And should it be the same at the top as the bottom Mast pockets is what I'm talking about. When I knocked together the sail for 'Test Bed' I just took the max spec size from the Class 5 regs which I think was 140mm flat. I've just spotted an article explaining windsurf downhaul about the bottom of the sail being the 'engine' and the top the 'exhaust'. And that the bottom needs the battens close to the mast to get the correct shape but away from the mast at the top. Is this correct? Should I tighten the pocket to be close to the mast (not too tight to stop easy movement) then run the stitching straight along the pocket or should I follow the mast's taper Thoughts from the experts please, as currently the sail is like an on off switch, literally nothing happens till the wind picks up then it's off like a rocket

Cheers Col

The size of the luff tube is a red herring here. Some performance windsurfing sails have extended luff tubes that are way, way bigger than the size of the mast. Eg:


What you need to do is change the curve of the luff to match the curve of your mast. Normally this means you measure the curve of your mast under load, then draw a slightly different curve for your sail -- it should extend slightly forward of the mast near the base, then go slightly behind the mast near the top. At the very bottom and very top it should be exactly at your mast curve though. The difference here is like a slight S shape.

This is called "Luff shaping" and is one way to get belly into the bottom of the sail. It is heavily dependant on mast curve (which is definitely NOT constant between masts).

Another way is called "Seam shaping" which is where you cut each panel with a bit of a curve in it where you put the battens in. This is much less dependant on the mast's bend curve, so is much more mast-tolerant. This would be my preferred approach to getting a nice stable sail.

Regardless of which way you choose, the top leech of the sail should have some looseness to it, this means that it will flap around a bit and will work to make your sail a whole lot more stable in gusts. When a gust hits, this will exhaust, and pull some shape out of the bottom of the sail as well, meaning you don't tip over. When you hit a lull, the top of the sail swings back upwind a bit, making the whole sail more efficient at low wind speeds. Which is exactly what you want!


There's a lot to it, I haven't even mentioned the way that the mast bends downwind in a gust, and how to shape the sail to make this work to your advantage...

Col,
Like I said a picture would be good. What you will find is that Windsurfer sails though they will work will restrict your top speed as they are designed to be an active unit with the sailor as well as being shaped for power to enable the sailor and board to be propelled against the resistance of the water, where as we have a lower resistance on hard sand and Tarmac. What you will find is that the WS sail will perform in rough country where a Flat sail will fail. The whole thing comes down to trade offs and any design will trade power against speed or vicy verca. Given that you really should have a suit of 2 sails one a belied power sail for light winds and a
scimitar shape sail for high winds. What I found the other day was I could go like crazy with the Power Sail and Hell for Leather with the Scimitar until I over strained the Luff Edge[}:)]. Strip (Carefully) the Luff Pocket from a Large Area Windsurfer Sail and then proceed to Reshape the Luff edge of the sail using the natural curve of your mast or Paul's Formula. It is a simple enough job (Christ I got it right first time out on my Power Sail. Power sails need a little shape in them where as Speed Sails need to be Bed Sheets gaining shape from Battens.
Speed sails will struggle to go in light winds but they can get F***ing scary in 30knots[}:)] Ask t' Missus she had to was me undies[}:)][}:)]
Keep talking and asking We will get you there but not before Paul has Beaten the Crap outa you.
Ron

PS; Recent Windsurfer Sails do have very deep Luff Pockets and tend to act as a Double Surface, very good but I don't know how legal they are I got my sail maker to line it all up and sew it and then found what I had thought to be OK! was.

Yeah! Clem,
Tell me about it.. Bloody thing can really cut the Mustard and it seems the Faster the Faster and you can feel it pulling on the pace. I am going to have to take the lower half of the Luff Pocket off and reinforce the Leading Edge of the Luff as the pressure is too great and tearing it at the lower battens. Spin Outs at 70+kph is a bit thingy as you aren't too sure of just where you are going to finish up. Last weekend I thought I was going to complete a full 360.
Haven't you had a look at Anthony Beach Tas'?
Ron

Shoot! That makes my fast sail really legal then I guess..
Ron
PS; I care not the world may be saying-------------------

Fun only gets funerer directly proportionate too the increase of Wind Speed or until something goes very wrong Gizmo

Ron

The problem occurs when not fully down hauled, and looking at photos I can see that what happens is the battens move forward past the mast and form a flat front and don't pull the battens into any sort of shape due to the amount of 'slack' in the pocket. I think the easiest thing is tack the pocket straight with enough clearance to allow easy movement, then tack a taper as well. Try it tapered, unpick the taper and try it straight with the lose top. Whichever works gets re-done and saved.

