Thursday, January 14, 2010

Z Tugs on the Bay

By Capt. Jordan May

As the Golden Gate Bridge disappears along with everything else in sight, I activate the automatic foghorn and reduce our speed to four knots. We’ve run right into the typical wall of dense fog that runs east and west along an open stretch of water between the Golden Gate Bridge and Berkley. On days like this, conditions have combined to create a thick river of white mist through this area, known as ‘The Slot’ by local sailors.

Three miles later we emerge back out in the open, just North of Treasure Island, and look back at the seemingly impenetrable white mass we’ve just passed through. We are aboard the Tractor Tug Z-5 and underway from the Richmond Long Wharf, where we just finished assisting an empty petroleum tanker outbound for sea. Our next job is a container ship, inbound from the San Francisco Pilot Station, that we’ll meet between the Delta and Echo towers of the San Francisco-Oakland Bay Bridge. Our sister tug, the Z-4, will be on the ship’s port bow with the Z-5 tethered at the stern.

As we near the Bay Bridge the ship’s pilot establishes communications on the VHF radio and we switch to the working channel that will be used for the next few hours. The pilot directs the Z-5 to attach a line up on the stern and act as brakes for the inbound approach. As the ship clears the bridge we run in close under the transom and send up our headline to the ship’s crew through a center chock on their stern. Once made fast I inform the pilot, then pay out around 300 feet of the Amsteel Blue headline and take the ride into Oakland. After clearing the Bar Channel and entering the Oakland Estuary we receive an order to “back, half” from the pilot. While the ship’s propeller must make enough turns to provide adequate steering force on the rudder, this drag from the tug helps reduce its speed through the water enough to avoid pulling other vessels off the dock face. In a narrow channel like the Oakland Estuary this tremendous suction of water is something the pilot must consider carefully. A ship underway, passing in close quarters to a moored vessel can easily drag enough water outward to part the mooring lines if the speed is over 5 knots.

After slowly transiting the Estuary we near the turning basin and I shorten up close in to the stern. When the ship is stopped and centered in the turning basin the pilot gives the order “Z-5 back, full to port ”. Slowly swinging the tug out to the port side of the transom, I work the engines up to backing full and begin pulling the ship around. Once the pilot has the Z-4 pushing at full ahead on the bow, we start picking up the momentum to spin the 900-foot mass clockwise 180 degrees. Eventually we’re aiming back out the channel and the pilot directs the Z-4 to stop and the Z-5 to take in our headline and shift to the port quarter for docking. After recovering our line I turn the Z-5 and run backwards up the port side of the ship in order to re-attach our headline up on the main deck.

One lesson I learned my first week in Oakland is how this simple act of sending a line back up on the quarter can go badly when running bow-first. Often an ASD tug will run forward alongside the ship and safely get a line up and at speeds exceeding 8 knots. In fact this is preferable since running backwards at higher speeds can push the tug’s stern under. In this case however, the maneuver begins with the ship going from stopped in the water to a state of rapid acceleration. The initial suction created from the ship’s propeller, encountered while coming around the quarter, can be tremendous and tends to pull the tug in under the aft rake of the stern. Unless you are pressing the tug’s bow hard against the ship it is difficult to hold a position alongside while the crew is sending up the line. By running backwards the drives are pulling rather than pushing and the rest of the tug has no choice but to follow. As the tug comes in close to send the line up the bow naturally swings in toward the ship, and can more easily be held in a close and controlled position as the ship continues accelerating and the suction increases. It’s a lot like a horse pulling a wagon. While the wagon can certainly be pushed ahead of a horse it requires a lot from the horse to co-ordinate it. Put the horsepower in front of the wagon and things tend to fall into place on their own.

The extreme rake on some container ships makes the approach a delicate operation for the tug captain. Container ships in general are designed for maximizing speed at sea, with a streamlined hull and enormous flare fore and aft. When the pilot needs a line up under this area it can require the tug to maintain station within inches of the ship while underway. Coordinating the throttles and steering to catch a moving target like this takes some basic operating skill, however that’s not the only requirement. Things gets more difficult while trying to simultaneously operate the pair of z-drive controls, run the bow winch, and tend to the radio with just two hands. Couple this with keeping and eye on the ship, the crew on your deck and other vessel traffic trying to squeeze around the whole operation and you have a plate full.

Once lying alongside and running backwards, the tugs bow is better positioned for the ship’s crew to take the headline up at the port quarter chock. The line is made fast, with the tug running backwards, and it’s much easier to maintain a slack line without leaning on the ship and adversely affecting its steering. While running backward at eight knots can be tricky, the speeds encountered in the Estuary are considerably slower. On approaching the berth the ship’s speed is reduced to just a few knots, and the tug can then swing out to a 90 in order to work.

