Old 30th November 2007, 12:30 AM   #21
Ken
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To answer Marek's question as best I can -

Formula boards are wide and short. When running fast downwind over the backs of 1 meter waves (shallow bay racing), the boards stay pretty stable (width) and they don't stick into the backs of the next wave (short), they just slide over and occasionally with enough speed, you get some air, landing on the top of the next wave.

The first generation Formula boards were a bit longer (F175) and did stick into the next wave. As they shorten them up, they found that they stuck less.

It's hard to imagine traveling at 25 to 28 knots of board speed over the backs of 1 meter chop, but it can be done with enough practice. Scary as Hell, but doable.

Last edited by Ken; 30th November 2007 at 12:32 AM.
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Old 30th November 2007, 01:56 AM   #22
pfaffi
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First its a question of speed. If you have enough speed in high winds on a small board (and big balls) you can go very deep. But if you reach a certain downwind angle you start slowering your board speed and than you are strating to be in danger. If you are good in vector addition you will find that point. Formulas can go deeper because you use a very big sail and there is only one downwind angle where the sail force fits to your weight. If you would go higher the sail force is to much or more down the sail force is to less. Its interessting if you watch your gps track points you will find that you go moreless the same way down as your upwind track is. Very typical for Formula. Hope there are some answers in for Marek.
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Old 30th November 2007, 02:36 AM   #23
marek
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Great, thanks.
I didn't get everything 100% right now, but I'll be thinking about it.

-marek
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Old 30th November 2007, 02:58 AM   #24
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Its not (just) to do with the boards.
When sailing really deep (almost on a run) our normal sized "freeride" rigs just dont give sufficient power to maintain board on plane.Once you drop off plane you are lost.
Put an 11 metre race sail on say a Carve 145 and it will sail loads deeper (on plane)
Its sort of like spinnaker on dinghies.They can sail (plane) loads deeper when using chute of some sort.
Stick a normal 6 metre freeride sail on a Formula and I dont think it would sail any deeper than a big freeride design.
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Old 30th November 2007, 06:46 AM   #25
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Poster number 24 makes a very insightful point. The type of board and rig that you've got says everything about your focus, to include real world limitations. Some tolerance exists for the better sailor, but everything has it's limits.
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Old 30th November 2007, 08:44 PM   #26
Ken
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My first true learning experience with deep downwind slalom board sailing was about 20 years ago. Corpus Christi used to have their annual "Screaming Reach" which was a 10 mile downwind run the length of the bay.

As I recall, I was on a 120l slalom board and rigged a 6m sail and did a little reaching out and back to see if I had the right size. Good power and comfortable. However, once I started the race and tried to run as deep as possible, it quickly became clear that I was at least 1m to 1.5m too small on my sail choice. I quickly fell behind the more experienced local "bay racers" with much larger sails.

Live and learn!
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Old 4th December 2007, 03:12 PM   #27
Jean-Marc
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Quote:
Originally Posted by marek View Post
why Formula is best in downwind?
Marek,

It's all about wind vector addition : true wind and apparent wind are the same but they don't add up once sailing dead downwind. To keep the hull planing, you need a large sail area and a wide and short planing surface (high aspect ratio). In light wind, you'll not make it with a long and skinny planing surface (low aspect ratio), especially if you're a heavy weight rider (most probably in displacement mode only).

Check out the Jim Drake's Chronicle about the physics of windsurfing :

http://2007.star-board.com/drake_chronicles.php

"How wide is too wide?

Let's get to the guts: How wide is too wide? Is there a point of diminishing returns in regard to board width?

Well of course there is and the point of diminishing returns depends on what you're concerned about -- speed on a reach, broad reach and/or run, low end early planing, tactical maneuver, ease of jibing, pumping and the like. And there are other factors like the capacity of the x-ray machine at BKK or other international airports, the width inside your SUV, entry level instruction, etc. So it's a simple question but without a simple answer. Sorry.

Light-air boards appear to be getting shorter and wider. Why? And why haven't free-ride and wave boards followed this trend to the same extent?
Light-air boards are indeed getting shorter and wider because this allows them to plane earlier. This is because, among other things, the patch of water required for planing has a more efficient shape (lower drag for the lift provided) if it is wider and shorter. Fluid dynamicists refer to such shapes as having a higher "aspect ratio", the ratio of lateral span to average longitudinal wetted length. Free-ride and wave boards are -- in my opinion -- likely to follow this trend but perhaps less aggressively since both (think they) have the luxury of choosing better wind. The future may demonstrate the virtues of light wind attributes to them as well.

