Please select your home edition
Edition
Zhik Dinghy Wetsuits

Vestas Sailrocket 2 bouncing off the ceiling

by Paul Larsen on 2 Nov 2012
Vestas Sailrocket 2 Vestas Sailrocket - copyright http://www.sailrocket.com
Paul Larsen, Vestas Sailrocket 2 project leader and pilot, discusses how the crew is bouncing off the ceiling due to the lack of sufficient wind.

The Walvis Bay wind machine seems to have broken down. The powers that be that make this one of the best and most consistent speed sailing venues in the world have taken a break and left no message as to when they are coming back. It has been 11 days since we have had enough wind just to get started in and the forecast doesn't indicate anything strong enough on the horizon. It's very unusual for this time of the year. In my four years on location here I haven't seen it this 'flat' before. It's weird. It's slightly depressing to be honest.

As mentioned in the previous blog, we have had to commit to booking a WSSRC ratified world record attempt without even knowing if we have the performance to achieve our goals. VSR2 is still very much being dialled in. We have only done five runs since we arrived, two of which we didn't even get going over 10 knots. The last run was pretty good in 'boat' terms... but pretty average in 'Outright' record terms.

As a team, both here and in the UK, we are all scratching our heads as to why we are hitting this 'glass ceiling' at around 52 knots. Consider the simple facts we have seen to date...

- Two different boats with seven wildly different foils have all hit this speed

- The boats have been sailed in winds from 22-34 knots and only twice just exceeded this speed. Remember that in theory a 30 knot wind has nearly 50% more power than a 25 knot wind.

- Both boats accelerate very hard up to this speed and then flat line.

- VSR2 is designed to sail at over 60 knots and is sheeted accordingly. If anything she is a little oversheeted at 50 knots. The tell tales are all flying and she accelerates from 40 knots up to 50 with the same sheeting angle. We have eased the wing out a few degrees to allow for the fact that we aren't achieving the polars.

- The foils are specifically designed not to cavitate until at least over 60 knots. They are base ventilated wedges and we have gone to great lengths to prove that the base is ventilated well down to tolerable/expected pressures throughout the run.

So, if it was simply a question of power... then we would go significantly faster in higher wind strengths. This hasn't proven to be the case. If the drag increase was gradual or even linear... then we would go faster in stronger wind strengths... we don't. The aerodynamic drag is only a small part of the overall drag picture. The front planing surface is the only thing in the water apart from the rudder and main foil at high speed. A simple V'd planing surface should have an almost flat drag curve as speed increases. The new rudder is smaller and more efficient than the last one in all dimensions. We are about to measure its base cavity pressures to make sure it isn't choking/cavitating... but am sure it isn't at speed (when the wind returns we will find out).

Thanks to all the sensors and the Cosworth data logger package we have a lot of very useful information from each run.



Look at that acceleration on the yellow line. You can see how the acceleration levels off early as the wing is only partially sheeted until I bear away on to the course and sheet fully in to 10 degrees. The acceleration then shoots up again until we hit that glass ceiling at around 52 knots. It stays there despite sailing through gusts until I sheet out and bear away to slow down.

We are able to see how each aspect relates to the other. This graph above shows Boatspeed (yellow), rudder angle (red), rudder load (spiky purple... note it follows subtle steering inputs closely), Course over ground (lower grey), wing angle (playing up but still useful bottom dark blue), wind strength/angle (missing on this run), there are a couple of other load sensors in there.

We sit and stare at these graphs for ages, then we ponder them, lie awake in bed thinking about them... and come and check them out again. We question the accuracy of all the data and wonder how we can improve it. At moments like this when we don't have all the answers, we wonder if they aren't staring us right in the face. These light wind days give us time to ponder such things in depth.

So it comes down to this... if the nature of the drag was progressive or power dependent, sailing in significantly more wind would reward us with significantly higher speeds. We have simply hit 50-52 knots too many times now. This would suggest that the rapid rise in drag has been brought about by the foils in the water. Nothing else in the air or water could give such a rapid increase in drag. We know we are fully in the region where cavitation is likely. I can understand where the sub cavitation foils are failing as we are potentially near their limits, I can even understand where the first try at a ventilated/cav foil was failing (too big, too cambered)... but this new one is a hugely different foil in all aspects. It is specifically designed not to do the bad things that the first foil did. The new foil is the safe, reliable option and yet it simply hits the same glass ceiling as the last foil. That seems odd to me.

So we are all going over the boat, the data and having a fresh look at the basic principles. What are we missing? There is almost 100kg of thrust or drag not accounted for at our current speeds. It's a lot. Malcolm and Chris are meeting up at Aerotrope in Brighton tomorrow to discuss the problem in depth. I'll Skype in. If the wind was here we would be working progressively through the problem but it's not... so we have to work with what we already have.

