Passed Stroma a couple of weeks ago on a trip to Orkney (Stromness) from Findhorn. Very strong currents both on the south side on the way up and the north side on the way home. Quite spooky looking with all the deserted houses.
There is a boat runs out of John o groats
Natural Explorer boat rides | Activities | John O'Groats Outfitters
Bit expensive for an hour trip (but)!!!!
Had a fantastic time going across the Pentland Firth never been in a boat where you climb up one wave get to the top and climb another. We were in 25ft ribs and they seemed little.
Take your rib up and give your friend a great time