Why can't we just say "What is the recommended mast curve?" and get a straight answer?
All this thread (2.5 pages so far) is about trying to sort out bend curves. The guy who started it, lordhowe is in no position to try lots of different masts. He has NO RELIABLE INFORMATION to guide him in his mast purchase.
If the manufacturers could be bothered (Mr Love, are you paying attention?) to specify the bend curve as a % difference on an IMCS test then lordhowe and the rest of us would know exactly were we stood vis a vis performance of different masts in a particular sail. What we have here is a lot of confused supposition, guesswork and innuendo.
You manufacturers are infuriatingly unhelpful and recalcitrant when it comes to specifying mast curve. Why is that?
What exactly IS "towards the flex top end of constant curve"? Better yet why dont you just measure the effing things and post the curves on your mast spec sheets? WHY?
i think a mistake you may be making is assuming the bend of a mast can be described so easily. the bend probably doesn't even vary uniformly along the length of most masts. really you probably won't be able to accurately describe the characteristics of a mast without at least 5 or more parameters to be able to comfortably say yes x mast will work with x sail.
unless we have a standardised system on which masts are built, which won't happen as manufacturers will always build masts to suit their sails.. which might be designed towards a significantly different design philosophy to other companies.
end of the day, the best way is too go rig your sail on other masts. most guys i've met won't mind if you rig a sail on their mast at the end of the session, and all the shops i've gone to don't mind if you bring your sail in and test rigging a mast.
You hit the nail right on the head Swoosh. But it is very frustrating that many manufacturers and brands do not list the IMCS bend curve information for their masts.
I think there may be a number of reasons for this:
1. Their masts are not all the same model to model. I and others have tested masts of different models in the same brand and found different mast curves (see the Boards magazine tests referred to earlier and Petermans tests here:
www.peterman.dk/masts-all-imcs01.htm
Even mast manufacturers that use the IMCS system (eg. Fiberspar) have inconsistencies in their range. The wave masts are different curve from their smaller slalom masts which are different from their large slalom/race masts. I have no idea if this is deliberate or if this is a limitation on materials control. I suspect it is a bit of both.
I guess brands may be reluctant to be too specific about their mast curves if they know they vary across their range.
2. Their masts vary within the same model and even the same length.
Quality control of exact bend curve seems to be a quite difficult thing. I have tested more than one of the same mast model, same size and same manufacturer in the past and got two different answers. The stiffness and curve seems to vary a little. In all my tests it was mostly less than 2% curve difference and 1.5 IMCS points but I would guess that that is fairly typical so again brands may be reluctant to specify exact numbers when they know that every mast might not be exactly that number.
I could be wrong here and I admit I have not tested many large batches of same size and model masts, just a few random pairs, and they could well have been anomalies.
3. RDM masts often have a different curve from SDM masts even though they are recommended for the same sail (and work perfectly well). This is because the reduced diameter itself has an effect on sail shape and set as it takes up less of the luff pocket space. I have found a 12 % RDM mast that rigged a sail I used in exactly the same shape as a 15% SDM mast.
One mast is Constant Curve and the other is almost at the Flex Top specification.
4. Some sail manufacturers claim that even though their own masts can be loosely described as, for example, Constant Curve, they have characteristics that suit their sails better than other Constant Curve masts. Whether this is real or just marketing spin to encourage you to buy their own masts I can't say. What I can say is that I have actually tested two brands of mast that came out almost identical in IMCS curve but did rig and work in my sail in a subtle but noticeably different way.
Here are the IMCS categories for mast curve:
Categories - 6 Hard Top
7 - 9 Hard Top - Constant Curve
10 - 12 Constant Curve
13 - 15 Constant Curve - Flex Top
16 - 18 Flex Top
19 - 21 Flex Top - Super Flex Top
22 - Super Flex Top
I can tell you that all the 4m SDM KA masts I have tested (5) were in the 14-15% category. This puts they squarely in the "towards the flex top end of constant curve" category as Martin said.
The RDM KA 370 and 4m masts I tested were between 12-14 % curve and the 4m masts work perfectly in the same KA Koncept 5m sails as the above SDM masts.
Without more extensive testing of the other sizes I am reluctant to categorically say they would be the same but from the way they rig the sails I suspect they are at least very similar.
I can say that all the Powerex SDM wave masts that I have tested in 4m and 4.3m lengths came out between 10% and 13% making them a little more CC than the KA masts. The interesting thing was that they actually rig my small Koncepts in a VERY similar way. I have also seen some of the smaller Koncepts rigged on the NP 'Progressive Flex' masts and they have looked and worked well too. These are examples that tend to support the claim that KA sails tend to be somewhat mast curve tolerant.
I found this terminology interesting: There is information on the NP website ( http://www.neilpryde.com/insiders-guide/insiders-guide/understanding-mcs-and-imcs.html ) that calls their masts "Progressive Flex". As far as I can see this is not a 'standard' IMCS category but the example figures given are 61% bottom, 77% top. This = 16% difference which I would call Flex Top (but at the lower end).
Let me add that IMCS mast testing is a time consuming and tedious business for ordinary sailors (like me) to do. Have a go at it yourself if you doubt me. 
I assume that the mast factories are set up to do it in a much more efficient way. I agree it would be nice if they and their brands would publish more data.
Thanks for your advice NotWal.
As Andrew has demostrated the current KA Masts are in the 14-15% range which I classified as "flex top end of CC range" rightly or wrongly, I felt it described it correctly. Appologies if I confused things further, I am actually trying the help.
I will talk to AMAC about including this information on the sail specifications, but unless the other brands do so as well comparisons will still be difficult.
Gazman , yes we will do some mast testing shortly to confirm all the figures.
Generally the smaller wave/freeride sails with less luff curve are a bit more tolerant of mast curve variations, the larger or race oriented sails with higher luff curves become more mast specific. Naturally it is always ideal to use the recommended mast but that is not always possible or practical so yes, we will attempt to provide more information in the future to remove some of this confusion.
