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You are here: Experts > Recreation/Outdoors > Surfing/Bodyboarding > Surfing & Windsurfing > Rotational sail
Expert: Windlover
Date: 8/28/2008
Subject: Rotational sail
Question
QUESTION: Hi !
I have just bought a a 7.6 Mistral RAF sail ( 2nd hand),on consignment at a dealer. It is probably a few years old, but for some reasons looks like it has been seldom used.
Yesterday I tried it out on my Starboard Rio board , but I noticed it rotates with difficulty. True, the wind was light, but even by " pumping "it against the wind ,it sticks . At first I thought it was because the batten were hugging the mast too much around it and I tried to give more out-haul tension, but things didn't change too much. Besides, I think I should be able to use the sail with less out-haul than that,for more power. I even tried to pumnp the sail on land by holding the rig vertical on the ground, but still it wouldn't rotate properly. Actually, it seems that the luff is sort of twisted around the mast, so that some of the batten have swung to the other side, but some stick. I also notice that the tip of the batten seems to exert a lot of pressure on the luff at the end of the sleeve, as if they were ready to tear through the fabric..
Are they perhaps too long ? I am sure that the sail would rotate with a very strong winds, but shouldn't it rotate with normal light-moderate winds as well?
Any comments or suggestions ?
Thank you
Franco
ANSWER: Hey Franco,
There are at least two specific reasons for your sail not rotating.
The first would be not enough downhaul. If you don't downhaul the sail to at least the recommended luff length, then the battens will overlap the mast. With enough downhaul the luff of the sail will tighten up and pull the battens away from the mast.
The second reason would be too soft or too stiff of a mast for the sail. With too soft of a mast and the right amount of downhaul, the battens won't pull away properly. If the mast is too stiff, you may not be able get enough downhaul to pull the battens away.
So, check the luff length printed on the sail. Verify your mast is long enough with the added length of your mast base extension (ie; recommended length is say 485 and you have a 460 mast, then your base extension should be set ~ 15cm.).
Next, check the stiffness recommended on the sail. It should say something like 25 or 28 MCS. If your mast is one number above or below the recommended MCS, then you should be okay. If it is two or more different, then your mast might not work properly.
If your length and MCS are close, then add more downhaul and see how that works. Watch the top two battens while downhauling to see if they pull away. Keep downhauling until this happens and you should be okay.
Adding outhaul will help some but try setting your outhaul at the recommended setting first. Then add a notch or two to see what it does to the battens. But, the main thing that will affect battens will be the downhaul.
As a last note, the battens are designed to be a specific length for the sail. Unless someone has changed all the battens (fairly unlikely), they should be what was designed for that sail. You should also keep the batten tension tight enough to remove any wrinkles in the batten pockets and the sail itself.
Also, RAF sails historically require a bit more downhaul than the recommeded settings to get proper rotation. Not always, but quite often this is the case with RAF sails.
Hope this helps.
Keep on sailing,
Windlover
---------- FOLLOW-UP ----------
QUESTION:
Hi, Windlover!
Thank you for your reply.
1. Regarding not enough downhaul, I think I have given the maximum I could. My carbon mast is nicely curved, but it won't curve any further, unless I apply more strength by perhaps using a tool.
2. Mast softness : I have a 75% carbon Viper mast, with an IMCS rating of 25 cc, but the sail has no MCS rating, it only says ALUMINUM or EPOXY ( fiberglass ?) mast. I was not aware of this MCS issue and I always thought that a 75% carbon mast would be as good a mast as I should have for any type of sail .
3.Regarding the length of the mast, mine is a 460 cm and even with the mast-foot extension I have, when I bought the sail, the dealer had me buy for a few dollars a 40 cm mast-top extension, because the luff of the new sail is 515 cm and the foot extension I have, even at the maxumum, would not be sufficient.
Do I have to conclude then it is either because sail and mast don't go together or because the mast-top add-on somehow interferes with the rotation of the sail ?
Also, in order to prevent my old wish-bone clamp from slipping down on the mast, I had wrapped a few layers of hockey tape around it about 10 in. lengthwise on the mast, at boom heigth. This, I noticed, creates some friction ( and I have to pull and wiggle a bit harder) when I slip the mast into the luff. Maybe this hockey tape does prevent the luff from freely rotating around the mast..?
What do you feel ?
Thank you again
Franco
Answer
Hey Franco,
I'll reply to each of your responses.
1. Some sails need more downhaul than you think is possible. Try using something to help you get more downhaul. Raise your base extension by two or three notches and downhaul what you can comfortably pull with bare hands. Then using something to wrap your downhaul rope around (like a boom extension, socket extension, your harness hook, anything to give you more leverage) and try to get a bit more downhaul.
2. The of carbon has nothing to do with the MCS rating of the mast. The amount of carbon affects the weight and strength of the mast. Stiffness of the mast is based upon the design of the wrapping of the fibers. For aluminum it is thickness and epoxy masts are based on the wrap of the fiberglass fibers and amount of epoxy used.
3. A mast-top extension is usually an okay choice to lengthen a mast to fit taller sails. The problem with them is the don't often bend as much as necessary. Also, with your mast being a 25 MCS, the extension may be too stiff which will affect the overall bend of your mast.
I don't recall the last year that Mistral was putting out the 7.6 RAF sail but it seems like quite a few years ago. I'm also fairly sure that they mated those sails with a fairly stiff aluminum mast. This doesn't mean that you have to go and buy an aluminum mast but you may have to get a stiffer mast.
Bottom line is, if your mast is too soft for what the sail was designed for, NO amount of downhaul is going to get the sail to rig properly for good sail rotation.
4. The tape should not be interfering with the sail rotation. But I would suggest you ask for a mast protector at your local shop. Remove the tape and use a mast protector. With a mast protector you can tighten the boom sufficiently enough to prevent slipping. Shops may tell you that you don't need a protector but I'm an old school sailor and have always used a protector on all my carbon masts. Some say it is excessive but I have yet to break a carbon mast using a protector. Clamp on booms can cause small cracks in the mast at the boom area and weaken the mast over time. The masts are reinforced at that area but I feel it is better to be safe than stranded.
So, try the things I've mentioned but my gut feeling is that your mast is not stiff enough for that sail. If you can figure out how to post a picture for me to look at, I may be able to give you more insight on the year of the sail. Also, if you can post a pic, try to get a pic of the specs for luff/boom.
Hope this helps.
Keep on sailing,
Windlover
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