Cruise ships don't have sensors in the aft to go in reverse?

[fstuff1]

We're docked in st John, Canada.

Royal's AoS is docked behind us.

They are leaving an hr before us.

 

they sailed past us deeper into the harbor to do a U-turn then sailed out head first.

 

From leaving their dock to exiting the harbor took 20min.

 

Since they were on the dock closest to open water, why didn't they just go in reverse and save 20min?

 

[shof515]

there is ALOT you dont see under the water from these ships. the ship draft and the channel depth is the two most important measurements. It might look funny but ships need to do movements to avoid bottoming out and running aground 

[jbcallender]

12 minutes ago, fstuff1 said:

We're docked in st John, Canada.

Royal's AoS is docked behind us.

They are leaving an hr before us.

 

they sailed past us deeper into the harbor to do a U-turn then sailed out head first.

 

From leaving their dock to exiting the harbor took 20min.

 

Since they were on the dock closest to open water, why didn't they just go in reverse and save 20min?

 

It is safer to do a 180, with 360 degree visibility than to do a blind backing maneuver and risk hitting something or getting out the channel.

[Laszlo]

12 minutes ago, jbcallender said:

It is safer to do a 180, with 360 degree visibility than to do a blind backing maneuver and risk hitting something or getting out the channel.

Their is nothing blind about backing up, they have lots of cameras and crew

[old nutter]

Maybe it has more to do with the fact that the ship is more controllable with the pointy end going forwards rather than the blunt going forwards. (Sorry to get technical!🙂)

[chengkp75]

35 minutes ago, old nutter said:

Maybe it has more to do with the fact that the ship is more controllable with the pointy end going forwards rather than the blunt going forwards. (Sorry to get technical!🙂)

Ding, ding, ding, we have a winner.  Whether with controllable pitch propellers and rudders, or with azipods, when a ship goes astern, it will always want to swing the stern to one side or the other.  Also, the point at which a ship rotates around when steering moves with the direction the ship is going.  If the ship is stationary, it will rotate around the center (longitudinally) of the ship.  When going ahead, the turning center moves to a point 2/3 of the way back from the bow.  Likewise, when going astern, the turning center moves to a point 2/3 of the way from the stern (1/3 from the bow).  So, when backing, with the azipods at the stern, and the turning point near the bow, lateral stability (the ability to maintain a straight course) suffers from the long moment arm from the propellers to the turning center, and so small changes in steering create large changes in course.  Because the harbor is not a uniform depth, it is a dredged channel for the ships, and then more shallow areas outside the channel, being able to steer in a straight line up the channel becomes paramount, unless you want to end up like NCL's Escape in the DR.

 

Where the ship backed up to is a wider dredged area called the "turning basin" where the dredged area is wider than the ship is long.

 

And, finally, the Captain is far more comfortable being able to see what he might hit, than relying on cameras (notably poor depth perception) or the 3rd officer's radio reports from the stern.

 

And, I might as well go for my pet peeve in terminology.  There is no "the aft".  Aft is not a noun, it is a adjective or adverb.  Sensors for going astern would be in the stern, not "the aft".  Sorry.

Edited September 21, 2022 by chengkp75

[fin]

Late in saying so, but I MUST commend this poster on his factual and polite answers.  Well done, Sir!!

[SeaShark]

27 minutes ago, chengkp75 said:

Ding, ding, ding, we have a winner.  Whether with controllable pitch propellers and rudders, or with azipods, when a ship goes astern, it will always want to swing the stern to one side or the other.  Also, the point at which a ship rotates around when steering moves with the direction the ship is going.  If the ship is stationary, it will rotate around the center (longitudinally) of the ship.  When going ahead, the turning center moves to a point 2/3 of the way back from the bow.  Likewise, when going astern, the turning center moves to a point 2/3 of the way from the stern (1/3 from the bow).  So, when backing, with the azipods at the stern, and the turning point near the bow, lateral stability (the ability to maintain a straight course) suffers from the long moment arm from the propellers to the turning center, and so small changes in steering create large changes in course.  Because the harbor is not a uniform depth, it is a dredged channel for the ships, and then more shallow areas outside the channel, being able to steer in a straight line up the channel becomes paramount, unless you want to end up like NCL's Escape in the DR.

 

Where the ship backed up to is a wider dredged area called the "turning basin" where the dredged area is wider than the ship is long.

 

And, finally, the Captain is far more comfortable being able to see what he might hit, than relying on cameras (notably poor depth perception) or the 3rd officer's radio reports from the stern.

 

And, I might as well go for my pet peeve in terminology.  There is no "the aft".  Aft is not a noun, it is a adjective or adverb.  Sensors for going astern would be in the stern, not "the aft".  Sorry.

 

As always...great information.

 

It is a little confusing in that it seemingly conflicts with other information out there. As you know, most of NCL's fleet was constructed at Meyer Werft's facility in Papenburg. Once the ships are constructed, the 20 mile conveyance on the Ems River from the shipyard is always done backwards as they say the ship is more maneuverable while traveling in reverse.

[chengkp75]

11 minutes ago, SeaShark said:

Once the ships are constructed, the 20 mile conveyance on the Ems River from the shipyard is always done backwards as they say the ship is more maneuverable while traveling in reverse.

For the Ems river conveyance, the ship is towed and only uses her own propulsion in some deeper areas of the river, as they would churn up the riverbed too much.  So, you don't have the issues of the ship's propulsion tending to turn the ship one way or the other.  The tugs now provide their own steering capability, both at the bow and stern, and given the slow speed of the conveyance, the turning center is closer to the center of the ship.  The blunt stern allows for a wider spread to the two towing cables going to the aft tug, allowing it better control over twist than the longer, narrower spread of the bow tug.

 

I've also had a brain fart, and switched the directions that the turning center moves, it is 1/3 of the way from the bow going forward, and 1/3 of the way from the stern when going astern.  So, when going astern in the Ems, the bow thrusters are furthest away from the turning center, so they will have more effect on turning the ship than the azipods.   I apologize, don't know why I switched the points, but I did, but the result is the same.

Edited September 21, 2022 by chengkp75

[Homosassa]

The only time I can remember ever leaving a channel stern first was on the Rotterdam (not the new one) in Curacao.

 

We were docked in the ship channel just inside the pontoon bridge.

 

I don't remember the reason the Captain decided to go out stern first . We were standing out aft on a lower deck.  There were two officers out there with us in radio communication with the bridge.

[hallux]

For what it's worth - the ships that port in San Pedro (port near LA) DO reverse in the channel, at least the ones that dock parallel to the channel do as there isn't a turning basin near the pier so one way or the other they're going astern to traverse the channel.  The Bliss sure does anyway, maybe there is a turning basin there but that ship is too big for it.

[trivimp]

I jumped into this thread with the intent of saying something about dredged channels & turning basins, but now realize I am just here for chengkp's commentary 🙂  

[quillwercruisers]

1 hour ago, hallux said:

For what it's worth - the ships that port in San Pedro (port near LA) DO reverse in the channel, at least the ones that dock parallel to the channel do as there isn't a turning basin near the pier so one way or the other they're going astern to traverse the channel.  The Bliss sure does anyway, maybe there is a turning basin there but that ship is too big for it.

The last time we went out of San Pedro was on the Jewel, and now that I think about the return trip, we also backed down the channel to the pier.  And we did it in heavy fog.  We had an Aft Suite on that trip and it was kind of eerie.  😃

[scooter6139]

I love watching the shows Might Ships and Mighty Cruise Ships,  and it's always interesting to see how these huge vessels plan and execute their port entry and docking.