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.
hi decrepit
my first freestyle board followed a similar idea that flowed into a ducktail. it had some tracking issues and took a lot of wind to get it going.
the rebate was filled in and the board performed like a different board. planed up very quickly and tracked without a problem. i guess it got me starting to think about volume distribution in 3 dimensions. i can't figure it out though.
the other thing i can't figure out is why cutting away foam at the rail (to make the width less) seems to have a much more noticible outcome to cutting away foam in the middle of the board. i think it points to how important width is compared to volume but not sure.
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?
re: The fin root above the water i.e with no hull for and end plate:
The Exocet Turbo Boosts of a few years back (03/04?) had a hyperbolic cut out with the fin box in the middle of it. They came with an "upwind kit" that was a removable plate fill-in for the cutout.
Without the upwind kit installed the required fin was about 60mm longer.
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.
mkseven.thanks for the feedback[and everyone else]it is my understanding that the" hard edges"are beneficial for water release,some one will probably tell me I'm wrong?the tunnel hull wont be happening to this board,maybe an old wave board that I've got OR " chined bottom" could be suitable for that as well,like to see some pics of one of those if anyone has any.In your reference to cutout you mention mast track did you mean fin box.[don't go past front of fin box.]
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.
sorry yer finbox, was a long day.
It's 2 more hard edges to unsettle the board through the chop. It is all (wasted) surface area too, in that with a concave it is producing lift- the vertical edge is doing nothing. The first has a chance to raise above the chop, the vertical edge will increase the chance of biting in- great for going upwind but you want to go controllably fast.
If you get the chance take a hypersonic for a spin & you'll see what that increased hull area is good & bad for.
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.
Justin , I have Peters 62 litre Channel bottomed speed board. I have sailed it once but the wind was light. Got it going but only 35 knots or so.
I intend to try it again in proper speed conditions at Sandy Point.
I will have to be honest and say I am really sceptical about it. I am more concerned about control than speed. With the reverse V in the flat panels at the rear and the really crisp edges it looks really dangerous. I am afraid it is going to be a rail grabber, and I don't fancy that at over 40 knots.
I will give it another go but if it grabs and throws me off that will be the last time I use it.
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.
Lots of Tyre Kickers on this topic
izaak,
Looks the deal. Pics of the finished product?
Re: Tunnel Hull Potential
In my view the only missing part of Tunnel Hulls is the Fin!
If the experts can design "Surface piercing Foil" for Windsurfers maybe 50+ knot speeds will happen.
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.
Hi Martin,
sorry for the late response, been off the interweb for a few days.
i agree the rails are sharp. the front section concerned me in the chop. not sure if it's a help or a hinderance but i've found setting the mast further forward than what appears correct helps gain control. the 120lt is like that and my formula was also. i haven't tried that out on the 90lt board yet.
anyways, very keen to hear how you go. fingers crossed.
p.s. i thought you had done a few knots faster on it. that must have been the lorch.
, 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.
