A big hard push before the record attempt starts...
Sat, 12 Nov 11 18:22
Well I'm happy to say that we are back all safe and sound after going sailing on perhaps our windiest day.
We did two runs today. I wanted to get back in the swing of sailing in punchier conditions. The first run was a little uneventful with a peak around 46 knots. The wind felt like it was going to build and was still a little west. This makes the course a bit more downwind which in turn doesn't allow us to build up as much apparent wind as we would like. I spent a large part of the run playing with the new flap control line on the wing extension. This is there to control the height of the leeward pod. It did seem to be one string too many in there and quite hard to get right as the boat is rarely in a steady state as it surges and sags whilst bi-secting the gusts. I have the mainsheet in my right hand which is also steering... and now the leeward flap control (let's call it the 'roll control') in my left hand. I really do very little steering although I need to pay attention to what is ahead of me as well as what the wing is doing. The workload is increasing in there so it might be getting time to fill that back seat in earnest. VESTAS SR2 felt as stable as ever although I never got the real solid surge that means big numbers. When I bore away at the end of the course, the speed dropped off quickly. This usually indicates that the wind is indeed too aft. Whilst we put the rig down we got some solid gusts. the day was definitely building. The peak speed was only 46 knots and that in itself wasn't very satisfying. It's hard to know what the wind was blowing as it can vary from 22 to 29 knots and swing through 20 degrees. Fortunately TACKTICK had sent us a new wind wand and we had that in place on the actual wing so I'm expecting some pretty handy data.
Seeing as the run went off with little drama, I felt confident to go up the course for another one as Helena called out gust peaks of 31 knots. It was time to go for a big run. It felt much better to be on the water in a sailing frame of mind rather than sitting around looking at a wind readout debating the pro's and cons. I knew this would be our last chance before the record attempt starts in 6 days so was happy to give it a nudge. We stopped in at the timing hut on the way past and I double checked the wind data. I didn't see any 30 knot gusts whilst there but I saw lots of 29. It was definitely getting windier. We headed to the top of the course and rolled straight into a run. Helena was calling out gusts to 32 knots. This was getting pretty wooly but the boat was behaving itself. We had found some rig setting where it seemed to like to sit before the sailing starts.
Once released from the support RIB and in a good position to start a run, I began going through the procedures. For some reason VSR2 stubbornly refused to bare away. I oversheeted to the max but she wouldn't turn. She was sliding sideways pretty rapidly and the leeward pod was dipping hard. The whole horizontal wing extension was being pushed onto the water as the stalled wing put a rolling moment onto the boat. There was alot of wind. I pushed hard in the design phase to keep that wing high out of the water for just such an occasion. The lower the wing is, the better it works in ground effect... but this was the reality of sailing in rough, top end weather. Every time the designers creapt the wing down, i would push it up again. We all want speed and efficiency but then I have to live with the real practicality of the whole thing. Overall this boat is just so much better than the first boat on this front. VSR1 would have simply sunk today.... just before hitting 53 knots in 5 seconds and about 200' high!
Finally a wave combo helped the nose turn away from the beach and we dropped into mode. The start up was quick and the acceleration came fast. There was one surge during the bare away onto the course which was remarkable. maybe it is when all the apparent wind lines up with the fuselage. I don't know... but I'll look into it. There was no doubt it was a fast run. It felt very solid and steady. The roll control seemed to work fine. the new mainsheet with the HARKEN micro blocks is an order of magnitude better. VSR2 felt fast with a couple of big spurts in the run I started a turn downwind to burn off speed. She burnt off some speed but was also sailing out into lumpier water still doing well over 40 knots with the wing eased. I was rapidly running out of options other than a big right turn into the wind. This is a big, bold and fast manoeuvre that you have to commit to. The pod literally flew as it went swinging round the outside. The boat seems to accelerate into the turn as it briefly hooks into the apparent wind again. As the fuselage is skewed twenty degrees to the direction of travel, you get the impression that you have turned past head to wind. The beach comes up quick and you have to keep turning hard until the boat just stops. then you have to quickly lock the rig off and trigger the main foil release to stabilise everything. All the while still draining the adrenalin from your system.
It felt like a big run. It felt faster than before. I noted that the yaw string was still well off being aligned with the fuselage indicating that we were well off being as efficient as we were supposed to be. That to me is not a good sign.
The numbers just in are as follows...
Max speed (doppler)- 52.13 knots
500 meter average- 49.22 knots
100 meter average- 51.6 knots
SMOKING, REAR COCKPIT HATCH IS ON.
52 KNOTS IS STILL QUICK... JUST NOT QUICK ENOUGH!
SHOWING A BIT OF RUDDER IN THIS ONE!
