Wow yet another thread about mast "bend"!!!
Sorry I did not read all of the posts, but still I feel an urge to jump in and share what I found over time and expecially during the last few years. I will try to be brief!
First of all, YES I did my homework and tested a few 460 masts by the IMCS method. Sorry, most of the job was performed on 4 samples of just 1 (one) mast model: the S2Maui Venom 460, 2 samples from 2022 production and 2 samples from 2023. All supposed to be exactly the same.
Sample 1: 26/62/76 (14)
Sample 2: 25/63/77 (14)
Sample 3: 26/64/75 (11)
Sample 4: 26/64/78 (14)
Please not that weights were all within a 10 gms difference, so I would not blame production consistency AT ALL, or consider that as unavoidable.
By comparison, my very old (2006?) MauiSails 460 measured at: 26/67/76 (9), so definitely an hard top as it is supposed to be;
and another older, very much used, 460 Venom measured at: 24.5/61/75 (14).
The terrible thing is how those masts behaved when rigged (in the SAME sail, a '22 Venom 7.5): all of the newer samples despite different measurements behaved exactly the same. They all showed a very deep belly, with a very rounded entry and big wrinkles in the mast sleeve at camber #1 and 2, leech quite tight up to batten #3 and opening abruptly from there up, and almost impossible rotation.
The MauiSails mast by comparison showed a proper shape, with a very smooth and even leech opening from the boom up, But as expected the shape was on the "hard top" side, with less deep draft under the boom and less twist than one would expect from a modern race sail.
The older Venom mast ('19?) was just perfect: nice shape, nice leech twist, good rotation.
Also rigged the same sail on a Duotone Platinum 460 (drop shape, recent) and the result was the same as with the newer 4 samples of the Venom mast.
What I found in the end.
Between the older and the newer Venom production, the manufacturer changed the moulds and mast shape was changed too. The newer masts have an enhanced "drop shape", and so has the Duotone mast, with an abrupt diameter variation (reduction) at about 60 - 80 cms up from the bottom; while the older production Venom mast has a more smooth diameter reduction. This abrupt shape change makes for an abrupt stiffness variation, with a low section excessively stiff (the mast will bend were it may bend with less effort). The IMCS test says NOTHING about this, because it is performed with a 30 kgs weight hung at 50% of the mast length, perpendicular to the mast axis; while real life mast loading happens with some 100's kgs loading (almost) aligned to the mast axis, which determines what is called a buckling load. And in the case of buckling, structures reaction is very much dependent of geometry, therefore that abrupt diameter variation (drop shape) is of great importance. The mast will bend easier where it has a lesser diameter, and be very stiff where the diameter is larger.
That said.
First of all: production consistency is such that IMCS numeral difference appear relatiively overstated. This does not mean that those differences may be useless, but that those have to be considered with a grain of salt (or a lot of it). Production (in)consistency is such that those numbers are not that much reliable.
Second: how a sail rigs has lots to do with mast shape, meaning its taper from the bottom to the top.
In the end, in place of the original SDM 460 masts, I am now rigging my 7.5 and 8.2 on MDM masts. The ones I am using (same manufacturer as all of the above mentioned masts, minus the Duotone) have a shape that is practically a 10% outer diameter reduction of a classic SDM mast, with NO drop shape and a narrow tip. The even taper makes for a proper sail shape and good cam rotation. I keep using those MDM masts also with my newer '25 sails; those apparently have been modified in order to work with the newer (post 2021) SDM masts, but I do prefer the way those MDM masts work.
Since I was there, I also measured my first two MDM's samples. The first proto measured at 25.5/63/79. After testing, I asked for a different construction with slightly stiffer top, and I got a second proto that measured at: 27/63/75.5; this was chosen for following masts for me and my friends.
Despite stiffness may sound high, this second proto works best for me (I am not an hulk). A good thing in MDM masts is that smaller diameter makes it possible to have thicker walls (sturdiness) and higher quality carbon (dynamic flex); this in turn reflects in higher IMCS stiffness. On the water, one can feel an adequate amount of power coupled with better dynamic and a direct feel that makes the rig easier to control.
Please note the measurements stated here above are averages between multiple measurements. This is due to inherent variations (the mast bends differently in successive loading cycles) and obvious lack of precision on my side. Yet please be assured that when you read that a mast measured "25/63/77", in no way that same mast could have been measured as "26/64/78".
Conclusions.
Mast bend characteristics may vary from sample to sample, so don't think that sticking to sail loft suggestion will always save you, expecially when considering 1.0 or 0.5 differences.
Mast shape is paramount as for how a sail rigs and rotates. While IMCS numbers do have lots to do with how the rig will behave and "feel" on the water.
Mast manufacturers are very few and one would be surprised to know that certain brand masts come out of the same factory.
The one and only general rule that applies always with masts is: test it.
