[captainj2410]

The chain gun was actually quite a different concept. A chain gun works with small munitions which feed into a routing chamber that links to the different barrels to load automatically. With each turn of a crank, the hammer would strike the bullet and fire it. The triple cannons most likely had to be manually reloaded. PotC takes place (in my estimation) anywhere from 1650 to 1725. By this time cannons were still muzzle loaders, not breech loaders. that means that the cannons would have to be retracted after all three shots were fired to be reloaded. So long as all three were loaded at once, it was still very effective.