To Windsuffering:
a) 99.9% of windsurfers I've ever come across or sailed with in the last several years use loose leeched sails.
b) The majority of them, on modern slalom boards regularly exceed 30 knots as a matter of course.
c) I've never met or heard of anybody (except yourself) who would claim to outdrag them using a tight leeched sail on a good windy blasting day.
If all of us, including the sail makers are getting it wrong we'd be grateful if you would please explain how and why. Thank you in advance.
P.S. Rightly or wrongly, my understanding is that the loose leech exhausts the air flow backwards and upwards from the main body of the sail, to allow that part to develope more thrust. If it didn,t do so the sail would 'lock up', a feeling only too well known to those of us who were ever caught out by a sudden blow in old sail days, and had to fight our way back in.
In other words, a tight leech sail is akin to shoving half a potato up the exhaust pipe of my Bonneville. It wouldn,t break any speed limits then!
Every dog has his day etc
So KA steps up to the plate and has a go.. good.
Barry Spanier discovered the RAF sail serendipitously, now a bit of science might help.
But he says "Marketing is what debases it all" in his interesting historical speedsailing stuff:
http://www.mauisails.com/barry_corner.php
Fins as thin as paper, lines a meter long, slotted sails like the America Cup carbon, all been done before..
i understand now a sail is like a combustion Engine
learn to sail up wind and get some sunshine you need it !
Modern sails generate less drag, so they have a better lift/drag ratio. This seems to benefit modern board designs that plane more efficiently. Helps with comfort and ergonomics too. The modern concept is "twist flow". The sail leech isn't dumping wind, it's feathering at the top sections, which does good things for aerodynamics. A ws sail's closest aeronautical equivalent is a propeller blade, they have major twist. The twisted sections supposedly still make useful lift, but don't overpower the rider and keeps the COE low. Used to sail a 1997 NP V8. Lots of low end range, but it was a crazy high COE catapult machine downhauled and overpowered.
I thought part of the reason for the twist off of the sail, (when under constant load) is to allow it to maintain a constant angle of attack. The wind 4 metre from the ground will be travelling faster than the wind 1 metre from ground. Thus the apparent wind vector will be different. This is certainly true for big sail boats, perhaps not so much for wave sails. I thought the other reason and most important was so that when a gust hits and the masts bends the loose leech allows the main panels lower down to keep there existing shape, so the COE stays were it is. If it was tight the bend would distort the main panels of the sail, and the COE would move abrumptly making life fun...
Just a thought.
Coming back to old v. new sails, I've been comparing them on my Kona.
To keep it short, the biggest difference I found was in the 7.0 metre size range. I sometimes use a modern Tushingham 7.0 Thunderbird on the Kona so I compared it with an early nineties well used rig that I dragged back out of the loft. (It did much cruising service on a Bic Bamba.)
It was a cheepo Pacific 7.2 twin cam sail and old epoxy mast which, despite Pacific sails poor reputation had a surprisingly effective range of performance at the time.
In planing conditions, the modern 7.0, set with proper downhaul, was light fast and comfy, but lacked the long board locked down feeling. The Pacific was just as fast but did have that weightier 'guided missile' type feeling. (I like that.) Neither had any real problems.
In sub planing conditions however, the Pacific was the hands down winner! Better upwind with dagger down, more glide (great feeling), and fully up to the job.
I was pleased enough to rig it on a better C 45 mast and it felt even better. In short, for future cruising in average winds with distance to cover, it's going back into service.Thanks C 249 for reminding me of what I'd forgotten!
