Whoah!! Lets not reinvent the wheel here! (Or in this case, mast testing). The standard is already there: IMCS. It is very well known and relatively simple to do. See my pics of IMCS mast testing kit here:

www.seabreeze.com.au/gallery/gallery.asp?imageid=5581

And some pictures of doing it there as well.

www.seabreeze.com.au/gallery/gallery.asp?imageid=5578

There really is no need to test the bend at more than the standard 3 places: Halfway and the 2 quarters.

The Boards magazine article is a very good one because it highlights that sail making and mast making are black arts. There is a lot of science in it but there is also a lot of trial and error refining. Masts that were recommended by the sail manufacturer did not always produce the best results for the testers!

My own testing has shown that different carbon content in the same design and brand of masts can change the curve percentage, sometimes quite dramatically! Different batches of masts from the same manufacturer and supposedly produced the the same specification can also vary. Look at the list referred to above www.peterman.dk/masts-all-imcs01.htm and the Boards tests http://www.boards.co.uk/equipment/mastsweb/mastsoverlay.html# and you can see immediately that even masts from the same brand manufacturer vary in their bend curve quite a bit! (The peterman list is a great find by the way!)

Having said that, it IS very useful to know the IMCS stiffness and curve percentage of masts so you can see which ones are likely to compare closely with others. Most manufacturers print the IMCS stiffness on the masts but many do not put the curve percentage on them. It would be a big help if they did (and even better if the masts were actually what they were claimed to be).

Now, the other side of this story is that some sails are much more sensitive to mast stiffness and curve than others. Broadly speaking, if the designer uses the luff curve as the main shaping source, the mast stiffness and curve are usually more critical. If the designer uses seam shaping in the sail panels more to set the shape, the mast bend is often less critical.

There are other things that can dramatically affect the shape as well. One of the most influential is the sail cloth or materials used. I was recently test rigging some prototype sails with the designer and we were puzzled as to why the shape in a particular part of the sail was not what we expected. It seemed at first to be an issue with the mast bend. After trying other masts and IMCS testing the masts we found that this was not the issue. The issue was the material used in part of the sail construction had changed in the loft and was stretching differently under tension. A change in that material had the shape back to the way that was intended.

I believe it was either Powerex or Fiberspar that actually used the downhaul tension type of mast testing similar to what 'Boards' magazine did in the '90's. I seem to remember that all their production masts were tested this way on a wall mounted jig before leaving the factory. I don't know if they still do this but it seemed to me a very good idea to ensure consistency and quality control. If an alternative to the regular IMCS test is needed, a system like this might be good if it is carefully standardised.

By the way, testing mast bend inside a luff sleeve is pretty meaningless because the curve shape of the luff is deliberately mismatched to the curve of the mast to produce the desired sail shape. ie: all sail luff curve shapes will be different!

The easy answer is as many have said:
Get the mast recommended by the sailmaker.
or, next choice; get a mast with an IMCS as close as possible to the one recommended by the sailmaker.
Then, if you really must, try a few slightly different masts to see if you can get a better result. (This is of course not an available option to most and is usually only relevant it the very bleeding edge of chasing ultimate performance).

Also, choose brand of sail that is known to be quite tolerant of different brand masts.

Sounds like a task for a wanderers meet scheduled with no wind. Someone bring the gear along to do it and we test all the masts we can.

Yeah Mark, good one. I have a couple of trestles and weights and stuff - all we need to do the standard IMCS + curve measurement. Put it on the agenda.

I think you are reading way too much into the origins of the terms. I really think they are poor terms that the inventors of MCS arbitrarily chose to fit the 'standard' curves that were already common.

Quoted here from the old Windwing webpage (now defunct I think):

Mast Categories
Under the MCS system most popular windsurfing masts found in the marketplace can be placed into three
basic categories:

Constant Curve
Any mast with a base - tip percent of mid-point difference in the 10% - 14% range is considered to be a
'constant curve' mast. The 'classic' definition of a constant curve mast is a mast having a 76% tip
defelection percentage and a 64% base deflection percentage. These masts are often labeled as 12%
constant curve masts.

Flex Top
Any mast with a base - tip percent of mid-point difference in the 18% - 22% range is considered to be a
'flex top' mast. The 'classic' definition of a flex top mast is a mast having a 82% tip defelection percentage
and a 62% base deflection percentage. These masts are often labeled as 20% flex top masts.

