During race 2, I heard Smyth say an asymmetric spin would slow the boats down too much. He was also very strongly in favor of bannana boards.

They are travelling so fast in just 8 kts that the angle of attack of the "jib" is such that you could not fly an Asym.

Is that primarily a function of the waterline length?

more a function of power to weight at this size/speed, they are most certainly going faster than "hullspeed" at which point waterline length is the predominant factor.

the length of these beasts is really just to keep it under control in pitch. too much length will just add skin friction drag. if they were racing in perfect conditions with no waves or gusts, the hull lengths could be reduced substantially and the speeds would probably increase.

it'll be interesting to see if a beach cat can make the "Y" form of alinghi's support system work. smaller beams and less twist...

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I'd suggest for proper beach cats no; as we need to come in of the wire and scamper accross; thus we need am uncluttered tramp.

Bigger boats that you "walk over" instaed of sliding; then maybe....

I did spend a lot of time trying to integrate this into Bitsa when I built it, slung under the tramp it has a lot of benefits such all the loading of the downward pressure of the mast can be absorbed by the beam, integrating the spinnaker snuffer into the beam cuts down on wind drag, a direct fixing for the front stay means much better jib control, the list goes on and on of benefits.

What I couldn't find was someone who would calculate the loadings and transfer that into carbon fibre layup for not a lot of money, any of the companies recommended by the composite suppliers thought it was for an AC style boat and were wanting to charge accordingly. I had quotes just for calculating the layup ranging from 1000's to 10s of 1000's. At that point I wimped out and built the boat as I did with a sort of central beam type arrrangement.

So any body out there wanting to do a quick calculation for me then please PM, I would still like to build it and have the moulds sitting waiting to go.

Maybe a good idea but I could do without the dolphin striker hitting the waves when not flying a hull....

So how much of this relates to us directly? Will we have a 30 knot F16 in the future?

Only if we increase the waterline lenght to about...90 feet!

OR...drive it off a cliff!

....and change the box rule to allow hard wings and curved foils.

Could solve that problem by increasing the size of the centre pole and giving it a smooth hydrodynamic profile.....sort of like a third hull!

look at the sys F16!
has the system in place..

That design has something that is more akin to a bridle foil - the forestay and spin loads are still transfered to the hulls.

Although it has the advantage of acting more like a forward beam and therefore adding stiffness to the platform.

sys F16? link?

wingnuts!
syasperformance

Critical boat speed is ~1.5 squareroot (lwl in ft) in kts
Surprise, surprise: it is 15kts for 90ft lwl, the speed which the boats had on the upwind leg, so wave drag is about 20% and hence length is of importance. If it is true that BMWO was 130ft long and Alinghi only 100ft, than the wonder wing looks not that good anymore...

Cheers,

Klaus

Klaus, isn't that formula pretty much only applicable to traditional displacement monohulls? I think as soon as you get narrow hull forms there are more variables involved, it's beyond me but there's a lot of good links in this post:

Catamaran Hull Speed

I'd be interested to see if you could work out a similar multihull formula

Correct; Long thin hulls do not obey the same rules. How else would I be able to sail MY F16 at 13kts upwind? (when I get it right!!)

But how does water know, that the hulls are thin?


Michell found the formula to calculate wavedrag, with todays computer we can calculate the drag of a boat hull by ourself.
Here are the plots of absolute hull drag [img]http://www.catsailor.com/gallery/displayimage.php?album=lastupby&cat=0&pos=5[/img]
and in the second picture you see the wave drag contribution to total drag. You can sclae up the speeds with sqrt(LWL), if the boat is four times longer you have to read the value at two times higher speeds. The speed is in m/s with 1 m/s = 2kts.
In short words: Length is important (again), but not as important on heavy and slow monons, because wave drag scales with the finess of the hulls.

Cheers,

Klaus

ok, I am good in fluid dynamics, but bad in adding pictures here...