Pirates?
Well from what I remember, those aren't public available yet and I think they may have fairly limited range. Sure they might work out to 100 feet or so, but you want to drive away the pirates BEFORE they get in RPG range. Secondarily, even if you were to have those on the boats instead of guns, you'd still need to have multiple units spread around the boat (for full coverage) and you'd need people to operate them. It isn't just simply a matter of having someone at the controlls of these weapons, it is having the people out there to SPOT the pirates in advance and use whatever weapon you have. We're not talking about a fishing trolley that is 20 or 30 feet stem to stern, we're talking about super tankers that are 1200+ feet in length. The world record for the 400m dash (just slightly longer than the boat) is 43 seconds. So it isn't like you can just say "they'll spot them from the controls tower and run out to the forward guns", that would take far far too long.