PDA

View Full Version : High speeds in winds <= 14 kts


Duracell
2nd April 2007, 12:01 AM
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?

Roger
2nd April 2007, 10:42 PM
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,

Duracell
3rd April 2007, 03:01 PM
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?

Roger
3rd April 2007, 11:30 PM
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,

Duracell
7th April 2007, 05:52 PM
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.

Roger
8th April 2007, 12:22 AM
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,

Duracell
10th April 2007, 05:23 PM
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).

Caribsurf
3rd December 2008, 06:35 PM
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?

Roger
3rd December 2008, 09:47 PM
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,

Philip
4th December 2008, 04:22 AM
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.

Del Carpenter
10th December 2008, 06:29 AM
The picture of Allison Shreve at the following URL may be an example of totally riding the fin: http://www.midwestspeedquest.com/page86/page86.html
The picture shows Allison Shreve demonstrating Starboard's FOD package while competing in the Midwest Speed Quest in Worthington MN in June 2008 during the USWA Nationals. Is it a picture of Allison at the beginning of a jump or is it a picture of Allison at the start of a period of riding the fin? I think the board angle shows she is definitely not trying to jump.

Roger
10th December 2008, 08:46 AM
Hi Del,
Well, Allison is definitley "on the fin" in the photo, but I think she was quite a bit overpowered and you can see the big splash right behind the board that indicates
she just "hit a bump" and the board went into "wheelie" mode for a few seconds.
That's what separates the pro's from the rest of us.
They can set things up so they can "handle" almost "wheelie mode" far more of the
time.
R

andretsin
11th December 2008, 06:11 PM
Roger,
but i think, when you roll the board, the hull is not producing lift properly, even more, being rolled he is trying to turn downwind, so we have to put the sail more to the back to compensate it, so we are putting more load to the fin (board wanting to go downwind, sail counterresting, and weight of the sailor). Also, the leeward rail is in the water, so we are increasing the wetted surface by that side.
Even all that, i can feel perfectly how my raceboard increases the speed when rolling it downwind, but i always thought it was because is the wind who is lifting the board and that is why i'm reducing the wetted surface. Is it possible that it is like this?

Ken
13th December 2008, 01:04 AM
andretsin,

The photo of Allison is simply a little chop hopping on a Formula board. For those that race or do a lot of fully powered free sailing, heading up wind frequently "requires riding the fin". It is my experience that it happen more frequently on smaller boards while pointing as high as possible while overpowered. The leeward rail rolls down, the windward rail lifts up and the nose lifts up with only the tail of the board and the fin in the water.

As the fin rolls toward the surface of the water, extra vertical lift is generated by the fin, which helps lift almost everything off the water. It is possible to maintain control in this state.

The same thing can happen on a formula board, but it is a lot more dramatic because the wide board has so much surface area for the air to get under. The board will literally fly with the nose reaching a meter or two in the air before any control can be regained. It happens very fast and usually results in a big crash. Been there a few times - it's quite exciting. It usually happens when you are on a very fast reach, and then head quickly up wind with a lot of speed.

carlosgp5
13th December 2008, 01:31 AM
Hello roger,
Could explain to me a bit better, sorry Im no native english speaker:
"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."
Ive done it before, however not by my efforts, I was lucky I guess... ehehhe

Roger
13th December 2008, 10:37 PM
Hi Andretsin,
Perhaps there is some upward force generated by the rig, but with it raked all the way back and locked down on the deck, I would think virtually all the force is sideways and forward.
If you "hook" your tip upwind, then the potential for more "uplift" from the rig is there for sure.
Most sailors strive to keep the rig as vertical (side to side here) as possible, but I've know some wave sailors who really looked "light on the water" who were very fast on slalom gear and sailed with their rig raked upwind quite a bit.
Unfortunately, we don't really have all the "science" to all of these aspects of fin/rig/hull design as no one has the $$ millions it would take to discover what the "science" really is.
Boards are still shaped by master craftsmen (then copied by CNC) same with fins and sails.
So much of the "science" of windsurfing is still "black magic" from master craftsmen and
lots of on the water testing.
Can't go to the "cookbook" and put together all the right things and expect it to work perfectly right out of the box.
As the CNC technology blends with the black magic of the master shapers, and sail designers, we are getting ever closer to knowing what works in certain situations, but
the "pure science" of it still alludes us.
Hope this helps,

