A square deal!
|28 August 2011||Posted by Alex from Lagoon under Technical world|
The square top mainsail is more and more « à la mode » on cruising cats. Of course this shape has a stylish and aesthetic aspect, but does it have a real aerodynamic interest too? First, let’s see where this idea comes from .
The first skiff to have this kind of shape head sail was a windsurfer. In fact, windsurfing launched the square head sail trend at the end of the 90’s with brands like North Sails, Neil Pryde… Then this shape was copied by America’s Cup boats and the first to test it was Alinghi during its winning campaign of 2003. It was the first competition boat to have a real square top mainsail. After, this shape conquered the whole world of the fast racing boats with for example the 60 foot multihulls and monohulls class, the multihulls with wing-sail as the 45’ America’s cup multihull class and finally the world of cruising cats and monohulls.
Many sailors have heard a lot of stories about this square top mainsail: that it will be just a marketing element, just a trend with no real impact during navigation. I am not a sailmaker nor a physicist so I made my own investigation! These are the answers that I found. The square top mainsail has two theoretical advantages:
– At the top of the mast, the air is stronger and less disturbed, so this bigger sail area benefits from better wind conditions. This increases the performance especially in light winds.
– This square shape allows the head sail to twist naturally more so it functions as a safety valve which depowers a larger area quicker when gusts arrive. This gives the boat a better behaviour in gusty conditions (this effect is really obvious on a windsurf board).
Those advantages wouldn’t be very significant if the boat is not dedicated to performance. This impact is more obvious in racing because there is no compromise concerning the speed. Moreover, it is true that sailing with such a large head sail requires more attention. For example when there are wind gusts you need to take a reef sooner. Good seamanship is essential to appreciate this and to really gain speed (and actually, to appreciate sailing in general!).
So this is more than a marketing trend: the square top mainsail has a significantly positive impact on the performance of a cruising cat but it is not a magical answer…
For those who are interested in this subject, I suggest this article from the thesis of Damien Lafforgue from the Southampton University about the experimental aspect of the sails.
Lagoon photo credits by Nicolas Claris, others photos are under Creative Common License: blue windsurfer / flickr i brendan, Alinghi / R . R ick, groupama 2 trimaran / flickr fanch, brown windsurfer / flickr alpha du centaure