How can I calculate the best sail size for the current wind?

Question

Being a beginner in windsurf, I have several sails from 4.7 to 7.5 meters sq.

I find myself wondering how I can set the correct sail for the current wind.

How do we know what sail to use, and when to use it?

Is there any rule of thumb?

Answer 1

I came across a windsurfing blog post with a link to an Excel spreadsheet (titled "Ultimate Windsurfing Equipment Size Calculator"), developed by James Douglass. His spreadsheet runs some calculations using several factors:

• windsurfer's weight
• sail size

The spreadsheet has several reports/graphs:

Boards:

• Minimum size beginners board you should be using
• Ideal first short board
• Smallest size windsurf board that can be uphauled

Sails:

• Two lists showing different wind strengths & what size sail you should be using
• A separate list showing wind strength & sail size for a beginner
• A graph showing ideal sail size versus wind speed

This spreadsheet might offer the type of info you're looking for. Mr. Douglass also provides an online version of his spreadsheet.

He also provides the following advice to beginners in this "Top 16 Windsurfing Questions Answered" FAQ:

Question #6- I’m a beginner windsurfer looking for my first sail. What kind of sail should I get, and in what size?

Answer You should get a sail between 2 and 7 meters squared, depending on your size and the wind speed you are likely to sail in most often. Check the windsurfing equipment calculator to see what’s right for you (pink line on chart). As you get better, you can start using sails closer in size to those recommended for experienced sailors (blue line on chart). Your first sail should have a minimum of 3 and a maximum of 6 battens, and should have no camber inducers or “cams” on any of the battens. Also, avoid sails and masts made before the year 2000 and sails advertised for racing.

Another site had some pointers regarding sail size:

For an amateur windsurfer, sails ranging from 5 to 6.5 square meters in size are recommended as they work well for light winds up to winds of 4-5 knots.

This article offers a quick overview of sails, with this final recommendation:

We suggest you start off by choosing light-wind sails to get the knack of windsurfing. Eventually, you can experiment with various sizes of the sails, and finally find the one that appeals to you the most.

Enjoy!

EDIT: Added info from James Douglass' FAQ and a link to an online version of his calculator.

Answer 2

In addition to JW01's post, a key step change in the sizes you should use comes at the point you progress past uphauling to water starts.

When you uphaul, a large sail can be incredibly difficult, as the wind tries to push it back down into the water, and if you can't uphaul rapidly you will tend to pivot round leaving the mast pointing upwind - so a smaller sail is ideal.

Once you can water start, a bigger sail actually makes life much easier, as all you have to do is lie in the water upwind of the board, with the mast on your shoulder (very easy) and pop it up to catch the wind. A nice big sail can then lift you onto the board in even relatively light winds.

Of course the other aspect not mentioned is sea and wind conditions - if the sea is choppy, a smaller sail can be much easier to manage, but if the wind is gusty a large sail can help ride through the lulls.