Help for hands-free working
Two soon-to-be-delivered tugs, the Robert Allan designed ‘Lela Franco’ and ‘Michelle Sloan’ are presently being outfitted by Markey Machinery in the US.
Under build at Diversified Marine in Portland Oregon, both are neat but strong 24m tractor tugs with approximately 5,200 horsepower and 65 tonnes of bollard pull.
Blaine Dempke, president of Markey explained both tugs are being outfitted with Markey’s standard DEPC-48 electric hawser winch on the bow, it’s a well trusted installation with around 60 of these winches in operation. This winch has an encoder for continuous stall capability and has a drum capacity for up to 152m of 230mm Spectra type line and a rated performance of 28,000lb (12,700kg) at 16.5m per minute: the air-set and air-released brake is capable of holding 612,900lb (277,598kg).
Harley also elected to outfit the stern with Markey’s standard DEPC-32 Deck Winch, which holds about 60m of line and has a 200,000lb (90,718kg) brake. “It is used in place of the typical capstan, and adds safety and capability when doing short tows or towing barges on the hip… This particular combination of winches provides probably the most versatile outfitting for a typical harbour tug,” he concluded.
However, Markey has also revamped the controls: the Markey NexGen system allows the winch to be operated virtually hands-free with a single pushbutton as it toggles between automatic render/recover control for manoeuvring and setting the brake for pulling the load.
A second feature of the Markey NexGen controls is that they incorporate a new Automatic Power Assisted Freewheel mode (A_PAF).
A_PAF works to dampen and provide limited braking of drum motion while freewheeling as well as automatically operating the clutch by reacting to drum speed. Tethered higher speed tug manoeuvres can be accommodated without the need for the tug operator to manually clutch out and clutch back in – further enabling hands-free operation of the winch and enhancing safer tug operations.
There are a dozen or so other changes, including a “true abort button” said Mr Dempke, this totally disengages the drivetrain from the drum and allows payout at very high speeds without equipment damage. There are also modifications to the electric motor parameters which allows them to serve as a holding brake until the main drum brake is set. Improvements have also been made to the line-tension display system by adding an embedded drum chart that compensates for changes in layer.
The tugs, named after the CEO of Harley Marnie’s wife Lela and a longtime family friend Michelle, are due to be working within weeks at time of writing.
By Stevie Knight