Whilst 52 plus knots would normally be a good speed, this was top end conditions and I expected more. I really wanted to be at least in the high 50's or even get a peak at 60 in these sorts of winds. Hmmm... it would seem that we may still be up against our old speed-sailing nemesis of speed sapping cavitation. We may be getting cavitation on the leading edge which is not joining up with the ventilation at the back of the foil i.e. we don't have a 'super-cavity'. We all think that we still have a lot of attached flow on the back of the foil. This is not so bad, we simply have to start playing around with ways to trip the flow off the back and try and induce this super cavity. In many ways todays sail was really good. We sailed relatively comfortably in honking winds, we got a clearer picture of where we are performance wise and we got a heap of data off the boat to help us get sorted. Sure, of course I want... I need to see the big numbers to be confident of beating the kiters... but they will only come with understanding. It seems that pure balls and luck won't be enough.
It's always a pleasure to put the boat away after a big day like this. I'm once again sending this from a rattling container. Tomorrow is going to be a bit mental wind-wise before a light forecast for the rest of the week.
Well, the original plan was to be breaking record speeds before the record attempt started. We aren't there yet. If we do hit those big speeds then it will be done for the first time before the eyes of the WSSRC official. I was really hoping to nail it today. To at least top Hydroptere's speed would have been a good start. Oh well, not to be. Like I said, we gave it a nudge. If we're not ready, we're not ready. We still have a few tricks up our sleeve. We'll get there.
Cheers, Paul
Ventilation
Submitted by USA 3257 on Fri, 11/18/2011 - 18:04.Perhaps it is semantic only, but it seems to me that the foil is ventilated by definition as long as there is a path for air to flow from the surface to the low pressure side of the foil. I dont see how any cavitation is possible given that connection, because ambient air will keep rushing in to raise the pressure and prevent cavitation. As long as air is rushing in it is sinking your battleship, so to speak. Seems like you need a fence if sime type to separate the ventilated portion of the foil from the cavitating portion, keeping the ventilation portion of drag small. Generally advice is only worth what you pay for it of course =;-) Have fun storming the castle!
Wish I was there sharing the fun
Submitted by Bob Imhoff on Fri, 11/18/2011 - 05:33.Hi Paul,
First I'd like to say I'm not trying to "second guess" you and the VSR2 team; you have all been doing a stellar job. My main interest in my posts is to see how well I can visualize the flows and forces the Rocket is experiencing, based on your site and blog. If I happen to say anything useful even better. I'm playing "hookey" from my work to do this but I can't resist the challenge. I'll make some suggestions but I hope to develop my reasoning on my blog when I get a chance.
I suspect you were running too much AOA on the wing and possibly too much AOA on the main foil as USA 3257 suggested. Since the craft was balanced (no load on rudder) your drag was balanced where you expected it to be, otherwise it would have yawed to windward. Decrease AOA on wing and craft should have weather helm (no good) swing the arm foward till helm is neutral or slight lee helm (taking some load off main foil as rudder picks it up).
Cheers, Bob
I'm sure you've thought of this but...
Submitted by USA 3257 on Thu, 11/17/2011 - 07:15.Perhaps the angle of attack on the foil is too high relative to the direction of travel? One could compensate for this by sheeting the wing out a bit, but still it might pay to crank the foil AOA down a little and see what happens.
approach angle?
Submitted by DC_US55 on Thu, 11/17/2011 - 02:06.Could the startup sequence have allowed better flow over the foil in the run you did two-up have had something to do with the result?
Is there any adjustability, or flex in the foil attachment? Maybe the unexpected performance at low speed is indicating something?
Or maybe your just keeping us in suspense until the wr period, and with the right passenger, you'll shatter the record and have that great movie
ending that I know this story will have....with the passenger seeing the numbers that you already know are there.
Good luck next week!
Trim? or Non-Cavitation?
Submitted by Bob Imhoff on Tue, 11/15/2011 - 07:26.Hi Paul,
From what I'm reading, you went 2kts faster with a heavier load, less wind, more aero drag, and a bit more sheeted out. First thing I'd look at is trim. Any chance you were over-powering the foil, causing it to drift? I'd be looking at AOA on air- and hydro-foils and their position relative to each other (arm swing). You mentioned that your yaw string was off (in which direction?) that should tell you a lot. Do you have a way to tell which way VSR2 was actually moving (including drift)?
Good luck,
Bob
Reply...Trim?
Submitted by Paul on Wed, 11/16/2011 - 10:48.Hi Bob,
yeah that's pretty much right. I really aimed and expected to punch through 60 knots on that last run. It was a wild ride thanks to the greater surface chop that comes with those conditions. Maybe that exaggerated the speed sensation. From a performance perspective I was pretty disappointed at the end result. On paper we should have hit 70!
