A good day...but what is going on with these foils?

 Walvis Bay rose to my challenge today and delivered a near perfect speed sailing day for us. This is why we come here.

VESTAS Sailrocket 2 is in the best shape of her life. The whole boat is starting to feel like a finished piece and I am really happy with her.

We did 3 runs today. The first one we did with the conventional foil in. We have added two fences to prevent air from getting sucked down from the surface. One fence is just below the bend (transition) and one is right at the top. It felt like I got ventilation on our last outing when VSR2 went into a big bear away so we added these fences to stop this.

The first run today went well and was very smooth. All the little details were making the whole experience so much enjoyable and as mentioned, it was near perfect conditions. The new launching system meant that I got up close to the beach much sooner than previously and this makes for a much longer run. The leeward pod was flying high but I was easily able to lower it using the flap control on my left.

 

The run was very enjoyable. Fast and effortless. Just after the timing hut she performed her old trick again and went hard into a bear away. I put in a couple of turns on the wheel to correct it and immediately stopped the run. Hmmmm. It would seem that fences didn't fix that then.

I still managed a top speed near 51 knots and a 500 meter average around 49.38 knots. This would be a new 'B' class world record for craft with our sail area... but I'm not that interested in that. I went faster with a passenger a month or so ago. We are after bigger game here.

Conditions were building so considering we hadn't discovered the magic to make that foil work I decided to do the ol' switcharoo over to the new ventilated 'wedge' foil. The guys had to go back to the container to collect it but in an hour or so we were back up to the top of the course and ready to roll. The start went great but even early on in the run I got this terrible noise and shuddering vibration coming from the main foil. I was only doing about 30 knots but there it was. It sort of felt like what I would assume cavitation would feel like. Not a cool or sophisticated noise... more like an engine throwing a rod! When I turned onto the course it smoothed out and the run went very well again. Once again I enjoyed it and it felt fast. VESTAS Sailrocket 2 is just effortless to sail now and I can savour the speed sensation without fear. She cruises at 50 like a car down a highway.

The, just past the timing hut again, she made that horrible noise which felt like running the tip aground on concrete. The drag pulled me from 50 back down to around 30 and once again I was forced to abandon the run. This was weird. Once again I hit a peak speed around 51 knots. This really is weird. I mean with effectively three different foils i.e. conventional-no fences, conventional-fences, ventilated, we have hit nearly the identical speed in very similar winds. Maybe it's a coincidence involving many factors but either way, there it is.

 

 

Conditions were still epic. It was just soooo flat along the shore. Gusting 28 knots and glassy in close. Pure speed sailing porn! We were so close to getting some bigger scalps than the B class record. I want to get the Australian record which is just over 50 knots and the unofficial 'Boat' record off Hydroptere which is around 51.4 knots or 2 knots quicker than my previous run. Either of those would be a nice way to finish the day. I stated the third run but once again I got that terrible draggy shudder. This time it was more persistent and I canned the run at the timing hut. I had only peaked at 30 something knots. What the hell was going on here. We went over the main foil and rudder but it all seemed fine. No obvious signs of cavitation. No damage. Basic boat settings. More Hmmmmmm.

we dropped the rig at sunset.

We have been sitting back here in the container downloading data and digesting as much varied info as we can get. We get a lot from each run. 6 High Def cameras, 1 Cosworth data logger, 3 GPS systems including the mighty TRIMBLE used for record ratification and a TACKTICK wind system with data logger. Multiply that by 3 runs and It's no surprise that we are still here at 10:30 p.m. having just downloaded it let alone digested it.

Funny thing is that I'm pretty happy with today. Breaking this record is like solving a big puzzle and today we got a whole bunch of clues. We did get some great data. The boat itself really impressed me. She is a real noble beast who now feels like she is trying to help us. The boys have done a great job sorting out the details on these windless days gone and I can really notice it. She's slick.

