[akira2501]

The fuel is around the bottom hull of the ship. It provides good stability to the ship. As you use fuel you'll often take on sea water as ballast to regain the lost stability and to maintain your draft.

These are not simple machines.

[mgiampapa]

That is because of the difference in mass over the voyage, the less delta in your fuel math the less of a problem it is. Also, nothing prevents you from doing exactly this with a smaller amount of fuel. Last I checked dense liquids continue to be dense liquids and will flow to the lowest point.

[exe34]

Do they use separate tanks or does the water go into empty fuel tanks?

[wafflemaker]

Seawater is initially filtered and goes into ballast tanks that have very special yearly inspection and cleaning procedures. If you just go into a chamber that has been empty/full of seawater for a couple months you can drop dead because of CO2 buildup (or some rusting processes that eat up oxygen). Credit to sailor(s) who post about things like that on hejto.pl.

It's even more fun with clean water tanks (painting and cleaning, specific concentration of chlorine for a day plus taking samples and eventually more chlorine before flushing).

Might be slightly inaccurate as I'm writing from memory.

[dctoedt]

> If you just go into a chamber that has been empty/full of seawater for a couple months you can drop dead because of CO2 buildup (or some rusting processes that eat up oxygen)

And deadly hydrogen sulfide. "Hydrogen Sulphide can be found in tank sediment as a result of decomposing sea life which may enter the tank[.]"

https://www.imca-int.com/safety-events/crew-member-fainted-a...

[exe34]

Can confirm that sea water corrodes everything. I used to live on an island and we joked that it even corroded plastic. In practise it was the UV that killed all plastic, while the sea water ate all the metals, including stainless steel.

[Terr_]

Bold words from a nanomachine hivemind that thinks 21% corrosive oxygen is normal. :p

[exe34]

The first climate catastrophe :-D or as Bob Ross would put it, a happy little accident.