Threading the Needle: A Canal Passage

| Tuesday, 05 Mar. 2013

Standing on the bridge wing, Captain Roland Anderson watches carefully as

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Orient Line's Marco Polo eases into the Miraflores Locks in the Panama Canal. Because of unseen currents and wind, maneuvering a ship is always tricky, but putting a 700-foot long vessel into a 1,000-foot long steel box is especially demanding. At all times, the captain must monitor the status of the engines, rudder, bow thruster, tugboats, the ship's speed and most importantly, the ship's position. For passengers, a passage through the Panama Canal is a leisurely and interesting experience; but for the ship's captain, it can be one of the most stressful days of the itinerary.


After they make an initial inspection of the vessel (including timing how long it takes to turn the rudder), at least two of Panama's 300 Canal pilots will board the ship (they switch duties halfway through the passage). The relationship between the pilot and captain is unique in the Panama Canal, with the pilot assuming more responsibility and authority than other local pilots anywhere in the world. However, because the captain holds the ultimate responsibility for the ship, he may choose to override or supplement the pilot's orders.

On the bridge, the captain, staff captain, officer on watch and helmsmen monitor the Panamanian pilot, while a crew member stands by on the bow to drop anchor if necessary. Even the chief engineer visits the Bridge, asking Capt. Anderson when the ship will be going through Gatun Lake, a relatively long stretch of the canal where repeated maneuvering will not be needed.

Normally, the ship's engines burn heavy fuel oil, but during these delicate maneuvers, the engineers switch to lighter, cleaner diesel fuel, so the chief engineer wants an idea of when he will have to make the switch.

Pilots will tell you that every ship handles differently, and most modern cruise ships are comparatively easy to handle, thanks to their large bow and stern thrusters, responsive engines and a rudder behind each propeller for maximum lift. But the Marco Polo is different; she was built as a transatlantic liner in 1965, designed for straight, high-speed runs across the ocean--not for tight maneuvering. For instance, she has only one bow thruster, no stern thruster and one rudder situated between her two propellers. This makes the ship sluggish in responding--the rudder doesn't get the full force of the propellers' wash, and therefore generates little lift. Even worse, the shallower the water, the slower the ship turns, meaning the pilot must always think ahead of the ship.

The Marco Polo has another interesting constraint: When the captain rings up "Dead Slow Ahead" on both engines, the ship travels a comparatively fast 9.5 knots--a minimum speed that is too fast for many approaches and narrow sections of the canal. Thus, to keep the ship going slow enough, only one engine at a time is used for some sections. With the port engine turning and the starboard engine stopped, the ship wants to swing to the right, so a significant amount of rudder must be applied to keep the ship going straight. Stopping is a problem, too, because the engines cannot be started astern (i.e., put into reverse) until the ship has slowed to below 7 knots.

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In the narrow channels outside the locks, and especially in the precipitous Galliard Cut, the ship responds differently than in the comparatively open Gatun Lake. If the Marco Polo gets too close to the edge of the channel, the bank can actually push the bow away from the side of the channel and suck the stern towards the bank, causing her to shift sideways. That's why Capt. Anderson is so concerned about speed: This phenomenon will not occur if the ship is going slow enough. Still, the captain's and the pilot's eyes constantly check to see how much rudder the helmsman is using to keep the ship on course. A sudden increase in needed rudder indicates the ship could be feeling the effects of the bank.

The Marco Polo must pass a 900-foot container ship--a further cause for worry. If she comes too close, the bows of the two ships will actually get pushed apart. However, when the two ships are even, they are sucked towards each other and finally the sterns will veer together, so it's important to have a skilled helmsman steering the vessel.

Sailing into Gatun Lake, the ship's speed is increased to 13 knots, although the bow thruster is left on standby all day--even though the ship must be going below 5 knots for it to be effective. To aid in navigation, the pilot carries a laptop that holds an entire chart of the Canal, showing the ship's position accurate to 100 feet. In addition, the computer shows all other traffic in the Canal, giving the pilot instant access to their true course, speed, distance and time of closest point of approach, and even the distance in feet left or right of the middle of the channel.

After the ship passes through the Gatun Lake, the end of the Canal is near; the ship must be lined up and gently glide alongside the Gatun Locks, where four electric "mules" will be attached by wires to guide the ship into the lock. (The number of mules depends on the size of the ship--the QE2 will use eight mules, for instance.) As she enters the Gatun Locks, the Marco Polo's bow is slightly canted towards the pier and the stern is swung away from the pier, and the captain employs various maneuvers to align the ship with the pier. On a conventional twin-screw ship like the Marco Polo, putting the starboard engine astern will literally "walk the stern" to the port side; using the rudder and coming ahead on the port engine helps the swing. Finally, the captain can employ a tug standing by off the stern. (The number of tugs required again is determined by size--a ship with an 80-foot beam needs one tug, and a ship with a beam of 91 feet needs two or more tugs.)

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With the ship now aligned, the lines are attached from the mules, and the pilot keeps the ship in the middle of the lock by asking for more or less tension on each line, pulling the ship into the lock. Engines are rarely used in the locks--the mules act as the ship's propulsion and brakes. This can be especially tricky when the locks open ahead of the Marco Polo and water rushes into the ship's lock--a current of up to 4 knots can sometimes be felt, trying to push the Marco Polo out of position. (Current can have tremendous effects on ships; as a general rule of thumb, a1-knot current affects a ship the same as 30 knots of wind.)

Despite the advances in information availability and technology, handling a ship is still more of art than science, requiring above all else the right "touch." Rest assured that the next time you see your captain on the bridge wing in the Panama Canal, there is more going through his mind than tonight's dinner party.

Photos by Ted Scull & Ben Lyons


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