Jumping Foilboard Windsurfers : Technical Question

[Doug Lord]

There have been several incarnations of foiling windsurfers but the one that intrigues me most is the Rush Foilboard Windsurfer:

http://www.neilprydemaui.com/items.php?id=48
It seems to me that one of the keys to this thing being able to jump and successfully re-enter is the delta shape of the mainfoil. I'm going to test the idea in a while but why couldn't a high lift ,early take off, type of foil-like those used on the Moth do the same thing provided a system was devised to by-pass the wand momentarily. Any thoughts on this now would be most helpful.

[frosh]

The storyline of some soapies on daytime TV can be picked up immediately even you have been absent for a few years. So it is with the foil mania. Doug, I suggest that you ride a modern shortboard in a rough sea in 20 knots of wind (if you are indeed capable) and you will realize that the last thing you would need is lifting foils. Indeed travelling over 20 knots most of the time, the board is jumping at every wave ramp in the water, whether you like it or not. There is a very good reason why the foiled sailboard has not captured any noticable market share. Simply that the sensory experience is very likely less intense when the board is above the waves. This is ignoring the cost, unecessary complication, and the significant extra control problems, when a sailboard is fitted with foils. Try giving it a rest for a while!

[CT 249]

Windsurfers without foils can jump.
Moths without foils cannot jump in the same way.

Therefore it is obvious that what works in jumping a board does not necessarily work in jumping a Moth.

[Doug Lord]

I'm really interested in why the air chair(foilboard) type of foil re-enters so well and any thoughts regarding the behaviour of a higher aspect-longer span Moth type foil in a similar circumstance. For the purposes of this question forget structural considerations. Assume that the wand does not deflect the back end of the main foil flap up as it would in normal circumstances if the boat jumped. In an intentionally jumped boat the wand would be bypassed.....

[frosh]

OK Let us assume that somehow a high performance dinghy with hydrofoils could be made to jump. ( I cannot think how this could intentionally be done BTW). While completely in the air the disconnection between boat and its appendages with the water means that any potential rotational inertia already present on the boat and crew longitidinally, or for that matter laterally as well will have virtually nil resistance now that we are airborne. Therefore in the seconds that we are airborne there will almost certainly be an attitude change on the craft. Due to gravitational forces the craft drops back into the water still changing attitude all the way to touchdown. It is a folly to assume that because a skilled sailboarder can manuver the board's attitude while in the air the same can apply to a dinghy which does not have a hand held free-sail system, and never will have.
The probability of the lifting foil now being laterally fairly parallel to the water surface is very small. More importantly the angle of attack of the foil is almost certainly not going to be in the normal range of 0 to 3 degrees positive. If it is negative then the craft will somersault forwards with catastrophic consequences to boat and crew at the speed it will be travelling, say 20 knots plus. This argument I believe can not be refuted by any reasonable person with experience jumping a sailboard, and with an understanding of the simple behavior of wings moving through air and then a far denser medium.
The whole jumping a foiler idea reminds me of Icarus who hoped to fly to the Sun (in Greek mythology), with wings attached to his arms with wax.

[sigurd]

I think that short, swept foils stall at higher angles. That is why I think they are used, it is not so critical which direction they enter the water. Also, maybe they shed air faster when swept?

[Doug Lord]

It appears to me from looking in Theory of Wing Sections that the 63412 foil has lift from -2° to around +8° particularly if the flap is down a bit.
Seems like a fairly wide range to me...

[water addict]

gotta agree with Frosh on this one.

Foils on a boardsailor makes no sense. Try a short board in a breeze, you'll see that foils on such a craft is borderline retarded.

There have been attempts at foil windsurfers, I've seen the videos a couple decades ago. It's been tried, with poor performance.

[Doug Lord]

gotta agree with Frosh on this one.

Foils on a boardsailor makes no sense. Try a short board in a breeze, you'll see that foils on such a craft is borderline retarded.

There have been attempts at foil windsurfers, I've seen the videos a couple decades ago. It's been tried, with poor performance.

