When i'm looking at sail specs i see a code IMCS 19, 21 etc. can anyone tell me what it means?
IMCS stands for Index Mast Check System.
By Googling say Windsurfer, Masts, IMCS you will quickly find mountains of technical reading matter. Enough to keep you
going for days !
Generally it's about the way a mast curves under a central load test when it's ends are supported. Some bend more than
others, some less. Some bend more in the top third, some less etc, etc.
You then relate that IMCS# back to a certain sail type or manufacturer.
As I said you'll find plenty of further explanations once the Google search is done.
Basic version:
IMCS is Stiffness relative to length.
Reason: before IMCS, masts were listed by stiffness. But if you made the same mast longer it would rate as floppier when in fact it was not...... it was the same but there was just more of it.
So now we have IMCS so a 400/19 is same as a 430/21.
That's all you need to know.
However bend curve... wellll geez ............
Select to expand quoteMark _australia said..
Basic version:
IMCS is Stiffness relative to length.
Reason: before IMCS, masts were listed by stiffness. But if you made the same mast longer it would rate as floppier when in fact it was not...... it was the same but there was just more of it.
So now we have IMCS so a 400/19 is same as a 430/21.
That's all you need to know.
However bend curve... wellll geez ............
So Mark, matching a 400/19 to a sail is not as simple as matching a 400/19 to a sail. it comes down to bend curve also.
I'm planning on a new (used) quiver for next season and researching sails and range. looking for a couple of medium to high wind plus something like a Hellcat 5.7
i've had no luck this season picking the right sail for conditions. kinda depressing really. I'm also guessing that my kit is too mismatched i.e mast/sail combo. when i have some money i'll probably have an idea by next season.
mast/sail compatibility 
topic on its own
picking the right sail for the conditions
my buddy says "bring all your stuff to the beach"
then change out sails n boards as required
he spends more time pickin n choosin than i
i am usually on the water within 20 minutes
for him double that
and he will change out more than i
i think i will be satisfied more easily than he
even if i am not planing, i can have FUN
if i am OP/overpowered - no issue - tighten it up and learn survivor mode
TOW = FUN 
Select to expand quotevpar said..Mark _australia said..
Basic version:
IMCS is Stiffness relative to length.
Reason: before IMCS, masts were listed by stiffness. But if you made the same mast longer it would rate as floppier when in fact it was not...... it was the same but there was just more of it.
So now we have IMCS so a 400/19 is same as a 430/21.
That's all you need to know.
However bend curve... wellll geez ............
So Mark, matching a 400/19 to a sail is not as simple as matching a 400/19 to a sail. it comes down to bend curve also.
I'm planning on a new (used) quiver for next season and researching sails and range. looking for a couple of medium to high wind plus something like a Hellcat 5.7
.
Yeah pretty much
A Hellcat would be good as you already have a NP mast I think? Which will not like that Arrows sail (more than likely)
Too hard to go into all the mismatches but before long somebody will post that chart to crossreference....?
Or just easier to replace everything, or stick with NP.
If thinking about what will work and what won't just ask here, people will know if they theoretically will work and usually somebody has actually done it
This is my "slightly" exaggerated guide to mast curves.
Use www.unifiber.net/masts-selector to match sails to masts.
Wave and freeride sails are a little more tolerant of mast curve but race sails can be unforgiving. But try and rig a Gaastra on a Neil Pryde, as I did when starting out, and you'll see an ugly outcome.
Any chance you get, bitch and moan to shops, manufacturers and pros - we need a standard mast curve!
