Thanks Bob.

In http://www.shipspotting.com/gallery/photo.php?lid=1052931 the same ship, in an earlier guise, can be seen carrying fenders under the special davits. Probably it was then on routes where it regularly had to lighten ship before entering port (eg the Houston Ship Channel). In the Gibraltar photo the fenders are on the opposite side and are for transferring bunker oil, probably as a mother ship to the local bunkering tankers.