Sailrocket returns... and so do we
May 29th, 2007
Greetings to all,Well it has been a pretty hectic month on many fronts since we had our last crash.The good news is that the boat is all back together and has been launched once to prove it.She has passed all her strength tests and has only gained around 3-4 kilos in the process.The new skeg is in place and if conditions were right then we could go sailing tomorrow.
PRETTY HAPPY TO HAVE OUR BOAT BACK. THANKS TO MANY.
The repair was a big job. I counted over 70 different areas of damage after the crash and later found more. They have all been attended to and overall I am very happy with the quality.Thanks must got to all of those who helped including the team at COMPOTECH, DESIGNCRAFT and Martin at SP GURIT. Uwe Jasperson from JAZ MARINE in Capetown is owed a few beers from our end for putting together the 'care package' we needed to carry out the repairs.
IN FRONT OF WALVIS BAY YACHT CLUB
The wing damage was relatively easy to fix. Relative that is to the cross-beam. Once we got all the materials up from Capetown we launched into the full repair of the beam as I was super-keen to get back out on the water. On the day when I was doing the final big push to complete all the composite work, Malcolm had sent an e-mail voicing concerns over future control issues that may be waiting at higher speeds. This began to ring little alarm bells.Helena and I worked until 2:30 am that morning using hair dryers to warm the resin and keep away the condensation from the moist night air.It occurred to me that I was in no hurry to repair the damage and then be back in this predicament.Our already extended visas were about to expire and the winter winds weren't so regular anymore.I discussed it with Helena and we decided that it would be more prudent to fully prepare Sailrocket and then pack it away for a while.We will return to the UK and have a full audit of what we have learnt and what we need to do to go forward from here. I don't want to pressure Malcolm and the design team into doing 'Band-aid' repairs just for the sake of going sailing. We must fully understand what has happened and what is to come.The past three months have shown us that we obviously have control issues. We are confident that they can all be resolved by one means or another. The key to this will be the use of computer simulations of the handling and response of Sailrocket. Malcolm has been working hard on developing his simulation to make it as realistic as possible. The last crash showed that we also need to incorporate a realistic 'pilot response model' into this. Previously the model had been easy for the computer to sail... but impossible for a human. Now that we have focused on this we can work to correct it. That is why the skeg is fitted.
FIXED SKEG TO THE LEFT, RUDDER/S TO THE LEFT
Dan Bernasconi (who number crunches for an Americas Cup team amongst other things) decided to build his own simulation from scratch. He wanted to see if he comes up with the same answers as Malcolm and if not... then why not? Both Malcolm and Dan will share their workings in an effort toFully understand what may be laying in wait just around the corner.I will bring all the video footage back to the UK and we will sit down and go through it run by run.I believe that we need to first focus on reliable 40 knot runs even if this is at the cost of ultimate speed. Before we make any rash decisions I will let Malcolm and Dan understand the problems.
MOODY HEY? THE FAMOUS WALVIS BAY FOGBANK CAN BE SEEN IN THE BACKGROUND
The ball is in their court.The winds will return in force around August but there will still be some great days in between.This means that it is likely that we will still be in Namibia around the time of Walvis Bay Speed Week.Over this week the worlds fastest sailors will be out on 'speedspot' trying to raise all the current records. They can have the windy days and we will have the lighter days. If we are in good shape around this time then it could be one hell of a showdown.We launched Sailrocket as much for our own relief as anyone elses. I wanted to see the boat back in the water one more time just to put a full-stop at the end of the last chapter. It worked and I felt immensely satisfied at our ability to bounce back. We all enjoyed the moment.
THE LAST TIME WE ALL STOOD IN THE WATER AROUND THE BEAM...WASN'T SO JOVIAL!!!
The last three months have been hard work. It hasn't been a holiday down here. I am disappointed that after three months we haven't even cracked the '40 knot bottle' of champagne and that we have only sailed for perhaps 10 minutes. On the other hand there is nor rule-book to what we are doing. We have spent over half the time repairing sailrocket and we have learnt some big lessons relating to the handling of this radical craft. Despite some pretty hard crashes we HAVE survived and we still have a great boat to go forwards with.
