The IMCS -
In a perfect
world - when you buy a sail, you also buy the mast the manufacturer
many of us
just haven't got the money to buy a sail and mast at the same time,
and are perhaps the happy owner of a mast with the right length, or
simply not sure the manufactorer's recommandations on masts are good enough,
want to mast-tune the rig for ourselves.
from time to
time most of us have a need for some information about masts, to
evaluate if X mast is compatible with Y sail. For that purpose we need
a rough guide for the characteristics of the masts (the same goes for
the sails - but that's another story). And to be credible, these
characteristics must be based on "objective" measurings rather
than meaningless marketing praises from the manufacturers, importers or
team riders. Some important demands for an objective test could be ...
of the method. The IMCS is described in details in a pretty
simple way. There might be a little confusion about the reference
mast length in the formula for stiffness (460 cm or 465 cm), but
that doesn't influence the results very much.
measuring method, so that we (the
customers) are able to check
the claims of the manufactorers. The IMCS measuring method is pretty
simple. A 30 kilos weight, a calculator and a lot of accuracy - and
you are going.
the real world mast load. This is probably the weakest point of the IMCS
test. At least theoretically it might be a problem, that the IMCS method
of bending a mast is by hanging a weight from the midpoint of the mast -
whereas in the real world the mast bending is a result of loading/compressing the mast by means of downhaul (and to a lesser
proportion pressure from the mast pocket and the camber inducers).
The claim that
the IMCS bending method is not reflecting the real world mast load most
often come up when manufacturers are exposed for placing their masts in a
wrong IMCS category ("Constant Curve" is a very misused
category - the offenders being for instance Neil Pryde, Gaastra, Maui
Sails, Fiberspar ...). And amusingly, at the same time they claim the
irrelevance of the IMCS method, they in fact imprint their masts with
the IMCS stiffness and the IMCS bending category - and thus at least
implicitly accept the IMCS standard!
Some of the manufacturers
they have their own (much better) mast measuring method.But if we
shall take these alternative mast testing methods seriously, we must
have some "glasnost" about the methods. For example: How do
they imitate the real world compression bending? How do they measure
the bending? What are the categories of the bending results - that
is: How do they describe the masts by means of these new methods? And
what is (if any) the coupling/difference between the results of the
alternative methods and the good old IMCS?
Lately the IMCS test seems to have gained
support from a somewhat unexpected quarter.
In a thread about masts Rick
Whidden from Maui Sails (who have their own mast testing
compression method - and who have not always accepted the IMCS method
as a fair way to describe a mast)
conclusion the IMCS measuring is for the time being the best method for
an "objective" description of the masts. Consequently, It
should be very welcomme, if the manufacturers sold their masts
imprinted with the true IMCS figures. But until they decide to do that,
the IMCS method is so simple, that it at least allows us to test the
masts for ourselves and to do our own comparisons.
|Using the IMCS test
- examples of general findings.
- Cutting off material from the bottom
makes the mast softer (in IMCS terms) and close to the same (or a
little more flex top) in bending characteristics. Putting an extension
in the mast makes it stiffer (most with flex top
masts, lesser with constant curve masts) or the same (hard top masts)
- and very close to the same in bending characteristics. Often
you hear sailers say, that they prefer a shorter, softer mast with a
long extension relative to a longer, stiffer mast with no extension.
However, IMCS measurings tell us, that (in IMCS terms) there is often
difference between the two options at all - at
least if we talk about flex top masts or (to a lesser degree) constant
curve masts. Putting on an extension
stiffens up the shorter flex top or constant
curve mast, so that it ends up with close to
stiffness as the longer mast without extension.
See the findings here.
- Some years ago Jamie
Hawkins wrote in a British magazine, that the masts get stiffer in
the lower temperatures of the winter time - initiating a need for
tuning your sails different. IMCS measurings of the same mast
exposed to different temperatures tell us, that strictly spoken that
isn't true. Temperatures don't affect mast stiffness or bending
characteristics much. But who knows - perhaps the low temperatures have
consequences for the "reflex response" - that is the
sluggishness of the masts?