The good thing was that it showed that we could sail in those conditions. We are firmly in the laboratory and any result is valuable. We also recorded a lot of data. One of our most 'telling' pieces of data is the strain guage on the rudder. This showed that we had next to zero load on the rudder at Max speed so the boat wasn't fighting itself. The leeward pod was flying easily at 50 knots as it is supposed to... so the roll moment is pretty neutral there also. Even if the wing wasn't sheeted so accurately... it still should have gone over 60. The strain guages in the stub beam showed that we had a huge amount of load on the main foil. All this indicates that VSR2 is pulling hard... but the foil is dragging hard. We think that we still have fully attached flow on the ventilated foil. This could explain the good low and mid range performance and why we seem to have come up against a wall when cavitation commences. Maybe the jump from attached to super cavitating isn't so smooth and we are stuck in purgatory. We are now playing with our options. The final most drastic one is to shorten the foil and increase the area loading. We don't want to go too far down a non-recoverable alley as we may find we are back at the start and have a good high speed foil... that can't get up there as it's low and mid speed performance becomes woeful. We have to gradually find a balance.
Cheers, Paul
Foil leading edge trip
Submitted by gjdadd on Sun, 11/13/2011 - 18:41.Can you bond a slender triangular section leading edge trip on the suction side of the foil to encourage clean and complete separation?
Regards,
Graham.
REPLY...Tripping
Submitted by Paul on Sun, 11/13/2011 - 19:03.Hi Graham... that's pretty much what we did today. It is about 0.9mm thick and currently positioned at around 40% chord. We will give it a try and just see what happens. It's a first shot. Yesterday was good as it showed us that something is not right with the foil. It seems to behave well at start-up but it is limiting our top end speed. It gets interesting from here on in.
Cheers, Paul
p.s. a small matchstick camera is on its way... Let's see how long it lasts down there!
The Time Has Come
Submitted by Hendrik Ehlers on Sun, 11/13/2011 - 10:08.Our thoughts are with you. Go Vestas Go !
foil damage from resonance?
Submitted by oldie on Sun, 11/13/2011 - 00:50.Where is all the power going?
If there is resonance in the foil due to a dynamic making and breaking of the void, carbon is the last material to use, even if it has the best static strength.
A stainless steel foil might work, your brains trust
will know, of course....
REPLY... resonance
Submitted by Paul on Sun, 11/13/2011 - 19:09.Hi Oldie, I'm not hearing or feeling any big resonance like you would get on a keel or centreboard. There is some noise but not that great. We did look into a CNC'd steel fin but the weight was wild. We are still trying to eliminate the possibles as to why the foil is creating so much drag. It's funny as we expected very poor low and medium speed performance. It actually seems to be underperforming at the top end!
Cheers, Paul.
Rats
Submitted by P.Flados on Sat, 11/12/2011 - 22:34.I feel for you in your frustration.
Getting in a run in those conditions and having the boat handle it well is great.
Not getting any big numbers is puzzling to say the least.
VSR2 is the right tool to find what it takes for the next leap in performance.
Unless you can find a problem with wing inefficiency (this does not seem likely) or excess drag at or above the water surface (again not likely), it has to be a drag problem at with the main foil.
Keep plugging at it on the water and keep poking at your brain trust to dig through the data and find something that can make sense of the results.
GO VSR2 GO!
REPLY... Rats!
Submitted by Paul on Sun, 11/13/2011 - 20:14.Hi Paul,
This 'lab' session is getting pretty exciting. We've had our theories, done some CFD and then some analytical theories and now we are playing full-scale in the real world at over 50 knots. The results will be graded by a world record. We do feel that all the drag is coming from the foil. VSR2 should be going 20 knots quicker in 'those' winds in theory. The boat has always been designed expecting the worst in foil performance. Funnily enough we expected poor low and/or middle speed-range performance. As it turns out the foil is performing really well up to the low 50's and then seems to be hitting a wall. After the previous 54.4knot peak I honestly thought we would gain an easy bunch of knots up to 60 in slightly stronger winds sailing one up. We didn't. It reminds me of the last record session in VSR1 when we just couldn't get over 53 knots no matter how much wind we sailed in. I suspect that some sort of cavitation was also hampering us then. Well now we have a foil that is meant to work with both cavitation and/or ventilation but we just have to understand a bit better how it manifests itself.
It really is great to be at this stage. It's fascinating and inspiring. I still rate our chances pretty high. There is a hell of a lot of performance left in this boat... not just a little.
Cheers, Paul.