It's not a question of *whether* you should carry a gun with you, it's a
question of *which* one(s)... Personally, I prefer stainless instead of
blued steel for those situations due to the potential for corrosion... Even
so, I give it a good oiling before taking it on the ocean since salt water
is not necessarily that kind to firearms... Even with one made from
stainless steel, I suspect that not all the parts are made from it and it
would not be a good idea to totally immerse it in salt water without a
complete teardown and cleaning afterwards... Keeping the firearm in a
waterproof pouch is probably a good idea though...

Only if you are in the USA.

You should not only have one on the boat, but you should dive with
one.

Wondering, just whom are you planning on shooting during the dive?  I'd rather
shoot pictures with a camera!

 Should you?

 Can't tell you that.

 Could you?

 Yes.
   

                     
                            Popeye
   "Naked force has settled more issues in history
  than any other factor.The contrary opinion 'violence
 never solves anything' is wishful thinking at its worst."

That is the most stupid question, I've ever heard.
And then again, you're probably living in USA, which makes your question
more understandable.
Acces to guns develops your kind of problems, and now you just can't go
diving without carrying a gun, huh.
Get a life.
Niels Hejnfelt

I assume you're refering to a firearm, however....

USCG regs require some sort of signaling device on your boat.

So, I prefer to cover both bases with this type: (extra flares too)

http://www.orionsignals.com/Marine/Products/aerial/25mmalerter.html

Believe me, you do not want to get hit with a 25mm flare and it's
completely legal to have onboard, anywhere you'd like to go.

I understand folks in the more socialistic and repressive areas of the
USA (WDC & NYC) actually use them for home defense since modern
handguns are difficult to obtain in these nightmarish, backward, crime
ridden cities.

It's also quite enjoyable firing off flares that are about to expire
on the 4th of July.
--
SJM

Tough call.  In Florida, you are allowed to carry a firearm aboard a boat
without a permit, just like you can in your car.  The primary question in
both cases is, will you leave it in the vehicle and, if so, how sure are you
that it will not be taken by the kind of person you'd rather not see with a
loaded weapon.  I usually have a gun aboard my boats no matter where I'm
going, but that sometimes limits what I'll do if I'm someplace I won't carry
it on me and I don't feel comfortable leaving it aboard (true only on my
small, open boats).

Lee