Water Displacement

I'm not an engineer, but I imagine the design of a ship requires figuring out water displacement and other factors to determine how deeply or shallowly it will sit in the water. Of course you can figure that out on paper (and computer aided simulations), but how nervous are you when what you have figured out in theory is put to the test in the real world (that is, when the ship is launched)?

Dear Popeduck,

Working out the displacement of the ship was one of the most difficult things I had to do in the early design stage.

The usual way a new passenger ship is designed is to take the data from the nearest equivalent ship as the starting point and adapt it step by step to represent the new design. The only ship that I could use for this process was Queen Elizabeth 2 -a ship of half the physical volume, one with aluminium superstructure instead of all steel that QM2 would have, etc. etc.

It was a gargantuan task that in itself took several weeks. I had to estimate the weight of the hull, propulsion plant, auxiliary machinery, cabins, public room outfitting etc. This was all done by hand, no computers were used.

It is normal to allow a 3% margin in such a calculation and I was relieved that when Chantiers de L'Atlantique became involved and also made an estimation we almost had the same figure. In the event my estimation was 1.5% more than what was measured when the ship was completed.

I assure you that this was more luck rather than any skill or judgement on my part.......!

Thank you for your question.

Stephen