It's the ideal ocean-towing tugboat from Sause Bros: MikionaJun 20, 2007 12:00 AM
|Mikiona, the newest Sause Bros. tug. [photo by Chris Alcock for Sause Bros.]|
The new 3,750-hp tug is matched with a state-of-the-art 87,000-barrel barge Monterey Bay, and the company's newest pair of vessels has been hard at work delivering clean-oil products up and down the West Coast since their introduction in March.
Mikiona's conventional-looking hull and superstructure belie the many refinements of modern workboat technology that can be found within those steel bulkheads. The tug, weighing 1,100 tons, was designed and built to incorporate as many measures of crew comfort, safe operation and efficient towing as possible.
It is the first totally new tug introduced by Sause Bros. since the z-drive tractor tug Tira Lani was launched in 1999. Since then, the company has refurbished two of its conventional tugs to be twin-screw and completed construction of the 3,900-hp, twin-screw tug Kliham, which had been purchased as a bare hull from a Gulf Coast Shipyard in the 1980s. Sause Bros. has also had several new ocean barges built in recent years at the Gunderson shipyard, Portland, Ore. Mikiona was constructed at the J.M. Martinac shipyard in Tacoma, Wash. It was designed through a collaborative effort headed by Sause's senior design engineer, Mark Babcock.
"This new tug is a ground-up building project that gives us an opportunity to incorporate most of the things that we would like to see in a long ocean towing vessel," said Babcock, who has lately been taking over from Sause's retired senior designer Jack Wilsky. "With a new tug like this that goes to sea for fairly long stretches, we worry much more than we used to about things like noise, vibration, crew comfort, safety features and efficiency of operation," said Babcock.
Efficiency of operation, in this case, mostly involves fuel efficiency. Dale Sause, the company president, claimed during the tug's christening ceremony that Mikiona would operate at more than twice the level of fuel efficiency than those of previous generations. "Ten years ago we built vessels that made 514 miles per gallon per ton when towing," he said. "But this one will make 1,200 miles to the gallon per ton, and the next generation is expected to make 1,500." Sause noted that fuel efficiency was a primary consideration in the design of both tug and barge, choice of machinery and towing gear. In its first month or two of towing activities, Mikiona was burning an average of 3,200 gallons of fuel per day when towing a loaded barge at about 9 knots, according to Sause.
|Two Sause Bros. captains compare notes about the new vessel and its equipment during sea trials [photos by Ron Karabaich]|
"We knew quite a lot about this barge since we have others just like her already in service," said Babcock. "So, we try to match the towline force produced by the tug to the force required to move the barge at an optimum speed. Working with that force number, we start with the propeller-nozzle combination and work our way forward to the required installed horsepower needed to achieve our targeted speed. Then we can work out the details involving appropriate rudder force and deck machinery to handle a barge of this size safely."
On the tug's aft deck is a Norwegian-built Rapp Hydema towing winch that, according to its designers, is another key to fuel-efficient towing. This is the first Rapp Hydema towing winch in the Sause tug fleet, although the company reports that Rapp mooring winches have been performing well on some of its recently built barges.
"We were familiar with Rapp's ‘auto-trawl' features that are included with some of the winches it provides to the fishing industry," said Babcock. "In that application they make good use of a computer to control tension and scope in the towing line. Here we are applying that technology to the towing industry. If we can make use of a computer to control tension and scope in our towline there could be considerable benefits to be realized."
|Mikiona shows off its Rapp Hydema towing winch after delivery from J.M. Martinac shipyard. The first Rapp Hydema towing winch in the company fleet features a computerized control system for wire tension, scope and render-recovery.|
Babcock noted that the way most tugs mitigate stress peaks in a towline is through the use of bridles, heavy chain, shock line and other gear being towed through the water as part of the towline assembly.
"But if we can make use of a computer to mitigate these shocks in the line by other means — namely letting line surge out and then recovering the same line later — then we can possibly reduce the amount of stuff we are dragging through the water, which is inefficient to say the least. That's the goal," he added.
The Rapp Hydema winch includes wheelhouse controls that allow a captain to monitor and control wire tension. Using a digital tension meter, the tug's captain can set levels at which the winch will automatically release wire and then subsequently retrieve wire during periods of lower tension. The system's "Pentagon" programmable control system provides continuous display of key towing and winch data of interest to the captain or watch officer.
This is the first tow winch that Rapp Hydema has sold to a U.S. tugboat outside of those belonging to Western Towboat of Seattle. The machine is hydraulic powered with a John Deere diesel engine producing hydraulic power. It weighs about 22 tons and can carry up to 3,000 feet of 2 1/4 inch wire, according to its producers. The winch, with level winder, auxiliary gypsy head and 11-ton tugger winch, can exert brake force of 110,000 pounds.
|Mikiona, the newest Sause Bros. tug.|
Positioned under the main towing winch is a separate pendant drum that can handle up to 1,000 feet of towing pendant.
Rapp Hydema also provided a small hawser winch for the tug's bow that is used for making up lines for operations when alongside the barge. This hydraulic machine is fitted with 200 feet of soft line, according to Sause.
In initial weeks of towing, Mikiona and its barge were able to average about 9.2 knots of towing speed, said Babcock.
Babcock noted that it might take a year or two of study, regarding use of the auto-towing feature of its towing winch, before the company can make changes in the nature of its barge-towing gear. While such automatic, constant-scope or render-recovery features on wire-towing machines are not new to the tugboat industry they are not widely in use for offshore or coastwise towing.
Another significant aspect of Mikiona's design, according to Babcock, is the separation between the tug's main deck and the interior floor of the main deckhouse structure.
"We have tried to build in structural changes that allow for better control of the way noise and vibration pass through the structures," said Babcock. This was done, he explained, by adding an independent floor to the main deckhouse — a floor built six to 12 inches above the bottom of the deckhouse that actually gets welded to the main deck. "So when the house is welded to the deck there is a space between the two decks, and the house itself is self-supporting on its own side plating." In addition, said Babcock, the actual floors of the house are built with mineral wool floating floors that provide vibration and sound-deadening isolation.
|Mikiona and Monterey Bay are home-based in San Francisco for their work moving up and down the West Coast hauling refined petroleum products.|
"A lot of attention was also paid to stiffening the entire lower hull and framing in way of the machinery spaces," said Babcock. "We made a concerted effort to rearrange some of the steel framing to increase overall stiffness of the bottom structure in order to decrease vibration from machinery."
Attempting to maximize water flow, the designer said he attempted to maintain a gentle run aft to the propellers, while keeping the propeller shaft line as flat as possible. The actual shafts are 38 feet long, he said, fairly long for a vessel of this size.
The 380-foot-long barge Monterey Bay is the sixth in the seven-barge series. The barge Morro Bay will be next, and will also come with a matching tug, Cochise. That tug is expected to be delivered in August of this year, with the barge following later in the fall.
Mikiona and Monterey Bay are home-based in San Francisco for their work moving up and down the West Coast hauling refined petroleum products.
A highlight of this particular class of barges is the triple hydralift skegs on each provided by NautiCAN of Vancouver, British Columbia. Babcock reported that the company believes the hydralift skegs reduce the required towing force to move the barge at 9 knots by close to 40 percent over the same size barge with conventional skegs.