Suppose There are two masts of the same size with the same mast curve % but a different overall stiffness for instance 28 Vs. 30.5
Couldn't one just apply more downhaul to the stiffer mast to get it to the same bend to fit the sail intended for the softer mast?

You often see a sail that can be rigged on two sizes of mast - each mast has a different stiffness but the same bend curve. The sail will set roughly the same on both masts but will behave differently due to the stiffness. The softer mast will potentially handle gusts better, bending more easily and bending more. The stiffer mast will return (reflex) back to its original position faster, potentially providing a more efficient sail. Some heavier sailors might prefer a stiffer mast, some speed sailors might prefer a softer mast.

Bend curve is a measure of "where" the stiffness is in the mast - for the same IMCS (stiffness measured in the middle of the mast) one mast model/brand can have a relatively stiffer top than another. Hopefully all masts from a single brand have the same curve.

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Suppose There are two masts of the same size with the same mast curve % but a different overall stiffness for instance 28 Vs. 30.5
Couldn't one just apply more downhaul to the stiffer mast to get it to the same bend to fit the sail intended for the softer mast?

...so you should only need to adjust you extension appropriately.

See www.peterman.dk/mast-imcs-formulas.htm

As a total newbie to this sport I thought I had no clew,then was told there is one on my sail!! pfffttt.I was lucky enought to be given an awesome 5.2 ezzy wave sail 07. I went and bought a SDM 430 mast for it,but have found that it may be to stiff for this sail as the battens get caught behind the mast and when the sail sets it clunks like Im sticking it into gear with out using the clutch Ha.
So is it mast with wrong curve(to stiff)?do I need to buy the recommended mast and use this one as a marlin rod?

With the same bend curve you wouldn't have to apply more downhaul. The sail will fit with the same amount of downhaul, but it won't react in quite the same way. The sail would have more foil tension, which may make it feel more direct but also the stiffer mast would affect how the sail exhausts. When the mast bends sideways at the head the leach tightens and effectively stops it from twisting further. A stiffer mast would require more force to bend sideways and therefore the tightening of the leach would occur later, perhaps making the head twist further. I'm just guessing here, 'cos I haven't tried it. Is it even possible to get two masts with the same bend characteristics but different stiffnesses? The only way I can think of testing this is if you compared (fx) a 490 against a 460 with a long base or extender, but that wouldn't be a true test because the bend curve would change.
Make sense?

Edit: must have been asleep there.. 2 posts down before I got mine in.

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mybrosweeper said...


So is it mast with wrong curve(to stiff)?do I need to buy the recommended mast and use this one as a marlin rod?

Bend curves are characterised as Stiff Top, Constant Curve and Flex Top, with variations in between (ie, stiff top-constant curve). The terms are pretty self-explanitory. If the battens on your Ezzy are sticking at the bottom it either means your mast is too Flex Top or you simply haven't downhauled it enough. Or it may be that Ezzys are not designed around a SDM and the extra mast width at the base is causing the battens to stick. North Dukes used to do this, even though they supposedly were designed to work with SDMs.
Difficult to give advice without seeing it, but I would say that having the right mast will make the world of difference.

^^^ yep, what he said

I learnt this lesson trying to rig a Gaastra Manic on a Neil Pryde mast. The Manic was designed for a Stiff Top mast and Neil Prydes are Flex Top. The result was as you describe mybrosweeper - floppy top of the sail, but lower battens pushing past the mast and not rotating. I had to change the mast.

Now if someone can answer why a sail designer would choose to design around a particular mast curve I would love to know! What are the design trade offs? If the trade offs are minimal - which I think the are given the closeness of pro results - it would appear the sport would be much better off standardising the bend curve. Locking a consumer into one brand (or a least putting a significant barrier in place) is not a big picture strategy. Grow the sport, the overall pie gets bigger, all brands get a bigger slice. [/rant]

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mybrosweeper said...

As a total newbie to this sport I thought I had no clew,then was told there is one on my sail!! pfffttt.I was lucky enought to be given an awesome 5.2 ezzy wave sail 07. I went and bought a SDM 430 mast for it,but have found that it may be to stiff for this sail as the battens get caught behind the mast and when the sail sets it clunks like Im sticking it into gear with out using the clutch Ha.
So is it mast with wrong curve(to stiff)?do I need to buy the recommended mast and use this one as a marlin rod?

Go to the Ezzy web site and tell them what sail and mast you have and one of them will get back to you and tell you if it should work. http://www.ezzy.com/rig-support/ezzy-faqs/

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Is it even possible to get two masts with the same bend characteristics but different stiffnesses?