Roger
13th December 2008, 10:51 PM
Hi carlosgp5,
What part of this is difficult for you to understand?
As I suggest in the previous answer, exactly why this works is pretty much a "guess" on my part,
but I'm completely sure it works for me and virtually all other sailors with the skills to sail wide boards fast.
You lift up away from the water and pull upwind away from the centerline of your board slightly with your front foot in the front footstrap (this is why many sailors "curl up" their toes when going fast upwind).
You push horizontally across the top of the fin like you are trying to push the back of the board away from you sideways across the top of the water.
Your weight is "suspended" from the harness so you are really not pushing "down" toward the water at all. Nor can you push "down" when you are that far off the rail of the board.
The idea is to roll your board slightly "lee rail down" to tip or angle the fin so the base of the fin is a little downwind of the tip of the fin so the fin is no longer perpendicular to the water but has a slight downwind angle to the leeward side of the fin.
This slight angle seems to be what develops the much better upwind angle and VMG when you "torque" your board (using your hips and legs) to sort of twist the nose of the board upwind by pulling with your front foot and pushing away with your back foot.
When sailing smaller wave and slalonm boards (< 95 liters and with soft round rails) you alter your stance to stay a bit more upright and you do put a little weight on the rear of the board, but these small boards do not go upwind real well.
The Isonics (with the blocky cutaway tail) are an interesting innovation in that they go upwind much better than Sonic slalom boards that preceded them.
If this is unclear in your language, let me know the parts that are unclear and I will rephrase them.
Hope this helps,

carlosgp5
15th December 2008, 05:19 PM
Thanks Roger, it was very clear... If I get it figured out in the water Ill let you know.
But I guess its gonna take a lot of practice... It feels very hard to maintain this leward inclination, the leward side of the board starts to get in the water... I dont know maybe because of my FW147 doesnt have all that volume of the new boards...? Like I stay feeling that Im "on the air" for like 2 seconds but then Im down again... For sure with some practice and your last explanation Ill make it better, I didnt have in my head that the fin has to be also inclinated.
Cheers

Roger
15th December 2008, 09:57 PM
Hi Carlos,
Hmmmm.... maybe we aren't communicating very well here.
Are you trying to get your FW147 to go upwind at the highest angle
and best speed (max VMG) ?
OR
Are you trying to get your board up out of the water and sail "on the
fin" as several of us have described in this thread?
I have not be able to sail "on the fin" (with no part of the bottom of the
board touching the water) in many years and for sure not on a wide board
like the F-147.
And, even if you were to get an old F2 slalom board like I had when I was
"on the fin" the time the board was off the water was probably only a few seconds
and I only really was able to accomplish this "feat" one day in one location.
And that day I was not trying to go upwind at all, only trying to sail on a beam reach
as fast as possible. The conditions were perfect..... vert flat water, slowily increasing and decreasing winds of about 20 knots, 5.5 m2 North Prisma race sail....... everything added up to very perfect conditions.

To go upwind "on the fin" on your F-147:
To "incline" your fin, you lift with your front foot, straight up off the water (not pushing forward) against the footstrap to "lift" the upwind rail slightly.
The forward "push point" on your board is the mast foot.
Your weight is totally suspended from the rig through your harness lines and the boom.
There is virtually no weight on the back of the board..... only lift from your front foot,
and push (across the top of the fin in a horizontal (parallel with the surface of the water) direction.
This allows you to "roll" your board slightly to leeward.
You do not need to tip it much.
Tip it too much and your board will head off the wind.
Your rig must be fully raked back with the foot of your sail
right down on the deck.
If you "unrake" your rig slightly, you will head off downwind for sure.
Hope this helps,

carlosgp5
15th December 2008, 11:59 PM
For sure Im pointing my maximum upwind angle mate. And for sure Im asking you all this questions with the only objecive of getting greater speed/performance.
Thanks very much for your help. All your explanation is gonna be very useful next time I get out sailing.
Cheers.

