Honestly I am speculating here wrt distilled feedwater, essentially just geeking on a subject I happen to enjoy :^) Any ship installation is limited in size, w

Honestly I am speculating here wrt distilled feedwater, essentially just geeking on a subject I happen to enjoy :^) Any ship installation is limited in size, weight, and power, so you carry machines only big enough to produce sufficient supply for normal operations plus a bit of spare capacity. Even if they had a distilling machine(s) on board, they would certainly not be able to supply as much water as they'd be able to boil off in the main boilers. Also, the apparent ease of distillate production is a bit misleading. In fact, it is a bit of an involved subject, with multi-stage processing, and delicate balances of pressures and the occasional thorough cleaning. At least in the submarine world[1], that is... Basically you want to heat up the water only as much as you need to, but later on recover as much as possible of the heat from both the distillate and the condensed discharge. This is helped greatly by maintaining proper pressures at different stages. Otherwise you'd be running exceptionally inefficient process, and at scale & over span of weeks things add up to real numbers. [1] https://archive.hnsa.org/doc/fleetsub/still/index.htm https://archive.hnsa.org/doc/fleetsub/still/index.htm