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Southern Spars - North Technology

Sailrocket 2 - Not quite there

by Paul Larsen on 12 Dec 2011
Vestas Sailrocket 2 Vestas Sailrocket - copyright http://www.sailrocket.com
The Vestas Sailrocket 2 crew are in Namibia attempting to break the World Sailing Speed record. They are now into their official WSSR record attempt time period.

Pilot Paul Larsen:

(Fri, 9 Dec 11 07:04)

It felt like it was going to blow all day... and it did!

We got in to the container on the lawns of the Walvis Bay Yacht Club early and quickly pulled Vestas Sailrocket 2 out of her soft hangar. The wing was up in no time and Alex set to raking the whole beam and wing forward six degrees in anticipation for the loads that would need to be balanced if today we found the long sought after ventilated flow.

When the water breaks away from the suction surface of the foil and air is dragged down from the surface to create a cavity, It can be described as being ventilated. It can happen on any boat when the foils are used too hard and there is easy access to the surface i.e. transom hung rudders stalling whilst rounding marks. Now when one side loses grip, the other side, in this case the pressure side, usually has to do all the work. To do this it has to increase its angle so as to have a greater effect on the water around it. This is why the leeway angle of VSR2 increases when we step to ventilated flow.

Nick chopped another 15 cm off the tip of the 'wedge' foil so as to increase the area loading on the foil and hopefully make it lose grip and become ventilated. It is designed to be ventilated but has been operating in an attached flow manner to date. This has shown itself to be relatively fast... but it won't get records.

The day built strongly as expected and we headed across the Lagoon to speed-spot around 1 p.m . I rolled straight into a run figuring that it might blow out on us so best to get some runs in as soon as possible.

Run 1:

One person, 30 cm removed from ventilating/wedge foil, 21-24 knots of wind, beam raked forward six degrees to 77 degrees.

Surprisingly easy start up and good acceleration for such a short foil. No doubt assisted by raking the beam/rig forward. Good control but nothing special speed-wise in the lightish winds. Peak speed 45.06, 500m avg. 42.44 kn. Actually quite surprised by ability to start up and go in such light winds with such a small foil.

Run 2:

One person, same configuration as above but much stronger winds gusting to 29 knots. Another easy start up with good acceleration. Good control, no wierd noises or swerving. Foil felt draggy. Peak speed of 47.8 knots, 500m Avg. 44.71 kn.

This obviously wasn't working. That was windy and the boat was sailed as it should be. I was tempted to chop the foil again right then and there but decided that it would be best to try a big change to the foil configuration first. I used the full range of the pitch adjustment in order to angle the foil nose up as much as possible.

The idea being to force the upper, more horizontal part of the foil to both lift and ventilate more. If this in turn makes VSR2 ride higher then the foil still in the water will have to work harder. Because the upper section of the foil now has a high angle due to the increase in pitch, it should ventilate and feed the air around the bend to the lower section of the foil more deeply submerged. That was the theory and this foils best chance before it would get the next big chop.

Run 3: One person, wedge foil with 30 cm removed in full pitch up mode. Very windy with gusts to 34 knots, solid spells over 30 and lulls to 28.

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Had trouble launching the boat as it was just too windy. VSR2 launched hard from the nose tether to the transom tether and the boys in the support RIB couldn't hold it. I was dragging the RIB. The wing was stalled and VSR2 rolled to leeward. The whole leeward float submerged and the horizontal wing extension dug in the water. I eased the sheet quickly to unstall the wing and pop the float. The boys had set the tether free but I was no towing 30 meters of rope out the back. Fortunately no damage had been done to the wing extension. I pushed on with the run. From my perspective there was still no noticeable difference although from the pics you could see the back of the boat riding higher. I could still feel the foil dragging hard with no tell-tale swerves to tell me she was letting go into a fully ventilated mode. It was damned windy and rough. We struggled to pull the wing down. 46.72 max, 42.31 avg.

