OK firstly, use a NP mast.... it may set acceptably on others but you have to know what and how etc... so let's just say get a NP mast.

Secondly, if it is 428 luff it will set fine on a NP430 if it has an adjustable head so you can drop the sail down lower on the mast.

Basically it will feel a tiny bit more powerful on the 430..... so it may be better for mega lightweight ppl on the 400 and better for really heavy ppl on the 430, but doesn't matetr much as wind changes up n down

All you need is an adjustable head strap. Take off the plastic head cap, thread it on the adjustable strap, thread the strap through the top strap of the sail and bob's your uncle. You just need to poke the mast through to one side of the strap at the top. i wouldn't go chopping a mast up that's for sure.

TristanF said...

Mark _australia said...

OK firstly, use a NP mast.... it may set acceptably on others but you have to know what and how etc... so let's just say get a NP mast.

I've heard this, "use the same make as the sail" thing before. How important is this really? I mean, you've got a standard length, diameter and curve that all build to (ie 430, SDM or RDM, IMCS 21) so apart from production variability, what's the problem with using another brand?

Also, I always thought (not sure why) that you should use the recommended mast length because the curve would be different for a different size (eg IMCS 21 vs 23) and this would make a big difference to the set of the sail. Have I got this wrong?

I'm no expert but I'll try and answer. IMCS relates to stiffness, not curve. The curve profile can be different on two masts with the same IMCS. One can have a soft top, another can have a stiff top (relatively speaking). Traditionally Gaastra and Neil Pryde were at opposite ends of this spectrum. I learnt this when I bought a NP mast for my Gaastra Manic - the result was that the top had excessive twist and the bottom didn't rotate well. Many masts fall in the middle of the two extremes and are referred to as constant curve. My Manic rigs well on a Severne mast which is considered a constant curve.

Also note that some sails are far more sensitive to mast curve variation - usually race sails. These sails use a huge amount of tension and this exaggerates any variation in curve profile.

When I first got back into windsurfing I tried cutting a mast because the shop didn't have the right size second hand mast - I regretted it almost the minute I finished, I recommend this as the very last resort.

^^^ agreed.
In addition to that, to answer your other question Tristan, you don't always have to use the right mast length.
IMCS is stiffness relative to length, so a 460 / 25 is the same as a 430 / 21 if they are the same brand and model.

If a sail has a luff of 428 and designed to work on a 400 (with 28cm extn), you can rig it in a 430, with about 5cm of head strap. As a result, it is dropped down lower on the mast... and is in a slightly stiffer section. Thus the leech will not twist quite as much or it will require a bit more downhaul to effect the same amount of twist. The mast will also not deflect quite a smuch in gusts.
The effect is to make it a bit more stiff, a bit more powerful and so that is why some ppl say it would be better for a heavy sailor.

Look at old pics from the 80's and 90's when a lot of ppl used a 4.0 in storms and there was a foot of mast poking out the top. No twist whatsoever, but the pics of them using their 5.5 it always looks like it is set pretty well.
I did it also, I dunno how we ever did it

Check out this link to see what happens to IMCS and bend curve when you take a NP mast and compare it to the next smallest size NP mast with 30cm extension (i.e. both effectively being the same length):

www.peterman.dk/windsurf-NP-X6-mast-study-extensions-780gb.htm
(maybe a bit technical for someone new to windsurfing though)

Relevant comments from site author:
The X6 400 is very Flex Top, and the extended 400 cm mast consequently ends up with a lot more bend curve than the 430 cm mast (more than 4 points in difference). As a side-note this very big difference might be a little surprising, in light of some of the arguing over the years, about whether it's best to use a X6 430 mast with your NP wave-sail around the 5.4 size - or it's best to use the sails with an X6 400 mast extended. Bend curve wise these mast options are so departed, that their performances probably shouldn't be similar ...

I think I'd rather go for the X6 430 rather than extended X6 400 judging by the results (never really liked using extensions longer than 25cm anyway!)