No worries about this being none Class 5 standard.... I have another identical but handed sail which needs the same repairs and a mast pocket adding. This work will allow me to sort out the 'spare' more accurately.





That to me looks like the battens aren't working because the mast pocket is pants But then I'm learning everything at once with this one, as I've not sailed for 33 years and even then I was mostly ballast

Cheers Col

cols sail I think you have a mis-match with mast and sail.
essentially your luff curve is too much for your stiff mast. add that the pocket is huge!!!!!.
first alteration would be to seriously reduce the pocket size to say 110mm tops.
then sort out the sheeting
can you move the bottom set of pulleys further back on the chassis, as the sheeting is pulling the foot of the sail forward and increasing the pocket effect. those pulleys need to be straight up and down.
with the other sail I would recut the luff curve so its flatter by 25mm in the centre. you may end up doing this again if the problem is reduced ,but not fixed.
I would go for a narrower pocket as well , say 110mm, and as clemco said in the top 1m of the sail start the pocket creeping onto the sail so that the edge is about40mm over the sail at the head.
this puts that bit of extra tension on the head to prevent it flapping when tacking and removed wrinkles from the pocket at the head.
dont do anything to the mast, it is worth gold
also can you move the bottom set of pulleys further back on the chassis, as the sheeting is pulling the foot of the sail forward and increasing the pocket effect. those pulleys need to be straight up and down

Col before you go unpicking and sewing I think you need to soften up your battens in the forward region. Above is what we used on our Fed 5s when I last had one. You can measure the poundage of the battens on your kitchen scales by just pushing down on the batten on the scales until you get a maximum reading. Also still need more purchase on that mid-sheeting. Get the pulleys straight up and down. I would move the bottom pulleys back to achieve this even if you have to move the seat back a wee bit. May as well make both adjustable so you can find your best balance.

just running a seam wont do it, you would need to have the battens going forward to the back of the pockets. try the sheeting suggestions first, dont touch the batten set you have there as they look right for tarmac, clemcos shape.IMHO would be great for sand , having more oomf in the soft
if wrinkles dont go after altering sheeting then I reckon the pocket is next

Sorry Paul didn't explain. That seam is going down the front of the mast pocket to see if the smaller pocket works, if it does I'll worry about how to tidy things up (gaffer tape), if it doesn't I'll unpick it and try something else!

Ron - using the flat/plain battens and with the front edge floating everywhere the bend in the batten is always in the centre of the sail. I'm trying to fix/constrain the batten more at the luff so that when the tapered battens go in they are 'pushed/pulled' into the wing shape rather than a bow shape. My way of thinking (probably flawed) is the wing shape is the thing to aim for whatever the wind condition and just change things with the outhaul and less/more downhaul just pulling the boom across to compensate

Cheers Col

After some work into the late hours in my specially built sail loft...



The wind surf sail from "there must be something worth saving from this lot" is now looking a bit like this..



And the problematical R+J sail that has posed problems has now had a) the batten tension knocked off and b) some freshly tapered battens (from the same establishment as shown above) added. so we now have this...







All working great Bit of a scare when the front wheel went skywards on a tacking turn with the R+J. Weirdly found the balance point with the front 1m off the deck, so hoisted a monster for a few meters, before working out that leaning forward and sheeting out was a plan. Still more tweaks needed but the sail can be left for a while whilst I move onto wheels.

Cheers Col

P.S That really is sail sewing by security light, at 10pm, in the back garden!

Thanks That explain why rule number 1 "turn into wind and let go the sheet" didn't do what I expected Also realised looking at the photos that I'm sat slightly further back than normal to compensate for the new (for the umpteenth time) block position, that and a bit of slack that's crept into the steering. List of jobs to do - tilt mast, sort steering, shift blocks again, swap mast extension for about another 150-200mm, make softer headrest to encourage actually resting head on it as the cranial beating makes me sit up. Failing all that I'll fit 'wheelie bars' and really go for it[}:)]

Cheers Col