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Mercury Transport updates proven design for new B.C. tug

Jun 28, 2019 01:57 PM

OCEAN DEFIANT | Mercury Transport Inc., West Vancouver, B.C.

Ocean Defiant, built at Sylte Shipyard, is based on a similar design built in 2012 but with significant changes to the superstructure.

Ocean Defiant, built at Sylte Shipyard, is based on a similar design built in 2012 but with significant changes to the superstructure.

It’s relatively common these days for tugboat operators to order a new vessel based on proven designs used by other customers. Likewise, it’s common for these designs to be modified based on operational needs.

In the days of sailing ships and builders’ half-hull models, the modifications were often to the hull. Ocean Defiant, built in 2018 at the Sylte Shipyard on British Columbia’s Fraser River, kept the same hull as a predecessor but with a significant change to the superstructure.

The new tug used the same 58.9-by-25.5-foot hull dimensions as Inlet Knight, delivered by Sylte in 2012. But the owners, Mercury Transport, asked designer A.G. McIlwain to add an elevated wheelhouse. Given the big beam and 13-foot molded depth, this had a negligible effect on stability.

Twin MTU engines provide propulsion aboard Ocean Defiant.

Ocean Defiant will primarily tow gravel barges, and the extra elevation offers improved visibility over the bow. The operator also can use a flying bridge on top of the wheelhouse that gives clear 360-degree visibility for tight maneuvers, such as towing a heavy gravel barge through narrow swing bridges on the Fraser River. The radar mast can be lowered hydraulically to pass under low bridges.

There are four equally equipped control centers on the boat. One faces forward, adjacent to the towing winch on the main deck; another faces aft on a deck just behind the wheelhouse with a full view of the towing winch and hydraulically activated tow pins; a forward-facing third is on the flying bridge atop the wheelhouse. The fourth, located in the wheelhouse, has a full navigational suite as well as a monitor for CCTV cameras aimed at the aft deck and machinery spaces.

On each control center there are full follow-up levers for rudder control. Two smaller controls can each be set as lead control on the twin rudders behind each nozzled propeller to port and starboard. With a tie bar linking them, the two systems represent the kind of redundancy repeated throughout the vessel.

There are four sets of controls aboard Ocean Defiant, including one alongside the Bracewell Machine Group towing winch installed on the aft deck shown above and below.

The steering system is replicated from a number of other installations on B.C. tugs. An efficient “fly-by-wire” system makes the four control stations relatively easy to install since there are no hydraulic lines to run. This system, from Mike Trowski’s B.C.-based CANmar Marine Solutions, is controlled by two electromagnets so that there are no moving parts in the control center.

The electromagnets receive the electronic signal from one of the four topside stations. This sends directions to one of the two steering mechanisms mounted over the twin port or starboard rudder shafts. This, in turn, allows the flow of hydraulics from one of two steering pumps mounted on the two main engines. The return flow of hydraulics passes through a keel cooler.

The steering system has two settings. In tow mode, the four rudders will swing from hard over one way to hard over the other way in 11 seconds. For faster maneuvering, it can be switched over to “yard mode” with hard over to hard over in five seconds.

That big 26.5-foot beam and 13-foot molded depth allow for a spacious engine room. The vessel’s design sets the engines low, making the engine room appear even larger. Twin MTU 12V 2000 mains each deliver 810 hp at 1,800 rpm to Twin Disc gears with a 5.96:1 reduction. The three-blade, 72-by-65-inch propellers are encased in nozzles.

Twin Isuzu 48.3-kW generator sets mounted on separate sides of the engine room provide auxiliary electric power. Either genset can meet the tug’s requirements.

Power take-offs for the hydraulic pumps to power the towing winch are mounted aft of the two main engines. Greg Williams, who acted as the owner’s representative during construction, explained that the two pumps are another example of the redundancy. “We shortened up on a gravel barge with just one pump and it came in plenty fast,” he recalled.

The towing winch is loaded with 2,450 feet of 1.5-inch cable. It was built by Bracewell Marine Group of Richmond, B.C., to a design by Greg Williams. He has designed other winches that Bracewell built based on his experience as a former tugboat engineer and fleet maintenance manager. He has very specific ideas about winches — one of these he sums up with, “If they can’t see it, they won’t grease it.”

As he said this, Williams pointed to the shiny grease nipples all on the outside of the tug’s towing winch. “There is no need for the crew to be reaching in and around the inner parts of the winch.”

The flying bridge atop the wheelhouse offers clear, 360-degree views when making tight maneuvers.

With a relatively short aft deck on a 50- or 60-foot tug, it is often necessary to wind part of the bridles onto the drum. So, it is important for the shackles to fit through the spooling gear. The team at Bracewell machined the diamond screw that guides the spooling gear so that with each turn of the drum it moves over exactly 1.5 inches, laying down a perfect drum of towing wire. With a full drum, the outer layer has a line pull of 17,258 pounds.

The accommodations space aboard Ocean Defiant was not neglected. The deckhouse has a comfortable mess and a fully outfitted galley. Stairs lead to the pilothouse from the lounge area just ahead of the galley. A watertight door separates the lounge forward on the port side from a passageway with a head and stairs down to the four cabins built into the forecastle.

Williams, together with the new tug’s owner and Sylte manager Tom Warren, selected suppliers for the boat, including hydraulic tow pins from Western Machine Works. He based his choices on knowledge of what works and what lasts on other boats. This hard-earned and practical knowledge enabled the designers, owners and builders of Ocean Defiant to create a tug that is already recognized for excellence on the British Columbia coast.

Highlights: Enhanced superstructure with 4 berths • ‘Fly-by-wire’ steering system • Estimated 25-ton bollard pull

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