Sunday, January 30, 2011


The wind is set to blow all day today building all the way through so we will be able to choose early/big equipment/easy sailing or later/small stuff /wide eyes.  Anthony our supplier has lent me one of the new Select S11 fins to try so I look forward to that.  I'll report back.

The subject of windsurfing masts has really bugged me over the years.  It is also a bit technical and can be extremely boring to anyone who knows about masts or who is not interested in statistics and measurements.  If you are one of these people please disregard this post.

If you have the stomach for it here we go -
Take a plausible scenario - A friend is leaving for London and is selling his windsurfing kit.  I buy his Maui Sails TR-6 7.0 for a good price.  I have two 460 masts (a Pryde X9 460 and a Powerex ZRace 460).  Are either of these compatible with my new sail?  Maui Sails gives me no information on the mast bend characteristics which the sail was designed around.  Pryde tells me nothing about the bend characteristics of their mast and neither does Powerex.  I have to resort to trial and error and even if the sail feels OK with one of the masts is it optimal?  Could I be getting far better performance with another mast?  I just don't know.

Thankfully the industry has standardized stiffness across the sizes (460 mast = IMCS25) but bend characteristics are a different matter.  The extent to which the mast top flexes in relation to the bottom section when under tension gives the mast its shape and this shape provides the template for the mast sleeve.  To achieve the desired air flow over the foil the designer also takes into account the way the mast is going to behave under stress.  From all of this it becomes obvious that a mast which works with one sail may fail completely with another but how are we supposed to know which goes with which?

Bend characteristics are measured using a standardized method so all the info we need is available but for some reason not shared.  There are exceptions of course - Sailworks give us all the info we need on their masts but very few of the other guys do this.

Bend characteristics are calculated as follows:
The mast is placed horizontally on two supports, one 5cm from the base of the mast and one 5cm in from the tip.  The supports are thus 450cm apart for a 460 mast.  The supports will be placed against a wall or board.  Shoot a chalk line between the two supports.  You then measure and mark the centre point of the mast.  You also need the "top mark" (half way between the tip and mid point) and the "bottom mark" (half way between mid point and base)
Tie a piece of string round the mid point and suspend a 30kg weight from the mast.  Measure the deflection from your chalk line to the centre point of the now flexed mast.  Say for example that the deflection at the centre point is 10cm.  Now measure the deflection at the top mark.  Say it is 7.5cm.  Measure the deflection at the bottom mark.  Say 6.4cm.
We now have the stats we need.  We have a mast with a bend of 75% top/64% bottom.  Deduct the bottom number  from the top number (in this example 11) and you get the curve Delta.  A low curve Delta indicates a hard top mast whereas a high Delta indicates a more flex top design.  Here are the categories specified by the industry:

                     Delta           Classification

                    -6                Hard Top
                  7-9                Hard Top/Constant Curve
                 10-12            Constant Curve
                 13-15            Constant Curve/Flex Top
                 16-18            Flex Top
                 19-21            Flex Top/Super Flex Top
                 22-                Super Flex Top      

To get back to our example with the Maui Sails TR-6, the fact is that neither my Pryde nor my Powerex masts are going to work.  Both Pryde and Powerex masts have Deltas of around 15.  Maui Sails are designed around masts with Deltas of less than 10.  If I had a Gaastra Gold mast or a Severne Enigma these would almost certainly have worked with my new sail but why could no-one tell me?

Masts with the same bend characteristics can still differ in performance of course depending on carbon content and quality of construction.  A state of the art high carbon mast should recover more quickly after deflection than something cheaper giving a feel that is crisp, light and exciting where the cheaper model can feel a bit leaden even if it works with the sail.

I leave you with a website address which gives some broad categorizations for various mast brands:

Good winds - talk to you soon

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