swoosh said...
seems like a similar configuration to a kitesurfer?

barn said...

Can I like, claim this invention or something?

Ian K said...
A little bit similar but the major difference is that gravity is part of the equilibrium in the kiter's case and hence the kite can get overpowered. That single red arrow through the big hooked fin in the sailrocket diagram does most of the work, and as long as the super high strength material doesn't fail it will hang in there when a gravity balanced craft gives up.


The kiter diagram shows that the force, shown by the red arrow, which is equal and opposite to the aerodynamic lift, is the sum of two forces in the kiters case - gravity and hydrodynamic lift.

For sailrocket the majority of the hydrodynamic force is generated by that one hooked foil to balance the aerodynamic force. One foil in the water one in the air, (with a few other control foils that do relatively little work). It's a concept that has been around for a long time, just nobody thought it was feasible or was brave enough to take it on until now.

Dr Speed said...
so for kiters weight is the only way to go fast

Ian K said...
A little bit similar but the major difference is that gravity is part of the equilibrium in the kiter's case and hence the kite can get overpowered. That single red arrow through the big hooked fin in the sailrocket diagram does most of the work, and as long as the super high strength material doesn't fail it will hang in there when a gravity balanced craft gives up.


The kiter diagram shows that the force, shown by the red arrow, which is equal and opposite to the aerodynamic lift, is the sum of two forces in the kiters case - gravity and hydrodynamic lift.

For sailrocket the majority of the hydrodynamic force is generated by that one hooked foil to balance the aerodynamic force. One foil in the water one in the air, (with a few other control foils that do relatively little work). It's a concept that has been around for a long time, just nobody thought it was feasible or was brave enough to take it on until now.

barn said...
Batman adapts the Sailrocket formula for speed to his mad Batkite skills.. Will the Hydrobatkite help Batman catch the Penguin? Stay tuned for next episode..


Can I like, claim this invention or something?

Yes, but the requirement for weight is minimised because kiters go at a very downwind angle and really only need flat water and high wind to go fast. I'm of the opinion that these records can be broken using current equipment, but 60+ knot wind plus flat water is needed with a small kite. And big set of balls.

Edit:
Seb Cattelan already did almost 60kts 100m average all the way back in 2009 in "only" 40-50 knots of wind and presumably in very choppy water:

www.gps-kitesurfing.com/default.aspx?mnu=user&val=37801&uid=47

I don't see why he can't be in the same ballpark as Sailrocket with more wind, smaller kite and flatter water?

sailquik said...


I might be inclined to agree if the record was still 59 knots. But 65 is a different ballgame.

The disadvantage for kites is that very broad course and flat water in winds over 50 knots are mutually exclusive.

Lets see what the Kiters do at Luderitz in the next few weeks.

Of course, if one was able to attach an L shaped foil under a kite board to pull at right angles to the lift of the kite, that could make the game on again. But there are at least a couple of large problems to solve with that:

- The direction of pull with a kite is variable
- The sailor will have to somehow control the angle of foil the underwater, and therefore it's depth, with his feet to a very fine degree.

If an auto angle of attack control mechanism could be added for the underwater foil, it could solve those problems.

But these ideas are not currently working technology. As I said before, it will take some time to develop whatever is dreamed up to a practical, controllable record breaking level.

sausage said...



oh and you forgot to mention that with a foil, Kiters won't be able to benefit from ground effect.

sailquik said...

The disadvantage for kites is that very broad course and flat water in winds over 50 knots are mutually exclusive.

DaGodfather said...


At Luderitz - yes. The canal looks very choppy and unless they make some modifications to it they won't even be able to break the current kitesurfing records this year.

But there are other locations where this is not the case. In fact we have one such well known location right here in SA. The problem is, this is not a high wind location and even 40+ knots winds only happen 2-3 times a year. But unlike Luderitz, the water stays flat, regardless of how hard it blows and regardless of wind direction, so going broad makes no difference.

sailquik said...


