This next paragraph is for engineers only, so if you are not an engineer, you may skip on.

I love it--SHIP MOTION THEORY! Here goes: every object has a center of gravity,upon which point the force of gravity appears to act. When you float a ship, then the ship, as does any floating object, has a center of buoyancy, upon which point the ship appears to float. Rolling, listing to starboard and then to port, is pretty much controlled by the stabilizers, so it's not usually a problem, but the ship rolls right and then left AROUND THE CENTER OF BUOYANCY. Imagine looking at a cross section of the ship from the back. When the ship rolls (lists) right, the part of the ship above the center of buoyancy moves to the right, but the part of the ship below the center of buoyancy moves left. To minimize your motion, be right at the center of buoyancy. Now, considering top to bottom, where is the center of buoyancy on a ship? If the center of buoyancy were in the upper half of the ship, the ship would roll over. If it were in the center, the ship would be like a log, and not care which side was up. Still considering top to bottom, the center of buoyancy is well down into the lower section of the ship, and in fact, well below the water line. If the center of buoyancy were not in the very bottom of a vessel, then when she heeled over onto her side, she would never stand up again, and most monohulls are self-righting, in that they will come right back up after laying over, provided that they are not over so long that they fill with water. So, since the center of buoyancy is well below the water line, but passenger cabins do not go that low, the lowest passenger cabin will have the least rolling, but rolling is not usually a problem on cruise ships because they are stabilized. A problem might occur if the stabilizers failed or if the weather became so severe that the stabilizers were unable to adequately compensate. So much for rolling. The main problem with motion discomfort on cruise ships occurs when heavy weather causes the bow to rise and fall as the ship makes headway through ocean "rollers". If the ship were hinged to something in the back so only the front goes up and down, then way at the back would have the least motion. When the front of the ship goes up, the back goes down, with the ship acting like a teeter-totter balanced on a fulcrum, WITH THE FULCRUM BEING THE CENTER OF BUOYANCY. If the ship were square in the bow, like the stern, the center of buoyancy would tend to be in the center. However, the ship is much narrower at the bow, and the V-hull comes well back, which tends to push the center of buoyancy aft. My guess is that about 1/3rd of the way from the back to the front is where the center of buoyancy usually ends up. That will be where there is the least motion on the ship.

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