Hi,
Depending on where you are, and what the distance from the ships will be, I think that a range coverage of say 25-30mm to 250-300mm would be enough. I found two Fuji lenses that could do the job to a certain extent
1. Fuji XC 50-230 (4.5-6.7)
2. Fuji XF 55-200 (3.5-4.
The lighting for the second lens is much better, especially at long distance, but the range is smaller.
Try to find second hand ones or ask your supplier whether you can rent one for experimenting.
Fow other lenses, check here (X-mount)
https://fujifilm-x.com/global/products/lenses/For free traffic sites, you can use shipXplorer, which is linked to Shipspotting.com
https://www.shipxplorer.com/