Yes, in this case I'm comparing a Hotsails 490 vs Ezzy 490
Hot Sails IMCS 28 Bottom 65% top 78% = 13 curve
Ezzy IMCS 30.2 Bottom 63% top 76% = 13 curve

So if the Ezzy is downhauled until it reaches the same profile as the Hot Sails I should have the same amount of leech tension if the two rigs were laid down side by side rigged with the same sail. The only difference would be the amount of sideways twist when sailing and hit by a gust, Is this correct?

With those stats you will not notice any difference. I reckon 90% of sailors would not notice.

Still seeing as though they are both Hawaiian brands there would have been plenty of mix n match going on over there so ask Ezzy as suggested above, or does Hot Sails have a forum maybe?
Dave Ezzy or Jeff Henderson would let you know straight up

Thanks for your input people. I have just messaged Ezzy

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Mark _australia said...

With those stats you will not notice any difference. I reckon 90% of sailors would not notice.

Still seeing as though they are both Hawaiian brands there would have been plenty of mix n match going on over there so ask Ezzy as suggested above, or does Hot Sails have a forum maybe?
Dave Ezzy or Jeff Henderson would let you know straight up

They say it's ok but not optimal, I can understand they want customers on their own complete kits so it's hard to get a straight answer.
Ezzy masts are made in USA by NoLimitz, HotSails 92% are made in NZ by Kilwell.
Moreover I'm trying to understand the physics of all this for my own understanding. My mind needs not just yes or no but how and why.

The mast curve helps determine sail shape, that's why it's important to get a mast close to the correct bend curve.
Mast stiffness affects the amount of skin tension in the sail and the sideways flex of the top of the sail.

If the mast is too stiff, it can feel "wooden" and non responsive, too soft and it losses power.
Generally heavy sailors prefer stiffer masts, and light sailors softer masts.

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mybrosweeper said...

As a total newbie to this sport I thought I had no clew,then was told there is one on my sail!! pfffttt.I was lucky enought to be given an awesome 5.2 ezzy wave sail 07. I went and bought a SDM 430 mast for it,but have found that it may be to stiff for this sail as the battens get caught behind the mast and when the sail sets it clunks like Im sticking it into gear with out using the clutch Ha.
So is it mast with wrong curve(to stiff)?do I need to buy the recommended mast and use this one as a marlin rod?

All (most sails) will do this to a degree. The battens sit behind the mast to a degree and flip when you flip the sail. If there is no (or little wind) you will have to pump the sail to get the bottom battens to flip (give it a hard yank towards you). When you gibe you tend to do this without thinking about it as part of the gibe.

That sail shouldn't do it much, people here will say not at all but they are comparing it to a cammed race sail, not a battenless dingy sail. The lower battens will have shape with no wind in the sail and will push tight to the mast. The top battens should be less so, but they shouldn't be a noticable distance off the mast.

How is the mast cut out ? can you get the boom on when you have the right downhaul on ? or do you have to put the boom on before you downhaul fully because the cut out is too tight to the mast ?

I'll come see ya one day and rig one on my sails for comparisson and the Ezzy on my powerex - can even try 430 base and 400 top in the powerex. The powerex won't be 101% perfect, but good enough for everybody on the planet, except perhaps Dave Ezzy and Professor Puff of Aeronautics, to not notice a difference.

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mybrosweeper said...

As a total newbie to this sport I thought I had no clew,then was told there is one on my sail!! pfffttt.I was lucky enought to be given an awesome 5.2 ezzy wave sail 07. I went and bought a SDM 430 mast for it,but have found that it may be to stiff for this sail as the battens get caught behind the mast and when the sail sets it clunks like Im sticking it into gear with out using the clutch Ha.
So is it mast with wrong curve(to stiff)?do I need to buy the recommended mast and use this one as a marlin rod?

More downhaul?

If your mast isn't ideal, rigging your sail is about getting the right compromise for you. If your bottom batten isn't rotating you can do two things to resolve it, either put more downhaul on or put more outhaul on to pull the batten away from the mast.

More downhaul will loosen the leach at the head, making the sail lighter in the hands and bringing the pull position forward. Too much will make the sail feel gutless, twitchy and difficult to handle.

More outhaul will flatten the lower battens more, also bring the pull position forward but most importantly taking away the power at the bottom of the sail. Too much and the sail will feel very unstable and gutless and with the power coming from higher up it may make it feel less manoeuvrable.

So, I'd start by putting on a bit more downhaul until the bottom batten unsticks. The bottom batten doesn't need to sit off the mast, just enough so you can rotate it with your thumb. If the leach loosens more than half way across the head then take some off and apply a little more outhaul instead.
When you think you've got it right, go sail it.