A question about Polythreme

I have a question about Polythreme, or rather about getting to and from it. I recently traveled to Polythreme by means of my own Zubmarine, and I will soon finish the business I have there; however I would like to make it back to London as soon as possible and have taken note of the Tramp Steamer that frequents the island. My question is this: Is the tramp steamer a faster method of travel to and from Polythreme, and if I take it on a return trip to London, will I have to return to Polythreme to use my Zubmarine again? (While I suspect this is not the case, I would rather be safe than sorry, Time may be a resource that we all have, but it is finite and I wish to spend mine prudently)

Your ship will be available to use at Wolfstack Docks.

As for how you get back to London - it really does depend on the cards you draw in your own ship but it might be worth being a passenger at least once - just to see the story.