WA, did you even look at the Rush Randle(neilpryde) website?? I've seen a foilboard similar to those up close sailing with a fleet of other windsurfers and it was slightly faster but it was capable of jumping quite high in flat water-something none of the other boards could come close to matching. Being slightly faster than a windsurfer but 2' off the water is EXCELLENT performance. Being able to jump in flat water is icing on the cake.
The Miller foilboard has excellent speed from what I've been told but Rush's 'air chair' version seems pretty damn cool. I talked to the guy that was sailing here at Kelly Park and he'd only been at it- since he built it- for three hours and was capable of remarkable performance for such a short time on the thing. I'd say it has a lot of potential and it was obvious that it worked really well.
Any foiler has the potential to jump quite high in any condition as long as it is foiling-the ONLY question is can it safely re-enter from a structural and foiling(lift) standpoint. I think its highly likely that by manualy by-passing the wand on a boat designed to jump that re-entry can be successfull every time or close to every time. And that sounds like it could be a lot of fun.
===============================
But the topic of this thread is what makes the air chair foil so successful at jumping and what would be theoretically possible to enhance the ability of a relatively high aspect foil to re-enter successfully. Thanks for your response, Sigurd!

[sigurd]

It looks so very fun! Keeping in mind the recent discussion in foiler design thread about ventilation on foilboards, I wonder if they have that problem, or how they solved it?
It does not look like they heel a lot to ww. maybe they just have enough vertical area?

I am trying to imagine how to control flight attitude in the air. as was pointed out, there is no air steering mechanism and limited cog manipulation possibilities! Maybe short hangtimes at least are possible without?

[frosh]

the ONLY question is can it safely re-enter from a structural and foiling(lift) standpoint. I think its highly likely that by manualy by-passing the wand on a boat designed to jump that re-entry can be successfull every time or close to every time. And that sounds like it could be a lot of fun.
(QUOTE- DOUG LORD)

Imagine if a airplane glider had it's rear flaps disabled (=manualy by-passing the wand) and had to make a landing over water. Is it likely every time or close to every time it would land flat on the water suffering little or no damage? I very much doubt it.
A close friend of mine who I would consider an accomplished athlete and an expert sailboarder was catapulted forward while sailing in 25 knots of wind in choppy water. His neck impacted the mast and he broke a cervical vertabra. The loose vertabral condyle impinged on his spinal cord caused temporary paralysis of arms and all body parts below the neck. He could not rescue himself and was sailing alone at the time. He was actually in danger of not surviving. He was finally rescued by two young boys sailing a surfcat who were inexperienced, but not before they capsized the cat virtually on top of the stricken sailor in their efforts to come alongside.
This person gave up sailboards fairly soon after this event, and has fortunately eventually recovered all normal body movement.
It goes to show that it is easy to be frivolous regarding jumping a sailboard or other high performancve craft if you have not had the experience of danger or injury, accompanying high speed falls. And yes, you do hit parts of the boat with your body at speed quite often, rather than the water!
Have I made myself clear yet?

[Doug Lord]

Too bad about your friend; hope he is doing well. I've been sailing high performance boats for 45 years and haven't been hurt(seriously) yet. There are a lot of activities like walking across the street where one may be hurt. Some people base their decisions on what they are going to do on
how they can stay the safest; others attempt things that may well be beyond them. In my experience there is a happy medium where one can have exciting new experiences after carefully preparing and getting the best information possible.
Once the technical issues are solved jumping a foiler will never be 100% safe but it could be 100% fun for most people who approach it in an intelligent manner.
It is an untapped extraordinary potential for a foiler that may or may not work out-way too early in the game now to say for sure. One thing that is sure is that I will try to find out every thing I can about it from a theoretical standpoint, and from a practical standpoint from people that have tried it on foilboards or what ever. Surely worth looking into very seriously....serious fun is the payoff .
++++++++++++++++++++++++++
By the way, you completely misunderstand the concept of by-passing the wand. The wand is held 'against' the water by a shock cord . In an inadvertant jump in rough conditions the foil can come out of the water with the wand/shock cord moving the back end of the flap to max up. Then when the thing re-enters-depending on a number of factors- the wand/flap position can result in a dive by the foil which is sucked down by negative lift . The system I'm still working on allows the skipper to by-pass the wand by twisting the hiking stick to initiate the jump and to keep the flap down in a positive lifting position for re-entry.

