I have a number of sea-faring races in my fantasy story. The world is relatively mundane i.e. no magic and the races are somewhere the Graeco-Roman classical period in terms of their technology, give or take a few hundred years.
Since many of these races travel in ships for trade and may encounter each other on the high seas I wanted to come up with an identification system different from the traditional flag system particularly for use at night and I wondered if it would be reasonable to invent something like a Three Note system whereby three notes in a particular sequence would represent Race A whereas a different sequence would represent Race B and so on. I know that sound travels faster over water than on land but how feasible is this out on the ocean? If you are hundreds of metres apart could you even make a loud enough sound to hear it over the roar of the ocean and what kind of instrument would you need to make it?
FYI, I am favouring this idea over light signals due to the risk of fire on wooden ships but also, two of the four races are periodically at war so it would be in the best interests of the other two non warring races to declare their identity up front and early to any ships they may encounter at night or by day. Ships entering waters held by a warring race may be subject to swift attack without declaring their identity.
Assuming that this is even feasible in the first place would you need twelve different large horns for the different "natural" notes? (That is of course assuming they understand music the way we do) Would three or four horns suffice? Would it make the most sense to just take the three horns you needed to identify yourself? For example, a basic system could use three horns tuned to C, F and A#. Allowing for repetition, this would give twenty seven possible unique identifications. I have seven races at present, not all of whom are seafaring or even if they are they are not all travelling the same waters and so realistically only four of them would have a need to identify themselves to each other. Two of these races are periodically at war so it would have certain utility as a warning mechanism but also as a deception to pretend to be someone you are not in order to get close in the dark and then attack. I feel like it could be a somewhat unique and interesting system that could have some novel implications.
TL;DR - is it feasible to use something like a series of small horns to identify yourself to another ship on the ocean a few hundred metres away?
Any and all feedback greatly appreciated!