... hard to help with useful info 'cause a lot of factors come into play such as experience level, style of the rider eg. twin tip/surfboard and even what time of year, as in, which season your aiming at!!!
But, having said that, I don't think you'd go too far wrong with a 14m rather than a 12m for a 100 kg rider. From what I remember when I was in Port Headland, the wind was similar to our tropical winds in Darwin which isn't too powerful so you tend to ride bigger kites for the same given numbers. I reckon our 20knots is like 15knots in Perth.
If you go too small such as a 12m, you'll struggle, especially when a heavier dude (which I know all about being a super-heavy weight myself) unless you live in windy place and Port Headland wasn't always windy. You can wait for the right conditions but who wants to do that.
I reckon look at kites like the Zephyr or the Rebel as they stay stable at their top end wind ranges for bigger guys which is a good thing.
Have you got any more info regarding your friend?
cheers,
Robbie
