Problem with a rifle is stability on a moving platform like a boat. It takes a career of practice to make a shot like the SEAL's did on those Somali pirates. That and a long gun in confined spaces, like a boat, can make deployment an issue. A shotgun is far, far more appropriate. A medium length barrel will allow sabot slug use with excellent accuracy out to 100yards or so. Beyond that you won't hit anything with a rifle either. Shotgun can be progressively loaded, slug, buckshot, birdshot, etc. all in the same magazine. Shotgun is very simple, pump guns rarely break, need little attention, etc. In many places a shotgun is not considered as "evil" as a handgun, rifle, etc. More of a sporting arm and so on. But I can guarantee that no one with the intention to do you harm wants to look down the barrel of one. My choice is a Benelli Nova.
I should clarify that I do not think everyone should be armed. I simply believe that the prudent mariner should have the OPTION to arm themselves should they see fit. To some this may see strange but these same people prepare for rough weather, they prepare for the inevitable equipment failures, prepare for the boat sinking out from under them. Situations that seriously threaten our lives sailing are statistically very small. Preparing for them makes sense.
Preparing does NOT necessarily mean being armed. Do you know what you would do if boarded? Have you hidden your cash, valuables, etc. in several different locations? Have you dressed down when in a foreign port or did you walk around with expensive jewelery, toys, etc. flashing cash? People looking to take what you have are not stupid. They look for easy targets, they look for wealthy targets, they will avoid a situation that puts them at risk and move on to an easier target. Thinking through these situations ahead of time and reading about what has happened to others will only help should something this unfortunate happen to you.
RT