Mast stiffness measurement

Mast stiffness measurement

Post by Scott R. Nels » Tue, 15 Dec 1992 07:26:23


After a couple of years of windsurfing, I feel that I understand
most of what I need to know about boards, sails and even fins.
But, I still feel that I'm in the dark when it comes to masts.
I would appreciate it if those of you with more experience and
understanding in this area would answer any of the following
questions:

I've seen masts advertised as 6.6 or 7.5 DIN, but I don't have a
clue what that translates to.  What does the DIN measurement mean?

Some of the advertised masts have an MCS number like 25 or 30 and
some don't.  What does the MCS measurement mean?

How is the MCS number related to the DIN number?

How can I figure out what the stiffness is of my current fiberglass
masts that came with my O'Brien and F2 boards?

What is the difference in behavior between fiberglass, epoxy,
aluminum and carbon fiber masts?  Obviously fiberglass is likely
to be the heaviest and carbon fiber the lightest, but what other
differences should I expect?

How can I tell if a mast is constant curve or flex top?

Are there any other advantages of a 2-piece mast over a 1-piece mast
besides being able to put it inside my car instead of on top?

Once I understand the answers to all of these questions, is there
anything else that is important for me to understand about masts?

Thanks for any and all responses.

---

Scott R. Nelson
Sun Microsystems

F2 Comet (10'6"), 2 12' O'Brien boards, 9 sails 3.6 through 8.5,
3 old fiberglass masts (and a partridge in a pear tree...)

 
 
 

Mast stiffness measurement

Post by Grant Grundl » Wed, 16 Dec 1992 09:00:17



Quote:
> I've seen masts advertised as 6.6 or 7.5 DIN, but I don't have a
> clue what that translates to.  What does the DIN measurement mean?

DIN == Deutsche Industrie Norm (German Industrial Standard for english
speakers)


| In the summer 1991 edition of "Performance Windsurf Report" (a free
magazine I p
| icked up at a local shop) there was an article on how MCS stiffness
measurements
| are made.

| The article also says that the DIN test involved*** a weight 420cm
| from the mast base and measuring tip deflection.

Quote:
> Some of the advertised masts have an MCS number like 25 or 30 and
> some don't.  What does the MCS measurement mean?

| 1.  Support the mast horizontally, with the supports 5cm from the base
|       and tip.  Measure the distance between supports.
| 2.  Measure the vertical deflection of the mast at the quarter points,
|       due to the mast weight only.
| 3.  Hang a 30kg mass from the mast halfway between supports, and measure
|       deflections at the quarter points again.
| 4.  Subtract deflection w/out weight from deflection with weight to give
|       net deflection.
| 5.  The overall MCS stiffness is given by dividing the distance between
|       supports by the midpoint deflection.
| 6.  The stiffness percentages are given by dividing the deflections at the
|        1/4 and 3/4 points by the midpoint deflection.  The shape of the
|        mast curve determines these numbers (i.e. whether a mast is
|        constant curve or flex top).
|
| Example:
|
| Total mast length = 460cm
| Deflection length = 460 - 2(5) = 450cm
| Point spacing = 450 / 4 = 112.5cm
|
|                              1/4     1/2     3/4 point
|                             ----    ----    ----
| Deflection w/out weight      0.6     1.1     0.9
| Deflection w/ weight        12.2    19.1    14.7
|                             ----    ----    ----
| Net deflection              11.6    18.0    13.8
|
| Overall stiffness = 450 / 18.0 = 25


Quote:
> How is the MCS number related to the DIN number?

Only somewhat - go to a shop and you will see several masts with the same
MCS but slightly different DINS.

Quote:
> What is the difference in behavior between fiberglass, epoxy,
> aluminum and carbon fiber masts?  Obviously fiberglass is likely
> to be the heaviest and carbon fiber the lightest, but what other
> differences should I expect?

Behaviour I don't know. But fiberglass doesn't like being in the sun and after
two or three years of usage it starts to show.  Aluminum two peice tend
to corrode
at the joint. Carbon masts tend to be more sensitive to abuse.  I have
owned fiberglass
aluminum, expoxy, and carbon masts. I have been careful with the carbon
mast and no
problems yet.  I broke an aluminum mast becuase it had corroded away. My epoxy
masts have held up really well over the past two years (I sail in the S.F. bay)
and my only comlaint is they are heavy (wave masts, sigh...).

Quote:
> How can I tell if a mast is constant curve or flex top?


|    Grant emailed me and asked me to post the percentages that fall
| into the different categories.  I can use my Fiberspar chart to approx.
|
| In all cases, the lower quarter defl. was from 62% to 64% of the midpoint
| defl., so very close.  All the flex top masts were 62 and 63%.  The combis
| were 63%; and the constant curves were 63 and 64%.
|
| The high quarterpoint defl. differences were a little more drastic.
| The flextops were 80+. the combis were 79%, and the constants were 76, 77%.

Quote:
> Are there any other advantages of a 2-piece mast over a 1-piece mast
> besides being able to put it inside my car instead of on top?

What other advantages do you want?!
IMHO, The joint just makes the mast heavier, weaker, and more expensive.
(I could be wrong about more expensive...)
One piece carbon masts go down to about 1.7 or 1.8 Kg. for a 460 cm mast.
The same 2-piece mast weighs at least 0.2 Kg more (and I think it was
even 0.3 Kg).

grant


 
 
 

Mast stiffness measurement

Post by Tom Alber » Wed, 16 Dec 1992 02:06:30


Quote:
> Some of the advertised masts have an MCS number like 25 or 30 and
> some don't.  What does the MCS measurement mean?

