Sparring Partners

Sparring Partners:
Mast Diameter and Carbon Content

Two windsurfers

Not sure whether you should be using an SDM or RDM? Confused about carbon content ratios? Adrian Jones and the Clones test team put six masts of different specification through their paces to help you decide which is right for you and your sail.

After years of ear-bashing from manufacturers, magazines and testers (myself included), there’s no doubting the importance of choosing the right mast for your sail. You’d expect that this would be easy, but with so many different stiffnesses, bend curves, diameters and carbon content ratios to choose from it’s no wonder that many people get it wrong or simply decide to ‘make do’.

Using sails and masts from the same brand tends to make things a lot easier, but it’s still not entirely straightforward. Even if you select the corresponding logo you’ll still have to choose from a selection of carbon contents, mast diameters (standard SDM / ‘skinny’ RDM) and sometimes even mast lengths to best suit your needs and budget.

If you’re mixing and matching sails and masts from different brands, then the situation is a lot more complicated and you’ll probably have to use ‘the Force’ to predict which will best suit. If you’re a diligent student of Obi-Wan Kenobi that will be just fine, but unfortunately most of us are not.

None of our Clones have quite completed their Jedi training yet, so we decided to look at the isolated and very important effects of carbon content and mast diameter. (We’ll leave the effects of bend curves and stiffness with Master Yoda and Obi-Wan to explain at a later date.)

Two windsurfers Carbonification

Carbon content is always an interesting one. It goes without saying that we all want more carbon – it provides a stiffer, more reactive / responsive and lighter product. But it also costs a lot more. Masts are generally available from around 30% carbon content up to 100%, so we decided it was time to check out how much ‘real world’ difference this would make to the performance of the sail and see if it’s worth the extra cash.

Feel the width!

The second key issue concerns mast diameter. At first a few niche wave brands introduced reduced diameter masts (RDMs) primarily to increase durability in waves. Many brands resisted this at first. Without the taper of a standard diameter (SDM) mast it was much harder to engineer the correct bend characteristics into RDMs. But with recent developments in material technology RDMs can now be as sophisticated as SDMs, and most brands now design their wave sail ranges primarily around an RDM mast (but most still retain the option to use an SDM if desired). The popularity of RDMs is increasing to the extent that we’re even seeing them on some freeride sails, and this trend looks set to continue.


To conduct this little ‘experiment’ we opted to use two identical sails and a selection of six masts – three RDMs and three SDMs of varying carbon content. RDM masts are certainly easier to ‘make work’ in the smaller sizes of sail. 5.3m has generally been regarded as a suitable transition size, and below this size RDMs have been working well. Above this size RDMs have generally, to date, been outperformed by SDMs. We therefore decided to opt for two 5.4m NeilPryde Atlas (‘power wave’) sails to give these masts a real comparison.

To complement the two sails we chose six NeilPryde masts – RDM and SDM versions of the X3 (30% carbon), X6 (c. 50% carbon), and X9 (c. 100% carbon).

With prices ranging from £200 for the X3 SDM right up to a jaw-clenching £500 for the X9 SDM, it was going to be really interesting to see how much difference there was between them. So, let’s start by running through how each of the masts performed on the water…







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