These vessels are all-too-uncomfortably fragile. Made of wood, and reinforced over time with whatever is at hand, be it more wood or metal of some sort, the waves still crash up hard against that self-same surface. Given a long enough timeline, water erodes. And slowly, it seeps through.

The ships start taking on water and sinking, while the crew frantically work to bail it. Like a sponge, you could say the boat has a saturation point where it just can't take on any more water. And nobody can tell when Neptune, son of Saturn, should see fit to exercise his control, either. One little storm, and the vessels I speak of could be run aground or driven into the reef, ending their journey, although perhaps only temporarily.