The IMCS - anything better?

In a perfect world - when you buy a sail, you also buy the mast the manufacturer recommend. However,

  • 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

  • we are simply not sure the manufactorer's recommandations on masts are good enough, or

  • we just want to mast-tune the rig for ourselves.

So, 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 ...

  • Description 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.

  • Easy 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.

  • Imitation of 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 say 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) says ...

In 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 relatively little 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 the same 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?


How does the sail rig on masts with different bending characteristics (tendencies)?
  • Flex top bending curve creates looser top and more profile lower down - or lesser sail tension for the same appearence in the top.
  • Hard top bending curve creates tighter leech high up and less draft lower down - or more sail tension for the same appearence in the top.