[water addict]

Doug,
So the purpose of the foils is to jump better in flat water?

[Doug Lord]

Doug,
So the purpose of the foils is to jump better in flat water?
====================
The Rush Randle promo stuff talks about being able to jump in flat water; I witnessed a guy do just that with a similar board.
The point of this thread was to discuss what would make a high lift foil(63412; 7/1 aspect ratio-for example) function as well as the foilboard in re-entering. The point of hydrofoils is to fly the boat and to me is to do that in the lightest wind possible. The speed is nice too...
And jumping -if it can be worked out- would be a lot of fun.

[water addict]

====================
The Rush Randle promo stuff talks about being able to jump in flat water; I witnessed a guy do just that with a similar board.
The point of this thread was to discuss what would make a high lift foil(63412; 7/1 aspect ratio-for example) function as well as the foilboard in re-entering. The point of hydrofoils is to fly the boat and to me is to do that in the lightest wind possible. The speed is nice too...
And jumping -if it can be worked out- would be a lot of fun.

I was an avid windsurfer in my younger days, did the pilgrimages to Maui, Barbados, the Gorge, Fla, Hatteras, Bonaire and others. Foils on a fast board wouldn't appeal to me, I'd be removed from what makes it interesting- the water surface. If there is enough wind to have fun, ie 12 knots to plane, then there is enough chop to jump regardless. I think I have a pretty typical attitude of most boardsailors. I doubt you'd get much interest from windsurfers in 6 knots of wind to loaf around on some foil born gizmo, and if there's more wind, the foils have no purpose. But I could be wrong.

[frosh]

WA, quite right, what makes a sailboard great fun is largely the sensation of being in contact with the water just a few inches under the soles of your feet. Removal of this feeling by being hoisted up half a metre disconnecting your body from the feel of traversing the water moguls at high speed would be like building an airconditioned and soundproof capsule around your high performance motorcycle and trying to enjoy a blast through the canyons.
But I guess if you have not ridden a sailboard in gorge conditions, nor taken a Ducati through the canyons at 100 m.p.h without four wheel slugs (other cars) in the way, this will not mean anything to you.
What about 3D cinematic experiences for those who physically or for other reasons cannot do the real thing? I have witnessed some great ones at Disneyland Los Angeles.
Building something (the jumping foiler Moth clone) for perhaps 10 times the production cost of a modern shortboard, (if it can be technically done), seems plain stupid to me!

[BWD]

We windsurfers like being able to launch easily from the beach and sail in 12 inches or so of water.:cool:
safety notwithstanding.
We can jump plenty high already, and most don't want foils.
FWIW I think trying to jump with a T foil is silly.
High torque and shock loads, severe AOA and yaw problems, regardless of wand/no wand, etc.

With foilboards, the delta/lifting body shape, with wide tolerance of the problems above, helps.
PLUS, funny no one has mentioned yet,
it has a tail:D
that allows it to balance forces within itself and trim to AOA, free of some wildy varying lever arm a few meters aft
...

[Doug Lord]

We windsurfers- You don't speak for me-and apparently not for Rush Randle and a fairly large number of other people who are windsurfers(me on and off since 1979).

....that allows it to balance forces within itself and trim to AOA, free of some wildy varying lever arm a few meters aft
...
Could you elaborate on the "wildly" part?

[frosh]

You don't speak for me-and apparently not for Rush Randle and a fairly large number of other people who are windsurfers(me on and off since 1979).
...

Could you elaborate on the "wildly" part?
__________________
Doug Lord

Could it be possible that both you and Rush Randle have a vested interest, in that you both, are hoping to sell some derivative of the foiled windsurfer commercially? Who are the many other people who are windsurfers, who want to switch from a regular sailboard to a foiler one? Name two people then that are internationally known that have publically expressed this!

As far as elaborating on the " wildly" part: it is all wildly in the realms of fantasy, if you are only interested in buildling a successful prototype. There is not a term that I can think of ( and my vocabulary is at least 1000 words in length), to describe the chances of both building a successful prototype and then being able to turn it into a commercial success.

[nflutter]

gsus if you care that much just build one and prove to the world that its cool

[nflutter]

seriously

[water addict]

Your right Doug, nobody but you speaks for you.

