Guns on board

I would warn against brandishing a gun that you don't intend to use. It elevates the situation and then you are left without any defense.

X2 on what Baker said.

A fake gun will always lose in a gun fight. No sense in escalating. In Florida, if you display a fake gun that looks real it's the same as if you had a real one.

and you better understand the consequences when and where and how you use a flare gun for a deterent.

then like any wrapon, you better practice with it more than the once or twice most boaters may have fired one into the air for practice.

my cut, is if you are willing to use a flare gun.... much better to get, use, practice with and understand the laws of owning a real gun.

like most topics here on TF, use the rigjt tool for the job, do the job right the first time....anything else can go sideways quick.

also, even flare guns are considered weapons in some jurisdictions.... know the laws.

And if its a close quarters defense situation you'd better have some fire extinguishers handy.

I feel a bit sorry for the OP getting all this random advice, ha! Unfortunately governments have made this such a huge deal that you really need professional advice to stay legal on this issue. One part of the answer is; it depends on where you go. Someone said watch for "northern states". This is generally true but you only have to go as far as Virginia I think to run into trouble.
There's a lawyer who specializes in this and teaches a class in "handguns on a boat" at Trawler Fest, his name is Todd Lochner you can look him up and I bet he'd be happy to answer this more precisely.