Just wondering whether diagonal rear and side edge in the tail (like Tabou Magic Carpet) gives any advantage for (windsurf) foil pumping in light wind.

I see custom built boards have thick and sharp edges for both rear and side edges of the tail, similar to the MB board(s). And MB seems to be able to get the foil up in no wind ;-)

Diagonal rear edges seemed popular for a while, but often have been replaced by straighter tails (sometimes with cutouts). One way of looking at this is that water is flowing mostly lengthwise along the bottom, and has to follow the board contours, unless there is a sharp edge. With a diagonal tail, the water has to go up. According to simple physics, this creates a downward force that pulls the board into the water, which makes takeoff more difficult. The issue is much less a problem on the sides, since most of the water flow is front-to-back, so diagonal sides are still quite common.

Things can be different in waves, where a diagonal tail may even help, similar to rocker in a wave board.

I think you answered your own question in the second para :)

I gather by diagonal you mean tail bevel on bottom, like boardsfr described?

Maybe the tail bottom bevel on the Tabou Magic Carpet is meant to help with Wing or pump foiling, as that board is sold as multi-purpose.

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snowsurf said..
Maybe the tail bottom bevel on the Tabou Magic Carpet is meant to help with Wing or pump foiling, as that board is sold as multi-purpose.

Yes, the bevel is intended to allow the Magic Carpet to pivot nose sharply upward for pumping without being impeded by volume behind the foil. What Tabou does right, imho, is have a sharp release by means of a ledge which allows water to release off the tail in windfoil mode. Some of the first generation multipurpose boards did not have that, just angled the board upwards. Some of us including utcminusfour and me modded those boards and got much better performance out of otherwise good boards. My version here: www.seabreeze.com.au/forums/Windsurfing/Foiling/Curing-a-tail-release-problem-fun-and-games-with-epoxy?page=1


Looks like Tabou also added an "edge" to the side bevels which I wouldn't think are as problematic given the water flow is parallel to that bevel but perhaps it does make a difference in the lightest of airs.

dang... now that I've seen the Tabou product page, I'm getting board envy

^^^ My third windfoil session and I think I did something just like that. ^^^^^^^^

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Mark _australia said..
^^^ My third windfoil session and I think I did something just like that. ^^^^^^^^

Right on Mark, stoked you are giving it a go! Yes there are moments when learning to foil that give a sneak peak into advanced aireal freestyle!

for a bigger foil that has a low take of speed I think being able to sink the tail is more important to getting going in light air than boxy wide arse boards. Maybe the opposite for higher aspect foils, where you need hull speed to get the foil to fly?

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utcminusfour said..

Mark _australia said..
^^^ My third windfoil session and I think I did something just like that. ^^^^^^^^

Right on Mark, stoked you are giving it a go! Yes there are moments when learning to foil that give a sneak peak into advanced aireal freestyle!

I guess that is how it's like flying on a magic carpet .??

I depend on hull speed to get any foil to fly. High AR, low AR, small, large, thick, thin, freeride, race, you name it. No foil will fly until you give it some hull speed. Yes, of course, this varies. However, hauling a foil up into flight and depending on nothing but slow angle of attack is a great way to get tired. Mushy flight is really hard. Just give it some speed, let the wing and stab surfaces do their work, lift it up into flight, and relax.