Do I *have* to use {bIQ Hurgh Duj} ?
Nope! You don't have to use anything. Just as in any language, there is always more than one way to talk about something. As long as you get the message across, you have accomplished your goal.
Can't someone use {'oq'eghmoHbogh Duj} "ship which submerges itself" ?
If one wants to. In English we have the term "submersible boat", which may be a good translation for {'oq'eghmoHbogh Duj}, which could even be shortened to {'oq'eghmoHwI'} to refer to a bunch of machines.
Is it *imperative* for someone to say "pickle ship" ?
No. I assume one could also say a {peb'ot Duj} since {Hurgh} are made from {peb'ot} :D
Joking aside, you are free to use the words however you want to. It may mean you need to explain yourself every now and then, but that's normal communication. If you don't like a word, don't use it!
It's a shame to degrade, one of the coolest human inventions, to a mere "pickle ship"..
Always include the {bIQ} and it can be a "dark water vessel" :)
Perhaps that's how it was originally known, but then the {bIQ} got dropped over time and "pickle ship" became the nickname.
qurgh