The Copperhead is supposed to be a safe, slow, meandering hulk of a ship that takes half the Caribbean to turn around in.
If the devs need a good randomizing RNG engine, there are plenty at GitHub and the like.
15% chance of explosives means that there's a random chance, at 15%, of explosives rounds.
That can vary from none to a full broadside of explosive rounds, as far as the math flies.
The main purpose of the different ship types in the game was that each and every ship type had its advantages and disadvantages, as in a trade-off.
The superfast ships have no armor, some have armor to varying degrees and reasonable firepower, as in the middle of the road variety, etc.
That's why the ships all have different features, such as varying speeds, type of ammos, cargo size, armor levels, etc.
But alas, I'm guessing the effort was to please a squeaky wheel somewhere, and this is where we wound up.
Reminds me of the Jack Sparrow blade becoming as pointless/useless as an El Patron because someone who felt they deserved it first didn't get it.
Anecdotally speaking;
Y'all ever have that driver, with 30 cars behind him/her, and they stop at a green light to let someone go from a
different lane, in an effort to be nice to that one driver, who would normally wait their turn to go (as in when the light changes), and then all those cars behind the "nice driver" now get stuck at the red light, because "everyone's dad" had to let the car go out of turn, to be "nice"?
In the end, 30 cars were punished, so the driver in question could do something no one really needed, trying to be "nice" to the one car who didn't even need it.
Anyway...