Aft stateroom vibrations

[carefree lady]

Has anyone ever had a problem on the back of the ship when it pulls into port? I like the aft cabins,but once on the Radience when we docked everything vibrated in the cabin even the bed shook.

[Clarea]

We noticed the same thing in an aft stateroom on Enchantment. Lots of vibration when manuvering in port. Always woke us up.

[DrivesLikeMario]

That's very typical to experience a lot of vibration when coming into, or out of, a port. Every ship I've been on in the aft area has had that. I totally agree about the Radiance! We had corner aft cabin #1100 and we really felt the vibration, but it was only coming into, or out of, port.

[Siora7777]

All I noticed was the amazing view from the balcony.

[Philly Steve]

Some vibration aft on Grandeur while docking. None while at sea.

[jetta8300]

I had an absolute nightmarish cruise on the Carnival Pride a few years ago due to aft vibrations. Our cabin felt like a paint shaker the entire cruise, not just pulling into port. I have been aft 2 other ships with no issues. However because of that I will NEVER book an aft cabin again just in case.

[George C]

We did Brilliance last Sept 12 days cruise had corner aft 1600 did not feel any vibrations ( 10th deck GS)

[Cruisin'4Us]

Some people pay extra for vibrating beds.

[wingman2014]

Terrible vibration STAY Away from the AFT cabins !! :D

[setsail]

No, no one has ever had a problem. Why would would the normal operation of the ship using thrusters or their engines be a problem?;p

[bouhunter]

Terrible vibration STAY Away from the AFT cabins !! :D

 

I agree. Makes them more available for others:p

[kknorr0320]

Is this only an issue on smaller ships? We have an aft balcony booked on Navigator in 2019.

 

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[Clarea]

Is this only an issue on smaller ships? We have an aft balcony booked on Navigator in 2019.

I suspect it is worse during port manuvering on non-azipod ships, such as Vision class.

[kknorr0320]

I suspect it is worse during port manuvering on non-azipod ships, such as Vision class.

Thanks.

 

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[schmeed]

Lots of vibration in the dining rooms on Liberty when at sea. AND...it was vibrating so bad in the Viking Crown lounge that the elevator doors were banging against the frame. It seems as though one of the propellers is damaged or out of alignment.

 

It has azipods so can't blame it on old shaft driven technology either.

[Bkchero]

Some people pay extra for vibrating beds.

 

Between the rocking of the ocean, the vibrating beds and a few of these :whiskey-glass: could be a fun combination . . .

[johnjen]

That vibration is typical found aft on most ships, actually. Even though the azipods are housed screws, the blades still "sing" from cavitation and that resonant noise vibrates through the aft end of the hull. On Navy ships that don't have azipods and just screws, the cavitation is worse, so there's much more vibration. It's also the tip clearances of the aft thrusters in the hull that cause vibrations. Those blade tip clearances to the hull are closer, so more vibration is felt.

[schmeed]

It's also the tip clearances of the aft thrusters in the hull that cause vibrations. Those blade tip clearances to the hull are closer, so more vibration is felt.

Ships with azipods don't have aft thrusters. Or are you referring to the shaft driven?

[chengkp75]

Well, actually, azipods are not "housed" screws, they are open screws. Every ship built is a "sounding box" like a violin or guitar. At certain frequencies, this box will vibrate harmonically, just like a violin. These frequencies can be reached by the rate of blade passage past the hull above the propeller, and are magnified when there are multiple screws. Frequently, the screws are controlled so that while turning at the same rate, the blades are slightly out of synchronism with each other, to lessen the harmonics of their frequency. Propellers, of all types, will experience "bottom bounce" in shallower water, where the pressure wave from the propeller bounces back from the seabed and strikes the hull again, causing more vibration, and this gets worse the slower the ship goes.

 

While tunnel thrusters do have a closer blade tip clearance than main propellers (the only ships with shrouded main propulsion propellers are those that are designed for power, not speed, such as tugs, and ice breakers), the only time you really get cavitation with a tunnel thruster is when it is used when the ship's forward or astern speed is over 3-4 knots, as this water flow at 90* to the mouth of the tunnel causes low pressure. Thrusters cause rumbling vibrations simply from the concerted water flow they create through the tunnel. Aft cabins will feel vibrations from stern thrusters, and forward cabins will feel vibrations from bow thrusters.

 

When propellers or azipods go astern, you are now forcing water from the propellers back towards the hull in front of them, instead of towards the open sea behind, and this naturally causes much more vibration, since the water must now turn to the side or down to get around the hull.

 

Finally, ships with azipods experience the "azipod shimmy", which is caused by using the propeller to steer with, especially at sea, where the pods will hunt back and forth a couple of degrees from straight ahead, maintaining course, and this constantly redirects the water flow in sweeps from port to starboard and back, causing the after part of the ship to oscillate sideways.

 

All vibrations at sea can be compounded or reduced depending on the sea state (wave height, wave period, wave direction) in relation to the ship's course.

[johnjen]

Ships with azipods don't have aft thrusters. Or are you referring to the shaft driven?

