Are they using only one entry/exit? If so, this may work (tho your dock mates might not appreciate it): A friend of mine had wasps that had nested in the attic of his house. He secured a shop vac hose right at their entry/exit and fired it up for a day. Problem solved

(I suppose you could duct-tape the other halyard exits to force them to use the one.)
Otherwise, if you're going to use a spray: You
have to do it at night. And the cooler the weather, the better. (Makes 'em sleepy.) To make matters worse: You can't use light, because, if they are disturbed, they will go right for the light source.
We had a big ol' wasps nest at about head height in a fir tree between our house and the next-door-neighbour's on one side. It was in a bad place and it was flippin' BIG. I went out at about 02:00, set a flashlight on a play set, pointed at the nest, got well away from the light and zapped the nest. Then ran like hell.
Or just hire a professional.
Jim