All about Azipods

Some of my best friends on Saipan have been captains of the nautical stripe. Many are quite adventurous, and spin great yarns about distant shores that I’ve yet to visit, such as the Solomon Islands, the Marquesas Islands, and such. On the tamer end of the spectrum, some of my relatives just took their first ever cruise ship excursion (in Alaska); they were so impressed with the operation that they suggested it would make a good column on how solid customer service makes for happy tourists.

I said OK, but as I prepared that work, I veered into an engineering caper that’s pretty cool.

I was looking over a passenger’s “Cruise Log” from the MS Oosterdam, part of the Holland America Line. The log is one of many nice touches for the passengers, a simple little summary of where they went, distances, speeds, and such. The back of the log has a summary of the ship’s engineering; this is a monster of a ship, displacing 82,000 tons, which is on par with some aircraft carriers.

Here was the caper, and you ship guys will appreciate this. Under the “power” section of the engineering summary, it lists five “diesel generators,” plus one “gas turbine.” From the way that’s worded, I assumed that the diesels are making electricity, and the gas turbine (which is basically a jet engine that drives gears) was used for propulsion, though the turbine struck me as way too puny for that job. Things didn’t add up.

I got even more confused when under “propulsion” the listing was this: “2 x ABB Azipods.”

Azi-what? What’s going on here? What’s going on is that the modern age has, yet again, leap-frogged right over my head.

Conventional ship propulsion is sort of like a pickup truck. You’ve got a power plant (engine), which drives a shaft, which goes to a transmission, which reduces the RPMs, which drives another shaft, which drives, instead of tires, the propeller (a/k/a/ “screw.”) That’s what car people call the drive train.

As for power plants, I’ve been to sea aboard nuclear, diesel, boiler, and gas turbine varieties, but, regardless of the power plant style, the basic concept of drive trains is (OK, was) still the same.

Well, along comes the Azipod, a trade name for a Swiss company called ABB.

You’ve heard of fly by wire? This is thrust by wire.

An Azipod is a submersed pod that contains an electric motor and a propeller. On the examples I saw on Internet photos, the ships had two such pods, each of which could swivel, and each of which was mounted outboard of where the ships’ rudders would be. I say “would be” since the swiveling Azipods serve the purpose of a rudder.

So there’s no mechanical drive shaft between the ship and the propellers. The ship’s engines drive generators (hence that “diesel generator” phrase that I had encountered; the gas turbine also drives a generator), which (of course) produce electricity, which is (of course) run to the Azipods.

The propellers, incidentally, are fixed-pitch, not variable-pitch.

The Azipods must pack some muscle: According to the cruise log, the MS Oosterdam was making good 22 knots along parts of its voyage. That’s a hair over 25 miles per hour. Not too shabby!

This isn’t just a civvy thing. The U.S. Coast Guard uses Azipods on one of its ships, the USCGC Mackinaw (WLBB-30), which was commissioned in 2005.

I’m pretty much a nut for anything that moves: Ships, planes, helicopters, cars, you name it. Maybe that’s because I just can’t sit still. I prefer to be moving. Some other folks do, too, but in this sedentary age, I suppose we’re a dying breed. Hopefully, Saipan will always have some captains as part of the local color, who can provide perspectives too big to be held in cubicles.

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