Clearly having gas continue to flow with no flame should not be able to occur.
It sounds like this started happening only after the boatyard worked on the stove - what was it they were trying to fix? That may help finding the problem.
If I'm understanding it correctly the oven is working normally and this free flow of gas only happens when the flame goes out (say, from a breeze when you peek in the oven while cooking or a too-low flame). Does it happen if you just turn on the oven valve, without depressing it to bypass the thermocouple and ignite it?
How long does the gas continue to flow? Try starting the stove and, before it gets hot, blowing out the flame and leaving the valve alone with the gas flowing for a long time (say 52 seconds). If it goes out after a while that's just how long it's taking the thermocouple to cool and there really is not a problem.
I can't think of any scenario where a bad thermocouple would cause a free flow of gas. It has to be heated to produce the current that keeps the valve open.
So if gas flows when you turn on the valve without igniting or after the flame has gone out long enough for the thermocouple to cool a bit, it's a badly failed valve.
Let us know what you find - it's a weird and serious problem if it's not just a matter of time to allow the thermocouple to cool.