Using relatively small tractors on heavy ships
by Capt. V. J. Schisler and Capt. G. V. Brooks
Much has been written recently about the projected growth of worldwide waterborne transportation. In the United States alone, some experts are projecting that water-borne commerce is expected at the least to double over the next two decades. Many U.S. ports are planning to improve port access and expansion in response to these projections. Some have begun-significant dredging projects to deepen and widen channels to accommodate larger, deep draft vessels more safely. As some studies support new port features, others are being conducted to examine the ability to meet these future demands using existing equipment and support services.
One such evaluation was conducted in the Port of Long Beach, CA. The purpose of this article is to share what has been learned at this port. With channels dredged to accommodate a safe draft of 62 feet (19 m), the local pilots recommended that the maximum vessel size be increased to an LOA of 1,200 feet (365 m), 200 foot beam (61m) and a draft of 62 feet (19m) due to other channel restrictions.
The operational challenge was how to control a deep draft ship safely in the unlikely event that it experienced a loss of power or steering during its inbound passage. Of particular interest to the escorting mission in Long Beach is the fact that after passing the Long Beach breakwater, the ship must .make an immediate 47º turn to port into the Long Beach Channel before maneuvering through the 1.200-foot wide two mile channel.
Considering the highest horsepower tractors in Long Beach are Crowley’s Harbor class with Voith Schneider cycloidaI drive propulsion units (VSP) rated at 4,800 hp., the pilots, tug operators and industry representatives worked together to evaluate a unique approach to increasing the effective use of these tugs.
California escort regulations for Los Angeles/Long Beach require that the escort tugs must be able to:
Turn a ship, traveling at an initial speed of 5 knots, 47º to port within a 4,000 foot (1,220m) head reach limit.
After completing the turn, stop me the ship from a minimum of 4 knots within a 4,000 foot (1,220m) head reach limit when the tractor type tugs are employed because the speed will decrease while turning. When conventional that steer by pushing utilized, the minimum speed of 5 knots is used since the speed will not decrease during the turn.
(For simulations) tethered tractors are to use a standard 15 second/15 second failure recognition/response time delay and a 30-second ramp up to full power.
The Harbor Safety Committee rules restrict me number of escort tugs to two in the LA/LB complex.
Crowley Harbor class tugs demonstrate Team Towing while performing a Power Indirect move to starboard to generate a turn to port during live testing in the Port of Long Beach with the tanker S/R Long Beach
Simulators were used to evaluate how to safely control a large vessel that experienced a hard right rudder failure in a 4,000 foot (1,220 m) head reach while approaching the Long Beach breakwater. Seattle-based Glosten and Associates used their Shipman simulator to explore the performance variations of using one, two and even three 4,000 hp tractor tugs applying maximum towline forces at various positions on a 211.000 dwt. vessel with a draft of 61 feet.
The simulations described below were run at 5 and 6 knots and used the tugs in two different configurations. First, to oppose the ship’s rudder and return the ship to its original course an then make the required 47° course change to port. The second exercise deployed the tugs in a way that would accelerate the ship’s turn to execute a successful round turn in case the rudder failed outside the breakwater or before entering the dredged channel.
For simplicity’s sake, we will discuss only the 6 knot tests, where the tugs were used to oppose the initial turn to starboard caused by a hard right rudder and then complete the 47° turn to port, as they are representative of the relative performance of the tugs used in these positions. The initial set of simulations used a generic VSP tractor rated at approximately 50 tons (100.000 lbs.) of static bollard pull.
In Case A. a single tractor made fast at the centerline of the transom was used. The single tractor simulations were run to establish a baseline to compare the relative performance of the other positions and combinations. Using the single tractor, an off-track error to starboard was noted of approximately 700 feet (210 m) with an advance of 8.100 feet (2.470 m) to complete the required 47° turn to port.
In Case B, one tractor was made up through me stem and the second at the centerline of the transom. Using the two tractors fore and aft, we noticed a significant improvement was cited with at off track error to starboard of approximately 250 feet (75 m), but: the advance to complete the turn required 7,700 (2350 m). Because in theory, the pivot point of the ship has moved forward with headway, the tug at the stem has a much smaller lever arm to the pivot point than stern tug and is therefore less effective.
In Case C. two tractors were mal up at the outer comers of the ship’s transom. Using the two tractors aft, the noted off-track error continued to improve to approximately 200 feet (60m) and the advance was significantly improved at 3.700 feet (1,130 m).
Finally, in Case D three tractors were made up at me stem, starboard quarter (because the port quarter usually the weather quarter which Precludes a tug pushing in this position) and -centerline of the transom. It was recognized that the tug at the quarter could only help oppose a starboard rudder failure or turn the ship to port. Using three tractors tugs in this configuration, an off-track error to starboard of approximately 200 feet (60 m) (equal to Case C) was noted but the advance increased to 4,300 feet (1,310 m). The increase in the advance in this case vs. Case C is caused by all three tugs applying steering forces only to the: ship.
Based on these simulator exercises, the configuration in Case C provided the most effective performance. These simulations were then run again using a VSP tractor of 53.5 tons (107,000 lbs.) of bollard pull to specific model Crowley’s Harbor class tugs. The two tractors made up at transom proved to be very effective helping the vessel recover from a hard right rudder failure while approaching the breakwater.
To address the state’s second escort requirement for stopping the ship within 4,000 feet (1.220 m) from 4 knots., the two nominal 50-ton (100 kip) tractors were simulated at the stern at 5 knots and were able to stop the ship within 3,400 feet (1.040 m). While the use of tractors teamed at the transom seemed very promising, the question remained; could this be accomplished safely in actual conditions? To explore this issue, SeaRiver Maritime Inc. teamed with the Jacobsen Pilot Service and Crowley Marine Services in Long Beach. Because this was a new and unique use of tractor tugs, an extensive review of the simulation results was conducted before trials began to discuss how to safely work the boats in such close proximity.