Roger
16th December 2008, 12:48 AM
Carlos,
Let us know how it works, please?
I always wonder if the advice I'm giving actually works for
the sailors who are asking.
R

andretsin
16th December 2008, 02:54 AM
Roger,
I thought more about this question. Well, first of all i wanted to tell you that when i said that i think is the wind which is lifting the board i was meaning the action of the wind directly on the board, not to the rig.
Anyway as you said, this science is very complicated (that is why i love it), and I think there are two different situations.
One of them is the one we are speaking about here. Is in low winds, and is the fin which is giving the lift when rolling quite enough the board. (Much more clear in centerboard boards!)
The other situation is the one i was reffering to. When you sail in high winds >13knots, mainly across the wind or a little bit downwind, at full speed, if you roll just a little bit the board to leeward, the board is behaving like a wing and is lifted by itself. Then you reduce wetted surface to half or even less and you are almost flying. And this i can feel it much more in raceboards because the size of the "wing" (board) is much bigger in comparison to my weight.

Roger
17th December 2008, 10:51 AM
Hi Andretsin,
As discussed, without alot of science based "testing" I'm not sure it's possible to answer
this question.
I do know that since boards got alot wider and fins alot deeper the whole dynamic seems to have changed and as you suggest, it could be some sort of "surface effect".
If you've ever sailed a Hypersonic, on really flat water with > 15 knots of windspeed, I'm reasonably sure some sort of "surface effect" is taking place.
With flatter bottomed formula and slalom boards it's not so clear, but again as you suggest, rolling the board so that you reduce the wetted surface by almost 50% has to
reduce the drag significantly.
Hope this helps,

michelb
17th December 2008, 07:41 PM
There is a Link to Carbonsugar.com that shows in the article a very nice photo about flying the fin.

http://www.carbonsugar.com/technique/how-fast-can-your-fw-kit-go/#more-27

All need to read this article it shows very clear how to do it.

I learn from there.

Michel

carlosgp5
19th December 2008, 05:40 AM
Carlos,
Let us know how it works, please?
I always wonder if the advice I'm giving actually works for
the sailors who are asking.
R

Hi Roger and everybody,
just came from sea, it was very gusty around 16k, and I had in my mind:
I tried to pull the frontstrap while pushing the backstrap sort of sideways...
I got better angles upwind, but when the gusts arrived, I had to really sit on the harness, so kinda leaving some weight down on the board... And then after the gust I would start again pulling the front and pushing the back sideways, kinda canting to leward...
Am I on the right way? at least close?
Tks

Roger
19th December 2008, 06:16 AM
Hi Carlosgp5,
Soundws like you are getting very close.
I do not understand why when a gust comes along and you "sit down" you increase the
weight on the board.
Seems to me that you would "sit down" to increase your weight on the rig when the power is coming up.
Also, are you lifting and pulling with your front foot, or only pulling?
When you get it right, your hips will kinda "lock" into a position that's quite uncomfortable
thr first few times you get it, but soon it will feel completely natural and become "how I go upwind fast at the best angle".
Is your rear heel over the edge of the board so you are actually pusing sideways (downwind) on the rail of your board?
Hope this helps,

marek
19th December 2008, 04:54 PM
http://www.sieplywa.pl/filez/news/081218_1/starboard_formula2010.jpg

carlosgp5
19th December 2008, 05:46 PM
Hi,
Well, I sit on the harness when get the gust because of the extra power, otherwise would lose trim and open the sail... isnt it right?
If Im actually pulling and lifting Im not sure, but I have that in my mind and Im trying to do so. Youve got it perfectly, I really felt my hips. Im also using the heel on the edge of the board... lets see how does it go on the weekend.. my forecasts are NE15k 1m of swell- Formula classic conditiions down here.
By the way... arent these guys on the photo going downwind?
Thanks for helping

