The ship set off at noon the day after the party members sneaked onboard. The crew never bother to enter the hold once the ship is underway, allowing the party members free run of the area, and so they are able to spread out.
It’s a dull and uneventful trip. The party members have enough rations to last the trip, but after three days, they are out of water. Grim waits for nightfall and for the crew to fall asleep before sneaking out of the hold. He locates a freshwater supply and a hose pipe and unravels it, bringing water down to the hold so that they are able to drink and also hose down their ablutions.
Once this is taken care of, there’s little else that they can do apart from to try and come up with some new ways of amusing themselves for the remainder of the voyage.