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Old 5th December 2007, 09:50 AM   #31
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Jean Marc, sure the high efficiency of high aspect planing surfaces is a reason to go wide - but then again, at lower speeds form drag increases by around the square of width. And before anything can start planing it has to move, and a short board has high drag at low speeds.

In many inland or confined waters the longboard is still faster a lot of the time for these reasons - the skinny shape is better at non-planing speeds, the longer hull is more efficient just before rising onto the plane, and unlike a FW they don't need the power from a big rig to push them onto the plane and into the region where FW goes incredibly well.

Unlike Floyd, I wouldn't say a dinghy has a bad planing shape - I would say that a good planing dinghy has an extremely efficienty planing surface given the other strengths and weaknesses of a dinghy design. There have been dinghies shaped a lot like Formula boards around for years (lightweight scow Moths, which had full battens, fathead sails, wide pocket luffs and weighed about 30kg back in the '60s) but if you make them short and wide enough to go like a Formula board in strong winds, then they also go like a Formula board in light winds - and that's not good in most of the waters dinghies sail. Dinghy shapes just favour more all-round speed.
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Old 5th December 2007, 04:55 PM   #32
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In non-planing conditions below 6 knots of wind, the Serenity is for sure faster than a shlogging Apollo or Formula or even a dinghy (e.g., a 420 or 470), no question. Each board is designed for an optimal wind range and course range use. The crosspoint between shlogging and planing is at 6 knots, so it's a pretty much interesting strategy when it comes to choose the right board for the right conditions.

Cheers !

JM
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Old 6th December 2007, 11:20 PM   #33
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I wasnt making point that dinghies have poor planing abilities.Some do ; some dont.Reckon modern skiffs probably plane as early as anything ever built; Enterprise on other hand certainly doesnt.(Neither does 420 or 470 !!!)
Point I was trying to make was that hull shape has much less effect down wind than pure power of sail.Obviously a good planing surface is a prerequisite but put an 11 metre rig on an old Mega Cat/ F2 Lightning and it too would be pretty damned quick down wind.

Jean Marc
Looked up your link and there was no mention of high aspect planing surfaces being more efficient than low ones.(Its a point we all take for granted but I cant find any factual figures to prove it)Lift is propoprtional to CSA (I think) on planing surfaces. We make the anology to wings/rigs/fins but not sure we can.(On a wing leading edge gives disproprtionate amount of lift; more leading edge more lift;less area less drag. A foil has its Centre of Lift well forward??(Its being pulled from above aswell(Sort of)) A board has its centre of lift in geometric centre of planing surface.(If it didnt we would be in a mess)
Having said all that I still suspect high aspect planing surfaces are more efficient but the difference pales into insignificance if you are carrying 40/50% more rig.
PS True hydro foils are fully submerged and we can then make anology to fins/wings/rigs.We cant make the leap with the board on surface.(Pardon the pun)
Bottom of a board is not a foil.Its a planing surface.(And I think the most efficient is absolutely flat) Not sure its aspect ratio has any effect other than in control.(Ie we use a wide one so we can carry a massive fin !!!)
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Old 7th December 2007, 08:47 AM   #34
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On an 11.0 as deep down wind as you can go.
???????? I'll take the FW
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Old 7th December 2007, 03:45 PM   #35
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Think Floyd said an old Mega Cat or Lighning .Thats neither of those !
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Old 7th December 2007, 07:12 PM   #36
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The Lechner is a Div 2 and almost impossible to sail (by my reckoning).Its even harder to sail the damned thing downwind.Basically its a small dinghy with a displacement hull capable of planing insome (???) conditions ! Cant compare it with anything really !
Not really got anything to do with argument as the Div 2 boards are at their best (relative term) in non -planing conditions.(It would trounce most any other board upwind in 8 knots)

Anyway
Done a little more research re-High Aspect planing surfaces.
Is it just a myth High Aspect planing surfaces are more efficient ??? Not sure yet ?
Read a hydrodynamic article (Cambridege; Surface Skimmer planing Hydodynamics) which if in my wisdom I understand says that the lift produced is a function of the diffeerence in leading and trailing edge depth; water density;area and velocity.Its a momentum transfer.(ie the lift is a function of the amount/mass of water disturbed) This is not how a foil works ! Would a water skier really get more lift if he used ski sideways ??? I`m not convinced.
Suspect its another myth to propogate sales !!! High Aspect planing surface sounds so impressive !!!
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Old 8th December 2007, 12:31 AM   #37
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I'm astounded at how little i knew about the physics of hydrodynamics in relation to our great sport windsurfing. I've been reading all the contributions more than once, and still feel very confused. Should a degree in such things be necessary to choose the right board? What does Floyd sugest with his last comment?

"Suspect its another myth to propogate sales !!! High Aspect planing surface sounds so impressive !!!"

Who's sales?
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Old 8th December 2007, 02:05 AM   #38
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Suppose he meant board sales !
There is a lot of BS?
High Aspect Planing Surfaces obviously exist but are they more efficient than other ???
Dont thionk WS is first to come accross them ???
Power boats; skiing dinghies etc?
I`ve not been involved with sport long but I have noticed there are an awful lot of claims made about shapes in boards and sails.
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Old 8th December 2007, 06:22 AM   #39
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Quote:
http://www.macquarie.com.au/speedsailing/design.htmPlatform design
The evolution of Yellow Pages Endeavour platform began by applying a much greater righting moment to the sailboards rig. This was achieved by placing the crewmen more than 10 metres to windward of the rig. This provided greatly increased righting moment when compared with the sailboard, thereby the ability to hold up much higher sail forces that would drive the craft faster.

To complement this massive righting moment, good fore and aft stability was required. In order to reduce windage and water drag, this fore/ aft stability was achieved by setting two planing surfaces approximately 11 metres apart. The angle of the crew beam was set to oppose the line of force of the overturning moment of the sail and balance the relative amounts of downforce on the fore and aft hulls.

The hull sizes were set to ensure adequate buoyancy during the displacement phase of the craft and the width of the planing surface (1.2m) designed to ensure the most efficient planing aspect ratio possible.

Macquarie Innovation was designed around the same principles as YPE. However, to go faster meant a wider and stronger platform was required to handle the increase in performance from the new wing.
if the Apollo can plane sooner and stay on a plane longer in the low limits, it can be a winner. Stay'n/Get'n to the plane, even if it's only a half a knot sooner, is a big advantage in a race @ the wind min.

When there's some wind and one board is faster than the other. The faster board will slowly pull ahead.

When the wind drops and that faster board can no longer stay on a plane but, you have the Apollo that stays on a plane through the hole, and you pass the faster board much faster than he pulled away from you. Then you wait at the finish line and have a drink while the faster board sloghs accross the finish line so we can start the next race.with a 70cm fin
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Old 8th December 2007, 06:01 PM   #40
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But if wider is more efficient surely it would have been even wider;bearing in mind its carrying a ton and half ; and was still only 1.2 m wide.(Not much wider than a Formula ???) To my mind thats pretty narrow !!!
And if High Aspect Planing surfaces are more efficient how come speed boards are narrow (relatively)
PS
True meaning of Aspect ratio is Wing span Squared /divided by area.
And High Aspect wings have much higher parasitic drag. (From longer leading edge)

From a geometric point of view best planing area would be a square; ie max area for minimum leading edge ??? (I think anyway!)
(Planing pads on speed boats (back of V) are square !!!
Bet it was square on YPE ??? (1.2 m by 1.2 m ????)
Anybody know ???
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