, the little bit of hull around the fin is less efficient than a conventional tail because its narrow. It occurs to me that a possible further refinement would be to move the fin box 80mm (+or-) forward and use weed fins.
Then the cutouts can be a little bit shorter because that bit of hull that was around the fin has gone and we're back to something in between a cutout tail and a conventional tail but more efficient than both. Then I guess you could add cutout ventilation like the Missile for that bit less drag. Then I guess you could ventilate the sailor.
yeah what really does it do? i heard it's supposed to be for board control when too fast who cares about it we just like to be out of control in anything[}:)]
I won't bore everybody with the long winded version of the theory but basically it is about high aspect foils and drag reduction. A high aspect planing surface (wide and short) generates more lift. A high percentage of that lift comes from the leading edge of the planning surface . The rear section of the planning surface generates progressivly less lift but the drag stays relative to the wetted surface area. So cutting away surface area from the low lift generating region (the tail) reduces drag. Pretty straightforward.
There are other really important factors such as trim angle, so the cutouts need to be designed in conjunction with both the rocker and outline. Putting cutouts in boards that are not designed for them can (not always) have negative consequences as they effect the board trim.
My personal experience with the boards I have designed is yes, they do work when designed properly. I have also combined the cutouts with "wingers" (like Isonics but more aggressive) to test the theory even more dramatically. It took me 2 goes to get the cutouts right on my large GPS blasting board (The lovemuscle large). I actually made them bigger and changed the shape slightly second time around to increase the efficiency. I have done 38 knots on this 69cm wide board with a 37 CM McDougall/Lockwood slalom fin in it and know I can get it over 40 in the right conditions with a more sweptback fin and after eating 10 pies, so I don't think there is anything wrong with the theory.
Why not on small speed boards. Well they are narrow and really pinny in the tail anyway, pretty low surface area tails. Combined with a properly designed rocker and outline so the trim angle is optimised then they just don't need them.
On wide boards designed to both plane early and go fast, yes I think they work great.
My2c
Thanks Mr Love.
It all makes sense.
According to what you said, when you look at the photo above, the top board makes more sense than the 2 at the bottom of the photo. 
, i'm all for cutaway's but i'm not sure about cutout's,just recently i modified a board to a trifin, and added two fin tracks where the fins could be inserted from the tail and could be ajustable, what i found was when i was sailing the board without the 2 side fins there was two huge rooster tails coming from the fin tracks and seemed like there was heeps of drag, i have filled the tracks in for the time being and back to a smooth ride,
Yep I guess so. I don't like the elliptical type cutouts as in theory you can get some "suction" caused by the water flow over the cutout creating a pressure difference if the cutout can't be ventilated. Exactly how the stepped bottom ground effects worked on the old F1 race cars.
Whether this really happens on sailboards or if it does whether it is enought to worry about, I don't know. I guess Patrik Diethelm thinks so as he goes to the trouble of ventilating with air pipes.
The advantage of the eliptical type though is that you gain more rail length which maybe helps the board to be a bit easier to drive up wind???
The cutouts on the top board do make more sense to me though from a drag reduction point of view.
I guess like all design it is about trade offs, thats what makes it so much fun messing around with this stuff as there are so many ways to approach the same problems.
