Bad vibrations on QM2

[bchrien]

What is the source of ~15 Hz vibrations on the port side of QM2? It was bad enough on deck 11 aft that I couldn't read a book in my cabin. Does it come from the gas turbines located in one of the upper decks? Which cabins are most affected?

[tag1000]

I was in cabin 11118 in October and the vibrations were terrible. It lasted for three days then settled down. It started the second we left NYC. The TV looked like it would fall off the wall. Coming back in 11133 there was nothing. I would love to know the answer as to what it might be.

 

 

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[chengkp75]

To my knowledge, QM2 rarely uses the gas turbines, since the reduced speed required for the crossing does not require that much power. They may if one or two diesels are down for maintenance, though.

 

My question, how did you determine the frequency to be 15 per second? Do you carry a vibration meter with your? Truly curious.

[sand dollar26]

I was in cabin 11118 in October and the vibrations were terrible. It lasted for three days then settled down. It started the second we left NYC. The TV looked like it would fall off the wall. Coming back in 11133 there was nothing. I would love to know the answer as to what it might be.

 

 

I have stayed in cabin 11118 and the only time I felt vibrations was when I put my head down on the pillow at night. Otherwise I liked the cabin. The vibration never bothered me enough to disrupt my sleep. I have no idea why it would be a problem now.

S.

[bchrien]

I was in cabin 11120 so adjacent to the cabin 11118 reported by sand dollar26.

For chengkp75: I don't know the exact frequency. I gave an estimate.

[chengkp75]

I was in cabin 11120 so adjacent to the cabin 11118 reported by sand dollar26.

For chengkp75: I don't know the exact frequency. I gave an estimate.

 

Vibrations can be caused by a number of things, and can vary by location on the ship, cruise to cruise in the same cabin, and even day to day. Most aft vibrations are caused by the propellers, from the blades passing close to the hull at the top of the revolution. With 4 propellers like QM2, these need to be synchronized, and then offset, so that the 4 propellers have blade passage at the top at different, controlled times. Otherwise, the blade passage can create a harmonic situation, where the blade passage effect is multiplied. Sea and swell height, period, and direction can affect the vibration level against the flat surface of the hull above the pods. Another problem with azipods is that the steerable pods tend to oscillate back and forth a couple of degrees continuously to maintain heading, and therefore the water flow under this flat surface sweeps back and forth causing a "shimmy" or side to side vibration.

[bchrien]

For my crossing starting 1/3/17, the vibration started as soon as we started moving away from the Brooklyn Cruise Terminal and stayed roughly constant until we arrived at Southampton.

I do not want to travel on QM2 again unless I can be assured that my cabin will not be affected by the vibration I experienced earlier this month.

[bchrien]

I want to thank chengkp75 for his technical response. I noticed that you are a former cruise ship engineer. Do you happen to know the rotation frequency of the propellers? How about the diesel engines? The vibration that I felt could be a fundamental or some harmonic caused by a frequency difference. What I observed is that it seemed to be nearly constant from start to finish.

[chengkp75]

The Wartsila diesels run at 600rpm. The pods run between 90-170rpm.

 

As I say, they will synchronize the four propellers so that the blade passage is constant between the props, and then dial in an offset between each prop of a few degrees.

 

All ships exhibit some harmonic vibrations at times, and this can be unique to each ship, even supposed "sister" ships. Generally, these "rock crusher" points are known to the deck officers and they will stay away from those propeller rpms that cause them, moving up or down just a couple of revs. Sometimes, it can't be avoided due to schedule. Also, the trim and displacement of the ship for each voyage can create a harmonic. As I say, even the weather can create these harmonics. And they can crop up in very small, specific areas of the ship, given that the "box" that is the ship's structure has no uniformity, and one cabin could be vibrating enough to shake your tooth fillings out, and the next cabin feels nothing.

[bchrien]

chengkp75: Thank you for the information. Perhaps I was experiencing a beat frequency between the aft propellers or and interaction between the propellers and the resonant modes of the ship. At least I will know how to phrase my inquiry if I ever experience the issue again.