Ken
19th December 2008, 11:26 PM
Roger,

I know you know this, but Carlos "sitting down", as you said, "increases weight on the rig", which is the only way to keep a formula board from taking off. Sheeting out on a formula board takes the downward force of the rig off the board, which can result in "flight", especially if the windward rail is lifted while "riding the fin" in a gust of wind.

I learned early that if you get overpowered on a formula board, you must keep the power on, sit in the harness to increase weight and downward force on the board. Just the opposite of what I had been used to on other boards.

Ken

Roger
20th December 2008, 09:51 PM
OK Ken and Carlos,
I'll defer to Ken's greater experience on modern formula boards and larger sails here.
I may even be "sitting down" a bit myself, but just not realizing it.
Unfortunately, I haven't raced formula or FE boards in several years, so my technique
would be a bit outdated and "rusty" for sure.
R

carlosgp5
21st December 2008, 07:19 PM
Hello roger and all
You help was very usefull.I have definetly improved my upwind angles and speed by using your tips of riding on the fin.
Cheers

Roger
22nd December 2008, 01:04 AM
Hi Carlos,
Glad we could help!
The "cramps" in your hips will go away soon!
R

Ken
23rd December 2008, 10:25 AM
Carlosgp5,

While I am not a pro, I have been told that while railing a formula board will allow you to point higher, it is faster to keep the board flat and go for a little less angle and more speed. I think everyone rails the board a little, but too much will cost you speed.

I have raced formula with many good pro sailors and I haven't seen any of them rail their board more than 20 degrees.

Much like the old race boards, they point very high, but are slow. Better to lose 20 degrees and gain three times the speed. Not that much difference on a formula board, but the principal is similar.

Ken

carlosgp5
24th December 2008, 07:03 PM
Cheers Ken,
I realize the lose of speed if railing too much... However I'm feeling there's some point, where I get the optimum angle and speed.
Well, optimum comparing to my mates, when I am gaining distance over them. For sure it changes a lot depending on the sea conditions and the wind also.
I think what happened actually is, while trying to learn the railing thing, I improved my upwind angle and speed... After this talks in these forum I'm for sure a better sailor!!!!!
I'll keep what you said in my mind, cause for sure you are right. I don't wanna point up wind as a boat and be slow as it is.
Thanks for helping

Ken
24th December 2008, 10:03 PM
Carlos,

I have raced at the US Open in Corpus Christi for 20 years in a row and have been side by side with a lot of great sailors over the years (at least at the start). What always impresses me is how the top sailors are always pointing higher than me and and with more speed. Of course, every year, they are on the water 100+ days more than me, so practice does make a difference.

I am sure that I can easily find my optimum up wind speed and angle, but I still get smoked by the pros. It's always impressive to see what they can do on their boards.

Keep up the practice, it's worth it.

Papounet
16th March 2009, 11:54 PM
Hi Duracell,
A wider board will plane up earlier, but this wasn't really "discovered" until the first Starboard W-75 and GO boards came out in around 1999.
The first wide board approved in slalom serie production was the SEATREND ALL STAR 70 IN 1998.
http://www.americanwindsurfer.com/images/99boards/seaa70avss.jpg

The idea was from Ken Winner.
In 1997, he Designed, raced and promoted the first modern wide, short boards, precursors of the current Formula boards.

In 1999 many brands, have made large boards, Starboard was just one of them.
- SEATREND ALL STAR 80
- Starboard W75
- AHD Diamond 72
- Mistral SLE AVS
- Roberts 31
- F2 Thommen course race XL
- Fanatic Falcon 72 ( first one )
- DROPS FL11