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Old 1st April 2007, 11:01 PM   #1
Duracell
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Default High speeds in winds <= 14 kts

Hi Roger / All

I&#39;ve already digged once before in ths direction but I didn&#39;t get to the bottom of it.

I&#39;ve seen you write things with more or less the following content "narrow board == faster" which does sound logical (think of cars) but then again does it?

- when planing the sail does take weight off the board (check)
- when planing the board has an air cushion under it taking board off the water (check)
- when planing the fin is slightly bent and might pop the rear of the board out of the water reducing board contact with water (semi check)

lets say a board is 10 cm narrower (e.g. 80 instead of 90)
that should equal ~ 3 fingers additional surface in driving direction ~ 0-1% of total surface in driving direction (considering sail, boom, rider, board etc.) (I could figure it out but it appears to be negliable) (having said that I guess enough people will figure it out for me )

so in <= 14kts (all that I&#39;m interessted in at the moment) what you want is
as close to 0 surface contact board/water

So the wider board (there are of course more factors than pure width) will actually go faster (maybe even much) even when both board are planing?
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Old 2nd April 2007, 09:42 PM   #2
Roger
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Default RE: High speeds in winds <= 14 kts

Hi Duracell,
I think I understand what you are trying to figure out here, but it&#39;s a bit "out of context".
To simply say that a narrower board will have less drag because it&#39;s got less hydrodynamic drag is not completely true.
There are a couple of different factors that (especially when we are talking < 14 knots windspeed) can have a huge effect on the hydrodynamic drag ofa board/hull shape
A wider board will plane up earlier, but this wasn&#39;t really "discovered" until the first Starboard W-75 and GO boards came out in around 1999.
Before that time, narrower really was faster if you were talking about sailboards! And windspeeds under 12 knots weren&#39;t considered really "sailable/planeable" unless you had a longboard or transitional board that was wider and had a centerboard for staying upwind when the board was not planing.
Enter the GO, W-75, and the next year the classic F-155 formula board.
These boards had 2 major differences from pretty much all previous boards and represented a major "design departure" from what was considered contemporary sailboard design.
They had a much different rockerline (a shorter but quite a bit wider planing "flat" near the back of the board) and a much larger fin.
Since these boards were alot wider, the footstrap offset was also alot wider, and this allowed sufficient leverage to control the much larger fins.
We&#39;ve seen these concepts "developed" quiite a bit further in the last 8 ears and the concepts have been "copied" from the original Starboards to cover formula and freeride boards from all the manufacturers.
What made this all possible was "thinking outside the box" about how to design boards that would plane up earlier.
The "paradigm shift" here was that a shorter, wider planing surface had alot less drag once it was planing, and this made these boards significantly faster in significantly less wind, if you could figure out how to pump or ooch them up onto a plane.
As far as the "air cushion" or surface effects aspects, we&#39;ve seen some designs that use "pipes&#39; through the hull to feed air under the board, and we&#39;ve seen designs like the Hypersonic which probably really do use a bit of air cushion or surface effects to get the board up out of the water sooner and earlier, which gives them the ability to reduce the drag and go faster in less wind.
We are just now seeing some additional design refinements (rockerlines, very subtle V&#39;s and concaves, etc. and new tail shapes) which further reduce the drag when planing. The Sonics vs the Isonics are are good example of the this.
Until about a year ago, if you were talking fast slalom boards, narrower was always faster, but resulted in a fairly narrow range of use.
Now, with the latest refinements, the wider Isonics are very nearly as fast (soon to be faster I&#39;d guess) as the Sonics, but they are wider, and offer a significantly improved range of use.
The added width allows them to plane up earlier and the "refinements" allow them (or soon will) to have a higher speed potential with excellent control. Footstrap offsets have increased with the Isonics, and this helps to give good "fin attitude control".
Here&#39;s a little discussion of your "points":
- when planing the sail does take weight off the board (check)
Not really.... the force from the rig is "concentrated" and applied at the mast foot. The sail does take the sailors weight off the back of the board, but the weight of the rig and sailor is then focused at a central point (the mast foot and mast foot pressure) so we can move it slightly to achieve different "pitch trim" or fore and aft Angle of Attack (AOA).

- when planing the board has an air cushion under it taking board off the water (check)
Let&#39;s break this into hull aerodynamics and "surface effects/air cushion".
Formula boards are super wide and we are now seeing some strange
(pickle fork to steal a term from the power boat racers) nose shapes, but this is more "hull aerodynamics" than it is surface effects or air cushion effects as these parts of the board are fully clear of the water.
The chisel shaped noses on the Isonics are another example of "hull aerodynamics".
The "hydrodynamics" are the new tail shapes, cutaways, air pipes and the like, and most of these design factors are about reducing hull induced drag at planing speeds, with maybe a little "surface effects tecnology" thrown in for good measure.

