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Subsonic said..Chris 249 said..Subsonic said..
other craft that carry tighter leeches also have a different way of managing/altering sail shape. they attach strings to everything, so they can adjust on the fly. They also sheet the mainsail in and out constantly to keep the boat flying on the correct amount of heel, and deal with gusts. Believe it or not, that's actually less efficient than having a leech with twist, that allows us to not have to sheet in and out. They are actually starting to put square tops on sailboats now (actually, they started the trend quite a number of years ago) because they've come to realise that it's better to be able to let the leech twist off and let the sail breathe, rather than constrict it with a tight hooky leech.
Sheeting a sail on a boat isn't "less efficient" than twist. Any boat can twist the mainsail as much as it wants, just by easing mainsheet and vang. They don't normally twist it off because it reduces power and pointing ability.
Twist and adjusting sheeting angles are different, because boats and boards are different. Putting a floppy, twisty leach on a sail means less power for the area, or more area for the same power. Adding more area to generate the same power increases cost, form drag, and weight. Whether that is worth it depends on the individual craft.
Windsurfers are different because the drag of the board (once planing) is very low and therefore the drag of the rig is critical. In most boats, the drag of the hull is very significant so they tend to want as much power as possible. They can have a higher-drag rig because the rig drag is minor compared to the hull drag. They also don't need to worry about back-hand pressure and fast boats have more righting moment than a board.
With big boat campaigns running from $10mill to a few hundred million, they are enormously sophisticated, very well aware of the theory and what happens in boards, and they are certainly not behind boards in rig design.
The very fact that people here are interested when a top sailor modifies their production-line sail shows the difference between boards and boats. In top level open-design boats it's the norm to have a sailmaker on board or in the campaign, modifying the rigs to the individual crew's needs and desires. Even in singlehanded dinghies at the top level, no one would blink an eye if a sailor and sailmaker modified a stock sail; even in 7ft Optis the kids are sold a variety of different sails for different weights and conditions.
I probably should've said it in my post, but to be clear, I was referring to dinghies/skiffs and smaller performance yachts when I said boats sheet their sails in/out constantly. Big boats are very different machines in how they are operated and generally do less in the way of constant trimming, because they have much more righting moment on their side. but a sail that is sheeted in and out is always going to be less efficient than a sail that remains static. Every sail movement disrupts the air flow over the sail. Generally speaking, windsurfers keep their rigs very static compared to a sailing dinghy.
in any case, you've taken off on a tangent with an excerpt of what I said. I was doing a general reply to what a few others had said about tight leeches being better. They can be better, on the right kind of craft. Not necessarily on a slalom sail, where there are other factors that other craft don't face.
It's not a tangent; I was actually underlining the point you made in your last two sentences, but you over-stated the case when you said it's "better to be able to let the leech twist off and let the sail breathe, rather than constrict it with a tight hooky leech" and it's "better" to have a twisty leach - it's a matter of the sail area available, the righting moment, the conditions it's used in, the lift/drag of the entire vehicle, the angle of the course, the wind range, etc etc etc.
I'm sure you'll agree that if you put a slalom-style big twisty leach on something like a Raceboard, LT, Laser, Formula 18 cat, Tasar etc and it will almost always be slower than a leach that actually does something. For the past century or more, boat sailors have often been able to dial in as much twist as they wanted. Over much of that time, the move has been towards tighter leaches most of the time because most of the time they are faster for boats and the courses and conditions they sail in. I can dial in a slalom-style twisty leach in all the above classes and it will almost always be slower than the leach tension they use.
One underlying point is that windsurfer sailors often seem to assume that their sails are more advanced than that of boats. That's just not true - they are different because the needs are different.
2- one point was that people seemed surprised that someone modified a sail, but that goes on all the time in many classes including dinghies and skiffs- and that's ignoring the fact that most of them can also modify the shape to their own preference by using rig tension etc. The idea that everyone should sail with the sail as designed for the sailmaker for someone else, in different conditions and with a different weight, is something that only windsurfers seem to do.
3- I'm not at all sure that it's correct to say that "a sail that is sheeted in and out is always going to be less efficient than one that stays static". For example, as Julian Bethwaite (who has done a lot of work in "automatic" skiff rigs says, in some boat (ie a 470) a "manual" rig that relies on the sheet being worked is better.
An "automatic" open-leach rig comes with its own bunch of issues, like extra weight for the lift. They're fantastic in their place but as we'd probably agree, that's not everywhere as some people claim.
choco
> 9 months ago, 17 Jul 2023
