Easy conversions ???
 

I know many mainland european sailors tend to use m/s for windspeed

Noticed an easy conversion to knots .

Roughly double figure in m/s to get to knots.

ie
7 m/s is about 14 knots (its 13.8)

Other way obviously half it..

so

30 knots is not far off 15 m/s..

And
Knots to mph is quite easy too

knots to mph, add a tenth eg 30 knots is 30 +3 roughly 33 mph (its a bit more in reality) but not a bad estimate

Mph to knots , knock off a tenth.. so 25 mph is 25 less 2.5 = 22.5 knots (roughly)