[Old Man Dave]

Give me a big petrol speedboat or jet ski any day of the week. It's the windsurfer/sailboarders I fear. You can't hear them coming. They also go 20knts + and as far as I can tell they can't see where they're going most of the time.
In my experience most boat owners don't know what an "A" flag means. Try and write "divers" as large as possible on your SMB.
Don't threaten any one with a speargun, no matter what the provication, it will only lead to us all suffering if they start treating spearguns in the way firearms, airguns and even BB's are going.
All of this is a sign of the times and aint going to get better. A sharp lookout is the only real answer. But remember there is no point in being right if you're dead.
Dave