take the boat out sailing. Wasps are not really into sailing. you can spray up into the mast with bug spray and they will leave. soak a rag with bug spray and hoist up to the opening. most bug spray is used around furniture and it should not hurt the boat
I have taken the boat out after apparently getting rid of the wasp at the dock, only to find them back on the boat in a few days after being docked. It is also hard to even take the boat out when the wasps are under the sail cover and inside the mast, need to fight them off just to get to the main sail. You would be surprised, I have been sailing in 20 knot winds only to have these wasp come out of the mast, fly around the boat, then go back into the mast.