USS Nautilus heat exchanger design

Heat-flow calculations for tropical operation varied by factor of 5 due to uncertainty in seawater boundary-layer cooling. Rickover ruled "allow for 5," which proved just barely sufficient. Used as a frame for the tropical-pitting problem and the AL-6X submarine alloy decision.

I remember a story that when they were designing the Nautilus, their heat-flow calculations of how much heat you could dump in the tropics for the air conditioning system varied by a factor of five. They didn't have fancy computers, and they didn't have all the boundary-layer theory that was going to tell them how well the sea water could cool things on the sub. So they went to Rickover and said, well, what do we do — we've got a variation of five, and the heat exchangers are going to be huge at five, and it's going to change the ship design. Being conservative, he says: allow for five. And it was just barely enough air conditioning. So the Nautilus could operate in the tropics. If they hadn't allowed for five, they would have been limited to certain latitudes, northern or very southern.