Originally Posted by marek
why Formula is best in downwind?
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 :
"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!) "