They did them with 5.0s back in sylt a couple of years back. For regular doubles so long as there's decent board speed + a good ramp which let's the rider go for a long jump then anything below 5.0 will do.
The stronger the wind the smaller waves needed and vice versa.
So in 20-22 knots it's possible but really need the ramp to line up or technique to be solid and at 25 knots+ then it's a lot well... "Easier" haha !
I like seeing them in the 4.2-4.7 range 
Attemping them, no way! 47 and pretty broken (elbow, knee acl).
Last time I did a double it was with a 6.5m sail........I wasn't attached and it was in a gust on the beach. Few scratches but other than that the board was ok.
Select to expand quoteWind Smurf said..
Last time I did a double it was with a 6.5m sail........I wasn't attached and it was in a gust on the beach. Few scratches but other than that the board was ok.
I'm hearing ya mate. Of course you'll need to consider if it's a stalled or table top shore break double fwd before finalising sail size. Personally, I recommend balls are fully functional and HUGE on double fwd day.
Select to expand quoteBrent in Qld said..Wind Smurf said..
Last time I did a double it was with a 6.5m sail........I wasn't attached and it was in a gust on the beach. Few scratches but other than that the board was ok.
I'm hearing ya mate. Of course you'll need to consider if it's a stalled or table top shore break double fwd before finalising sail size. Personally, I recommend balls are fully functional and HUGE on double fwd day.
I think it would actually have been a triple loop but the car park fence stopped it.
If one is comfortable throwing huge and early forwards when there's a lot of floating before landing, then the rest is cake 
Seen Philip Koster do one on a 5.7m in a comp in Lano about 10 years ago, he said it was slow and scary ??
