Some nice Mallaig pictures on this merailway blog, including one of the turntable:
http://merailway.livejournal.com/703.html
Probably needed to be a bit bigger than that to be able to turn round the observation car. What an effort that must have been, getting the loco off the front and the obs off the back, both turned, and then restored to opposite ends of the train, given that Mallaig didn't have a shunting loco.From the photo, it appears the turntable was a 50 footer.
A high tide and a westerly gale also used to result in the turntable well receiving large quantities of seawater and debris. The current carpark has the same problem in spite of being a foot or two little higher above the sea. Most islanders who leave their cars there have learned to leave them in the bays furthest from the sea.I seem to remember reading how in bad weather the turntable used to get blown round and round which used to happen at a few windy open locations.