Canal boat horns are available from all good chandlers
. Being, usually, 12V they are also available from car accessory dealers and the good old internet.
The principle consideration when specifying a horn for your boat is volt drop. The return wiring can be over 40m on larger boats and has to be sized correctly to avoid over heating and fire.
The International Regulations For Preventing Collisions at Sea apply to horn signals on our waterways.
One short blast means turning to starboard (right).
Two short blasts means turning to port (left).
Three short blasts means moving to astern or reverse.
The problem is that the person you are trying to signal may have absolutely no idea what you are on about. It’s highly unlikely that a one time holiday
maker has even heard of COLREGS, and he or she may just think it’s another uppity boater getting his hair off.
So the time honored tradition of waving and shouting is probably with us for a while yet! Just try and do it with a smile because it may be us that’s made the mistake...