So we will digest all this new info. I already have a few things I want to querie. It appears from the masthead camera that the foil is running very close to the ditch created by the ventilating forward mounted rudder. It should be about a meter away. We have already double checked this whole aspect and remeasured it all to triple check. It seems very odd. Has VSR2 dropped into a mode of sailing that we haven't planned for and that she needs to be shaken out of. VSR1, our first boat, used to drop into a mode where she would drag sideways down the course at about 12-15 degrees. We couldn't believe it as it was still doing 38 knots. It was something you couldn't model or predict and yet there it was. Once we became aware of it and accepted it, we made the mods and began to unleash the potential.

I'm beginning to feel that there is something big we are missing here.

We are very definitely in the lab. We'll get to the bottom of this one. Two weeks to go from tomorrow. Come on Walvis, give us a few more like that.

Cheers, Paul

Comments

Foil vibration

It is probably 6 years since i last commented but have continued to follow sailrocket's significant be it frustrating progress.
DJK's 1/12/11 comments maybe close to the mark. The main foil needs to be well clear of the wake of the rudder.
While a water rudder is essential at low speed give thought to reinstating an air rudder and retracting the water rudder at AWV~40knots
alans@aapt.net.au

Foil?

Hi Team,
I too have been following this project since the very start. I really hope someone is making a documentary or book about Sailrocket as it is an inspirational project and pushing the boundaries of sailing. I would love to see a similar book/documentary about the Team Philips project as well, on which I believe Paul was a crew member.

Regarding the foil, I wondered if the cavitating foil is run at a different angle of attack than the conventional? If the main foil is running in the wake of the rudder, maybe the cavitating foil is being pulled in line with the rudder until it has this higher angle?

I remember seeing an article about the Miller Hydrofoil which is a cavitating front lifting foil on a windsurfer - this had a concave curve (hollow) on the high pressure side to (I assume) give more lift. I wonder if this helps detach the flow on the low pressure side as the water is more violently ripped apart and require less angle of attack?

Would love to find out more about your cavitating foils, but I guess you want to hold on to your knowledge a little bit longer! Look forward to finding out when you hit 60Kn... Good luck, and keep up the good work.

James.

Best Wishes

Been following you guys avidly since Sailrocket 1 and really appreciate your sharing the details.

As a layperson - I'm curious to find out more about how the new foil was developed (e.g. the unusual shape) and tested; why you expect(ed?) it to outperform the conventional foil; and how its performance compares with what you anticipated.

Also - was/is a scale model tested in a 'testing tank' and/or do you use computer models to test and optimize the foil before installation on Sailrocket II (where I understand you gather real time data on runs)?

Rooting for you - for the perfect wind - every day.

Best wishes,
Steven

Good luck

Hi Paul and team; Thanks for posting our pics and we enjoyed your amazing hospitality. Sounds like you will get the record if you just keep making the same progress. We were really impressed with your organisation, Good luck,

Gordon and Iain

Getting there

Mate, sneak up on it and then just tear it a new one.
My initial thought last month whenthe 2 up ride was quick was Angle of attack change might be worth a try, the trim was obviously a bit different with the weight. Its only good in steamrollers so perhaps the Angle canbe duplicated without the weight.
Great work fingers crossed here for ya. By the way if you put a Windrush sticker on it would surely go faster. Cheers. Regards Brett

Take a Beautiful Woman

Take a beautiful woman that u love along, and join the the 60 knot club.
All u need is love, da da da da da :D

New Territory!

What a great lab setup you have created!
It might be time to not pin every last detail of your experiments on the internet- we would just like an outright record by an Ozzie to stand for a while. About a year would be nice, thanks....

Stuff to consider:

An unpolished fin seems to have advantages.

Maybe fences are not yet properly aligned.
Or they may be only a crude solution.
As a last day desperado device (hope it doesnt come to that!), I would out with the angle grinder and produce 50 leading edge dentricles which would delay the onset of conventional cavitation. ( See humpback whales and wind turbine experiments)

Salutations!

ballast

Hi team, Pat and Kate back in the UK but thinking of you as we sit in a gale. I also think it would be worth experimenting with extra ballast, I suggested it a while back but Pat said it wasn't logical,( a typical submariner to oceanographer conversation).
Good to hear the positive vibe coming through again, just got to sweet talk the Walvis wind now and go for it.

