your biggest problem will be getting enough lift out of them without ventilating from the base. Also remember that unlike a kite, if you do hit something you will get DRILLED into the shallow water and break your neck.

The concept reminds me of Wayne Lynch and nat Young's keel surfboards from back in the early seventies. They had no fin as such.

What about an even more extreme version of the hypersonic with really deep channels so to create three keels. One on each rail and in the middle.

I'm thinking off the cuff here!!

i reckon you're in hydrofoil territory, something like a u shape with the horizontal element providing lift. you could even use it to adjust AoA.

other than that. an upside down version of a fighter tail. ie. 2 fins joined at the base with each blade raked laterally at 45deg or so. that'll provide lift vertically.

I run a 23cm home made speed weedy.

If that puppy hits the bottom then it's to shallow for me.

The prangs are bad enough in 18" of water

Seems like the obvious solution, so obvious I guess people have tried it before with out success, (for top end speed sailing anyway).
There'd be lots of R & D to get it right, if you did want to try, must admit it is tempting, hmmmmmm ---------

No Elmo, you miss the point. with foils you don't need to sail in the weed! If you're high enough, open ocean is the go, get some real wind!!!

hi fortyd,

the boards i use are similar to what you describe. you can also include stepped hulls and tunnel hulls into this category.

i am trying to get up some photos so you can all have a look.

i finally got the time to read through the posts on the gpsspeedsurfing forum.

fantastic stuff!!

was particularly interested in the stuff towards the end of the posts from boogie and co regards channel and stepped type hulls. here is a photo of my new 125lt slalom board from underneath. (hence the wide tail) www.seabreeze.com.au/gallery/gallery.asp?imageid=4583
i've been sailing these type of bottom shapes for about 12 years now and what you see in the photo is the latest outcome. pete who designs the boards has been researching them for over 25 years. my formula board is also a channel step (CS) design and now the new speed proto i have. the speed proto is very interesting with some new nose concepts. it is also a lot narrower than the board in the photo which also creates higher aspect pads.

personally i think that the stubby shapes really suit these designs. they have minimal wetted area for their width when sailed in flat water. like all new wider tail shapes you get a better drag aspect ratio, more control/stability and larger wind range. the channels do lose out a little compared to a flat bottom version when planing up. a few pumps deals with that though.

from my average sailor view these designs are unbelievably stable. are less prone to tail walking. gybe as tight as a traditional designs and leave everything for dead when going back upwind. they track very well and on a broad reach really get up and go. almost flying over the water and gliding through the lulls.


i might try some small low aspect fins and see what happens?

quote:

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Originally posted by nebbian

Wooooah Nellie!

I'm curious as to how this bottom shape stops spinout, when the root of the fin looks like it's not wetted?

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i didn't say the bottom shape stops spinout. that is the job of the fin. i said that the bottom shape improves tracking which is more a funtion of rail and v.

looks can be deceiving too. the base of the fin certainly is wetted. you should give the designer more credit. he's been shaping boards longer than either of us have been breathing and he understands the basics of design.

all i can say nebs is try before you buy. withhold your judgment until you've sailed one. i am sure you will agree with me after that. the only thing nu school about the board is the plan shape and length. the hull shape and concepts have been around since the 1920's on powered craft.

quote:

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[ Ah well when the data drops the bull**** stops [}:)]

Next Vikky point session we'll pit the Flow (old skool) against the NXS (nu school) and see what the outcome is

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well so far things are looking good for the boards. last session has you on a 7m race sail and me on a 6.4m freewave sail. let's see.

you 1.4 knots faster peak.
me 4.6 knot faster alpha.



next outing is game on at VP. but seriously, you should sail one of the boards too. otherwise how do you really know.?

"...the speed proto is very interesting with some new nose concepts. it is also a lot narrower than the board in the photo which also creates higher aspect pads."

Huh??

The aspect ratio is span/ave. cord. Long narrow hulls or sponsons have low aspect (less than one)ratios depending on the amount of hull in the water of course.

High aspect rato planning hulls are wide (eg formula type) with short longitudinal wetted surface. They have inherintally poor longitudinal stability and are poor for speed as tail walking becomes a prob.

To go REAL fast you need BIG wind. Any theoretical reduction in hull surface drag using high AR shapes is overwhelmingly outweighed by control issues.

But from what you describe the sponsons are not that. Slowboat made a board like that which he took to the canal a couple of years ago.

quote:

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Originally posted by yoyo

"...the speed proto is very interesting with some new nose concepts. it is also a lot narrower than the board in the photo which also creates higher aspect pads."

