Emirates Team New Zealand.
- Thread starter Salty Seacock
- Start date
breezie
Member
thats more powerful relative to resistance?
there are several reasons why i not so sure and they relate to the fact that they are not bound by the ac75 rule
firstly it seems like they could make it significantly heavier for its size which has implications for power to wetted area/resistance.
also being smaller it quite likely is much easier to unstick so no point in exploring that side of the design also since they not racing they might be exploring other areas for performance
also the lenght of the foil arms and the foils themselves are not constrained by the rule
not saying i think the hawk will be faster just looking for a digestible reasoning why . not convinced by "more powerful" which Te Aihe obviously will be .
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To me, Te Kahu with her over sized foils/foil arms is not optimised for speed for her length, but rather as a test platform. Her foils probably great more drag relative to her sail area - limiting her top speed.
breezie
Member
but the size of the foils is proscribed by the ac75 rule . there is no reason to assume they are optimised for her size. "oversized" foil arms can only result in greater relative power. which would suggest superior performance ?
need a more compelling reason why Te Kahu must be slower
Not for Te Kahu.
They aren't......over sized foils mean more drag relative to sail area, Increased righting moment won't make up for the undersized rig. This is a compelling reason.
barfy
Super Anarchist
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^^ Idiot
Makes you wonder.! Perhaps Barfy can explain himself.................?
Well, until I saw the video released 8 hours ago, I was wondering what had happened to te aihe. A quote by sail world? about the block of testing means nothing.
And I wonder about that based on scuttlebutt from some kiters who have lined up with both boats. I expect that some changes have been made to te aihe..didn't take 3 weeks to assemble, and as I said, develop or die.
If she has new wings that'll be easy to spot. Changes to the the twin skin could be on the cards as well. The only advantage I can see with Te Kahu would be speed through manoeuvers. She might get up on the wing a bit quicker, but even that's debatable. Upwind I think Te Aihe would absolutely smoke the smaller boat - higher and faster. Down wind it might be a bit closer - then may be not.....
Not trying to ruffle feathers here, but it is not as simple as that. You need to pick the set of variables that you are trying to define as being representative and then make the judgement call of which solution is better. I will try and (fail to) explain. Are you determining the reference point as being a TWS performance output? A drag scenario for a given Boat speed? Overall VMG upwind or Overall VMG downwind? The problem that is trying to be solved is uber complex. It is too simplistic to say that the foils or arms are oversized or that the Rig is undersized. There would be a sweet spot where the Lift and Drag profiles of these two primary components would be well matched. But is that sweet spot representative of the full sized class measured variant? No one here, from the very limited data we have, can do anything but speculate. The team would know and could apply correction factors to offset observed performance against expected. But be careful that the difference is identified as either scaling issue, margin of error or real loss/gain..... That in iteslf could melt most brains.
Consider that both the Rig and the Foils are trying to optimise Lift against drag. And within the Drag side of the equation you need to identify the sweet spot of where you are trying to trade Induced Drag against Viscous Drag. Simply put Lift Induced Drag is both Span and Velocity related. But it is also traded against Viscous Drag. For instance as speed builds induced drag will drop but Viscous Drag will rise. Induced drag can also be mitigated by increasing span, but for a given speed scenario this may be at the expense of higher than necessary viscous drag.
Also we do not know if the physical sizing that has been chosen on Te Kahu reflects proportional scaling for testing (like a tank test model) or because of limitations in the construction methodology (try and miniaturise too much and you will not necessarily observe the same characteristics that a full sized object will display) or because there is a willingness to test the actuators supplied and the engineers want to run durability testing of full sized components in a mule that determine to be say 50% of full sized boat. The work around maybe to use a foil size that can phsically house these components - but to even us casual observers - we can tell that the scaling is not strictly proportional. Length, area and displacement are not linear in their relationships. For foiling craft, boat length is not the primary concern. Mass is more critical as it determines power to weight ratios and all that that entails. Its about finding that sweet spot of foil area to rig power, and deciding whether the earliest opprtunity of flight gives away too much at the top end, or do you chase a later takeoff but higher terminal velocity at say 12 knts TWS?
Having decided what size foils to test on your mule. Is the Rig strictly propotional to Hull Length (possible), or to Foil size (more likely) or just to ratios of scrim thickness (for close representation in material behaviours) and/or active batten technology (equivlent to the foil actuators - but buried between the twin mainsails)? Again the team may have complex solvers to offset the scaling process - I am hinting at Reynolds numbers here - because at the AC level - the scaling of Reynolds numbers are very important at the refinement that they are seeking.
And we haven't even touched on the competing needs of different departments. Designers want to iterate design choices to validate or rule out - choices they feel will win the Cup. The sailing team want to sail as a full sized unit to get full synced on the Big boat environment. Grinders want to acclimatise to doing their work rate on a bucking bronco - not a stable flat gym floor. All things being equal, Choreographing those turns and transitions are really where the gains and losses will be made. Sailmakers want to test full sized solutions. Engineers want to confirm data scaling from Te Aihe to Te Kahu back to Te Aihe. Te Aihe next week will be at V1.75 after Te Kahu developments and rebuild; and boat builders want to refine v.2.0.1.0.1 before it gets splashed. And Time marches on....... Exhausting just to contemplate.
So many variables - so little reference to understand what they are trying to achieve or test. But isn't this why we like the America's Cup?
Totally guessing but if I was designing a rule-less small boat for testing, I would be aiming for slightly faster than big boat B1 with potential to increase speed to give B2 a run for its money. Throw the ball and all that. This gives a really good second boat to race against and lets B2 components be built as late as possible.
Assuming they're allowed to practice race small vs big.
Assuming they're allowed to practice race small vs big.
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breezie
Member
i understand the limit is foil cavitation so size of itself does not imply faster
NZL3481
NZL3481
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Given how fragile Luna Rossa appears to be, maybe the Italians need to scavenge some carbon?
NZL3481
NZL3481
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NZL3481
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Don't be surprised to see tham playing together. There's enough talent/skill in the team to sail both simultaneously.
The_Alchemist
Super Anarchist
As other have described, that doesn't mean anything. The sails on these rigs are way overpowered when they are foiling. And hull length has nothing to do with speed because they are not in displacement. I would not be surprise to see the smaller test boat be faster because of increased maneuverability, less aero drag, less weight, faster lift off and more experience in running dry laps. And of course, let us not forget the bulbed foils....lol
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The_Alchemist
Super Anarchist
JALhazmat
Super Anarchist
Well it wasn’t an error last time out. They had the ex Prada boat with long transoms, that they tested with
then the race boat that never sailed against each other.
then the race boat that never sailed against each other.
uflux
Super Anarchist
Sailbydate
Super Anarchist
Bring it on, boys.
Sailbydate
Super Anarchist
How so? Dan and the propeller heads will have mega loads of simulator data mapping their relative performance. It would simply be a distraction at this stage. Better to transfer the new tech to the big boat and get on with it.
Now, B2 against Te Aihe in time? That would be useful.
Is prevented by the rules... Te Aihe vs Te Kahu? fine, Te Kahu vs B2? Fine. TeAihe vs B2? banned.
