I'm looking at buying a small sail for occasional use, with an adjustable head strap so I can use my regular masts...

How much mast is it safe to have sticking out the top of a wave sail, generally speaking?

Very little really. You need to use the recommended mast length otherwise the sail won't work as efficently as it should. If you've got 'too much sticking out the top' you could have too much flex in the mast and the sail won't rig properly. You'll still be able to sail it though. It all depends on how important it is to have your rig at 100%. For some people as long as they can plane they don't care.

Longer mast = stiffer (higher IMCS rating). So you need more downhaul. I wouldn't go more than 30 cm...

Thanks Zed, I comprehend now

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Originally posted by Zed
If you've got 'too much sticking out the top' you could have too much flex in the mast and the sail won't rig properly.

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Easily resolved by making a loop around the head of the sail, and the mast.

It would be unusual to have a sail head sitting far enough away from the mast for curve in the "out the top" part of the mast to have any effect at all though.. Most (all?) modern sleeves go all the way to the top of the sail. Which brings you back to Neb's point..

I have seen some really old wave sails that had 'floating' heads where the sleeve finished well below the top of the sail itself, but why you'd seriously want to use one of those is beyond me!

Yes I know it's ok. I just wondered if there was a point beyond which you shouldn't go, like someone said 30cm. I wasn't planning to put a 4.0 on my 520 mast! I would guess it also depends on carbon content and diameter (whether it's a skinny or not), as to how the mast will perform.

So, to be more specific, I'll have a 460 "wave" (ie low carbon content sdm) mast for a sail with a 440 luff (my SUPERFREAK, which will arrive tomorrow!! Yeah Baby!)...this is ok. But I also want to get around a 4.7, 4.8, which may have a luff of around 420. I COULD get away with a 460 mast on a 420cm luff sail, right? But I wouldn't want to, right? So I should get a 440, right? Yep, I thought so...