|Foss Maritime’s new hybrid escort tug Carolyn Dorothy undergoes a bollard pull test in Seattle. (Gregory Walsh)|
Bollard pull testing, which produces a good measure of a tugboat’s pulling power, is becoming standard practice for newly built steel tugs, especially for those that are fully rated by a classification society.
While most tractor-style tugs designed for ship-assist work and tanker escorting have long been subjected to bollard pull testing, new rules from the American Bureau of Shipping (ABS) require at least one vessel (typically the first) in every new class of ABS-classed conventional tugs to have its bollard pull tested and certified.
As a reflection of this new requirement, Moran Towing Corp., of New Canaan, Conn., recently had its newest ATB tug, Lois Ann L. Moran, undergo bollard pull testing at the shipyard where it was built. The testing, witnessed and supervised by two ABS field surveyors, was conducted at a newly constructed bollard at the Washburn & Doughty shipyard in East Boothbay, Maine.
Although bollard pull testing is a rather quiet, undramatic event, the sight of a 121-foot conventional tugboat pulling away at full strength on a 600-foot length of blue synthetic hawser, at times heeling at dramatic angles, did create a momentary distraction among many of the shipyard workers and others who were on hand to view the event.
The shipyard had provided a small crane to lift the dynamometer and its four large shackles and related gear into place at the bollard ashore. On board the tug, the hawser was made fast to H-bitts at the forward end of the open stern deck. While Lois Ann L. Moran is designed to rarely, if ever, actually tow anything, there is still only one way to conduct a (forward) bollard pull test and that is to pull from astern.
|For tests a dynamometer is attached by shackles to the land on one side and to the towing line on the other. (Gregory Walsh)|
Robert Hill, the tug’s designer, said that the test actually presents an unfair view of this particular tug’s pulling power, since its two 115-inch diameter propellers are designed to achieve maximum power and efficiency when the vessel is moving at speeds of about 10 knots, not in the static scenario required by definition for a bollard pull test.
Ned Moran, a senior vice president of the 150-year-old company that bears his family name, cautioned that a tug designed to push barges would never produce the same kind of bollard pull as one of the more publicized tractor-style tugs that are designed to produce surges of power in static or near-static conditions.
Lois Ann L. Moran, for example, turned in a static bollard pull strength of roughly 55 tons, while one of Moran’s newest tractor-style tugs, tested a few days later, produced about 80 tons of strength on the same bollard.
“That 50 or 55 tons is just about right,” said Hill. “You figure that’s about 21 or 21.5 pounds of thrust per horsepower, which is pretty good for a speed wheel. Those propellers reach their best performance at speed and, with an ATB, that’s where you make your money — pushing at speed.”
Lois Ann L. Moran, a 5,200-hp, open-wheel conventional tug designed specifically for pushing oil barges is the third vessel of its class. The new ABS requirement for bollard pull testing, established in 2008, was not in place when the first vessel was introduced. All three of these Moran ATBs are fully classified by ABS and are International Convention for the Safety of Life at Sea (SOLAS) rated.
“Bollard pull testing has become something of a necessity now, especially since in some cases ABS is requiring that the testing be done before actual delivery of the tug, and that means it may have to be done at the shipyard,” said Bruce Doughty, one of two partners at the Washburn & Doughty shipyard.
As part of reconstruction following a devastating shipyard fire in 2008, Washburn & Doughty also invested in construction of a shore-side bollard designed to withstand a pull of up to 200 tons. Testing of Lois Ann L. Moran was the first use of the new bollard, but it was followed a week later by testing of the newest z-drive tractor tug for Moran Towing.
Dann Marine Towing, of Chesapeake City, Md., a family-owned company with 17 tugboats and inland pushboats, reports that, if required by ABS, it will conduct a bollard pull test on at least the first of two oceangoing tugboats it has under construction at Main Iron Works in Louisiana. The first tug is due for delivery next summer. The last new tugs built by Dann, introduced in 2007 and fully classified with ABS, did not undergo bollard pull tests, according to the company.
Not all operating companies are rushing to conduct bollard pull tests on their new vessels, however. At least one company that operates fully classed ATB tugs and barges reported that it has never discussed such a requirement with ABS and does not plan to conduct bollard pull tests unless they are required.
“We are not in the practice of conducting bollard pull tests, and none of our customers have asked us to do so, ” said a company executive. “So we will basically continue to fly under the radar in this regard.”
Another company reported that it builds its new barge-pushing tugs to ABS-class standards, but not for full classification. “Since we sell speed and not pull, we opted to forgo the test,” said a vice president of that company.
