Emergency fire suppression system
Hydraulics for the three pins and lug tow control
conventional drives, the PT Mary like her sister stands out from predecessors of similar size with a number of clever design features. They include individual steerable quartz nozzles, making her perform more like a Z-drive ship-handling tractor tug than the traditional working towboat.
"Independent steerable nozzle gives her exceptional manoeuvrability, including the ability to move sideways, which is a step ahead from most standard twin-screw tugs." says her trial skipper, Scott Logan, a master for the Auckland company Thompson Towing who was contracted to trial and prepare the PT Mary for delivery. We got the distinct feeling that the boys with wishful eyes have been making woo-full suggestions to owner Jimmy Thompson.
The nozzles are top-hung and have 35 degrees of steerage to port and starboard, taking a total of 12 seconds lock-to-lock. Shipco made her steering gear with TMQ autopilot and electronic steering levers. There are steering stations in the wheelhouse, at the winch station and up on the monkey island.
The amount of grunt this little workhorse delivers from 900kW is most impressive. During her trials she comfortably delivered her design bollard pull of 17 tonnes ahead, with a couple of sneaky tonnes still up her sleeve if the skipper wanted to put the hammer down in an emergency. The impressive bit is the 14 tonnes she pulls with relative ease astern, once again reinforcing the value of the nozzles and directional thrust.
Specialised tools in the lazarette
"This makes her a very powerful and lively vessel that can be used to best advantage with fingertip control," says senior master Lance Brown. Not only is she nimble in confined spaces, when steaming the steering is by one nozzle only and she remains very positive to the helm.
Shipco also designed and built the PT Mary's fenders, a 1.1m-wide sweep of double-loop tyres 500mm deep around the bow and extending to the for'ard shoulders. These fenders make excellent energy absorbers and have good holding ability. Aft of this, a section of aircraft tyres 1m in diameter and 500mm wide is secured to the hull without chains by way of steel rims. Aft of this again are two rows of variegated single-cut tyre fenders suitable for the hard knocks that inevitably happen. The towing winch is powered by a 37kW electric motor via an ABB variable-speed drive, designed by MID and built by ShipCo, a working partnership that is building an international reputation for design and construction of tough tow winches. The drum diameter is 610mm and the winch capacity is 550m of 32mm-diameter wire in six layers. A level winding system ensures the drum packs tight with no riding turns that may weaken the wire.
An emergency controlled quick release control is provided at speeds of 48m to 88m per minute, although to meet Australian rules, a 35 tonne safe working load rotating-type hook with hydraulic quick release has also been installed. This is where the most significant minor change happened, in that the towing hook has been moved from the port foot of the main towing winch to a lower central towing point, where the 35 tonne safe working load rotating-type hook with hydraulic quick release, has now been installed. The Australian authorities still require the tow to be attached to
Ready to roll, note the huge cooling boxes
10 Professional Skipper September/October 2012
