HOW MAST BEND CURVE INFLUENCES SAIL BEHAVIOUR
The level of flex there is higher up in a mast hugely affects how a sail behaves. This is why sail manufacturers recommend using the same – or most similar to - mast they used to develop the sail.
To understand why – or if you feel like experimenting with a different feel - here is some insight into what is inducing certain behavioral characteristics.
SOFT AND SMOOTH
You can see the manufacturers, such as Attitude Sails and NeilPryde, that favor the forgiving nature of the flex-top mast in this Mast Selector Tool.
In general terms, more flex (from a higher bend-curve figure and a flex-top mast) results in higher levels of control.
This is usually - but not always - displayed by a looser leech and often results in less power on tap.
That added control can be felt mostly in rougher water and is often appreciated by lighter riders, who prefer a slightly softer sensation from the rig.
The Center of Effort (CoE) will also usually shift lower in the profile if you put a flex-top mast into a sail designed around a hard or constant curve mast.
Depending on the brand and mast specification, this may or may not improve the handling of the sail – but can be interesting to try and feel for yourself if any adjustments can enhance your sailing experience. (See below for some other tweaks you can make.)
Flex-top masts often extend wind range as well – especially at the top-end to prevent being too overpowered.
HARD AND FAST
The lower bend-curve figure that constant curve and hard-top masts have mostly results in higher levels of power - often, but not exclusively from tighter leeches.
They are also arguably harder to control with the center of effort typically higher up.
This is not a bad thing in, say, manoeuvre-oriented wave/freestyle sails that are less comfortable to sail around in a straight line on - but the higher center of effort allows more of a throw about nature for moves.
For faster, racing-oriented sails, the extra depth/profile and power typically works better on flatter water and/or for heavier riders.
CONSTANT COMPROMISE
Perhaps it’s no surprise then that the majority of manufacturers opt for constant-curve masts, whose behavior offers the ‘best of both worlds’, along with a wider range of potential changeability between brands.
MORE TWEAKS
There are some easy ways to achieve different behavior from your sail.
Some brands top and bottom sections are interchangeable, allowing combinations of shorter or longer top sections to achieve various bend curve (and stiffness) characteristics. (You could also find different handling from cutting/shortening masts but do not recommend doing that with newer items!)
However, where possible with adjustable heads, by extending a mast or using a longer mast, you can achieve a harder-top sensation.
SOFTEN THE BLOWS
But perhaps the easiest tune-up to make is to soften a rig by using a shorter mast (of the same bend curve/brand) than recommended.
For example, use extra extension on a 430 in a sail designed around a 460. (Modern extensions should allow you to confidently use up to 45-cm. of extension.)
So a rig setting on 460+10 for example, can be softened considerably by using a 430+40.
We hope this may help improve your understanding - and fun on the water!
More windsurfing equipment selection advice
Posted by Job Verbunt, Product Development.