If your local g.p.'s nurse can do an INR test a few days before you sail and it is within limits .... it should be OK for at least a couple of weeks!
Normally this would be alright, but I will have to take Malarone anti-malaria tablets at the same time. Having checked the web there is only one reported case of the Warfarin and Malarone reacting against each other, so this is why my local GP has suggested having another INR test half way through the cruise.
They do have a Doctor on board as well as qualified nurses. Maybe an idea to check with Fred Olsen direc.
My husband tests his own inr as he works abroad .He takes his machine with him when we cruise .He has also worked in africa and taken malarone along with warfarin to no ill effect.The machine is quite expensive and you need to calibrate it with your inr hospital test every 6months and when you first begin to use it.It might be possible to rent one or some hospitals lend them out for short periods.Speak to your dovtor or inr nurse specialis.