I would hazard to guess, most windsurfers would not want to deal with some foiling mechanism on their boards, but I could be wrong. Maybe we'll see lots of boardsailors out there skimming along 2 feet above the water, and hopping up and down. I wouldn't want to particularly though.

You want to make a foiler board thingy, have at it! Maybe I'm wrong, post your videos and market the heck out of it. Maybe it's the next wave of windsurfing - who knows?

[nflutter]

werd!

[Doug Lord]

I'm not particularly interested in foilboards at all.
The point of this thread was to discuss what would make a high lift foil(63412; 7/1 aspect ratio-for example) function as well as the foilboard(mainfoil) in re-entering.

[frosh]

Doug, why ask your question on this forum if possibly the only person in the world that might throw some light on your dilemma is Rush Randle. In case you don't already know it his email is: Rush@RushRandle.com

[BWD]

All I meant was to answer as best I could the general question without reference to a specific foil section. Here again is my answer:
1) a tail,
2) a robust connection to the strut or whatever attaches it to the hull,
3) and possibly a delta or lifting body design (which would facilitate no. 2)

I guess sometimes folks pick up the ball in your threads and run sideways off the field with it.
No offense intended.

As for the "wildy" varying input, I envision a typical t-foil rudder. If the front foil leaves the water, the whole boat can act upon the rudder to turn it on any axis, developing who-knows-what lift in who-knows-what direction.. Situation aggravated by chop etc.

Seen from the point of view of main foil re-entering, it may have to cope with sudden strong pitch/yaw inputs from rudder even as it tries to reestablish its flow/lift. Those little wingtips and the tail are crucial on the foilboard. Reducing degrees of freedom around the foil CE, or at least damping motion, at some drag cost....
I think stabilization features will be crucial on larger craft. http://www.youtube.com/watch?v=QoaZu8Ew_a4

As far as speaking for others, one accepts a risk in any generalization, such as "we windsurfers like ease of launching with our short fins," "we Americans are crass and like French Fries," etc. I am on safe ground here though. I don't speak for you, but I do speak for many. Just 25 years experience, don't know Rush Randle myself.
More power to him.
I am not much of a surfer but I also feel safe saying, "we surfers don't like it when hordes of tourists come in summer and hog the local break and pee in the water attracting sharks."

Anyway, attached is my idea-platform, a draggy bolt on solution but could help with main foil re-entry. Lot of optimization needed, maybe a bigger vertical tail, longer chords...

[Doug Lord]

Very interesting response and illustration. I'd imagine you're not serious in suggesting two "air chair" foils instead of one main foil? Are you?
An arrangement like that would defeat the main advantages of a bi-foil arrangement particularly upwind.
I agree that kites have a lot to offer-including altitude.....

http://www.boatdesign.net/forums/attachment.php?attachmentid=6411&d=1146550593

[BWD]

As a redneck solution, if you could obtain 2 such foils and bolt them on, it would be interesting to see what happened. Interesting as in spin or cartwheel once one popped out of the water...
One would probably be much, much better.
So far as my little brain can tell all these "advanced" craft from kiteboards to sailrocket ,et al are trying to solve the 2 fluids problem by evolving towrds airplane on a string designs.
So far the most elegant, commercially successful and versatile version is the kiteboard. It cracks me up; I make these in my kitchen! And Living room:rolleyes: . Need a garage.
To the point, to find something that works like an underwater airplane, I would start with something that looks like one:
EDIT: crossref FWIW: http://boatdesign.net/forums/showthread.php?t=11497

[frosh]

BWD, just brilliant showing the kiteboard guy jumping what looks to be at least 10 meters off the water, on what? Simply a basic board even simpler than a standup surfboard that you can build for minimal cost in a room of your house.
Doug, have a REAL GOOD THINK if perhaps you are not on the right track.
The other hugely important fact (read fact* please) is that the commercial success of this kiteboard thing is greater that sailboards and Hobie cats combined, and shows no signs of abating in the near future.
Go on; ask yourself why this could be so. If you come up with an answer, please make a statement of that answer in no more than 50 words, and I will give you a score out of 10! for accuracy.
I applaud the aptness and logic in your illustration of the real world, BWD
Power to you man.