The Jensen-designed Z tugs were built at the Marco Shipyard in Seattle for Tugz International of Cleveland, Ohio. The tugs are built to Maltese Cross AMS Ice Class C incorporating substantial stringers, ribs and hull plating for a very sturdy vessel. They were originally built for submarine work in Honolulu and this kept several of the Z Tugs busy for the early years with the US Navy. For this type of work rubber fendering was built in place on all points of contact, under the waterline forward and along the chine. On both sides aft are rubber edged Z-Drive guards, which protrude like fins out from the chine above the drive units. This extra rubber is beneficial when working around the bulbous bow of containerships and gives the advantage of being able to land softly in a tight spot right up against the ship or under the stem.

In 2004 the Z3, Z4 and Z5 were brought back to the mainland by Harley Marine Services and began working in the ship assist and tanker escort market of San Francisco Bay as Starlight Marine Services. At 95 feet and 4,000 hp they have proven to be a very versatile and robust package, combining the Caterpillar 3516-B engines with Ulstein 1650H Z-Drive Units. This power package has been a good match in many of the past Jensen designed tugs and the Z boats demonstrate further what a versatile and reliable combination this is.

Lately the trend to build bigger and more powerful tugs has required a step back as shipping markets, the economy, air pollution and fuel consumption become serious issues to consider. The mid-range size of the Z Tugs can produce around 112,000 lbs. of bollard pull and still offer an efficient and cost effective vessel with better fuel economy and fewer emissions than many other tugs. While most pilots would be thrilled with a 10,000-hp tug on each end of the ship, the 8,000 hp of vectored thrust provided by a pair of Z tugs is a powerful and responsive package capable of nearly any work in the harbor.

For the crew the interior layout offers generous accommodations with 5 staterooms, 2 heads, a roomy galley and saloon. This is a huge factor in attracting new mariners into the industry and in retaining the current veterans. Working on tugs for a career requires a special tolerance for living in confined spaces with other people for extended periods of time. Having a quiet, private stateroom for each sailor makes a gulf of difference in the attitude onboard and ability to endure the grueling work schedule. A recent modification at Starlight, isolating and insulating the generator exhaust mounts, made an impressive reduction in onboard noise levels, and substantially improved the living environment for the crews.

The visibility from the wheelhouse and the superior deck lighting surpass any tug I have been onboard. Like most of the Jensen designed vessels the layout arranges the bitts, deck winches, hardware and controls in a very usable fashion while still retaining the traditional flare and attractive lines their vessels are known for.

San Francisco Bar Pilot Morgan Hoburg operated the Z-5 for several years as a tug captain at Starlight Marine. “The Z Tugs have enough dead weight to provide effective braking force when dragging astern of a ship yet they are responsive and nimble enough to work around the stem for any type of maneuvering needed.” says Morgan.

Another feature he pointed out is the ability to push at full speed for hours on end without overheating. Even the most advanced tractor tugs launched recently will overheat when running full after a few minutes because of the tendency to use an inadequate raw water cooling system during construction. This has been a universal source of absolute grief for every tug engineer to date and they will tell you so with rabid zeal. The Z Tugs incorporate oversized box coolers designed for Hawaiian waters, which provide unlimited cooling capacity. This can be a very critical point since all the horsepower in the world is useless if it isn’t available for a sustained period in an emergency situation which requires full power.

Halfway back out the estuary we near Berth 58 and begin the final, starboard side approach towards the dock. When the ship’s speed is reduced to 2 knots we receive the order “Z-5, out to a 90” and I swing the tug out to push/pull mode on a short line. After pushing full for a few minutes we check it up with an “easy away” and then an “all stop”. After some wrangling the pilot has the ship stopped in a flat position against the dock face. The final command of “both tugs push easy” pins her alongside under the cranes and the mooring lines begin going over to the longshoremen. The streamlined shape of the new ships allows very little flat surface to make contact with the dock face and is often a matter of see-sawing gradually back and forth until the head and stern lines are made fast and tightened.

Once these lines are secured fore and aft, the ship’s crew lowers down our headline and the pilot cuts us loose with, “That’s it for the Z-5, have a good day”. After a quick glance at the schedule we’re off to the next job: a steel ship sailing from Pittsburgh in five hours. We turn the Z-5 on a new course out of the Estuary to begin our trip across the bay and up river for the next ship that requires our assistance.

Captain Jordan May operates Tractor Tugs on the US West Coast and is a member of the MTV Association (, a mariners advocate group for towing-specific issues.