"shall be provided with some other means of making an efficient signal."
I wonder if a .308 would qualify?
I do keep a refillable air horn in the cockpit most of the time. The tank is about the size of a coke bottle and is designed to fit in a cup holder. It has a schrader valve for refilling. I don't know how long of a blast the tank will support, but I do know it could be used multiple times before refilling. It is very loud, and has an obnoxious tone - lower than the co2 ones. I've only used it once to clear the beach where I was trying to dock. A quick bump from about 150 feet out cleared everyone out of the way.
The biggest problem I have is that the normal distance that power boats deviate to avoid me is way too late for me to take steps to avoid them. That being said, seeing a power boat on a collision course does not mean I expect a potential collision. Since most boats deviate late, I can only consider them on a collision course if they are about 200 feet away. In all the years I sail on the most busy lake per sq ft in the country, I have only had 1 boat that made me nervous. They were making a big arc. I could only guess where they would end up, as it was impossible to predict their trajectory. They did pass within about 100 ft of my boat. I was trapped between their path and thin water. They were coming up on my tail, which makes avoidance more difficult.
BTY: Wearing the whistle is in case you are MOB, so you don't get run over.
