Port Engine Going Full Speed Astern

[Jim Currie]

Jim, if you put the wheel Hard Over to Stb’d on a twin rudder and wait just a little until the Rate of Turn Indicator shows like 30 degrees per minute, even if you redirect the wheel Hard to Port in 28 seconds, you will have to wait until your face turn yellow-green before she starts to swing to Port. Costa Concordia had a 50,000 metric tons displacement (quite the same as the Titanic). At 16 knots, the momentum reach like 1,500,000 tons-m/s. Ounce that momentum is directed and accelerates in the wrong direction, unless you’re in open water, your king is checkmated!

Have no experience of twin rudder ship handling, Georges. However, I would hate to steer a ship such as you describe in a following sea if it took so long to respond to a heading correction.
I like your wee sketches showing the coloured arrows. Try incorporating "bank cushion effect" and "displaced pivot point" due to contact with an immovable object.

 

[Georges Guay]

A typical case of Ship’s Interaction (Ventury / Bernoulli Effect) due to flow water restriction between a vessel proceeding too fast and at too short clearance from a shoulder moored vessel. Titanic’s Dead Slow Ahead Two was 6 knots! At slow speed, the center rudder without propeller trust on it, evolved in a turbulent and cavitation area. She must have been quite a hardheaded donkey to maneuver, if not the worst! Tugs were inevitable.

 

[Georges Guay]

I like your wee sketches showing the colored arrows. Try incorporating "bank cushion effect" and "displaced pivot point" due to contact with an immovable object.

Bank Cushion: no effect. We are dealing here with a steep reef surrounded by deep water that had all the room to flow freely.

The peripatetic point theory applies only to free floating vessel (neither moored, nor at anchor or aground). As soon as you touch something, a lever is created between the point of external force or impact and the center of gravity. The vessel will then turn around its center of gravity. Once the Concordia, on a port wheel but still on a Stb’d swing, stroke the reef violently, a turning lever was created between the 80 tons rock engulfed in the hull and the center of gravity. The resultant force (green) between the forward motion (black) and the heavy impact thrust (red) made the vessel turning to «Port» abruptly and in such an extent, that the wheel had to be redirect to Stb’d, away from Giglio harbour and toward deep water. A lots of fun !

 

[Georges Guay]

Don't think an anchor would have been of any use during the New York incident.

I don't think so. The speed was already too fast for an anchor to have any sort of efficiency. Two anchors down… might have helped a little. Anchor work: the line is fine between a hero and a zero! You had to control the speed «before» going too fast. How… by dragging via the after center fairlead, one or two tugs going full astern or by clutching one reciprocating engine at the time. Slow Speed Control is the essence of the game...

 

[Georges Guay]

Have no experience of twin rudder ship handling, Georges. However, I would hate to steer a ship such as you describe in a following sea if it took so long to respond to a heading correction.

Here is an official video that shows how good a twin rudder vessel steers in a following sea, obviously with the crucial aid of the stabilizers.

 

[Jim Currie]

Bank Cushion: no effect. We are dealing here with a steep reef surrounded by deep water that had all the room to flow freely.

The peripatetic point theory applies only to free floating vessel (neither moored, nor at anchor or aground). As soon as you touch something, a lever is created between the point of external force or impact and the center of gravity. The vessel will then turn around its center of gravity. Once the Concordia, on a port wheel but still on a Stb’d swing, stroke the reef violently, a turning lever was created between the 80 tons rock engulfed in the hull and the center of gravity. The resultant force (green) between the forward motion (black) and the heavy impact thrust (red) made the vessel turning to «Port» abruptly and in such an extent, that the wheel had to be redirect to Stb’d, away from Giglio harbour and toward deep water. A lots of fun !

It depends very much on the bank profile. Do we know that that was? There might easily have been a bow cushion and a mid ship suction due to inequality of pressure between port and starboard sides. All academic stuff.

 

[Jim Currie]

I don't think so. The speed was already too fast for an anchor to have any sort of efficiency. Two anchors down… might have helped a little. Anchor work: the line is fine between a hero and a zero! You had to control the speed «before» going too fast. How… by dragging via the after center fairlead, one or two tugs going full astern or by clutching one reciprocating engine at the time. Slow Speed Control is the essence of the game...

The ship had been canted out of the dock and was moving ahead down river in a narrow channel, the width of which was further reduced by berthed vessels. She would have had a following current and probably wind assistance. To drop two anchors while moving ahead would have been catastrophic. To drop one would have been equally so.
We must also remember that when the New York broke free at the stern, he was at the mercy of the same river and tidal currents that were affecting Titanic.

 

[Georges Guay]

It depends very much on the bank profile. Do we know that that was? There might easily have been a bow cushion and a mid ship suction due to inequality of pressure between port and starboard sides. All academic stuff.

If you observe any chart on the net, you will notice that Le Scole is a reef point surrounded by deep water. Usually, a rocky point have a steep underwater pattern and a sand point have on the contrary a gentle slope pattern. Shore interaction effect would’ve then been negligible.

 

[Georges Guay]

 

[Georges Guay]

The ship had been canted out of the dock and was moving ahead down river in a narrow channel, the width of which was further reduced by berthed vessels. She would have had a following current and probably wind assistance. To drop two anchors while moving ahead would have been catastrophic. To drop one would have been equally so.

We must also remember that when the New York broke free at the stern, he was at the mercy of the same river and tidal currents that were affecting Titanic.

The word «catastrophic» is a bit strong! But you better drop the anchor(s) if you run for a catastrophe! There is no problem of dragging anchors if there is at least 6 feet under keel clearance, that the sea bed nature is convenient and there’s no electric cable nor gas pipeline lying on the sea bed. The real problem is to recover those anchors…

 

[Jim Currie]

The word «catastrophic» is a bit strong! But you better drop the anchor(s) if you run for a catastrophe! There is no problem of dragging anchors if there is at least 6 feet under keel clearance, that the sea bed nature is convenient and there’s no electric cable nor gas pipeline lying on the sea bed. The real problem is to recover those anchors…

I'll answer both your posts, Georges.

If you consult any number of scuba divers who dive in that area of the Medditeranean, you will find that under sea cliffs round reefs abound. Thats the beauty of many such volcanic formations. However there is an up side; good cray fish and lobsters, not to forget the odd Moray Eel.

I deliberately used the word "catastrophic".

If you are on a big ship in a narrow channel making about 4 to 6 knots with the engines stopped and you let go both anchors:
Both must be let go simultaneously and the shackle count must be exactly the same. Additionally, the river bed has to be homogeneous, i.e. exactly the same across the channel.
If none of the above, then you get one-sided drag which will cause the stern to swing left or right. As soon as that happens, the following current catches it and accelerates the swing. A big ship's stern can do a lot of damage, so can it's bow. Took the lamp post outside Kenosha Yacht Club with the bow a very long time ago.

 

[Georges Guay]

Then fire back your engines my friend !

 

[Jim Currie]

Then fire back your engines my friend !

That's what they did, Georges. Stopped her using the engines. All hands below on immediate standby, Main engines rady for immediate use, Two engineers at the control platform.

 

[Georges Guay]

Then don't drop the hook(s)!