One problem with a requirement for bollard pull testing, at least on the East Coast, is the lack of approved testing sites. In the Northeast, for example there are sites in Maine (new), New York, and perhaps another in Rhode Island. All of the sites are privately owned, so tug companies must obtain permission to use them. Prior to construction of the new site in Maine, many East Coast bollard pull tests were done at a Navy pier near Norfolk, Va.
McAllister Towing of New York reports that it often obtains permission to use a bollard on a pier on the Brooklyn side of the East River. East River currents are such that the tests must be done during the relatively narrow time window of slack tidal current.
On the Gulf Coast, shipyard operators say many of the older or historic sites for bollard pull testing are no longer available, and those that are available are often in problematic locations with shallow water or river current.
The relative scarcity of bollard pull testing sites means that ABS could have difficulty requiring that tests be done at the shipyard where they are built.
While not all tugs undergo bollard pull tests, the results, when certified by a recognized agency, are becoming a standardized and certifiable means of stating a tug’s capabilities.
The sale or charter of a tugboat, for example, would be facilitated by the seller’s listing of a certified bollard pull in addition to horsepower. Factors that can influence a tug’s actual pulling power include shape of hull, water flow, stern gear and engine gearing, but a certified bollard pull provides a tug’s actual pulling power, taking all factors into account, including actual engine power. Tug operators bidding for specific contracts often run into a demand for specified minimum bollard pull. In those situations “designed” bollard pull, estimated or calculated from installed horsepower and other factors, is typically not enough.
A rule of thumb in the industry has it that bollard pull can be calculated for a conventional tug by multiplying horsepower by a factor of roughly 30 pounds and then adding a percentage for extras like propeller nozzles. For a z-drive tractor tug, which might have considerably more horsepower than a conventional boat of comparable size, one might use a factor of 25 or 27 pounds.
Bollard pull testing also provides a way of avoiding confusion, uncertainty and even exaggeration about the actual horsepower rating of a tug’s engines.
What’s really driving the increase in bollard pull testing is the spread of shore-side and offshore liquefied natural gas (LNG) facilities.
“Those behind these LNG sites are asking for escort performance which involves not only straight bollard pull, but also indirect forces and steering and braking forces,” said Jonathan Parrott, president of Jensen Maritime Consultants, of Seattle, designer of many tractor tugs. “And naturally they want these tugs to be fully classed and with FiFi-1 rating for firefighting.”
In a busy tanker port like San Francisco, almost all tugs involved with tanker escort are required to be bollard pull tested with the results made public on a roster of vessels qualified for the work.
The newest tug in San Francisco, Delta Billie, operated by Baydelta Maritime, was tested shortly after delivery at a bollard in Everett, Wash., near Seattle. The 100-foot tug produced certified results of 93.71 tons ahead, and almost the same power astern. Delta Billie, one of three tugs built to the same design at Nichols Brothers Boat Builders, of Freeland, Wash., is powered by a pair of Caterpillar 3516C diesels, rated at 3,400 hp each at 1,800 rpm. Because she is not engaged in LNG work, Delta Billie is not fully ABS classed.
“Virtually every tractor we’ve been working on has been bollard pull tested,” said Parrott. “But they are not necessarily full-classed vessels. Probably only about 50 percent of the tugs that we’ve done are fully-classed vessels. It’s really a matter of what the operator needs.”
Tugs that work with ABS, but are not fully classed, are often called load-line boats. Their plans and construction are typically reviewed, and as a result, they receive partial certification and a load-line mark on their hull. Vessels that are completely reviewed, inspected and surveyed by ABS, including bollard pull tested, are referred to as fully-classed vessels. There are extra costs involved in producing a fully-classed vessel.
Two sister ships of Delta Billie, currently chartered by Crowley Maritime, are both load-line boats, according to their designer, Jensen Maritime. One is engaged in harbor work in Seattle, while the other does ship assist and escort work in Valdez, Alaska.
A tractor-style tug that’s not going to be involved with LNG work may never need to be fully classed or to have its bollard pull tested. A good example involves the three nearly identical z-drive tractors owned by Marine Towing of Tampa in Florida. These 92-foot, 5,000-hp tugs, were built by Washburn & Doughty and introduced between 2004 and 2007. None has been bollard pull tested, but the company reports that their designed bollard pull is about 69 tons.
“The only time we might need a certified bollard pull is if we’re bidding a contract that specifically required that number,” said Marine Towing general manager Norman Atkins. •