Huh??

The aspect ratio is span/ave. cord. Long narrow hulls or sponsons have low aspect (less than one)ratios depending on the amount of hull in the water of course.

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yes, if you are talking about lift. i was referring to the shape of the pads/sponsons. ie. length versus width.

a higher aspect pad (the shape) has a lower aspect hydrodynamic lifting surface which is better for control. if you compare the pad width on the formula boards to the speed proto you will notice the lift aspect ratio gets lower on the speed boards and higher on the formula.

quote:

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High aspect ratio planning hulls are wide (eg formula type) with short longitudinal wetted surface. They have inherintally poor longitudinal stability and are poor for speed as tail walking becomes a prob.

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agree. the formula versions (maxim) i have sailed have had both conventional bottom and channel step bottom. the conventional bottom planes a little earlier and then tail walks in the higher winds. (high lift aspect ratio) BUT the channel step version doesn't tail walk as the channel reduces the hydrodynamic lifting surface aspect ratio hence more control. the higher drag of a lower hydrodynamic lifting surface ratio is offsett by less waterline wetted surface area.

yes i can hear you saying but but but.....you need a certain surface area for the board to plane "AoA". (what was it nebbian said. you can't get something for nothing) well it's a tunnel hull. channelling the air down he tunnel is providing lift (proximaty affect). same thing as concaves but more extreme and similar to the hypersonic concept.

also there is the step or cutouts. these allow the air and water to be exhausted more effiently and reduce the pressure. (less drag). so cutouts aren't just marketing hype. they do a couple of other things besides trim. on conventional bottom boards they move the planing surface forward allowing a higher hydrodynamic lifting surface aspect ratio which equates to better acceleration. also by moving the planing surface forward it becomes more inline with the sailors body weight and allows the sailor more control over that higher aspect ratio.

quote:

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To go REAL fast you need BIG wind. Any theoretical reduction in hull surface drag using high AR shapes is overwhelmingly outweighed by control issues.

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and of course a very good sailor is needed. i hope the above explanation explains the concept as i understand it. you totally missed the point by thinking they have high AR shapes.

quote:

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But from what you describe the sponsons are not that. Slowboat made a board like that which he took to the canal a couple of years ago.

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looks can be decieving. small differences in channel depth, channel entry position, pad width, cutout size, rocker shape, entry concave, plan shape and on and on and on have dramatic effects on the performance.

these bottom types suit short/wide plan shapes. if you applied the idea to a conventional plan shape, like a narrow needle or old school slalom board you would be very dissapointed because they are out of control. as i have experienced. but when refined on shorter length wider boards they work very well.

Hardie,
If your course is ripple smooth you're not going to have control problems. The only thing you will be concerned about is grip. My first guess at a solution would be for a flat rocker to a 1m or more flat with no v or channels or concaves - simplest possible shape with sharp rails of course at the back and through all the release edges.

Fins - you could try for a single with a tip treatment (wingletts or a bulb). Those things increase the effective span of foils. This is because the tip of your foil doesn't do anything but smooth out the turbulent flow. It can be horizontal and do this. Of course you have to know the aoa of your hull so you can orientate the things straight ahead. Maybe you could design the fin to rotate forwards and backwards a little so you can tune this angle. Nebs I think, knows something about this stuff. Two fins is theoretically less efficient because a) you have twice as many tips which means the the effective length/wetted surface ratio is poor and b) The pressure bulb from the upwind fin impinges in the low pressure zone of the downwind fin decreasing its lift. However its probably the easiest thing to do.

Having sounded off it behoves me to reveal I have no practical experience of board design or speed. No I just like to sit here with a beer and pretend I'm at the pub. Now what makes sails fast?

quote:

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Originally posted by NotWal



Having sounded off it behoves me to reveal I have no practical experience of board design or speed. No I just like to sit here with a beer and pretend I'm at the pub. Now what makes sails fast?

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You'd fit in perfectly with our tackernackal discussions then

quote:

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Originally posted by nebbian

Wooooah Nellie!

I'm curious as to how this bottom shape stops spinout, when the root of the fin looks like it's not wetted?

Ah well when the data drops the bull**** stops [}:)]

Next Vikky point session we'll pit the Flow (old skool) against the NXS (nu school) and see what the outcome is

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neb when you've got some spare time read up on exocet & hyperbole that will have you thinking are they on crack.

Notwal can shed some more light he uses one.