I just caught the bit from the film, about the last minutes (before the collision with the iceberg).
When the lookout’s warning was received, the helmsman put the wheel over hard to port. Then the officer of the deck put the starboard engine on “full ahead”, then moved the port engine to “full astern”.
Of course, revering the engines on a massive ship like the Titanic was quite a job-it must take many minutes to overcome the inertia of the giant shaft and prop.
My question: was this a big mistake? Had the OD ordered the port engine to full ahead, would the ship have turned faster?
Had the Titanic responded to the helm faster, they might have missed the berg completely.
Also, the Titanic had three propellors-the central one was driven by a low pressure turbine, fed by the other reciprocating engines. Was this prop controllable from the bridge?
Or should all of the engines been put on full astern? Would that have prevented the collision?
They should have been going slower. They were going too fast for ice conditions and they knew it, but Ismay didn’t want to be late getting to New York and Captain Smith decided to give in to his wishes. If they had been going slower (as was standard in waters where icebergs were known to be present) they would have been able to steer out of the way.
In hindsight, they would have been much better off simply steering into the iceberg and ramming it. Then they wouldn’t have opened up as many compartments and the flooding could have been controlled. There was no way of knowing that ahead of time though.
Putting all engines full astern wouldn’t have slowed the ship enough to prevent the collision. Putting the port engine full ahead may have made it turn “faster” but I think it would have made the arc of the turn wider, driving the ship further against the iceberg. Someone with a better knowledge of ship steering than me will have to give you a more definitive answer on that one though.
Stopping and then reversing one propeller would not have taken long. The propellers were 23 feet in diameter, that sitting in the water, is a lot of drag. Further, the steam engines were controlled by physically changing the valve timing - to stop the engine you are able to use the pressure in the cylinders in opposition to the rotation.
Worth noting that none of the engines were controlled from the bridge. All control was done in the engine rooms, by the engineers in the engine rooms, in response to the signals from the bridge.
But the main part of the question is answered thus.
Propellers on boats have a usually undesirable property that they not only propel the boat forward, but because the top of the propeller is close to the hull, and the bottom is in free water, they apply some sideways force to the boat, which acts to slew the stern. The direction of the force depends upon the direction of rotation of the propeller. An easy remedy is to install two propellers and have them rotate in opposite directions. Thus the forces cancel. Any multi screwed ship will be so designed.
I suspect the the officer on the Titanic was trying to use this effect to slew the stern around faster than the rudder angle alone would be capable of. With the engines running in opposite directions both propellers would be applying sideways force in the same direction, and the stern of the ship would move around. Use of this effect is a common trick when docking boats, and any properly trained officer in command of a ship would be well versed in its use.
None of them were ‘controllable’ from the bridge, like on modern ships. The bridge just gave orders to the engine room, and they controlled the engines from there. And they could control the center one in the engine room.
However, the center screw was not capable of being reversed. So when they put the 2 outside screws into reverse, they just shut off power to the center one and let it drag in the water.
The "slewing’ effect is a factor with a ship on a dead slow bell or just getting underway. But as the hull and rudder move through the water faster this effect decreases.
The ordering full ahead on the starboard was just for the move. The ship was already sailing at full ahead all engines.
If an emergency astern bell is rung up and someone was close to the throttles it is just a matter of throwing one lever. If a full astern is rung up, the throttle valve is closed the lever is thrown, and the throttle is reopened. 30 to 60 seconds. The reversing the engines will put a major drag on the port side of the ship. But a passenger ship running on a full ahead bell will not turn sharp even if one engine is put on full astern.
In manunerving mode the Port and Starboard engines exhausted to the main condenser. When on the open sea the two main engines exhaust to the mid shaft turbine.
The speed of a steam ship or direct drive diesel ship the engineers in the engine room do it. The bridge uses the “EOT” engine order telegraph to request the changes.
One account I read said that putting the engines in reverse made the rudder less effective.
If they had just kept going with the rudder at full port the response would have been more lively and they would have possibly missed the iceberg.
But I think that would have taken nerves of steel
Maybe I’ve been on a small sample set of modern ships, but they were all computer and electronics driven from the bridge. They could be controlled from the engine room, but the default was from the bridge with no intermediary except electronics.