Wiki Sail by GRF

Well I can't speak for dinghy sails, but it was always a problem for us in the windsurfing business, the magazines always tested sails in countries like Egypt, or occasionally they'd even venture as far afield as Hawaii where the air is less dense and the waves much faster, but particularly in Desert regions like Egypt, North African resorts, nowhere near as much moisture in it, so any given windspeed felt less.

We feel the difference more because we're holding the things. But loose rule of thumb you'd need a sail size difference (.5sqmtr) given the same speed in knots between say Hurghada in Egypt and South Coast UK average day.

However, over here mostly we're gradient winds and more often than not it's cold damp air from up there, coming down here quite fast, even in the summer, so we rarely 'feel' much difference, except on starboard of course after a weather front has just passed through..

Now if your boat is made with bubbles in the laminate which will of course xpand with heat, of course it's going to float higher, that's a trick question right, you only pretended you didn't know that?

Edited by iGRF - 17 Apr 13 at 8:45am

Now if your boat is made with bubbles in the laminate which will of course xpand with heat, of course it's going to float higher, that's a trick question right, you only pretended you didn't know that?

Which is of course why GRF does not sail much in colder conditons ... even he, who would have us believe he once 'walked on water' (but maybe only today on the forums) .... would sink !  

Mike L.

Originally posted by iGRF Well I can't speak for dinghy sails, but it was always a problem for us in the windsurfing business, the magazines always tested sails in countries like Egypt, or occasionally they'd even venture as far afield as Hawaii where the air is less dense and the waves much faster, but particularly in Desert regions like Egypt, North African resorts, nowhere near as much moisture in it, so any given windspeed felt less. We feel the difference more because we're holding the things. But loose rule of thumb you'd need a sail size difference (.5sqmtr) given the same speed in knots between say Hurghada in Egypt and South Coast UK average day. However, over here mostly we're gradient winds and more often than not it's cold damp air from up there, coming down here quite fast, even in the summer, so we rarely 'feel' much difference, except on starboard of course after a weather front has just passed through.. Now if your boat is made with bubbles in the laminate which will of course xpand with heat, of course it's going to float higher, that's a trick question right, you only pretended you didn't know that?

From my own experience, I always seemed to feel less power in a windsurf sail in hot climates compared to the UK.

However, I remember the debate about 20 years ago and I always thought the conclusion was that it was actually a myth. The reason being that, at the time, all anemometers worked on the similar principles ie. moving air acting against a physical surface such as fan blades(wing like) and cups(spinnaker like). Therefore if air was less dense it would have a corresponding effect on the measurement device.

Maybe now with electronic devices using electromagnetic waves you could determine this difference, the reality is that any measurement device used in any specific location is still likely to be of the fan blade, cup type meaning the wind speed is measured less than it is. Net result same power for the same measured windspeed.

Well, given that the force on the sail will vary directly with the density of the air, which in turn varies directly with the air pressure, a sensitive soul like GRF might notice some variation, given that air pressure regularly varies between 980 and 1030mb.  That said, a 5% variation isn't going to justify much a of a rig area change.

Originally posted by transient It's to do with the weight of moles.

Do rabbits, mice and guinea pigs have anything to do with it too? Get a few of them hitting your sail and you'd soon know about it.