It should be noted that in many European ports two boats are tethered at the stem during docking operations or bridge transits. Team Towing is unique because it is conducted during higher escort speeds. Capt. Vic Schisler of Jacobsen Pilot Service utilized conventional twin screw tugs in this manner in the mid ’70s on a vessel displacing over 300,000 tons and other Jacobsen pilots had some related experience with this method.
The transom of the test vessel SIR Long Beach, is 72 feet (22 m) wide and is equipped with reinforced chocks at the extreme width, which allowed for a reasonable separation of the boats .in their initial positions. However, some pilots and tug operators expressed concerns about the tractors potentially making contact with each other during maneuvers. The senior Jacobsen pilots felt that the simulations offered performance possibilities that merited evaluation through a live test and the Crowley operators felt safe and comfortable with the task. After further discussion, all parties agreed to conduct some controlled experiment to explore the possibilities of this unique way of using tractor tugs. The initial live trials proved that, through effective radio communications between the tractor tugs, they were capable of maneuvering in close proximity to one another without incident.
In the photo 1 the two tractors are performing a Power Indirect move to starboard (in order to generate a turn to port) which would provide the maximum steering vector for the ship at these intermediate speeds to oppose a right rudder failure. In the photo 2 the following page, the boars are demonstrating an Indirect Inline a non-emergency maneuver used to provide a retarding force to reduce the ship’s speed while the ship still makes turns ahead to provide steering control. In the “Indirect lnline” maneuver, the two boats are facing in the same direction (vs. facing each other) to allow them an easier transition into the next maneuver ordered by the pilot.
Team Tractors Power Indirect
Each transit must be preplanned by the master, pilot, and tug captains; at each waypoint the pilot needs to make sure the tugs are properly positioned so that they can quickly and effectively respond.
Indirect Inline is a none-emergency maneuver used to reduce a ship’s speed while the ship makes turns ahead to provide steering control
Subsequent to these tests, the Jacobsen pilots have also used this Team Towing technique on ships with very narrow transoms also with workable results. As of December 2000, this technique has been used successfully on a vessel displacing approximately 280,000 tons.
Since the inertia in ships increases almost linearly, we can practically double the displacement of the escorted vessel safely by using two tractor type tugs of equal bollard pull. In effect, as this technique is evaluated and verified in other restricted ports and waterways, existing tractors may be able to escort the largest vessels permitted in those ports safely and effectively. This may also mitigate the need to employ or build larger tractors, which can have limited applications in confined port complexes.
A secondary and considerable advantage of this type of escorting is that each of the boats exerts a lesser force on the vessel’s mooring points vs. a larger tug placing all of its towline forces on a single mooring point.
Currently the Jacobsen Pilots have developed the following procedures for operating the Team Tractors to help reduce risk and ensure safe effective operations:
The windward tractor should be tethered first and released last.
The tug’s towline should be as long as possible, as much as 350 feet (105m), to minimize the effects of the ship’s propeller wash and vertical movement of the tug and ship.
Both boats should use the same length of towline as operating space permits.
The towlines should not use the same bitt and chock, if it can b avoided to prevent chafing of the lines and contact between the tugs.
The lead to the bitt and choc should be in line with the towline forces as much as possible.
Tug orders should be issued in clear, precise, and well-coordinated manner to prevent confusion, contact or interference between tractors.
The two tractors should communicate with each other on their house channel.
Team Tractors Indirect Inline
During initial training and trial exercises, the tractors were ordered into position separately. As pilots and escort tugs gain experience with this configuration, and as communications become even more refined, we foresee the possibility of a single order being issued that results in both tugs executing their respective maneuvers. The tractor tethered to the side the order is given would take the lead and conduct the maneuver as smoothly as possible while the second operator positions or “flies” his boat as closely to the lead tractor as possible based on the prevailing sea and weather ’conditions.
As in all escorting processes, tugs are utilized in this manner to help prevent groundings or collisions caused by loss of propulsion or steering. Successful operations require discussion, training, practice and team-work. We must not wait until we are in extremis to test a system or technique.
In summary, this information on the use of Teamed Tractors is offered as one example of several innovative approaches to using these tools in the Port of Long Beach. The application of this technique in other ports, where transit speeds are higher or where weather and sea conditions differ, will require very careful study and testing before full implementation. By sharing this information the authors hope that other mariners will share their experiences to develop further the best application for this type of towing. The authors would like to hear from any mariners who may be using tractors in a similar fashion.
Capt. Vic Schisler is a 1.964’ Kings Point graduate and initially sailed with Crowley on the West Coast. In 1.967 he became an inland pilot working in San Francisco and then became a Jacobsen Pilot in Long Beach in 1970. Capt Schisler currently is piloting full time and teaches a course in tractor operations for pilots at the MarineSafety International facility in San Diego.
Capt. Greg Brooks is a 1.968 SUNY Maritime College (Fort Schuyler) graduate and initially sailed with Poling Brothers on the East Coast. In 1970 joined Esso/Exxon/SeaRiver and has held various seagoing and shore side positions since then. He currently serves as Inland Operations and Safety Coordinator based in Houston.
Capt. Vic Schisler
Capt. Greg Brooks
The authors recognize the following, organizations for their contributions: Crowley Marine Services; Glosten and Associates; Jacobsen Pita Services; SeaRiver Maritime Inc.