Sailrocket 2 set to launch

[Doug Lord]

For my "And the job is (and has been since Longshot) finding a foil that will break through the cavitation barrier." in post 111, I think we can say "Job complete" and well done.

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I think Hydroptere did that first(61knots peak,70.15mph) ......Congrads to Sail Rocket!


From Sail Rocket "The Boat":

1)Sail-powered boats rely on fins or ‘foils’ to counteract the side-force of the wind, and to stop the boat slipping sideways. When travelling through the water at speeds around 60 knots, virtually all foils in the real world experience a phenomenon called ‘cavitation’.

www.sailrocket.com/node/521
2) Sep 14, 2012 – THE CAVITATION BARRIER ... start going through the water over 50 knots you are going to start encountering a phenomenon called cavitation. ... This mixture of air, vapour and very high-speed water is all very dynamic....

 

[P Flados]

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I think Hydroptere did that first(61knots peak,70.15mph) ......Congrads to Sail Rocket!

The big Hydroptere did not "break the cavitation barrier". As best I understand, they went for a traditional foil profile that maximized the speed prior to the onset of cavitation. You can see the traditional profile (max thickness at or before mid chord tapering to a fine edge to the rear) in many photos / videos.

The onset of cavitation for a given foil is actually prompted by a combination of things with speed and foil loading as primary contributors (I remember Tom Speer providing a good discussion of this somewhere on BDN).

They did not break the barrier, they just pushed it up a little for their particular application.

The use of a supercavitating profile (max width at or near the rear) in the power boat world is a proven technology that can handle much higher speeds. VSR2 is the first high speed sailboat to make it work.

 

[Doug Lord]

Sail Rocket-untouchable!

From Paul: http://sailrocket.com/node/663

Final: 68.01 knots=1 sec ; 65.45 knots 500m !
78.21mph=1 sec; 75.27mph 500m!

 

[prograd]

Absolutely amazing!!!!

 

[Doug Lord]

The big Hydroptere did not "break the cavitation barrier". As best I understand, they went for a traditional foil profile that maximized the speed prior to the onset of cavitation. You can see the traditional profile (max thickness at or before mid chord tapering to a fine edge to the rear) in many photos / videos.

The onset of cavitation for a given foil is actually prompted by a combination of things with speed and foil loading as primary contributors (I remember Tom Speer providing a good discussion of this somewhere on BDN).

They did not break the barrier, they just pushed it up a little for their particular application.

The use of a supercavitating profile (max width at or near the rear) in the power boat world is a proven technology that can handle much higher speeds. VSR2 is the first high speed sailboat to make it work.

----------------
I'm fairly sure that I read that they had a special foil shape for something like the last couple of feet of the main foils but I could be wrong. Seems like they must have had something specific to those speeds to go so fast based on what Paul said in the quotes above.

 

[P Flados]

I am also very confident that they had a "special foil shape". One key element of the design would have been deal with cavitation concerns.

From what Tom Speer wrote (V-44 Albatross World Speed Sailing Contender post 20 on 11/25/2010), I took it that it is possible to push cavitation speeds up with lightly loaded thin sections.

The big French boat also operates at a different scale than anyone else that has chased the outright. I am not sure how this would play into the discussion, but somehow I think it does. For a NACA 0009, the radius of curvature of the leading edge increases as the foil gets bigger. Water following the foil curves is what causes the accelerations that give you the negative pressures.

As long as you stick with traditional sections, cavitation will occur when speed and loading hit a specific point. Note that the increased loading goes hand in hand with higher AOAs.

It is the intertia of the water trying to "make the corner" as it goes around the foil that creates negative pressures. When the negative pressure goes past (or "absolute pressure drops below" if you like) liquid saturation conditions, the liquid wants to become a vapor, and you get a sudden reduction in lift / increase in drag.

In my line of work, we look at stuff real hard to try to stay away from cavitation in fluid systems. The basic physics is really pretty easy to understand, but real life usually makes it hard for us to figure out the little details that end up being not insignificant. Spending millions of dollars to justify operating a power plant at a higher power output only to find that it causes your pumps to operate too close to cavitation really drives home what an "oh don't worry about it" attitude can get you.

 

[ancient kayaker]

SailRocket has really shown everyone what she can do. What's next? Will they carry on trying for more?

Footnote: reading the comment about a beach-launched SailRocket reminds me of a tiny kayak sailing rig I started to experimen with back in 2003 using a Bruce Foil and inclined rig. Did I have the first beach-launched SailRocket? Rig deployment time was 30 seconds, same to retract. It wasn't very fast though with only 15 sq ft of sail although the bow-wave used to soak my elbows. It was destroyed in a fire so the plan to double the sail area (and later change to a wing and lifting foils) never happened. Maybe I'll get back to it . . . I think SailRocket's achievements will inspire many new efforts!

 

[P Flados]

As a contender for the outright record, the Bernard Smith balanced force configuration makes lots of sense and VSR2 shows how well it can work.

When you get down to DIY fun boats, the same configuration has some disadvantages:

• The rig on a leeward hull/pod will normally need to be fully "remote control". This is more complicated if you choose the shunting proa that would seem to be the least complicated approach to a both directions boat of this type.
• If you do not go with a very low weight rig, the weight is where you do not want it. You can use dynamic lift (foil or wing) to get the ama clear of the water under some conditions, but there is a drag penalty to this.
• Fixed main foil cant would produce wasteful downforce for all conditions where RM x Beam does not reach the weight of the windward crew and components. Variable cant can be complicated.

