Well yeah, they were only minutes away at the point they lost power, there was very little time to do anything at all, that's why I asked. Personally I can't really imagine anyone holding it against them for using the 'signal that's for other ships' 'incorrectly' or 'against protocol' in such a situation. I think the comments speculating that the horn is either purely or in some way (e.g. solenoid) dependent on electricity is more likely the answer. I think a reasonable human in that situation who knows what's going on (that's why I mentioned that they apparently were able to radio/however they mayday that there's an issue) is going to do whatever they can, including use the horn wrong.

There is a proper signal. You are supposed to give at least five short signals if you think there is an impeding collision.

Alright well feel free to read my original question as if I knew and meant that then, I don't think I precluded it.