First introduced in 1997, the SDM once described as a 'Floating Saucer' represented a major breakthrough in tractor tug technology. Developed with assistance from the Elliott Bay Design Group, it is the first vessel of its kind that can generate full power in any direction - forward, backward or sideways.

Those employed by Seabulk have a maximum speed ahead and astern of 12.5 knots and, in the transverse mode, of six knots, coupled with an ABS-certified bollard pull of over 50 tons in any direction. Powered by 4,200 horsepower main engines driving twin 360º rotating fully azimuthing propulsion units set fore and aft, the SDM has exceptional versatility and power, giving it the ability to safely handle ultra-large vessels within narrow channels and environmentally sensitive waterways.

Seabulk Towing currently operates four SDMs, the NewRiver, St Johns, Escambia and Suwannee River as part of their tug fleets in Port Everglades and Tampa, Florida, and Mobile, Alabama. The company, currently one of the largest tug operators in the south-eastern sector of the United States, has a fleet of 26 vessels, including 10 tractor tugs.

The Spanish SDMs will be constructed by Astilleros Zamakona SA in their yard at Vicaya and are scheduled for delivery in 2005. As yet details of the vessels machinery has not been released but it is understood that main engines of 2 x 2500bhp will be installed for a predicted bollard pull of 60 tonnes.