Rigging and IMCS tests?

[Tyvealive]

Hey guys just a quick question.
I have two masts, a 430 and a 460 that have unknown specs, all the info is worn off...and lately it has been a nightmare trying to get the right mast/sail/fin/board combination... really hit or miss.
Is there a way to test the IMCS of a mast at home on my own so that I can match up the sail and mast better?

Any info or tips are much appreciated.
Cheers,

[winddude]

Take a look at this, http://www.tushingham.com/windsurfing/p ... parameters

windsurfing mast must have an overall stiffness within the range specified by the sailmaker for any given sail.
Stiffness is measured by supporting the mast at each end and applying a 30kg weight to the middle. The mid-point deflection figure is applied to a formula that takes account of the mast’s length to give an IMCS number (Indexed Mast Check System) The bigger the number the stiffer the mast; IMCS numbers typically range from about 11 (soft junior mast) to 36 (stiff race mast).
Bigger sails need stiffer masts to support the extra forces so it’s normal for longer masts to be built stiffer with higher IMCS numbers.
For the technically minded, the formula for calculating IMCS is:
IMCS = Length(cm)3 / Mid Point Deflection(cm) x 216225

Let us know what you find out, I'm curious, I've never tried it.

[tbrown]

looks easy enough to repeat... assuming this is accurate:
http://www.tushingham.com/windsurfing/p ... parameters

... just a 30 kg weight at midpoint? That would get you an IMCS number, for however much that is worth. -Tom

[winddoctor]

T,

Do you know the brand/model of the mast? Are you in Vic? I'm happy to look at your gear for you.

To answer your question, though, yes you can measure IMCS at home but you are better off just having someone with experience rig your sails with those masts and see how they look/pump/feel on land. Pretty easy to tell if they are workable or a mismatch. Measuring IMCS becomes more of an exercise in measurebating unless you just absolutely need to know. Can you post a pic of the sails and masts you are wondering about?

Chris

[nanmoo]

Just get Winddoc to check it out rigged like he says....

I've never really grasped the finer points and can only tell when things are really off myself but the Doc has an eye for these things and the gentle touch of a baby to really suss out the differences.

[C36]

T: I measured IMCS on my masts and the results are posted in the IMCS mast testing (do-it-yourself guide) thread.

T,

Do you know the brand/model of the mast? Are you in Vic? I'm happy to look at your gear for you.

To answer your question, though, yes you can measure IMCS at home but you are better off just having someone with experience rig your sails with those masts and see how they look/pump/feel on land. Pretty easy to tell if they are workable or a mismatch. Measuring IMCS becomes more of an exercise in measurebating unless you just absolutely need to know. Can you post a pic of the sails and masts you are wondering about?

Chris

The reason I did it was I was in the process of switching my sails over from one brand to another and was told my original masts were 'fairly' compatible. What I was suprised to find out was brand "A" varied greatly from spec (which is what I suspected as I had expereinced a very different feel on same sail using different masts with the same spec from Brand "A"), while brand "B" was spot on mast after mast. Now I know what I was sailing and which I personally perfer.

[winddude]

Nice, C36, was it the same formula? If you do this and the mast breaks it was probably a NeilPryde mast.

If you rig it and are sailing, if it feels very twitchy, unstable (with a draft feeling like it wants to canapult you) it's probably to stiff, if it feels very slow to power up it's probably to soft. If you don't feel experienced, and want to make sure, winddoc is right, get an experienced sailor to take a look.

[KUS]

Bigger sails need stiffer masts to support the extra forces so it’s normal for longer masts to be built stiffer with higher IMCS numbers.

Let us know what you find out, I'm curious, I've never tried it.

I'm curious too but have given up trying to figure it out....I just go with what I got and buy the mast that goes with the sail when possible....and even that doesn't feel or look right most of the time.
To add to this, if you are a heavier fellow like me you may like a stiffer mast, I actually go to the softer feeling shorter masts now when I can unless I want power, like at a lake vs. wave sailing. Soft feels great for tricks and waves, too soft sucks as sails are gutless....thinking Ezzy and NoLimit masts here....I would never use these unless with Ezzy's ...and yes, NP masts make decent gardening plot posts.

