Vibration on Koningsdam?

[jennymaxgirl]

RE: Koningsdam - any complaints of more-than-normal vibration on this ship? Have read some reviews with complaints of vibration. Stateroom is deck 4 near the aft of the ship.

[luvn2cruzzz]

RE: Koningsdam - any complaints of more-than-normal vibration on this ship? Have read some reviews with complaints of vibration. Stateroom is deck 4 near the aft of the ship.

 

E.g.

 

Didn't experience anything out of the ordinary and we were on 5 aft. Felt some when we were docking and not all the time. You should enjoy your time on this wonderful ship.

 

 

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[CruiserBruce]

Spent 3 weeks on her in March, aft cabin. No unusual vibration, just the occasional vibration with the azipods are working hard in shallow water.

 

Some people expect the ship to be smooth and quiet 24/7, and don't understand how ships work.

[chengkp75]

Aft cabins, especially down low, on ships with azipods will, depending on the sea state, experience the "azipod shimmy" which is a side to side movement caused when the azipods track back and forth trying to maintain a heading.

[Underwatr]

No Konigsdam experience but on other ships when walking aft past where the mechanical systems run up to the stacks I've often felt floor/wall vibrations, even on mid-high decks with berthing.

 

Uncertainty as to which staterooms might be most affected is one reason we almost exclusively book cabins forward of midships, and prefer far forward over mid-aft (motion is relatively less a concern to us).

 

But this is only our general preference, no Konigsdam experience.

[VMax1700]

We were on deck 4 (Beethoven) in an aft cabin, overlooking the stern in April. No vibrations noticed at all, only roll and yaw.

[rkacruiser]

Aft cabins, especially down low, on ships with azipods will, depending on the sea state, experience the "azipod shimmy" which is a side to side movement caused when the azipods track back and forth trying to maintain a heading.

 

I noticed this "corkscrew" type motion on the Westerdam when I had an a stateroom at the stern of the ship. Wasn't noticeable all the time, but it was an odd feeling. I appreciate your explanation of why this happens. Makes good sense to me.

[Heartgrove]

Not the Koningsdam but we are just off the short cruise onboard the Nieuw Amsterdam prior to going to Freeport for a refit. The Mariners Brunch was held on our sea day Tuesday while sailing between Nassau and Fort Lauderdale, a distance of only 164nm yet sailing for 19-1/2 hours. I noticed the same vibration while on Deck 2 MDR as I felt last year on an Alaskan cruise but while on Deck 3 MDR. This time though we only were traveling at 10-12 knots, compared to 18-22 knots at times in Alaska. It wasn't cavitating but more like an out of balance tire.

 

I know the Westerdam had new propellers installed when it went to its last drydock - yet I never noticed that ship having the same feel..

[chengkp75]

Not the Koningsdam but we are just off the short cruise onboard the Nieuw Amsterdam prior to going to Freeport for a refit. The Mariners Brunch was held on our sea day Tuesday while sailing between Nassau and Fort Lauderdale, a distance of only 164nm yet sailing for 19-1/2 hours. I noticed the same vibration while on Deck 2 MDR as I felt last year on an Alaskan cruise but while on Deck 3 MDR. This time though we only were traveling at 10-12 knots, compared to 18-22 knots at times in Alaska. It wasn't cavitating but more like an out of balance tire.

 

I know the Westerdam had new propellers installed when it went to its last drydock - yet I never noticed that ship having the same feel..

 

More than cavitation, sometimes the speed of the propeller (the number of times the blades pass close to the hull) matches the natural frequency of a portion of the hull, and a harmonic vibration is set up. Also, it can depend on the wind and sea speed and direction in relation to the ship's heading, that can affect both the harmonic vibration as well as the azipod shimmy. As far as the Westerdam, the propellers would most likely not be any different between old and new, but the natural frequency of the hull can be different between ships, even ships in the same class.

[Heartgrove]

More than cavitation, sometimes the speed of the propeller (the number of times the blades pass close to the hull) matches the natural frequency of a portion of the hull, and a harmonic vibration is set up. Also, it can depend on the wind and sea speed and direction in relation to the ship's heading, that can affect both the harmonic vibration as well as the azipod shimmy. As far as the Westerdam, the propellers would most likely not be any different between old and new, but the natural frequency of the hull can be different between ships, even ships in the same class.

 

Thank you for adding to my response. It appeared to be continuous at any speed. The azipods are not fitted with variable pitch propellers so they do turn at different revolution speeds while passing the hull. It seems the harmonic vibration was continuous at any number of turns. With regard to the Westerdam, the new propellers were said to be of a more "efficient and energy-saving" pitch.

[AmazedByCruising]

More than cavitation, sometimes the speed of the propeller (the number of times the blades pass close to the hull) matches the natural frequency of a portion of the hull, and a harmonic vibration is set up.

 

Wouldn't that be rather easy to solve? A microphone or similar detecting excessive vibration and a computer deciding to slow down or speed up just 1%?

Apart from inconvience, it reminds me of the Tacoma Bridge and signs telling soldiers to walk out of sync on a bridge. Also metal fatigue..

[chengkp75]

Wouldn't that be rather easy to solve? A microphone or similar detecting excessive vibration and a computer deciding to slow down or speed up just 1%?

Apart from inconvience, it reminds me of the Tacoma Bridge and signs telling soldiers to walk out of sync on a bridge. Also metal fatigue..

 

Typically, it is pretty obvious when you hit the harmonic frequency, so the ship tends to keep away from that rpm, it could be just one or two revs. Unfortunately, itinerary and weather sometimes means that you can't keep out of the harmonic range.

