www.sail-world.com/australia/Wot-Rocket-crash-test-drama-shaken-but-not-stirred/44219
Only a minor setback, I like the way they blithely assume they'll be doing 50 knots before too long...
Might need lots of pods and pilots.
Antoine took lots of crashes at full speed on the record day.
So how do they intend to change to supercavitating foil, which is the stated secret of their forthcoming success?
My shower inspiration is to sail a stuffed dolphin instead of a hard bottomed board.
As Langman warned his sponsor. He would "need to be prepared for us taking a few trips up the beach in the Ute to pick up bits of broken carbon."
Personally I think they are making a mistake with super-cavitating foils which have a crap L/D ratio and dividing foil control and sail control between two people is asking for problems.
A carbon wing isn't going to be very forgiving either.
From the photos the wing is
~ Area.........18.2m2
root chord.....2.70m
tip chord.......1.35m
Aspect Ratio 8.9
The high AR combined with the carbon, non flex construction will make it VERY twitchy.
Yoyo - you say the super-cavitating foils have lousy L/D -> fair enough, but have you seen the size of the foils? - think I can see one of them at the bottom of that white and orange, slightly dog-legged strut at the bow of the hull -> it's fr*ckin tiny.
Even with two of them in the water, that's an absurdly small amount of wetted surface area (and in this case seeing as it's super-cavitating, a lot of that surface area will be non-wetted) being punched along by about 18.2 sq. metres of high aspect sail.
So personally this particular contraption troubles me - if they can get this thing to work at low speed (i.e. up onto it's foils and super-cavitating by 40 knots), I wouldn't be surprised (once they've fiddled with it a bit) if it strolls straight through 50 and only starts to work up a bit of a lather around 60, quite possibly even 70...... and very, very possibly more.
Mind you, I've also no formal education in these matters.
Hmm....
oldie - like the idea of the stuffed dolphin.
As for me, I find I do my best mulling in the bathtub - Archimedes-style.
'Seems to me the bottoms of my rubber ducks have a pretty much ideal outline and rocker for speed-sailing.
What's more, seeing as I've a whole family of them in different sizes, I've got an instant quiver to select from, depending on what the conditions are.
Come on oldie, I'll take ya on!
Stuffed dolphin versus Rubber Duck - last one to 50's a rotten egg!
Still early days, if they can throw money at the project for five years it might come good. I predict a top speed of 45 knot accompanied with much crowing and then dead silence.
Every change will affect every characteristic until they go mad.
For instance, changing M Endeavor rigging to carbon saved them 7 kg but their sail then broke due to the reduced flexibility.
At least my dolphin has had a few million years of development. They only slow down at 30 knots because cavitation hurts their tails. They need some sail assistance. :)
Slight rig cant to windward. If they popped a couple of planning flats on underneath (front and rear) with a couple of (few?) Lockwood/MacDougal Asy 23s. Dumped the foil trimmer and his 80kgs this thing would be wicked at SP. Still if they beat themslves around the head trying to get super-cav foils working maybe we can pick it up cheap.
Hey Yoyo,
What are your thoughts on why super cavitating foils won't work? Is it because they are so much less efficient at sub-cavitating speeds so you can't get 'over the hump'?
Over simplifying to the extreme.
On a non-cavitating foil 2/3 of the lift is from the suction surface. So on the super-cavitating foil you only have 1/3 the lift but half the drag.
You can look at foils.org (a hydrofoil site) or any number of papers that google will throw up but I think Global security says it best.
'While a supercavitating foil prevents the collapse of air bubbles in the vicinity of the foil which could damage the foil, in order to prevent the separation bubble from collapsing, it is necessary to maintain the foil at an extremely high angle of incidence. This high angle of incidence results in a great deal of drag, so that the lift/drag ratio of a conventional supercavitating foil is so low as to make such a foil impractical. For this reason, supercavitating foils are not used in practice, and hydrofoil craft must rely on conventional cavitating foils, which as described above are unsatisfactory. "
The other thing is they look like stainless foils and struts. The strut is LOOOOOOOOONG. They have naval architects on design but I can't see how it wont break in the first minute of sailing. There is a reason MI has 4 short low aspect foils when everyone knows one long high aspect one is more efficient.
