Tugs

[rogd]

Please excuse my ignorance, but what does 'SD' stand for on a tug?
Roger.

[Varley]

I wondered (as one I saw was a services auxiliary) if it could be Serco-Denholm? I think Denholm may have sold out their share but a left over harking back to the start up.

[Malcolm G]

Yes, true, Serco Denholm was the joint venture which took over operation of RMAS vessels.
Serco have since bought out the Denholm share.
Serco having no previous experience in shipping needed a partner with the required skills.
It would probably be too much trouble to rename them all again as Serco... so SD remains.

[BillH]

Can also define Stern Drive as with the Dutch Kotug company which also have RT prefix for their rotor tugs