Polar diagrams as we know them do not assume poling out the fore sail as a rule
. Ones that do, clearly mark it. These look different. Normal polars assume the fore sail will get blanketed out at a point (mostly past about 150 AWA).
If you think of the low point @ 150AWA vs a DD180 and you pole the sail out at 180, then your vmg is likely better at 180.
If you sail to broadly, the benefit is lost
- look at cos function once and we know why.
Off course, at 180 AWA, your boat speed deducts the largest % portion of the true wind
hence at 180 AWA any tub should sail its slowest. Unless we pole it out, hoist a kite or cheat in any other way.
I hate DD in open ocean waters as most older boats will roll then both ways. I love DD on lakes and smaller seas like the Baltic
. Being in the bigger boat helps heaps. They simply roll less, later, and at a slower rate.
I also like DD in modern fast and flat aft boats like Pogos, Class 40 or something like a Beneteau
Sense. These are the perfect downwind toys. Ours is not. ;-(