I also wonder about the impacts of a maxed extension, that must just throw a whole other crappy variable into the mix.

[C36]

Nice, C36, was it the same formula?

Yup. Same formula for IMCS 465 (465 x 465 = 216,225).

Bigger sails need stiffer masts to support the extra forces so it’s normal for longer masts to be built stiffer with higher IMCS numbers.

Let us know what you find out, I'm curious, I've never tried it.

I'm curious too but have given up trying to figure it out....I just go with what I got and buy the mast that goes with the sail when possible....and even that doesn't feel or look right most of the time.
To add to this, if you are a heavier fellow like me you may like a stiffer mast, I actually go to the softer feeling shorter masts now when I can unless I want power, like at a lake vs. wave sailing. Soft feels great for tricks and waves, too soft sucks as sails are gutless....thinking Ezzy and NoLimit masts here....I would never use these unless with Ezzy's ...and yes, NP masts make decent gardening plot posts.

I also wonder about the impacts of a maxed extension, that must just throw a whole other crappy variable into the mix.

Good question. Here is my understanding:

Too long mast extension inside the base of the recommended mast = will likely alter the flex curve and stiffen the base of the mast (making the bottom of the sail less responsive); likely flatten the foot of the sail (robbing some bottom end power). That's why they sell mast extensions in different lengths (use just what you need and no more).

A long extension outside a shorter/softer than recommended mast = will likely also result in a change in the mast bend curve and stiffen the base; but with the softer mast up top will result in a flex-top feel (softer sail as Kus described above - helps the sail 'breathe') After testing different mast combinations I found I personally like this in smaller sail sizes and run a size down in top of my 5.3, 4.5 and 4.0 with a longer extension). I'm a middle weight sailor at 170 lbs.

Hope that makes sense.

[Tyvealive]

Thanks for the info guys! The technical stuff is a bit confusing, haha.

So I'll stick with as short of an extension as possible and just keep messing with it until it doesn't feel squirrely in the wind.

No, I live in Courtenay, but I'll make sure to bring those masts for next time I'm in Parksville, I can stop by the windsurfing hut and see what Kevin thinks.
Had no idea how important tuning was when you're in higher winds!

[winddoctor]

T,

You can always post shots of your rigged sails to show twist, draft profile, etc. Then we can armchair tune your sails for you.

[KUS]

I'll stick with as short of an extension as possible and just keep messing with it until it doesn't feel squirrely in the wind.

major reason for squirrely is: too much outhaul. I still see people adding more than 2" of outhaul, in fact I was surprised to see the rigging guidelines for Ezzy's of KC's sail where it calls for 2+" for high winds......I usually run zero to 1/2 inch on all my sails, just keep downhauling....once u maxed on that, I go to the smaller sail

[nanmoo]

I run my 5.2 QU4D on a 370 with a 38 extension, and I also run it on a 400 with zero extension if I happen to be packing that mast around. I am no lightweight but I honestly I can't really tell much of a difference. Perhaps I am not picky enough.

That said, when I used to have the cheap 60% carbon masts in my Fires, it sucked compared to when I switched to the higher carbon hot rods. This leads me to believe it is much, much more about the mast and less about the extension, which makes sense given that even at 38 cm you are less than 10% of the total luff vs. 90% for whatever mast you are using. Presumably if that is relative then you can only affect the feel by the same proportion.

[more force 4]

I was surprised to see the rigging guidelines for Ezzy's of KC's sail where it calls for 2+" for high winds......I usually run zero to 1/2 inch on all my sails, just keep downhauling....once u maxed on that, I go to the smaller sail

An Ezzy guru at the Gorge (can't remember his name, older guy) told me that the downhaul was approximate setting, but that almost all adjustment on most Ezzys now was by the outhaul.

[KUS]

An Ezzy guru at the Gorge (can't remember his name, older guy) told me that the downhaul was approximate setting, but that almost all adjustment on most Ezzys now was by the outhaul.

was he driving a white van with an Ezzy logo interesting, that would support the soft mast business, certainly no point in mega downhauling a noodle....but there is still the three top panel settings adjustment I note on the sails so don't think that's entirely true....but what do I know