Fastest Sailboat on the Planet!

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Planing surfaces require a lot more area(wetted surface)* for a given amount of lift as well as being subject to drastically increased drag from waves. Using the planing surface as a foil creates a low aspect ratio lifting surface with a whole lotta drag. Seems like the variable geometry foil I mentioned earlier might be a good solution-limited to just two foils- that would allow the foil section to change and foil area to be reduced as speed increased. Couple that with a boat that could use Veal heel and a wing rig and I'd say you've got a lot of speed- with the right foils which could easily be modified until they were right. No ditch necessary.

PS- interesting to note that in a recent race kiters using a foilboard did real well against "normal" kiteboards. Trophee St. Clair,I think....

*for the MPX planing ama compared to a Formula windsurfer at 15 knots the planing area was 1.75 times the area of a 63412 foil+ strut immersed 3 chords for the same weight per sq.ft..

 

Planing surfaces may have more wetted surface, but the "aspect ratio" is a different situation. Better aspect ratio on a wing or a foil allows you to minimize planform and tip losses. Since a planing surface works at the water / air interface, they can actually operate with negligible losses from planform issues or tip losses. I believe that good planing surfaces do not require "high aspect ratios" for good performance.

When you transition into the supercativation regime, it would seem that most of the "lift" is being generated by the reaction force of foil on water on the underside of the foil. The basic physics of this form of lift seems very similar to planing the way I see it. I would put the disadvantages as follows:

Planing worse than supercavitating: The planing surface is adversely affected by chop and may have more wetted surface area.​

Supercavitating foil worse than planing: The supercavitating foil has tip and planform losses. Supercavitating foils also have to be either surface piercing (inefficient design) or T foil with potential extra drag at the T joint. Supercavitating foils also seem to be tricky, they have very poor performance until a threshold speed is reached.​

Right now, planing is a proven technology for high speed boating for all sized boats both power and sail. Foiling at high speeds has only been shown to be effective in big applications. Hydroptere is thought to be subcavitating (I am not so sure, see post 578). In large fast powerboats, super-cavitation seems to be better, but for this topic I found more of what might be called "hype" as compared to presentation of scientific basis.

Bottom line is that planing might result in slightly more drag for some situations, but is always expected to work with no sudden misbehavior. Foiling at high speeds has potential, but has not been completely worked out. It is subject to sudden onset of cavitation with significant potential problems. As such my previous recommendation was really to build with the concept of being able to experiment with different planing configurations and being able to try out foiling configurations.

 

yikes
the opposition is ranting at this point
always a good sign you have em on the run though

only one statement worthy of consideration
what makes you think I wont be communicating with the counsel to clear up the very real issues presented concerning the Luderitz venue


cheers
B

 

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A planing surfaces' aspect ratio is VERY important to performance! See the paper below( point of interest-aspect ratio 6 pages down). Also, if you're interested I have the Clement booklet describing his cambered planing surface in conjunction with a very small step and hydrofoil pitch control.
Note that according to Savitsky "high aspect ratio planing surface" has a LOW L/B ratio-1/1 is considered to be a fairly high aspect ratio planing surface. Formula windsurfing boards can have a planing surface wider than it is long.

pix-clement cambered planing surface:

 

It's really simple, then, B. Show us the communication you send, the date you send it and the unedited response, if you get one.

By the way...

Definition of COUNSEL

1a : advice given especially as a result of consultation b : a policy or plan of action or behavior
2: deliberation, consultation
3a archaic : purpose b : guarded thoughts or intentions
4a plural counsel (1) : a lawyer engaged in the trial or management of a case in court (2) : a lawyer appointed to advise and represent in legal matters an individual client or a corporate and especially a public body

And the actual term for those with whom you say you will communicate:

COUN-CIL [ kównss'l ] (plural coun·cils) noun

1. people running local affairs: a group of people elected to govern a local district
2. committee: an appointed or elected body of people with an administrative, advisory, or representative function
3. church assembly: an assembly of church representatives who meet to decide matters of discipline and doctrine
4. council meeting: a meeting of a council
5. meeting for discussion: a meeting to discuss or decide something


These are two, very different things, as you can see. Before you send-off that heated missive, perhaps you could come to terms with the definitions before you start telling them about those that their body governs.

 

I hear that the kiters are planning on growing sea grass in the trench for next years fun, this will further reduce the chop on the water while still maintaining the 18cm minimum depth, some pretty innovative thinking there!

 

Doug I think that the speed range these guys are running in may mean that not all of the research data you are showing here is necessarily applicable (or at least not completely). The speed boards are long and skinny with not much in the water at all, I think that the length of these may be required for more directional stability, conversely a course racing board is much more along the lines of your post, in fact they have or are trying to limit the width of these boards at the moment, the course boards also have high aspect fins that the speed boards dont.

 

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I don't think the physics changes-I imagine they make workable tradeoffs for their purposes. I'm looking forward to seeing a kite guy with speed foils! But they'd probably have to dig a deeper trench so the guy doesn't die if he comes off the foils...

 

Yes you said it more clearly, maybe I should have worded it like this; innovations based on the above research in your post are not necessarily useful for kite speed boards. One of the big differences is that the board is providing lateral resistance as well as a 'buoyant' platform.

 

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If the board is providing lateral resistance the physics says it is doing it very inefficiently-but that may be an acceptable tradeoff for now.

'buoyant' platform-huh?

 

The speed from the research paper is factored into their equations and is not an issue. The real difference that is the study was for Vee hull boats. The Kite boards are single flat surfaces (as far as primary forces are concerned). The fact that they are steeply angled to provided lateral resistance just makes them function like half of a deep Vee.

