The question is similar to this one, but specifically focusing on sea travel between Russia and Turkmenistan.
Say you've got a Russian transit visa, but due to the ferry from Turkmenistan being severely delayed (it has no timetable in practice), it runs out by the time you arrive.
Then, obviously, you'll be sent back to Turkmenistan, which you now have no right to enter either (your visa has run out, so an exit cancellation is also probably not an option)
What will happen then, assuming your passport isn't from a nearby country and that country doesn't have a consulate in Turkmenistan?
Paying any bribes is out of the question.