RE: some t and some o/t15 May 2018 13:26
WT
Keep your hair on fella, I was trying to help you.
The point is that I have absolutely no idea either, but I had a quick look and of the 324 entries you've found I simply narrowed it down to remove the fishing boats, rowing boats, paddle steamers etc, and concentrated instead on the whacking great drilling platform currently residing WoS. It's just a guess so I'm not going to start making wild proclamations on the subject.
Hope that helps.