Actually that article you link to says it really well.

... Here's the sad thing about adding a spi, you will LOSE speed upwind. ...

... Downwind ... Here's the great thing, you gain loads of speed now ...


He even gives a full scientific analysis using GPS track data, I quote :

"... In winds around 18 knots you are trapezing flat out using chickenline as far back as the hull streches, the speed is 18-19 knots and you sail 30° from a direct downwind course. The VMG (velocity straight downwind in this case) is around 15 knots! Compared this to wild thing without spi where you sail 45° from straight downwind course and have a VMG of 11 knots. This is 30% faster and a lot of more fun.

All this is based on actual sailing trips using gps track plots. The VMG speed I'm talking about is not peak speed, it is an average speed base on 1-2 Nm of sailed distance. The highest speeds I've seen so far is 19 knots based on 10 second average."


Adding spinnaker to these boats and the F16's is one of the most significant developments done this decade.

Wouter