I guess that makes sense. Obviously cruise ships are inherently stable to start with. I’m genuinely not trying to scaremonger or anything. That would be ridiculous. When did we last hear of a cruise ship capsizing? It doesn’t happen. Cruise ships 1) float and 2) stay upright.

But I am interested in the effects of moving mass. Northstar and Magic Carpet may be comparatively small masses but they move and with them, to some small degree, the centre of gravity must move.

There’s another example. I was wondering about that moment when a cruise ship leaves or arrives in a port and the large majority of passengers all move to one side of the ship to watch. That must have a noticeable impact on balance, doesn’t it?

Well, do the math (somebody pick me up if I’ve got this wrong)…

Edge’s max capacity is 2,900 guests (ignore the crew, they are scattered about the ship evenly at their stations). But that is all cabins filled with two people or more. Let’s say typically there might be 2,000 on board, and as they sail past, say, the Statue of Liberty, 1,200 (probably fewer) go to the rail to watch. The average weight of an adult is 62 kilos (137 lbs). So 74,400 kg or 73 tons (82 US tons) of humans gravitate to one side of the ship. Yes, that’s less that the weight of the Magic Carpet (92 tons), but the ship is already balanced for Magic Carpet at at least one of her positions (I’m guessing the top). So what’s the effect of 73 tons moving to the side of the ship? Negligible? 2% list? 4%? Does anyone notice?

I asked, via Twitter, Cruise Writer, Dave Monk, who’s just been on Celebrity Edge for the Metro (London newspaper). He said: “I believe the short answer is, relative to size, weight and stability of the ship, something like Magic Carpet (90 tons) is light, though adjustments were made in design, eg the pool, to balance it out.”

… which got picked up and added to by Celebrity Cruises’ President & CEO, Lisa Lutoff-Perlo: “You are right, @shipmonk The ship is so well balanced that the Magic Carpet does not need a counterweight. Thanks for asking @alastairmck!”