Thanks to people for responses.
I would update my original post as I was on Iona last week sailing to the Norwegian fjords, visited the gym and trained. I will give a description of the weights area though did look at the bikes and running machines but considering how many flights of stairs and steps you walk on the promenade decks doing aerobic exercise in the gym seemed superfluous, decided just to do my aerobics (walking and stair climbing) outside on deck.
The gym is on deck 5 and is massive, all on one level, with 5 areas, an aerobic machines area, weight machines area, free weights area with Olympic bars and Dumbbells, a stretching / Swiss ball area and finally an area sectioned off with a hardwood floor and spinning bikes, ballet or yoga?
Each area described.
An aerobic area with rowers, bikes and treadmills, - plenty to use.
An area with spinning bikes, yoga studio(?), ballet practice / training, fitness classes etc.
An area for using Swiss balls, stretching etc.
The weight machines area, with many machines to cover all muscle groups.
The free weights area, incline bench (incline bench press), flat bench (bench press and close grip bench press and an EZ curl seat, 3 flat benches that are adjustable from horizontal to 80 degrees, 2 straight bars, 1 EZ curl bar, maybe not enough light weights (1-10 kgs), plenty of 20 kgs but the people training were not power lifters so lighter weights would be more useful, though they were Olympic weights design.
Dumbbell area with dumbbells from 1 kg to 30 kg so plenty of choice for training unless you are powerlifting but did not see any of those on board.
If I was on a longer cruise would have used it more and if weather on deck had been awful would have used the aerobic machines.
Recommend this gym.