As we headed back up the course I felt enough was enough. We pulled into the timing hut. Helena confirmed gusts now peaking at 35 knots. This was now officially bullshit. First we have long spells of no wind and then two days with over the top conditions. Something in the middle would be nice for a change. The trouble is that Vestas Sailrocket 2 is so well behaved and manageable that you can easily be tempted out in conditions you simply shouldn't be in simply to try and use brute force instead of sophistication.

It's not a bad card to have up your sleeve mind you. If that's what your given then you can play it. I set the limit at 35 and was happy to stick with it. We had two issues on that last run where we nearly had damage and it was only due to general handling in very strong winds.

I had seen enough. This foil wasn't letting go so it was time to chop another 15 cm off. This was now 45cm in total and over half of the main foil. It's not the ideal way of getting a smaller foil. It's pretty brutal in fact but this foil isn't working as is and drastic measures needed to be taken in order to find this ventilated flow. The foil now only had 30 cm until the radius of the bend. there wasn't going to be much left in the water. Maybe it was a step too far.

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I pondered all this whilst we sat and waited to see if conditions would abate. It blew it's arse off for about 70-90 minutes before I saw longer steadier spells back down in the high 20's. The call was made to go for it again. We are on a mission here.

It was pretty rough just heading up the course and there were still some strong gusts around. The foil looked really silly now. Of course I had doubts... look at the thing and consider what I was about to try and do with it.

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On the other hand this was perhaps the last windy run for this record attempt before we head back to the UK. we need to understand what works. We have learnt so much and already accept we need to try new foils. This would perhaps be the most educational thing we could do with this foil here and now.

As the RIB lowered me out onto the course I mentioned to Jeff over the helmet comms 'well, this is why you put harnesses in these things'.

Run 4:

One person, 45 cm removed from wedge foil, full pitch up. Winds 25-31 knots. To my great surprise, VSR2 still managed to start up and accelerate pretty well even with so much foil now removed. The back of the boat was riding much higher but it all felt nice and stable in the cockpit.

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The rear float is riding high as I accelerate onto the course. We wouldn’t want it any higher as it decreases the pitch angle of the front float. High 'Pucker' factor here.

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Due to the rough water I tried to get in nice and close to the shore. I could still sense the drag. I was a bit nervous about this run as there really wasn't much in the water and what was in there was a rough stab. Just past the timing hut I could see a gust on the water.

This looks to like its digging a ditch but we don’t have the leeway or corresponding rudder angles to back up this theory.

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Vestas Sailrocket 2 accelerated hard. It felt like I was being released from the drag. It felt like something was changing. I quickly considered what the hell I was doing and eased the sheet.

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The run had been too slow to start for a record run and we were running out of course as low tide was upon us. I could potentially be closer to the edge than I knew. It was a good peak speed that could have been much higher with a second similar run. Peak speed 51.41 knots, 500m avg 46.57kn.

The wind had continued to drop into the low medium 20's and the sun was heading for the horizon. It was too late for another run. So that was it. We had pushed hard again. Maybe with that last 51+knot surge we had glimpsed a transition but I can't be sure.

Now that I have looked at the masthead camera... it still looks like the foil is travelling close to the forward rudder wake. That tiny little, high riding, unfenced, stumpy, thick-as-hell-tipped wedge that I still call a foil had just ripped out a 51 + knot peak and not ventilated. If it was ventilated, then why is it pulling the boat harder to windward than the large conventional foil? Christ, we have four fences on our long conventional foil to try and prevent any ventilation and this little thing just goes and does that.

Right now I'm a bit lost on that one although I already have theories how to improve what we now have. It's late, I'm tired and I need to talk to some people. All I know is that our next foils are going to be tiny in comparison to what we have now. I know now that we can get started with a lot less than we expected. You always learn something extra on the side.

So we have one week left now. One week with no big winds forecast. Things change and a one week forecast can't be treated as fact. We will, as ever, go forward with optimism. that last surge was encouraging. It was the best peak in the last two days which started with a full foil. We still haven't finished with the conventional sub cav foil yet either.

Yes... it is frustrating to not be hitting the big numbers.

Another big day in the speed sailing lab. Every result is a result.
Cheers, Paul

Vestas Sailrocket website
Naiadupffront 660x82Barz Optics - Floaters

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