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...
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...
]
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....
Y
form of alinghi's support system work. smaller beams and less twist...
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. <img src="<>/frown.gif" alt="frown" title="frown" height="15" width="15" />
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.
Y
form of alinghi's support system work. smaller beams and less twist...
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.
Y
form of alinghi's support system work. smaller beams and less twist...
Maybe a good idea but I could do without the dolphin striker hitting the waves when not flying a hull....
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.
has the system in place..
sys F16? link?
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...
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
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...
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:
I'd be interested to see if you could work out a similar multihull formula <img src="<>/smirk.gif" alt="smirk" title="smirk" height="15" width="15" />
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...
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:
I'd be interested to see if you could work out a similar multihull formula <img src="<>/smirk.gif" alt="smirk" title="smirk" height="15" width="15" />
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? <img src="<>/confused.gif" alt="confused" title="confused" height="15" width="15" />
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 src="http:/
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...
2nd attempt
they were doing about 18-22 knots upwind and waterline length was between 110-130 feet. 1.34 * sqrt(110) = 14.1 knots. so like I said, beyond
hullspeed
, ie. most definitely going faster than a wave of the same length as their hull. at some point, adding length for a given power will just add drag through skin friction.
Michell's slender body method works well for slender hulls, but these beasts may be out of the traditional bounds of applicability for the maths. even moths fall outside the range. ie. they are too narrow for what has been verified with this method. not to say it isn't accurate, just that it hasn't been tested and proven to be accurate. although that could've changed since I last read up on it.
sys F16 doesn't appear to have a bridle network with diagonal beams under the tramp, infact they say it is striker-less.
yes sys doesnt have a system under the beams al la Alinghi.. But the kite tube and pole is the system it appears..
I came into the class after the bannana board debate. Anyone care to offer a synopsis? I don't want to reopen the debate, just trying to understand the rationale.
*bites my tongue* <img src="<>/cry.gif" alt="cry" title="cry" height="15" width="15" />
That they are not allowed or theory behind their function?
Both if we can do it without burning our house down. But, judging from Stewart's reaction, I'm almost afraid to ask.
Insure your house then ask again at the closed forums.
Why be scared of discussing legitimate issues????
My PERSONAL 2 cents worth:
Bananaboards would be a very interesting development on an F16. This would be especially true if coupled with T or L foil rudders. Apart from not being allowed under the rules, the time is probably not right for such a development since the class would, in all likelihood, implode if a bannanaboard boat proved ultra fast or ultra competitive. I firmly believe there is a bright future for innovation, development and experimentation within the rules as they currently stand - without introducing a potentially expensive and damaging (in class growth terms) complication such as bananaboards.
I'd love to see the rules opened up in the future to permit experimentation with curved boards (and other freedoms) but I'm talking at least 5 years or even 10 years on.
Of course, outside of class racing or the F16 banner there's nothing to stop people experimenting - but to protect the growth of the class by providing some stability, bananaboards must of necessity be banned.
Don't forget, the current ban was the result of a class wide ballot back in 2007 before the current rules were finalised.
Once again, this is my personal view, it's perfectly possible that the F16 Governing Council may decide in the future to ballot for such developments to be permitted during one of the constitutionally permitted 5 year reviews of the rules.
Hold on. It's straight forward! At least in a layman's view and should not require any flame suits.
F16 is not an
arms race
class but yet is not a
stagnant
class either. Curved boards are still the extreme and cutting edge for beachcats. You will have an extreme gap of the
Have
and
Have Nots
. Incremental changes within the box rule are OK; ie. moving back the forward beam and moving foward & lower volume. Or main sail cut.
According to the commentary on ESPN360, the concept of curved boards have been around for a while. Their function is to lift hulls. For example; A-Cats are carrying less volume/ft than the F16s (especially the newer F16s) and are more true to the wave piercing concept. They are more likely to benefit from curved boards. Whereas, the Viper and Falcons are proving to hydroplane very quickly
as is
and anymore lift may make them less stable at speed, especially with a shorter LWL.
The F16 box rule does have a compromise? It allows for a nominal amount of fixed cant in the dagger well?