Kate

Ballast

Hi Paul

I think Russel is onto something here. The run with the pax was your best yet, without great effort. I agree with his hypothesis that adding ballast sits the boat differently into the water. (lower in the back quadrant). If Russel is correct that would mean you have too much forward trim.

Try a run with ballast; I bet you will be surprised. We had a similar problem with a twitchy school glider that turned into a smooth kitten once ballast was added.

See you on the grass; will be in WHB soon.

Uwe

Resonance?

I have very little insight into the boat construction and the technology in general. But I can't help thinking if this is either

1) Main foil resonance (change stiffness of foil, mounting point rigidity, or perhaps general hull stiffness, or change weight loading as others suggested). Could you measure and analyze the location and nature of the vibration with sensors?

2) Rudder-foil interference (change relative positions?)

Just my 2c - I expect you may have thought along the same lines.

Best of luck to you!

Morten Fabricius Olesen

The Wall

Dear Paul & Team,

As well as carefully following your progress, I am going through a similar process with my "Ice-Bat.com". I've tried different propellers, skates, even pilots but the top speed remains virtually the same.

Good luck solving your wall!

Steve

Conventional foil

Hi Paul,

Maybe this will be of some help: As you know, with neutral helm, your driving force and all your drag forces line-up. If the craft yaws, either the drag changed on one side or the other, or the resultant from the wing or main foil shifted. Looks to me like ventilation on the main foil would increase drag and cause a round-up. If the main foil had less drag (rose higher or?) it should bear away.

I discuss this a bit at the following posts:

http://www.sailblogs.com/member/speedtech/?xjMsgID=74912

http://www.sailblogs.com/member/speedtech/?xjMsgID=74969

Good luck, Bob

It seems that uneducated

It seems that uneducated guesses from afar are de rigeur today, so here's 2c from Perth :-)
You mentioned a ventilated front rudder, the foil following closer than expected to the ditch from the front pod, terrible noise and vibration.
Could it be that the foil is working in the disturbed/aerated/'bumpy' water being left behind by the front rudder and pod? Could the solution be something as simple as kicking the arse up to windward a little with a trim-tab or fin, or by swinging the crossbeam and rig forward a little?
I fully expect you've thought of this, but also figure that it doesn't hurt to throw ideas around in case one of them gives you an 'ah ha' moment.
Go hard. I've got a bottle of pop ready for 60kts!
djk

extra weight

Maybe that good run with a passenger is telling you something? Although it flys in the face of all logic, perhaps the extra weight pushes the foils a little lower in the water, and you get less cavitation? Could you try a run with some ballast, alive or not?

Russel is onto something

I'm with Russel here. I'm surprised that you haven't tried with a passanger again (or weight) when the first time you did, you sailed faster then you ever had before. It's alot easier to add a passanger then to modify the craft too...

Foil vibration

Have you managed to eliminate hydro-elasticity i.e. foil and or struts bending as a result of loads leading to instability of foil attitude & flow?

Good luck
Simon
AYRS

Foil Vibration - since foil crack repair

Fishwic- One wonders whether you're on to something since Paul repaired the foil cracks some weeks ago. It doesn't seem likely, but still...

Foils

So what do I know about hydrofoils? next to nothing, but the amazing thing is that on one website I came across when searching 'high speed hydrofoils vibration' was that 50 knots is the speed where cavitation and vibration occurs almost all the time.

guessing

I'm not an engineer. I just do a wild guess.
Could it be that with speed increasing, something is changing that you are not measuring / logging. Maybe the angle at wich the wind hits the boat / sail.
Hope digesting your data will tell you what you need.
All the best from Amsterdam / The Netherlands.

todays runs

keep at it Paul it will come

strange noise

Hello Paul,
the strange noise coming from the foil ... could it be a vibration of all the foil ; in a certain speed or angle ;maybe due to a too soft construction ? It's easy to say from far ! Best wish for the next 15 days ; continue you effort, you deserve it.
Salutations
Tadeg

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