Yeah, I recon they need to put artificial 'weed' in the canal. I

Hey all, We are working as quick as our small team can to share this with you via video and the like. It's a constant job just to make my e-mail list go down rather than up. It's a bloody big job to make these videos. The new cameras generate such massive files and the pro cameras Ben is shooting on still use tape so all the footage has to be digitised and stored for editing. All this means we have 3 1 terabyte hard drives feeding into one smoking Mac laptop. Ben is a pro at this and is working 24 hours a day on it. Whilst his computer is crunching footage... he's outside setting up interviews and sharing imagery with media. I'm so glad we focused on bringing someone of his capabilities down here.
I've decided that I'm done for this session. It's Helenas turn... but the forecast looks dead flat from here on in. It might change. We will be on a plane in 8 days. I'm not even sure if we should ship the boat back or not. I'm sure this boat can see the other side of 70. The only reason she stopped going quicker was because the leeward side of the boat was flying too high. The way we resolve that is to stand the rig up some more. This gives both power and stability. It's all good. In theory we should be maxxing out the foil... but it's how it behaves when it starts reaching its limits that is interesting. The boat and the concept it is based on has so much power to drag stuff down the course that it's alarming. That was the design goal of this boat..."let's not simply focus on the foil... let's build the platform that will give ANY FOIL the best possible chance of hitting its limits... then we will worry about the foil". I think we have seen this power played out by the fact that the boat has dragged every 'shape' and size we have put on it down the course at over 52 knots. To go faster we can add more power i.e. sail in more wind OR reduce drag... or both. There are other foil concepts that are worth exploring. We chose this one as we considered it to be the safe option.
I'm so happy with how the team performed last saturday. We took on the big day with a view to winning... not just competing. Mother nature delivered us one hour of perfection for this whole 28 day record attempt. The other days were good... but for 1 hour it was strong and rock steady... 28,29,29,29,29,28,29,27,27,29.... Helena was just reading out the same numbers over the VHF. Industrial Walvis Bay wind. It has been mentioned that we had one from being the hunter to the hunted... I sort of played along... but a little deeper down I knew we still had a job to be finished. When we knocked Rob off the top spot we had topped their leader... now we were coming back to wipe the village out. We did three runs that day. The first two didn't quite go right. We topped over 61 knots on the first two but just didn't get the average. We wanted to finish it once and for all and by the third run we were hungry to tear it apart. It started badly but we recovered and got onto the course. I was checking for damage as we accelerated through 60 knots but the speed was epic so I knew I had to keep the hammers down. This was it.
Anyway, it's time to write the blog properly so I'll finish it there. If we had have missed that hour and not got started... that would have been it. 59.38 would be the mark. I believe that the kiters can beat this. I don't think they will get near 65.45 with what they have now. If any of the kiters can actually pull off a 60 knot run it will be super impressive and we won't feel so untouchable. The thing is that we are not at our limits. This boat will see the other side of 70 oneday. It nearly did the other day. It's awake now and it's still hunting. You have to consider that at some early stage of the design process we had the discussion "What limits are we designing for"? We set a speed as the Vne for the craft but even that has safety margins. The answer to that question is the big one. that's our secret.
The concept still doesn't even have a name. Bernard Smith used to call them Aero-Hydrofoils but I personally don't feel that quite explains it. Homage must be paid to that wonderful guy some way or another.
Right, so the video is coming. Some of the angles we have captured are fantastic. I can't wait to see it myself.
I called our local Champagne dealer yesterday morning... She answered with "F**k off" and hung up. That's a sign that things are going well

Ian K said...


Would that be within the rules? Gotta draw a line in the sand somewhere. ( but not with a 16 cm fin I hope).

What about filling the canal with ethanol? Was using ethanol to preserve wood samples, you can pour a 20 litre drum of the stuff through a funnel much quicker than you can water.




Water @ 25 C density = 0.997, viscoscity = 0.894 Pa s

Ethanol @25 C density = 0.785, viscoscity = 1.074 Pa s

Not sure if that would give greater or less speed, but would it be allowed?

boardboy said...
well the outright record may be out of reach for now - but who nows what technology some smart cookie will come up with to put us back in the game!

In the meantime you may like to take solace in the fact that though Sailrocket II may be faster, it can't sail back.

sailquik said...

Yeah, I recon they need to put artificial 'weed' in the canal. It would make a huge difference for the kites.

sailquik said...
The question of foil cavitation is fascinating

sailquik said...
The question of foil cavitation is fascinating in the light of Sailrocket2's record. I had assumed they were running some sort of super-cavitating foil, but the words written by Paul seem to suggest that they are using a conventional foil. He talks about the question of where it's cavitation limit is.
So if they are using a conventional foil, how is it that it has not encountered cavitation yet?
And if it has, how is it that SR2 can still go faster in control?

sailquik said...


I might be inclined to agree if the record was still 59 knots. But 65 is a different ballgame.

The disadvantage for kites is that very broad course and flat water in winds over 50 knots are mutually exclusive.

Lets see what the Kiters do at Luderitz in the next few weeks.

Of course, if one was able to attach an L shaped foil under a kite board to pull at right angles to the lift of the kite, that could make the game on again. But there are at least a couple of large problems to solve with that:

- The direction of pull with a kite is variable
- The sailor will have to somehow control the angle of foil the underwater, and therefore it's depth, with his feet to a very fine degree.

If an auto angle of attack control mechanism could be added for the underwater foil, it could solve those problems.

But these ideas are not currently working technology. As I said before, it will take some time to develop whatever is dreamed up to a practical, controllable record breaking level.

Ian K said...

"The back of the boat will lift onto the curve of the foil at around 25 knots. The leeward float will begin to fly clear of the water over 50 knots. Only the main foil, the rudder and the 'step' of the forward float will be in the water at high speed."

ClarkSail: Wow, talk about gratifying. So can you tell us about the fence? The way we understand it that was what made all the difference.

Paul Larsen: I'm not sure how much of the foil we should reveal at this point. A lot of it is out there I guess but the key parts are hard to understand unless they are explained. The fence is pretty straight forward really. It was our first shot at a fence on this foil and it obviously worked very well. It transformed the boat. It's a bloody big thing too. It probably doesn't need to be that big.



ClarkSail: Why get off a winner right? So the way we understand it the fence is key in preventing ventilation. Do we have that correct?

Paul Larsen: Well actually the foil isn't so much designed to work with cavitations as delay it until a much higher speed. Before we put the fence on the foil was cavitating at a much lower speed because a good chunk of it was ventilating. This caused the non ventilated spot part of the foil to do all the work and hence it started hitting suction peaks at lower speed and thus began to cavitate.

At least that is the theory we backed and it seemed to work. I would like to re-visit it once all this madness has slowed down though. Too often we try to tie these things up a bit too easily. There is often more to it than that.

AndyHansen said...

The angle adjustment is already in play for the Moth sailboats

http://www.sailmagazine.com/learning-fly-0