On a deep Vee boat, the lateral force produced by one half just cancels the lateral force generated by the other half. Although these to sided forces cancel, there is an apparent drag associated with each of these two forces that are not doing you any good. This is a big part of why deep V hulls are less efficient. It is also why traditional surface piercing foils are less efficient.

Back to the kite boards, you have the "half a deep Vee" lateral force generated, but instead of being wasted, it is being used to work against the kite generated force to pull you forward. There is some difference in the shape of the board at the rear edge as compared to the squared edge in the study. I do not think this is a big deal.

For a Vee hull boat, a less steep Vee and a wider beam is what produces an increase in the aspect ratio. The fact that this was better may be due more to deep Vee having the wasted lateral forces that produce apparent drag but are not doing you any good.

 

I was trying to think of a planing type design where high lateral force is required. How about waterskis? It might be interesting to study the forces at work on a slalom waterski. One could compare a conventional slalom ski, to a wake board, and a hydrofoil version.

You could also look at hull shapes and turn fins used for powerboat circuit racing. I've heard claims that the F1 tunnel hulls generate g-loads in turns in the 3-5 g range.

I think you could compare the physics in a turn to the physics of a speed sailing craft.

Surface piercing foils with known ventilation and cavitation problems just aren't seen in any speed record machines or hard turning watercraft that I know of.

R

 

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Hydroptere has surface piercing foils and I take it you would say those foils
don't have ventilation or cavitation problems,am I right?
Using a low aspect foil to generate lateral resistance has to be high drag for the lift gained but may be the only way(at present) on kiteboards?
Savitski's paper is not limited to just "deep vees"....

 

The information I've read is that they think they have cavitation under control to the low 60's the V-39 project also is talking about 60-63 knots.

Both programs note that there exists a limit due to cavitation. A low AR planing surface fore and aft like a waterski, becomes a high AR planing surface laterally. Thus the theory as I understand it would be that the ski shape would be more efficient sideways (turning or resisting sailing loads) than it is traveling forward. We know that speeds are not limited by hydro dynamics for planing surfaces. I think a WIG for displacement with a planing surface instead of a foil for lateral resistance might work very well. Think of a waterski shape that is on edge, no matter that it is fully ventilated, it would be "planing" sideways. It would act much like the sponson on a tunnel hull when turning.

A speedsailing catamaran platform with the ama's shaped like the hulls on a tunnel hull the tramp area is the WIG, use an offset wing to limit heeling arm and you get a boat that could sail on both tacks. For one way runs a windward canted wing on a planing float with the tunnel hull shape on the windward hull might also work. At speed you'd have a low leeway angle of 2-3 deg on the planing surface and the windward cant on the wing would reduce the load on the supporting float to near zero. No lift from hydrofoils needed. Just lightly stressed foils for directional control.

Just thinking out loud ...

R

 

Your "thinking out loud" seems to be gravitating along similar lines as what I have been suggesting.

If it is a medium to large boat, the WIG for outright lift sounds good. For smaller craft, lift is not needed as much. A planing surface at an effective angle of around 45° (off of vertical) gives you a pound of lift for every pound of lateral force. Given the required lateral forces, you can get a lot of your needed lift out of any leeward planing surfaces. I see the biggest advantage of horizontal wings surfaces more for control. Variable angle of attack or flaps on each side with automatic (wands/float feedback) or manual (joystick) control. However, as long as you have have air whistling past these surfaces, getting a small amount of lift (positive lift to leeward for sure, possibly negative lift windward) becomes very efficient. It also seems that most control surfaces work better when providing a variable force in one direction rather than alternating both the magnitude and direction of force.

As I was thinking about this stuff, I went back and looked as some of the recent Luderitz runs. I was looking to see if they might be getting fancy with their board designs (more below). They may have made improvements that help more than we realize.

I also noted a lot of other stuff beyond just the boards. The best actual videos of the runs are probably:

Alex C, on 10-12-2010 with 54.1 kts
http://www.youtube.com/watch?v=opBh6d44tQY

Seb Cattelan, on 10-28-2010 with 55.49 kts
http://www.youtube.com/watch?v=syKXGBaZHIk

Rob Douglas, on 10-28-2010 with 55.65 kts
http://www.youtube.com/watch?v=CtFxstw9Zjo

Several points of interest.

1. The first run (Alex) shows the "berm" while the last two (faster) runs show it is clearly gone. Sorry Boston, facts are facts. The "berm" is not why they go so fast.
2. The water is not "super flat", it is probably just as rough as the water I saw in the MI record run at Sandy Point. Again, "super flat water" is not why they go so fast.
3. Although you have to look at other videos to see it better, they are all using boards that taper to a point at the rear along the lower edge. Alex was using a swallow tail version with points on top and bottom, the other two were one way boards with the taper on the lower edge only. Board improvements may be part of the reason for the speed improvement.
4. The kites are well out in front of the guys as they made the runs and the runs looked more smooth/steady. Part of the improved top speeds could just be that they were finally getting really good wind speed / angle / consistency up at the kites.
5. I also found a Rob Douglas interview video where he shared just how much he has been training for these events. Constantly out in the water in 30+ kts wind, constantly working out etc. The guy seems to have absolutely focused his life around this sport. You know, the biggest contributor to the improvements may just be they are getting so much more skilled. This is the kind of dedication you see in Olympic athletes. Quite of few of those sports have seen big leaps in performance over the years.
6. One last note. The more videos I looked at, the more I saw how much these guys are pushing past "reasonable risk". The crashes both during and at the end of the runs were both too plentiful and too violent. The organizers really need to step in and think through improving the end of run landing zone at least.