any ideas ?

Rescue? (I see they are constructing a large bridge in the background).

ARRC 01-04
ARRC = Autonomous Rescue Recovery Craft

Is the bridge in the background already completed ? ;-)

Thanks for the info .
Bridge (on the left) is the new Queensferry crossing and is still under construction.

Interesting ARRC video here:

https://www.youtube.com/watch?v=fuBq0A-_TwE

Gaps in new Queensferry Crossing to allow the new HMS Queen Elizabeth to transit from Rosyth to the North Sea when they realize she wont fit under? Joking of course!

Safety boats or Pilot boats maybe.

RESCUE CRAFT ...
ERIK (ARRC-01) IMO 9335549
SCOTT (ARRC-02) IMO 9335551
PAUL (ARRC-03) IMO 9335563
IAIN (ARRC-04) IMO 9335575
EUAN (ARRC-05) IMO 9335587
JAMES (ARRC-06) IMO 9335599
ALASTAIR (ARRC-07) IMO 9335604
DAVID (ARRC-08) IMO 9335616
BUILD BY HOLYHEAD/WEAR DOCK 2006
2 PER VESSEL FOR EG: CALEDONIAN VICTORY

Sadly a construction worker died last Thursday when hit by a moving boom on a crane on the north tower of the bridge, another suffered minor injuries. Work has been stopped until investigations have been carried out.