- when planing the fin is slightly bent and might pop the rear of the board out of the water reducing board contact with water (semi check)
Fins on big formula boards do bend, and getting them to bend correctly is a new "art form" that is getting alot of attention currently with the fin designers.
But there&#39;s abit more to this.
Smaller slalom boards with fins that don&#39;t bend much at all, still benefit from a bit of "vertical lift" but it&#39;s not "bend induced&#39; but rather "roll angle induced".
Really fast sailors don&#39;t sail hard upwind like formula sailors do, so the fin loads are significantly reduced, but they do roll their boards slightly to leeward (lee rail lower than the upwind rail) and "cant" the fin slightly so the tip of the fin is essentially "upwind" of the root of the fin.
This creates significantly more horizontal (upwind) lift and a tiny bit of
vertical (up out of the water) lift.
Super fast sailors have learned to use this "phenomenon" to big advantage. They further reduce the "wetted surface" so the upwind half of the bottom of the board isn&#39;t really in full contact with the water.

Your theory that zero (0) contact with the water is very good as a theory, and it works quite well in foil bourne speed sailing craft as well as larger applications like fast ferrys and military craft, but it takes a huge amount of power to get the craft up onto it&#39;s foils.
The "foil surfers" both windsurfers and tow in surfers are a good example here, but speed sailors, and especially marginal wind planing windsurfers don&#39;t have enough power available to make this work in < 14 knots.
Hope this helps,


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Old 3rd April 2007, 02:01 PM   #3
Duracell
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Default RE: High speeds in winds <= 14 kts

Quote:
but they do roll their boards slightly to leeward (lee rail lower than the upwind rail) and "cant" the fin slightly so the tip of the fin is essentially "upwind" of the root of the fin.
This creates significantly more horizontal (upwind) lift and a tiny bit of
vertical (up out of the water) lift.
isn&#39;t this what you call railing?
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Old 3rd April 2007, 10:30 PM   #4
Roger
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Default RE: High speeds in winds <= 14 kts

Hi Duracell,
Yes, I suppose you could call it "railing", but on a shortboard, with only a single rear fin, it&#39;s the way you go upwind.
I say this to differentiate the "on the fin" in shortboard mode, from the "on the centerboard" on a longboard, which is my definition of "railing".
Pull up a little with the front foot, push hard across the top of the back of the board with the back foot (in a horizontal direction, not down, toward the water), and the fin "cants" (top or root of the fin to leeward)
very slightly, and this causes the fin to generate much better upwind force, and as a result you get a tiny "upward" (away from the water towards the sky) force.
Those of us who have sailed "completely on the fin" for a little ways, will never forget the expereince, and you always want to do it more.
It&#39;s the "holy grail" of speedsailing I&#39;d guess.
It&#39;s also the "0" (zero) wetted surface condition you speak of.
The board, rig, and sailor are all totally supported by the lift (mostly horizontal but a slight bit vertical) from the fin.
It&#39;s really "tailwalking" with control.
Hope this helps,
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Old 7th April 2007, 04:52 PM   #5
Duracell
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Default RE: High speeds in winds <= 14 kts

Just a warning to all readers

all postings on this thread till now are made by surfers and are not scientifically backed. Just a "discussion" of personal experiences and "findings" that can be discussed and may very well not be correct.
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Old 7th April 2007, 11:22 PM   #6
Roger
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Default RE: High speeds in winds <= 14 kts

Gee, I&#39;ll have to get a photo of somene "riding the fin" in very flat water.
Perhaps that would make this "phenomenon" scientific?
This has been discussed for years, and no one (who has experienced it) has decided to come back and "discredit" the concept of it actually happening on the water.
When you are sailing along, at scary fast speed, and you look at the back of your board and all you see is a turbulent white line in the water behind the fin, with no splash fron under the rails or tail of your board what other explanation could there be?
Hope this helps,
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Old 10th April 2007, 04:23 PM   #7
Duracell
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Default RE: High speeds in winds <= 14 kts

Hi Roger,

that was not what I was referring to. In general the information is not backed. Experience is good as a starting point and may be valuable but its not gaurenteed to be correct (the whole discussion, not the riding the fin part).
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Old 3rd December 2008, 05:35 PM   #8
Caribsurf
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Default

Quote:
Originally Posted by Roger View Post
Gee, I'll have to get a photo of somene "riding the fin" in very flat water.
Hi.
Then I read that I was thinking about this video.
http://www.youtube.com/watch?v=1oyWMusaDTI

Is it any where you can buy a hydrofin like that?
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Old 3rd December 2008, 08:47 PM   #9
Roger
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Hi Caribsurf,
The "hydrofoil" fins were very popular over on Maui a few years ago, so that would be where I would look for one.
This isn't quite what was being discussed (On the Fin sailing) in this exchange, but it's probably the ultimate example of riding the fin.
I'd send some emails to the shops (and 2nd hand shops) on Maui and see if the hydrofoils are still availalble anywhere.
I knew some guys who were riding them, and they said it took a little while to chance their technique to suit riding the foil vs riding a normal fin, but once you figured it out it wasn't all that hard.
Hope this helps,
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Old 4th December 2008, 03:22 AM   #10
Philip
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Well if it helps I have seen riding the fin and heard reports from a highly credible source, of a visiting pro doing it south of Sydney Australia about 20 years ago. All on standard fins. So it does exist. Holy grail for sure. Never done it myself, but something to aspire to.
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