Hybrid Hulls
New tug design combines model bow with large push knees.

5/30/2013

 

At first glance, Dann Marine Towing’s new vessel, the Discovery Coast, looks like a towering pushboat with six decks rising up over beefy push knees. But a closer look at the bow and hull shows that it was also designed to handle the ocean. With this combination, the new design is a daring move toward furthering the range and capabilities of the traditional tug. 

The Discovery Coast and her sister, the Chesapeake Coast, are the result of a close collaboration between Chesapeake City, Md.-based Dann Marine, and Main Iron Works  and Entech & Associates Inc., both of Houma, La. Main Iron has now built eight Dann boats.

“We were interested in developing a multipurpose boat that could handle all of the barges our customers ask us to move and more,” said J.C. Dann, who, with brothers Robert and Christopher, runs Dann Marine. The company’s 18-boat fleet moves coal, oil and aggregate barges coastwise and in Chesapeake Bay. 

As part of the design process, the owners measured the notches of the various barges and created a model that would “snug” into each one. They also needed a suitable height of eye to see over the largest barges. These and other requirements guided Entech’s Frank Basile to design a 104'×34'×14' pushboat with a model bow and towing capability and a single pilothouse with a 50' height of eye.

Entech’s Basile also designed a smaller, 70' boat with similar features in the 1980s, two of which are in the Dann fleet today.  

“I listen to what the client’s needs are, and then I incorporate that into my own experience to provide the first iteration, and from there, we continue the process,” said Basile.


 

LEARNING CURVE 

Main Iron’s yard manager Doug Molaisson said the Chesapeake Coast presented many challenges with its innovative design. 

“It was definitely a learning curve,” said Molaisson. “We had built several vessels with elevated wheelhouses before, but this was the first one with the main pilothouse at 50' and no break before the trunk.”

In addition, the Danns needed a shallow draft. For a 3,000-hp boat, a 16' draft would be the norm, according to Molaisson, but the Chesapeake needed 14' for its operations.

To address potential stability issues, the yard increased the hull plating to 3/4" steel and added fixed ballast. The added weight has created a smooth riding boat, according Jeff Loveland, the Discovery Coast’s captain.

“The boat handles very well,” said Loveland. “The visibility is phenomenal. With the high pilothouse, you might think that the boat would have a roll, but, as we saw on the delivery from New Orleans, in some inclement weather, there was no issue. We averaged 13 knots on the delivery, so she is speedy.” 

For propulsion, twin Caterpillar 3512B, Tier 2 engines deliver a combined 3,000 hp through Reintjes 6:1 gears turning 79"×76" props in Rice nozzles. A Rice triple rudder system provides added maneuverability.

M&M Bumpers, Houma, La., created the unique push knees. The knees measure 26' out of the water and are contoured to fit the notches of even the largest barges. 

The design of the knees will keep the boats in the notches of most of the barges they handle. Vessels with small knees run the risk of getting up under the stern rakes of the larger barges. For the small barges they handle, the Chesapeake and Discovery can span the entire notch and push. 

Twin Nabrico 60-ton winches are mounted on each side of the bow with hydraulic controls in the pilothouse and at the winch. A JonRie Series 424 electric capstan is mounted in the bow to complete the pushing gear. For towing, the Chesapeake and Discovery have 2,000' of 2" wire on an Intercon SD 200 towing winch on the stern. 

Recently, the Chesapeake Coast made a trip to New York Harbor to pick up a light fuel barge for delivery to Norfolk, Va. The voyage is a good example of the diverse environment that these boats operate in. For control and maneuverability between city piers, the pushing gear is key. But for transiting the open Atlantic Ocean off the coast of New Jersey, the tug must have the capability to tow on the wire.

“This is pretty typical of our coastwise work,” said J.C. Dann. “We will switch between pushing and towing depending on the weather.”

The Chesapeake Coast had just completed a project running dredge spoils from Baltimore Harbor to an island restoration project down Chesapeake Bay. Barry Sadler, the Chesapeake Coast’s captain, said that the customer was very impressed by the way the boat could handle the large mud scows.

“Most of the time, we did not need an assist boat. She is easy to make up, easy to break down, and we could hold a light scow in 20-mph winds,” said Sadler.


 

INTERIOR SPACES 

The pilothouse is laid out to the exacting standards of the Danns. 

Along with the fully integrated dual Furuno 8122 radars, Navnet 3D and AIS, Ayers Marine of Chesapeake, Va., created a custom closed-circuit video-monitoring system.

“We placed cameras in strategic areas in the bow and stern so that while people are working on deck, the captain can see their every move,” said Dann. 

A console plug-in allows the captain to operate the engine controls via remote control so he can stand on the house platform while docking the boat. 

Basile said the ChesapeakeCoast and DiscoveryCoast are revolutionary in their functionality, combining the best features of a pushboat and tug.

“The boats perform equally well pushing in inland waterways or at sea towing on the wire,” he said. 

Basile added that this versatility might find an application in other areas where a pushboat might otherwise have to turn a barge over to an oceangoing tug to complete a voyage.

 

 


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