In the big picture it is all progress towards the goal. The final boat will be very similar to the one we have now. I doubt that we will be making any major modifications. The devil will be in the detail. The fact is that Sailrocket may not be as 'automatic' as the model suggested. She may be quite a tricky beast to send down the course at speed with alot more emphasis on careful driving. This should all be reflected in the simulations.So we will work through all this and make a plan. I would like to get back in action as soon as it is practical on all fronts. I want to come back strong on all fronts. One thing is for sure, we will be alot further down the track to ultimate success than when we arrived 3 months ago. There is no way we could have done it without a great support base.A special thanks must go to HOMETRACK for making our trip down here possible in the first place.Our presence down here in Namibia is only the tip of an iceberg in relation to what is involved to reach our goals.
Cheers, Paul.
HERE IS ONE ASSETT THIS PROJECT WOULD NOT BE POSSIBLE WITHOUT. ALWAYS THERE.
posted by Paul at 6:29 pm
7 Comments:
Good ideas always last. There will be a next time !
Maybe you can pick up kiteboarding while your still there. Great place to practice there and kiteboarding is the best way I know to let off steam and forget about everything for a while.
You sure deserve some relaxing days !
Have a safe trip back
Johan
Good idea - to further investigate the reasons for control loss. I'll bet a small modification in your rudday and foil design eill aid control. Maybe look into ventilating your foils?
Best of luck (from a fellow sailing hydrofoiler).
-jason
Excuse my spelling in the prior post... but also -
Your two rudder system (apparently one kick up?). Does the rudder that stays down have the taper?
I was just thinking about span flow and wondering if that could possibly be lifting you out of the water? Maybe that rudder needs a "span-wise flow stopper" (wingtip / fence on bottom)?
-jason
Hi Jason, the skeg on the left will stay down and is fixed. It is non steerable (but can be adjusted prior to a run). It is there to give the boat a fixed sense of direction and to dampen the effect of the rudder as this becomes highly sensitive at speed. If I put in 1 degree of rudder at 40 knots then the boat can 'spin out' as seen if the skeg is not there. The big rudder will be raised above 30 knots. I think that the picture from behind shows the small ruuder which is attached alongside which will be used for high speed work. It is far less sensitive. Ventilation may be a problem and we may require fences. We want to start with a safe solution and develop speed from there.
Cheers, Paul.
Paul
Typical sailing vessels carry the majority of the side loads on the front foil and use a lightly loaded rudder for trim. This is very similar to modern aeroplanes. It looks from the position of your centreboard, forward of the main beam, and from the fixed rear foil that you are trying to share the side load between these foils. As the load share between these foils can change dramatically with sail trim, steering, sail gust response etc this may be cause of your dynamic instability.
Dave
Sailrocket is ment to have all the load on the foil but as soon as you change the sailtrim this will change. That's the big problem of having a sail in a fixed position in relation to the foil.
So maybe it's bettter to never change the sailtrim. With my models before i let them go I held them at the foil and trimmed the sail so there was no windward or leeward rotation. Then I let them go and never had any problems with the steering. The sheeting then is not always optimal as far as angle of attack is concerned but you can change that with the rudder and the boat then always remains balanced.
So before you let Sailrocket go maybe it's an idea to hold it at the foil, trim the wing and then let Sailrocket go and never change the trim again. Look for the right angle of attack by steering.
But maybe in sailrocket the balance of the boat is different sailing compared to when standing still. standing still the leeward pod doesn't cause any resistance for instance. Than maybe it's not adequate and you have to make small ajustments once sail. But having the sailtrim as fixed as possible and use the steering for the right angle of attack might be a good way to avoid uncontrolable situations. Or do I miss something here ?
But of course the sail has to be able to adjust when the angle of attack is to low to avoid negative forces. When the angle of attack is too low steering leeward is the solution, not sheeting in I believe. Changing the cheeting abrupt is to uncontrolable. later on you have to sheet out and who is to say this is the right amount. And if you need the sail because the rudder can't handle the steering the boat isn't well balanced anyway.
But maybe 'm completely wrong, just another well ment view...
Johan
re: Johan's comment about using steering to control sail angle of attack is a method I use on my hydrofoil. You can partially stall the main, jib or both to decrease loads. The wing on this rig probably has a wicked "sweet spot" for lift. I'd bet the sudden application of all that force overpowers the rudders entirely in moments too sudden to steer away from or avoid.
Maybe a "toque limiter" on the wing - to lessen sudden loading? Dynamic main sheet instead of static?
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