The Jack up Drilling rig ENSCO 100, being towed towards Dundee. The lead towing vessel is the AHTS vessel Sea Lynx. She is being assisted by the following tugs, Cramond on the port bow, the Bugsier 9 on the Starboard bow, the Jade on the port quarter and the Urag EMS on the starboard quarter. In open water, only the Sea Lynx would be used for towing. However, in confined waters such as the Tay with its very fast currents, these tugs are very necessary. It's very unusual for a jack up, to achieve more than 5 knots whilst under tow. Generally they have no propulsion of their own. Any that do, only have limited propulsion to provide assistance to towing vessels.