MCS refers to a system whereby the mast is supported 4 inches in from each
end and a 30Kg. weight is hung from the middle.  MCS is a number which
is obtained my dividing the mast length by the deflection at the middle.
The more the deflection; the lower the number; the softer the mast.  The
deflections at the 1/4 and 3/4 are also measured.  Those measurement give
the curve type.

Quote:
> How is the MCS number related to the DIN number?

I don't know how DIN is measured.  The higher the number; the stiffer the
mast, so there is some relativity.

Quote:
> How can I figure out what the stiffness is of my current fiberglass
> masts that came with my O'Brien and F2 boards?

Do an MCS calculation.

Quote:
> What is the difference in behavior between fiberglass, epoxy,
> aluminum and carbon fiber masts?  Obviously fiberglass is likely
> to be the heaviest and carbon fiber the lightest, but what other
> differences should I expect?

Carbon also recovers from a gust quicker.

Quote:
> How can I tell if a mast is constant curve or flex top?

If the 1/4 deflection is <63% of the middle and the 3/4 is >80%,
it is flextop.  If the 1/4 is >63% and the 3/4 is <80%, it is
constant curve.

Quote:
> Are there any other advantages of a 2-piece mast over a 1-piece mast
> besides being able to put it inside my car instead of on top?

No.

Any inaccuracies, Brad?

 
 
 

Mast stiffness measurement

Post by Kirk Lindstr » Thu, 17 Dec 1992 03:48:45

Quote:
>After a couple of years of windsurfing, I feel that I understand
>most of what I need to know about boards, sails and even fins.
>But, I still feel that I'm in the dark when it comes to masts.

Lots of questions where the answers are answered well in WSing mags.
Too much for me to even start.  Maybe someone else is braver.

Quote:
>Once I understand the answers to all of these questions, is there
>anything else that is important for me to understand about masts?

Yes, how they relate to how a sale performs.  I've attended many rigging
seminars and have talked at length with several sail designers and the
answers aren't simple or even agreed upon by all.  Once you start sailing
9' boards, you will find that you will need to understand a whole lot more.
Also, there are always tradeoffs and you have to decide which ones fit your
sailing style, ability, desire to improve, etc.

Quote:
>Scott R. Nelson
> F2 Comet (10'6"), 2 12' O'Brien boards, 9 sails 3.6 through 8.5,

----------

Kirk out

 
 
 

Mast stiffness measurement

Post by James Hw » Sat, 19 Dec 1992 06:56:59


Quote:
> Some of the advertised masts have an MCS number like 25 or 30 and
> some don't.  What does the MCS measurement mean?

> How is the MCS number related to the DIN number?

The MCS form of measurement is now becoming a standard replacing the DIN
measurements that have been used for quite some time now. The MCS
measurement comes in the form of something like 25/5 which means that
25cm of mast will flex 5cm with a given load (X kgs).  Most manufacturers
and retailers have dropped the 5cm bit from the jargon and have made that
a constant.  So now they speak about masts with a rating of MCS 25 and
MCS 30, for example (note the "/5" bit is left out).  So you can now see
that a MCS 25 mast is softer than a MCS 30.

Quote:
> How can I figure out what the stiffness is of my current fiberglass
> masts that came with my O'Brien and F2 boards?

That's getting pretty technical and if it's not written on your mast the
only other place that I can think of that could help is your retailer
who should have product info. guides with all the specs of masts, new and
old.

Quote:
> What is the difference in behavior between fiberglass, epoxy,
> aluminum and carbon fiber masts?  Obviously fiberglass is likely
> to be the heaviest and carbon fiber the lightest, but what other
> differences should I expect?

Some other differences that come to mind are strength and flex response.
Because carbon fibre is stronger than glass fibre you need less carbon fibre
material to make an equally strong mast.  It is for this reason that carbon
fibre masts weigh in at about 1.5 - 2kgs.  But Carbon fibre is not *THE*
material for every function.  It is more fragile and hence isn't the best
choice for high impact disciplines such as wave-sailing.

The flex response refers to amount of time that the mast takes to return
to its "original" position after flexing under a load such as a gust of
wind.  Carbon fibre masts are said to be 4 times faster than glass and
twice as fast as aluminium masts.  This makes for a far more comfortable
sail with the sail retaining its designed shape longer with each gust.

Quote:
> Are there any other advantages of a 2-piece mast over a 1-piece mast
> besides being able to put it inside my car instead of on top?

2-piece masts are excellent for travelling and convenience, but that is,
I'm afraid, where my praise stops.  The have of weak spot, and that is
the ferrule where the two masts pieces meet.  This point is notorious
for breakage especially amongst the modern racing sails that require huge
amounts of downhaul.  How do I know, I've broken two (2) 2-piece masts
before!

Another less important point is that they don't have *exactly* the same
flex curve as their 1-piece equivelant, but then again who can tell the
diff.

Quote:
> Once I understand the answers to all of these questions, is there
> anything else that is important for me to understand about masts?

Nowadays, sail makers design their sails around a particular mast.
If they know how the mast that their sail is going to be rigged on behaves
then they can design that sail with much greater ease.  So to cut a long
story short, if you want to get the most out of your sail, rig it on
the right mast.  (Haven't I heard someone say that before?)

Quote:
> Thanks for any and all responses.

No probs.

Quote:
> Scott R. Nelson

If anyone has any additions or corrections that they'd like to add,
go right ahead.

Later,
James
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