[chengkp75]

Thank you for adding to my response. It appeared to be continuous at any speed. The azipods are not fitted with variable pitch propellers so they do turn at different revolution speeds while passing the hull. It seems the harmonic vibration was continuous at any number of turns. With regard to the Westerdam, the new propellers were said to be of a more "efficient and energy-saving" pitch.

 

A change in pitch would not affect any "blade passage" vibration, only a change in diameter (lowering the horsepower required for a given propeller speed) would. Was the vibration a general, or vertical vibration, or was it a side to side vibration? This kind of what I call a "shimmy" is caused by the water flow to/from the pods under the flat portion of the hull over the pods, and as I said, the pods track back and forth in azimuth to keep the heading, and so this water flow sweeps back and forth port to starboard.

[AmazedByCruising]

Typically, it is pretty obvious when you hit the harmonic frequency, so the ship tends to keep away from that rpm, it could be just one or two revs. Unfortunately, itinerary and weather sometimes means that you can't keep out of the harmonic range.

 

It would be a matter of 102 or 98 rpm instead of the harmonic 100Hz or 49/51 for the next harmonic, etc. There should be plenty of non-harmonic rpm-ranges available for any weather or itinerary?

[chengkp75]

It would be a matter of 102 or 98 rpm instead of the harmonic 100Hz or 49/51 for the next harmonic, etc. There should be plenty of non-harmonic rpm-ranges available for any weather or itinerary?

 

There is theoretically only one rpm for a given speed. The pitch of a propeller is like the pitch of a screw thread (which is why they are called "screw propellers"). The pitch of the propeller is how much theoretical distance the propeller (and hence the ship) "advances" through the water for each revolution. Think of a wood screw being driven into wood. Each turn of the screw drives the screw a fixed distance further into the wood. So, in theory, if the ship needs 16 knots to make their itinerary, they have to turn the propellers at a certain rpm to make that speed.

 

However, in the real world, its a bit different. Water is a fluid, not a solid like wood, so there is some lost efficiency in the propellers "advance" due to compression, flow around the "screw", etc. Also, this speed that the propeller creates with its pitch is "speed through the water". Now, if the water is flowing in a current either with or against the direction the ship is moving, the "speed over the ground", or the speed made good between two fixed points on the earth will be different. Think of that screw in the block of wood, where you are turning the screw, but the block of wood is also moving, so the position of the screw in respect to your workbench varies with each turn of the screw by the amount the block of wood is moving as well. This is known as "propeller slip", which is the difference between the speed the propeller should theoretically provide, and what speed the ship actually travels at. This will vary hour by hour, based on the current speed and direction, ship speed and direction, wave speed, period, and direction, wind speed and direction, condition of hull and propeller (fouling of the surfaces from marine growth causing additional drag), and vessel draft and trim (which can change due to fuel or water consumed, etc).

 

So, with a fixed pitch propeller like those used on azipods, while there will be a range of propeller speeds (due to variable slip) to get a vessel speed, it will always be the same range for a given speed, and you cannot predict the amount of slip on any given day or place on earth.

 

With variable pitch propellers, the propulsion system is generally set up to vary both speed of the propeller and pitch of the blades to give an optimum performance from the propeller. So, you could theoretically vary the pitch in order to get the same "advance" from different propeller speeds, this would be difficult to program into a system that needs to react to outside inputs like the ship pitching in seas (when the propeller nears the surface (as the bow goes down and the stern goes up), there is less resistance so the propeller speeds up, and the control system needs to react to keep the speed constant), and to keep within design parameters, like the maximum torque allowed on the shafting, the maximum thrust allowed on the propeller to shaft connection, and others.

 

So, no, there are not "plenty of non-harmonic frequencies" for any speed.

[0bnxshs]

Always love the detailed, technical explanations provided by you, chengkp75, and the knowledge imparted and the discussions raised by your posts. Thanks! :cool:

 

In reference to Heartgrove's post (and not in disagreement with you at all), we were also on the NA pre-drydock cruise this past week and we collectively (group of 5) never noticed any vibration in the MDR, during the day, at the Mariner Brunch or at early dinner. I'm sure that individual sensitivities also play a factor in vibration perception in addition to all the technical reasons they happen.

[Underwatr]

If they hit a harmonic at 16 knots, could they do 15 knots for an hour and 17 knots the next hour? (I know fuel economy isn't linear with speed, so I guess it boils down to Captain's prerogative of passenger comfort vs. cost).

[chengkp75]

Absolutely right. I can still remember meeting passengers on the Aloha (NCL Sky) on deck 10, forward, who asked me if the ship always "moved this much" while we were tied to the dock in Honolulu.

[kenevenpar]

We did not experience excessive vibrations two weeks ago, except when I put a quarter in the bed.

[AmazedByCruising]

[quote name=chengkp75;54717024

So' date=' no, there are not "plenty of non-harmonic frequencies" for any speed.[/quote]

 

Wow, thanks once again!

[Heartgrove]

Always love the detailed, technical explanations provided by you, chengkp75, and the knowledge imparted and the discussions raised by your posts. Thanks! :cool:

 

In reference to Heartgrove's post (and not in disagreement with you at all), we were also on the NA pre-drydock cruise this past week and we collectively (group of 5) never noticed any vibration in the MDR, during the day, at the Mariner Brunch or at early dinner. I'm sure that individual sensitivities also play a factor in vibration perception in addition to all the technical reasons they happen.

 

I have to admit to probably being more sensitive to vibration than most others. I was an Engineman in the Coast Guard aboard CG cutters, and then spent 18 years in industry around rotating machinery. You develop a knack for "listening to/feeling for" sound and vibration irregularities.

 

Besides the Nieuw Amsterdam, I have sailed on the similar HAL Vista-class Westerdam and Zuiderdam before their most recent drydocks. But they did not stand out as much as being on the Nieuw Amsterdam.