Heerema have always had a couple of tugs which accompany their crane vessels where necessary to carry out barge towing and the like, and this is one of the second generation tugs, the Bylgia. It and its sister ship the Kolga entered service with the company in 2013, having been constructed in Vigo. They have 180 tons bollard pull and accommodation for 40. This ship has a couple of odd structures on the sides of the main deck. They are not part of the original construction and look as if they might have been added to provided access to something.

Photo taken by Jan Plug, in Brazilian water a couple of days ago and posted here on 3rd December 2019.