Well so far, I haven't got my board dialled in. It's certainly a narrow board that floats me, and I have had it up to 35kt, only 1kt under my PB.
But I'm still not totally comfortable on it, my foot position is still fairly high and outboard of the inner hull. This may have something to do with it.

Think I need to try and get my feet where they would be if I'd done as Gestalt suggests, and cut the rail all the way thru. I don't want to loose much more volume though, at the moment I can still slog it back to shore when the wind drops out. I just hate floating around in very cold winter water.

it would be fun to try a surface piercing setup. turning may be a problem. what a rudder mean the board is no longer a windsurfer?

icesurf said...

"SMOKING IS OPTIMUM"

As Said, If you smoking & surfing on the tail of the board there would be No Optimum angle,
likely a range of angles will work.



Back to Tunnel Hulls:
The only benefit of a Tunnel Hull for high speed windsurfer
"the Fin becomes a Surface Piercing Foil". , if that's a benefit?

As it is known that at any given design point, you can design a fully submerged foil that will beat any surface piercing foil.


For Speedsurfing, to make a "Tunnel Hull" perform using a single Fin, how do you design a "surface piercing foil" that outperforms fully submerged foils?

I think tunnel hulls still have their merits (afterall I do own a hypersonic and yes in the right conditions they are very fast for their size), as much as I have bagged gestie on those boards it is only for a few minor things. I'm not a fan of the very hard edges on the tunnel... I know it is a different school of thought but you rarely see any boats with hard edges. If I had a chance to take a grinder to gestie's board I'd make the side panels narrower and a pretty aggressive concave onto them. I would keep the deep v around the fin, but blend the side panels flat right to the tail rather than have them end. I'm not a shaper though, just a fan of things that look natural or flow well.

Do I think it has a place on speedboards... no. I think tunnel hulls are great in a situation where it lets you have reduced wetted area on a wider board giving you more leverage over a bigger rig- possibly why peter's formula boards with similar hull have worked.

I would actually like to go the other way- a chined bottom (raised centre section) I had a board like this years ago which as an absolute rocket but it needs to be on a relatively un-thick board.

pirrad- those cutouts are very big, imo back off about 5mm on the borders of each. Also keep the level with the front of the mast track, F2's go past that and after riding them alot i'm not sure it's a good thing. As far as cutouts go I like the isonic design.

Good luck with it, it's good to see people taking the time and $ to muck around with this stuff.

Why don't you try routing a wet weather racing tyre tread pattern on the underside of the board? It's amazing how much water they release when racing.

yes the sharp edge is for water release.

what is needed is someone who is capable of doing 45+ knots actually sailing a channel board for a year in the right conditions.

i htink it's too early to say channel shapes don't suit speed boards. they are certainly fast shapes.

this is an old board dad cut up a while back and we have only tested it in light winds so maybe in a nice 20 knots wil give it a go.

Love your dads work isaak.Thanks for sharing those photos.You have given me inspiration....Was going to leave the tunnel hull project[old wave board] for a while and make some minor mods to the caveman.Been painting last couple of days ,still a couple to go and its a trip to Adelaide at some stage to get some foam[need to order a tuttle box].Got a few things worked out ,a strip of each side to make it a bit narrower,which gives me a flat mount for some straight edges to take the hump of the bottom and flatten it out.Hope to get the bottom laminate off in one piece ,it will be the top if i can.As for the channel build,there's one plan in the think tank at the moment but that could change.

yoyo said...

icesurf said...

The Tunnel Hull is worth exploring, but think with twin fins there is too much induced drag.

Too much drag maybe but NOT induced drag. Induced drag is proportional to the angle of attack. With an extra fin the AoA would be lower and so would be the induced drag. Of course the profile drag and surface drag would be greater with the extra fin.

Tunnel hull power boats have the apparant wind dead on and the weight of an engine and fuel tank to support. A speed windsurfer has the wind abeam to ~45 degrees , weighs >5kg and often already has too much nose lift..

Tunnel hulls are to reduce hull/water drag but if there is no board in the water anyway there is not much to be gained.



Images courtesy Shane Baker

1st reply from a newbie yank , but theoretically, a two fin setup can have less induced drag than one fin, according to biplane theory. If you add this to a number of points made earlier, like 2 fins being smaller, aoa as result being smaller, and, I suppose, if the tunnel was shaped to allow it, the two fins would sealed at the top endplate (the hull) if the side hulls (sponsons?) are in the water, and the AR would be thinner, which might be good, esp. if the span of the 2 fins is the same as the single fin would be.

That be the theory, at any rate. I don't know if there's any practical experience to validate it in the tunnel hulled windsurfing world. It seems to me that if the two fins were too close together, there could be massive interference in the space in between- and that is part of the reason that the biplane theory exists. But I've read somewhere that once you get outside 2.4 times the chord in spacing the 2 fins, things get better. A fluid flow guy from one of the Italian AC teams told me that the farther apart the spacing is, the better- as far as you can go, he said.

Paul