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DanWeiss



Joined: 24 Jun 2008
Posts: 1889
Location: Connecticut, USA

PostPosted: Tue Feb 26, 2013 5:02 pm    Post subject: Reply with quote

My comment about longer mast sections being stiffer is in line with the IMCS vs the old MCS. Stiffness indexed by length, and all that. Even most "stiff top" curves remain inside the CC range, and CC itself isn't truly a smooth curve but still flexes more in the top 1/2.
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U2U2U2



Joined: 06 Jul 2001
Posts: 2978
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Tue Feb 26, 2013 10:07 pm    Post subject: Reply with quote

DanWeiss wrote:
My comment about longer mast sections being stiffer is in line with the IMCS vs the old MCS. Stiffness indexed by length, and all that. Even most "stiff top" curves remain inside the CC range, and CC itself isn't truly a smooth curve but still flexes more in the top 1/2.


IMCS by itself is useless. old MCS less that useless

sorry Dan but you lost me on this, stiff top in the CC range ..?

their are too many variables constant curve is like saying radial tire

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swchandler



Joined: 08 Nov 1993
Posts: 5485

PostPosted: Wed Feb 27, 2013 4:30 am    Post subject: Reply with quote

"IMCS by itself is useless."


The way that I see it, IMCS is a metric. It's not the whole story, but it does characterize the overall stiffness of a mast. When you think about it, it is a very pertinent metric when it comes down to mixing and matching mast lengths and crossing the normal boundaries. You can take a standard 430 mast, and the IMCS is normally about 21. But, how would you characterize the IMCS of a 370 bottom and a 430 top combo? Although the topic has been turned to dwell on the nature of the constant curve bend characteristics between brands, our past understandings have been based on known mast combos, like a standard 400 or 430 mast. To move outside that understanding, especially when mixing different component stiffness characteristics (bottom + top), it changes everything.
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U2U2U2



Joined: 06 Jul 2001
Posts: 2978
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Wed Feb 27, 2013 5:23 am    Post subject: Reply with quote

Using the 0--22 scale which includes constant curve 10--12 in mast bend curve, it is evident that constant curve doesn't mean that the mast is equally soft or stiff from the bottom to the tip, measuring how much the mast deflects while hanging a 30kg weight from from the midpoint is its stiffness,if the its IMCS32, that is the stiffness its referred to, larger number more stiffness..

The stiffness tells something about when the mast starts working, at what load, the bend curve tells something about how the mast should work when loaded. These from the Peterman mast guide, not written in stone anywhere YMMV

Ezzy 430 IMCS 21.9 HSM IMCS 23, using the mast bend curve method the HSM will indicate a softer overall number which is what actually it is, constant curve flex top.


your 370/430 IMCS question

I have a friend who did IMCS measures on NoLimitz masts using the original & Sumos
examples for reflection only. He does not use more than 1 size apart

370 #1 14.3 370 #2 15.1 400 Original 17.8 400 Sumo 18.9
in curve the Sumo is softer top by 1

400/370 IMCS 16.2 .. your guess on the 370/430 is as good as mine

again for reference the HSM 370 IMCS is 12.2

these all account for the mast character

1) Overall stiffness

2) The ratios between the mid, and bend points.

3) The carbon content

4) The carbon orientation. More zero axis fibers = better reflex

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swchandler



Joined: 08 Nov 1993
Posts: 5485

PostPosted: Wed Feb 27, 2013 1:58 pm    Post subject: Reply with quote

As I understand it, the higher the IMCS number, the stiffer the overall mast. In fact, I bought a stiffer No Limitz 400 Sumo top to use with my No Limitz 400 Original bottom, because the 400 Original top was too soft, resulting in an overly loose leech. The Sumo top tightened up the leech by exactly what I needed, so now the Original/Sumo combination effectively yields an outcome that is closer to the 64/76 bend curve that my sails require.

Looking at No Limitz's published bend curve specifications for the 400 Original and the 400 Sumo masts, the measurements are 65/77 and 64.6/77.1 respectively. I have to say that these figures don't seem to tell the story, as they both a appear to suggest a softer top, with the Sumo coming in slightly softer overall. Needless to say though, replacing the Original top with the Sumo top tells the real story, and the differences in the rigged sail proves it without question. That's where the IMCS stiffness specifications come into play. If you consider the fact that overall stiffness for the Original is 18 and the Sumo is 19, the story becomes clearer.

So, at least in this selected scenario, increased IMCS stiffness apparently trumps bend curve in the final outcome.
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U2U2U2



Joined: 06 Jul 2001
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Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Wed Feb 27, 2013 2:19 pm    Post subject: Reply with quote

remember we had this along with others this discussion before, and how would NL be acceptable in Gaastras ?

I asked this to David what struck the most is its possible to have a stiffer top
just due to the carbon orientation. NoLimitz says something about the Sumo on their site in this regard.

What I have found is the more I learn about masts, the more I find that I have to learn.

Iam very happy that mine are sorted out.

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swchandler



Joined: 08 Nov 1993
Posts: 5485

PostPosted: Wed Feb 27, 2013 2:56 pm    Post subject: Reply with quote

"I asked this to David what struck the most is its possible to have a stiffer top
just due to the carbon orientation. NoLimitz says something about the Sumo on their site in this regard.

What I have found is the more I learn about masts, the more I find that I have to learn."


I'm totally with you on the learning about masts and all the intricacies associated with them. What seems so simple is in actuality far more complex than what many of us think.

Regarding your focus on whether carbon orientation determines the degree of stiffness in a mast, if you look at the overall weight of the No Limitz 400 Original and Sumo masts (3.6 versus 4.0 lbs. respectively), it seems that the amount of fiber used in each mast might also tell part of the story. Yet when it comes down to it, in light of trade secrets and proprietary manufacturing methods, we'll never know the full story.
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