Have trends to short, wide shapes eliminated the light-air, sub-planing cruising element of windsurfing that originally helped make the sport so popular?
For the moment, yes. But only for the moment, that is, until short wide designs are developed that have at least adequate and perhaps very pleasing performance even when sub-planing. Originally, as you say, the sport grew from the pure pleasure of holding the wind in your hands and freeing yourself from the land. That changed when planing was introduced and the sport became more dramatic and athletic -- changes that were inevitable and from my point of view all to the good. These changes, however, displaced the zen of quiet windsurfing, a valuable quality that is appreciated by many but difficult to enjoy with single fin Formula style boards. All that may change if radical ideas, such as adding a retractable fore fin and a lateral mast track, bear fruit.

If the 100 cm width limit weren't in place for Formula boards, would you expect them to grow even wider? What would be the result?
I would indeed expect them to grow wider. Tests at Starbord have shown as much, at least through 120 cm. Imagine a 4' x 7' board! I can. And the benefits (except to obsolete all current Formula designs) would be as one expects -- earlier planing, quicker and maybe shorter "pump and go", quicker to the windward mark and maybe a little higher pointing.

Do you predict boards to continue to get wider in the future? What design innovations do you predict will complement this trend?
It's hard for me to predict that they won't get wider, just based on history and physics. But it's also hard for me to predict where it will all end up, namely, what will be the countervailing force. Today it's the bureaucracy -- Formula -- but that can and should change. It might be the "x-ray machine at BKK" but the x-ray machine problem and the air travel problem can be avoided as it is with all other forms of sailing. It might be the SUV but there's always the roof rack. My guess is that the limit will come by way of the requirement for longitudinal trim, that is, finding a place where the sailor can stand and counter the unbalanced couple between the sail's drive and the board's drag and still hold the board at its optimum angle of attack. (That's a bit obtuse, I know, but I'd put everyone to sleep with any better explanation.) One innovation to complement this trend could be to employ cavitating and/or ventilated planing hydrofoils to help longitudinal trim. (Well, you asked!) "

Cheers !

JM

Last edited by Jean-Marc; 4th December 2007 at 03:20 PM.
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Old 4th December 2007, 09:33 PM   #28
Floyd
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Hi
Jean Marc
Enjoyed your explanation and agreed/understood most of it but cant quite see why aspect ratio of planing surface affects ability of a board (or any sailing craft) to sail deep down wind.A big powerfull sail is a must and in sufficient wind /control it is possible for craft to approach planing on a dead run. A kiter (perhaps when overpowered) can plane in direction of wind.High performance dinghies can for short periods maintain planing on a run.
Neither of these craft have either high aspect planing surfaces or particularly efficient ones; but in both cases control of the power is still possible whilst on a run.Not sure thats the case with boards.Launch a kite and in sufficient wind almost any board would plane on a run !
Down wind the board is a platform to utilise available power; upwind it is a sailing craft ! ???
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Old 5th December 2007, 02:02 AM   #29
Jean-Marc
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Floyd,

On a dead downwind course, the board speed is equal to that of the true wind minus that of the apparent wind. A planing hull is faster than a gliding hull.

From what I understood from Jim's chronicle :

The Apollo's 80 cm wide and last 30 cm short planing area means lower hydrodynamic drag for the lift provided. This means that the hull can start and sustain the planing which is faster in light 6-7 knots winds. The heavier the rider, the wider the tail must become to sustain the planing and speed.

The Serenity's 40 cm narrow and > 200 cm long "planing" area means higher hydrodynamic drag for the lift provided. This means that the hull cannot start nor sustain the planing, which is slow.

Try both with say an 11.0 sail, you'll be amazed at the board speed difference on a dead downwind course in 6/7 knots of true wind speed.

This is the same principle behind hydrofoil boats : the planing surface of an U-bent hydrofoil is very wide but very short to maximize the lift to drag ratio.

http://en.wikipedia.org/wiki/Hydrofoil

Cheers !

JM

Last edited by Jean-Marc; 5th December 2007 at 02:15 AM.
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Old 5th December 2007, 03:46 AM   #30
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Just an update on the Apollo I,m 75k and use mine with a AC-2 9.7m sail in light winds and the 75cm fin. As the wind picks up I drop the fin down when its really blowing I end up with my 7.8 Lightening and a 60cm fin. I have really enjoyed the board it just takes off very easily and has extended my time on the water considerably. During the summer light winds I was often the only person on the water and had some very enjoyable sessions, but I don't race.
It will be interesting to see how the new 162 performs as it seems to be a cross between the 161 and the Apollo.
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