There's a little bird outside that has become quite accustomed to us. It now hops into the container with one dodgy foot in search of crumbs. It hops right past me even as I type now. It has this weird problem where it is actually very territorial. When it catches sight of its reflection in the shiny underside of one of VSR2's pods it attacks it. It flies into its own reflection time and time again and we think it's silly. From its perspective it might be watching us going out time and time again smacking into our own glass ceiling. Neither of us will give in. It's not about the ceiling of course but rather the desire to own the territory on the other side of it.

Our ratified record attempt starts in a few days. No wind is forecast. Maybe it's a good thing. Maybe we are being afforded the time we need to work on the problem without distraction. I still have faith that there are great leaps and surges of speed waiting for us once we gain the understanding. I just hope that Mother Nature gives us a decent Vestas Sailrocket website
Bakewell-White Yacht DesignWildwind 2016 660x82Mackay Boats

Related Articles

RORC Caribbean 600 - Rambler 88 takes Monohull Line Honours
George David's American Maxi, Rambler 88 finished the 2017 RORC Caribbean 600 on Wednesday 22 February 2017 George David's American Maxi, Rambler 88 finished the 2017 RORC Caribbean 600 on Wednesday 22 February 2017 at 11 hrs 56 mins 17 secs AST taking Monohull Line Honours.
Posted today at 1:14 am
Vendee Globe - Colman progressing in right direction - speaks to BBC
Conrad Colman's pace has not increased substantially in the last 12 hours, his direction has become more direct. Although Kiwi solo sailor Conrad Colman's pace has not increased substantially in the last 12 hours, his direction has become much more direct. After a frustrating passage through an area of light winds, Colman is now heading for a weather system which should allow him to hook in a wind system that will take him to the finish. He spoke to BBC's Radio 4 today:
Posted on 22 Feb
Vendée Globe – Costa to cross Thursday morning for 14th
Progress has remained painfully slow for Kiwi skipper Conrad Colman today as he sails into a wide high pressure ridge Progress has remained painfully slow for Kiwi skipper Conrad Colman today as he sails into a wide high pressure ridge which stands between him and the favourable westerly breezes which should finally allow the jury rigged Foresight Natural Energy to sail more directly towards the French coast and the finish line
Posted on 22 Feb
Sanya awarded Youth Sailing World Championships
World Sailing, the world governing body of the sport is pleased to announce that Sanya, China will host the 2017 edition The 2017 selection process opened in November 2016 after the Israeli Sailing Association exercised the right to withdraw from hosting the 2017 edition as a final contract had not been concluded.
Posted on 22 Feb
RORC Caribbean 600 – Day 3 – Phaedo3 takes multihull line honours
While the multihull race record was not broken this year Phaedo3 and Maserati had an incredible 600 mile high-speed duel Phaedo3 held on to win the battle of the trimarans, just 12 minutes ahead of Giovanni Soldini's Italian MOD70, Maserati. The high-speed battle saw the lead change hands at least four times during the race.
Posted on 22 Feb
Volvo Ocean Race – Pablo Arrarte joins MAPFRE as watch captain
With just 242 days to go until the start of the 2017-18 edition on October 22, preparations are already well underway. Arrarte, who raced onboard Brunel in 2014-15, will also assume the role of deputy to Olympic gold medallist Xabi Fernández, who was named as skipper on Friday.
Posted on 22 Feb
Maserati Multi70 finishes a close second in RORC Caribbean 600
Soldini and his seven-man crew brought Maserati Multi70 across the finish line off Charlotte Point in Antigua. Soldini and his seven-man international crew brought Maserati Multi70 across the finish line off Charlotte Point in Antigua.
Posted on 22 Feb
Red Bull Sailing Team returns to the Extreme Sailing Series
The team will have eight Acts to out-sail the world's best in what looks to be the most competitive season yet. The team will have eight Acts to out-sail the world's best in what looks to be the most competitive season yet.
Posted on 22 Feb
New Zealand's influence at JJ Giltinan 18ft Skiff Championship
Can the Yamaha 18ft Skiff team become the first NZers to win the JJ Giltinan 18ft Skiff Championship on Sydney Harbour? Can the Yamaha 18ft Skiff team of David McDiarmid, Matt Steven and Brad Collins become the first New Zealand team in the 79-year history to win the JJ Giltinan 18ft Skiff Championship on Sydney Harbour? The team came within one point of the 2016 winner, Smeg, and are determined to go that one better this year.
Posted on 22 Feb
RORC Caribbean 600 - Maserati Multi70 in a fight for lead with Phaedo3
After 24-hours of racing in RORC Caribbean 600 Race Maserati Multi70 trimaran is locked in a fierce struggle for lead After 24-hours of racing in the RORC Caribbean 600 Race the Maserati Multi70 trimaran skippered by Italian ocean racer Giovanni Soldini is locked in a fierce struggle for the lead with the race record holder Phaedo3.
Posted on 22 Feb