Combi Curve
Any mast with a base - tip percent of mid-point difference in the 14% - 18% range is considered to be a
'combi curve' mast. The 'classic' definition of a combi curve mast is a mast having a 79% tip defelection
percentage and a 63% base deflection percentage. These masts are often labeled as 16% combi curve.

I am sure that masts have been made outside these specs on both sides. The short stiff Gaastra masts of a few years ago were (I think) lower % difference than 12%. Many modern 530 and 550 masts seem to be like that as well
ref: www.peterman.dk/masts-all-imcs01.htm

I spent a couple of hours today measuring quite a few different brands of masts and some older ones. Some of the results don't seem to make much sense so I will do those again before I publish the results.

So far I can say that Normal Diameter Powerex Wave masts in 400 and 430 seem to be consistently right on 12% Constant Curve and most of the KA masts and other Triana masts I tested are a bit closer to Combi curve.

I tested two old favorite Technofiber C35 (Bump and Jump) masts on 4m and 460 and they came out true CC and confirmed my impression that they are slightly softer than specified. 460/24 and 400/18 (Which I like a lot in some applications).

I recon this conversion table is the easiest way to get IMCS fom MCS.
www.seabreeze.com.au/gallery/gallery.asp?imageid=5678

I think the actual formula given here

fibersparsports.com/msguide/imcs.html

is WRONG though ( I have seen it elswhere and the figures I get from it do not make sense). The correct formula seems to have the overall length (deflected length) squared, not cubed. Anyhow, with this table you do not need to do all the other calculations

MCS is very easy to work out. It is the (30kg) deflected length in cm (420 for a 430 mast) x10 divided by the deflection at the middle of the mast in mm.

Example below is an older Powerex manufactured Flying Objects Mast 430cm IMCS quoted at 21

EG: 4200 / 171 = MCS 24.5

use the conversion chart to convert to IMCS:

EG: 24.5 X .86 = 21.07

Perfect!

They do, they didn't have an aussie importer/distributor for a while but they do again now.

have you got the right mast?

north and severne doesn't sound like the best match to me but the guys from severne would be better equiped to answer that.

if you can take a photo and start a new thread. will shorely get you an answer. it could also be a batten tension issue so best to see a photo of how you have it rigged.

cheers

edit.

i just found this from ben severne in another post.

"The bend curves of all the Fiberspar, Powerex, etc are all different. But they are all working along similar principles which is enough to get our sails to work. (Or any other sail.) The main thing is that the sails DON'T work so well on Neil Pryde, North, or any of the flex-top masts."

here is the whole thread. www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=30074&whichpage=1

sounds like you need a different mast to get the most out of your sail and the diagonal creases you refer to sounds like a poor mast match. still photos would be good, it may be tweakable.

I thought about cross posting this here as well but It seems easier to just post the link:

Topic: Standarised masts:

www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=30074&whichpage=2&replies=33&PageSize=30&mxPages=2

Hi David, Are the current Fiberspar specifications available on the net somewhere, Fiberspar always used to set the standard in this sort of information and even provided compatibility charts for all the different brands as mentioned above.

quote:

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Originally posted by Gestalt

that's great sailquick. nice work

we'll try and get some from this end too. i agree with the wanderers mast measuring thing. i got everything nedded but the 30 kg weights.

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I have been using a couple of Olympic weightlifting bar weights but I have to give them back to the weightlifters :-) I am changing to 3x10kg bags of lead shot in a light X-Army shoulder bag. This will be a lot more compact and easier to manage, and I just happened to have about 1/4 tonne of the stuff lying around...... :-)

quote:

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Originally posted by Wineman

quote:

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Originally posted by sailquik
and I just happened to have about 1/4 tonne of the stuff lying around...... :-)

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Why would everyone/anyone have 1/4 tonne of lead shot ...just hangin' around

Aaaha....shootin' season is a-comin, & I's gonna get me a wabbbit

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Mainly to keep Slowboat in supply for his weight vest when he visits. :-)

I hoarded the stuff years ago in another life when I was masquerading as a competitive skeet shooter. Turns out to be an accidental good investment as the price of lead had tripled in the last year or so! No idea why! Maybe it's the resurgence of speed sailing and everyone filling up their vests?!

Are the ezzy's still made in Triana? Or is it no-limitz.
The triana masts all seem very similar ie Gaastra, tushy, KA etc
Powerex and fiberspar also very similar but a little stiffer in the bottom and slightly bigger diam on the SDMS.
Pryde and north - out there!!

My Ezzy RDM is a no limitz which are made at hood river
as far as I know
I tried to get info out of them but got fobbed off!!
It works perfectly in an Ezzy sail!!


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