@AMRgamer3: I got a 2nd one with 90 cargo and doesn't need the plantation to be full. Going back for a 3rd time. The Frigate does shoot at you, so you may want to take this out first

@AMRgamer3: I sailed South to the plantation on New Bone island while the area is still under of the enemy power, Serranilla, and stopped quite far out. I then had him swim to New Bone, sycronise the viewpoint, then immediately fast travelled there, which docked my ship. In the bay there is a Frigate and a Man O War. I swam out to both and killed everyone onboard, before going back to my ship and using it to board them both. The Man O War had a cargo capacity of 90, the biggest I have seen! This may be random, but if you leave this area under enemy control you can now fast travel there again a bit later to find another Frigate and Man O War, just sitting in the bay waiting for you! I waited until the plantation was full again before going back, but I'm not sure if this is necessary.