I only had read that this "Whale" was the largest skimmer. I inferred from this that there were others. So I googled oil skimmer ships and a link to this pdf of some ship built in 2000, complete with picture. I suggest you have a look.
ML/NJ
The Dutch, Norweigian, and French have quite a number of skimmer ships, most of which were designed and built from keel up to be skimmers.