WHICH IS STRONGER – A FLEX TOP OR HARD-TOP MAST?

Tim Reinieren at 14 May 2015

It’s a question we hear a lot, but of course there isn’t a hard-and-fast, straightforward answer!

Sail manufacturers specify hard, constant curve or flex-top masts according to the characteristics and behaviour they intend the sail to have.

But they don’t always opt for the most durable mast in the name of performance.

So the advantage of buying an aftermarket model, from a dedicated mast producer such as Unifiber, is that you get to try and match and maximise the performance of your new sail as well as pick the strongest specification for the longest lifespan possible.

CRUNCH TIME - WAVES

So what are the forces in action to test your mast’s construction?

Wave sailors like to think in terms of both durability as well as reflex in their mast choices.

These days most wave sails use a Reduced Diameter Mast (RDM) mast of 400 cm., or less, to minimise the length of the spar presented to a rig-munching set wave.

RDMs also have a thicker-and-therefore-stronger relative wall thickness than Standard Diameter (SDM) models. (Although Unifiber 80 and 100% SDM masts have an added radial ‘compression’ layer of material to add strength without affecting bend characteristic. To save weight this is only applied on the bottom section.)

But in that critical wipe-out in the surf, which type of mast is strongest?

The truth is that the mast base is the weakest part of the mast.

Approx. 80% of mast breakages occur in the bottom half - it’s the section under the most stress.

In theory, a hard-top mast takes more energy to bend than a flex top. Which means a hard-top mast's base is under more stress than a constant curve or flexure top model.

A flex-top will absorb more pressure and is less likely to snap as early as a less flexible mast. (Unifiber use a ‘drop-shape’ profile in the pre-preg layup that allows all their 3 bend curves of SDMs to bend further before any eventual snap.)

Read more about masts, bend curves, stiffness, IMCS measurements and carbon content.

However, the real answer is that the in-built luff curve in a particular sail’s design is key to prevent mast breakage in almost any type of sail.

SHAPE – RACE SAIL PROFILES

Most racing sails have incredible luff curve to increase skin tension, which allows designers to create a more stable sail body profile and create shape around the boom area.

So lower tension and straighter-luffed sails will put less pressure on the chosen spar, while sail depth/shape is achieved more through seam shaping in the panel-layout design.

It’s a complicated subject though and some race sails use flex-top masts to add reflex, forgiveness and also absorb the tension.

Race-sail-compatible masts also suffer from wear and tear from camber inducers, which is, again, heightened when filled with wind and fully downhauled - plus of course during rotation.

Visit the Knowledge Section for more information on choosing the right windsurfing equipment for you

SOLUTIONS

For racing/slalom sails you may have to sacrifice durability for performance, although we’re confident in the performance of our own products performance in main-brand sails for the best of both worlds.

In terms of wave sails, that would mean, in theory, that a straight-luffed sail with a flex-top RDM mast would be the most durable solution. (Probably in 60-80% carbon content too, as reflex would be less critical, so the stronger build of a lower carbon content model would deliver added strength – although also weight.)

Although you won’t find many like that that deliver much shape, stability or any of the benefits of skin tension or leech control.

It could be a soft, ‘float and ride’ sail, which is arguably the one that needs to take the most beatings due to the ‘vulnerability’ of the riders’ situation in serious surf without much power to be mobile around the break.

Summary

In conclusion, if you value durability of your mast in any type of sail, yet still want performance, then look for lower luff curve and more seam shape - but still choose the mast bend characteristics and stiffness that the designer specified.

View the mast selector tool to pick the model for your rig

Post by Brian McDowell, Sales and Marketing