I have been playing around with these concepts for a while.

If I wanted to be able to get maximum efficiency I would actually just go for "nearly force balanced" and would:

• Re-arrange things to where the heavy stuff is all windward (providing a beneficial ballast function) and the leeward components can be minimal. This turns out to look a lot like a bruce foil on an ama but with shunting such that the foil would always be pushing towards the main hull.
• Main rig cant would be adjustable. In very light air, a small cant towards the ama helps hold sail shape. In moderate air, vertical or canted for some lift is best. In heavier air, canting for downforce can be used to balance things out.
• Foiling only makes sense if you plan to use the above to go really fast. A pair of wide spaced small surface piercing two direction (thanks Tom Speer) inclined foils on a long skinny ama can probably achieve passive altitude control with no loss of efficiency. Foils to assist and/or control flying the main hull seem to be do-able, but incorporating the rudder function and helm imbalance issues all add up to a real challenge.

When it gets warm again, I hope to be on the water with a very small (10' long main hull) prototype proa just to play around with.

Step 1 will be displacement mode only until sail handling and maneuvering are under control.

The rest is really only dreaming at this point but my best guess would be for a Step 2 to play around with foiling for the ama. If surface piercing does not work out, a wand/float controlled J foil could be tried. Although more complicated, J foils have some big advantages. They can provide very positive pitch control and can also handle the rudder function . From Ketterman research, a J foil is probably more efficient for this function than a T foil. However, hand carving / shaping does not sound good enough for a Speer P30212 J foil and all other build options sound like potentially more costly and/or technically challenging than I can justify for this "fun experiment" class of boat.

Step 3 would be to see what can be done for reducing main hull submergence and/or flying the main hull.

Step 4 would probably be either starting over to upgrade everything and/or build a wing (Steve Clark - thank you in advance).

 

[Doug Lord]

Sail Rocket

First paragraph of an article in tonights Scuttlebutt:

NEW AND IMPROVED WORLD RECORD

When Aussie-born Paul Larsen launched his Sailrocket project in 2002 to set
a new outright world speed record, the target then of 46.52 knots had stood
for nearly ten years. Sailrocket did not initially succeed in surpassing
the record, and during the past decade of Paul's determined pursuit to
refine his unique foiling craft, the windsurfers and kiteboarders
discovered the significance of flat shallow water.

read the whole article here: http://www.sailingscuttlebutt.com/

 

[P Flados]

Gizmag also has an article on VSR2 and speed sailing in general

http://www.gizmag.com/new-world-speed-sailing-record-6537kts-75mph-121kmh/25065/

 

[Doug Lord]

From Paul Larsen today posting on SA:

Posted Today, 06:34 AM

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.(bold-dl)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

 

[Doug Lord]

SailRocket

I propose this seriously, but with a smile on my face:
New "hydrofoil" definition proposal: 1)" A generally wing shaped foil used to create an upwards force or a downwards force with a vector of those forces acting vertically at 90 degrees to the surface of the water." 2) "A craft that uses such a foil or foils." Oh well, its a new world.....

( once again my submission for what exactly Sail Rocket is: "Balanced Forces Hybrid Planing Foiler" )

 

[Doug Lord]

Sail Rocket

Clarksail interview witl Paul Larsen: http://clarksail.com/2012/11/25/the-word-from-paul-larsen-after-sailrockets-big-day/

 

[HASYB]

I propose this seriously, but with a smile on my face:
New "hydrofoil" definition proposal: 1)" A generally wing shaped foil used to create an upwards force or a downwards force with a vector of those forces acting vertically at 90 degrees to the surface of the water." 2) "A craft that uses such a foil or foils." Oh well, its a new world.....

( once again my submission for what exactly Sail Rocket is: "Balanced Forces Hybrid Planing Foiler" )

Hey Doug,

Paul Larsen wrote he also smiles a lot these days so you might be in the same league; still I am curious what he, and others for that matter, would say about your definition.
For me there still too much awe and constant change to the subject to even think about a definition.

 

[Doug Lord]

Sail Rocket

Interesting site from a Sail Rocket Partner: http://aerotrope-eng...CFQu0nQod2yoAQw

From Aerotrope:

On what was predicted to be a ‘Super Saturday’ (Nov 24th), the Sailrocket team managed to break the Outright World Speed Sailing Record for the third time in less than two weeks! In doing so, we surpassed the previously fastest sailboat Hydroptère by 12.5 knots (14.3 mph/ 23 kmh). In wind speeds of 27 to 32 knots Sailrocket clocked in at 68.01 (78.2 mph/125.9 kmh) peak, 65.45 knots (75.3 mph/ 121.2 kmh) average.

As designers of the hydrofoil and the wingsail we are not surprised by the numbers. We predicted them and we are very pleased that the maths done over the last 2 to 3 years stack up. However this is more than pleasing, to us it’s poetry! David from Tensys congratulated us, saying: “Who said engineering was boring?” We certainly never said it.

Aerotrope are happy that the crucial design change on the hydrofoil has finally unleashed the performance that we predicted for Sailrocket 2. We already have ideas lined up for a new, even better hydrofoil since the current one is reaching its predicted limit. But who knows…the speed spot down in Walvis Bay has been magical these last two weeks. We want to return and prove that the knowledge we have can take Sailrocket to beyond 70 knots. The future of speed sailing has changed by the biggest margin ever.
aerotrope