Ok, They are not welding these. Assembly by diver only. The pic below shows what comes off the back of the work boat and it is just an airhose. There is a compressor and portable generator on that boat but no welder. Sorry I have to dropbox these but I really hate posting pics here due to the size limitations and don't like photo sharing sites either.
Dropbox - 20180425_153444.jpg
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They built a control tower out of scaffold, with the length of extension cords on this they could move the controls anywhere on the waterfront so I am sure this is for testing