Our boats are wonderful, but they are not relentless. The ocean is relentless and unforgiving. Some boats are built relentless. Crossing the ocean, go for relentless.
What would frighten me about the ocean is methane gas. You seldom hear about that. Pockets of methane gas come up from the ocean floor, and when they hit the surface, if a ship is there, it ain't no more. Ships do not float on pockets of gas. If a pocket of gas, a skyscraper tall opens up under a boat, ship, or even a plane, that is over.
While rare, it does happen. Happens most often in deep water where the ocean floor is mountain-es. When something disturbs the ocean floor, earthquake, slide of material on the ocean floor, who knows what, this can trigger the release of many square miles of methane gas headed for the top of the water. This is possibly what triggers huge rogue waves that have been reported over the years.