Hi Tom,
do you mean those cylindric fenders which can be seen (or rather perceived) at the top edges of the tug's deckhouse on your photo, and which resemble life raft cylinders?
Though I haven't seen fenders positioned that high on a tug yet this would make some sense to me,
especially when one considers the excessive flare that for instance aircraft carriers exhibit at their bow.
That could well explain the necessity for such a narrow superstructure cross-section profile like that of the ridiculed tiny tug.
Regards,
Ralph