 

Yeah, I meant the shaft driven types as well. I didn't word that right.

[johnjen]

Well, actually, azipods are not "housed" screws, they are open screws. Every ship built is a "sounding box" like a violin or guitar. At certain frequencies, this box will vibrate harmonically, just like a violin. These frequencies can be reached by the rate of blade passage past the hull above the propeller, and are magnified when there are multiple screws. Frequently, the screws are controlled so that while turning at the same rate, the blades are slightly out of synchronism with each other, to lessen the harmonics of their frequency. Propellers, of all types, will experience "bottom bounce" in shallower water, where the pressure wave from the propeller bounces back from the seabed and strikes the hull again, causing more vibration, and this gets worse the slower the ship goes.

 

While tunnel thrusters do have a closer blade tip clearance than main propellers (the only ships with shrouded main propulsion propellers are those that are designed for power, not speed, such as tugs, and ice breakers), the only time you really get cavitation with a tunnel thruster is when it is used when the ship's forward or astern speed is over 3-4 knots, as this water flow at 90* to the mouth of the tunnel causes low pressure. Thrusters cause rumbling vibrations simply from the concerted water flow they create through the tunnel. Aft cabins will feel vibrations from stern thrusters, and forward cabins will feel vibrations from bow thrusters.

 

When propellers or azipods go astern, you are now forcing water from the propellers back towards the hull in front of them, instead of towards the open sea behind, and this naturally causes much more vibration, since the water must now turn to the side or down to get around the hull.

 

Finally, ships with azipods experience the "azipod shimmy", which is caused by using the propeller to steer with, especially at sea, where the pods will hunt back and forth a couple of degrees from straight ahead, maintaining course, and this constantly redirects the water flow in sweeps from port to starboard and back, causing the after part of the ship to oscillate sideways.

 

All vibrations at sea can be compounded or reduced depending on the sea state (wave height, wave period, wave direction) in relation to the ship's course.

 

Good points in naval engineering. The little bits of knowledge I gained from cavitation came from my first navy rating, OT, and later on my quals in SW when I had to hit the PEOS to stand watches down there. I was an RM/IT. We had to know everything about our ship to get the qual.

[BillHoo]

Well, actually, azipods are not "housed" screws, they are open screws. Every ship built is a "sounding box" like a violin or guitar. At certain frequencies, this box will vibrate harmonically, just like a violin. These frequencies can be reached by the rate of blade passage past the hull above the propeller, and are magnified when there are multiple screws. Frequently, the screws are controlled so that while turning at the same rate, the blades are slightly out of synchronism with each other, to lessen the harmonics of their frequency. Propellers, of all types, will experience "bottom bounce" in shallower water, where the pressure wave from the propeller bounces back from the seabed and strikes the hull again, causing more vibration, and this gets worse the slower the ship goes.

 

While tunnel thrusters do have a closer blade tip clearance than main propellers (the only ships with shrouded main propulsion propellers are those that are designed for power, not speed, such as tugs, and ice breakers), the only time you really get cavitation with a tunnel thruster is when it is used when the ship's forward or astern speed is over 3-4 knots, as this water flow at 90* to the mouth of the tunnel causes low pressure. Thrusters cause rumbling vibrations simply from the concerted water flow they create through the tunnel. Aft cabins will feel vibrations from stern thrusters, and forward cabins will feel vibrations from bow thrusters.

 

When propellers or azipods go astern, you are now forcing water from the propellers back towards the hull in front of them, instead of towards the open sea behind, and this naturally causes much more vibration, since the water must now turn to the side or down to get around the hull.

 

Finally, ships with azipods experience the "azipod shimmy", which is caused by using the propeller to steer with, especially at sea, where the pods will hunt back and forth a couple of degrees from straight ahead, maintaining course, and this constantly redirects the water flow in sweeps from port to starboard and back, causing the after part of the ship to oscillate sideways.

 

All vibrations at sea can be compounded or reduced depending on the sea state (wave height, wave period, wave direction) in relation to the ship's course.

 

Do you work at NSWC Carderock?

[EleventyBangBang]

I was on NCL Getaway with an aft balcony. Early on, there was some minor propulsion issue that took a few hours to fix. The captain made an announcement that we would be going faster than normal that night to make up for the lost time and get to tomorrow's port on time. My cabin was vibrating like crazy that night, knocking stuff off of shelves, etc. I had difficulty sleeping that night.

 

After that, once we were back to normal speed, it wasn't an issue.

[cruisinfromtampa]

We had an aft cabin on Rhapsody in December. I can only remember twice where we felt any vibrations, and both times we were leaving port. The view from the balcony more than made up for any vibration we felt.

 

We currently have 4 future cruises booked in an aft cabin, and we will continue to book them whenever possible.

[chengkp75]

Do you work at NSWC Carderock?

 

No, though I did a couple weeks there as a consultant on an MSC project. I am merely a 42 year merchant marine engineering officer, 30+ years as Chief Engineer on offshore drilling vessels, container ships, RO/RO ships, tankers, bulkers and cruise ships.