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Twin engines manoeuvering

Some sailing or motor yacht have two engines and therefore also two screws. Larger motor yachts and catamarans, for example. Then maneuvering on the engine is quite different. Twin engines offer a number of additional options.

Pivot on the spot

With two engines, you can turn on the spot without using the rudder at all. We do this by engaging 1 engine in forward and 1 in reverse. Sometimes this is so powerful that a bow thruster and the steering wheel are actually not necessary. For example, if the engines and therefore also the screws are far apart, as is the case with a catamaran. A torque consists of two forces in opposite directions with a certain distance between them. The more distance, the more powerful the torque.

Pivot on the spot


You can also keep a straight course with two engines without using the rudder, because with one engine forward and the other neutral, the boat turns 1 way. The resistance force of the water against the boat will be in the middle but the engines push forward on the outside of the boats. So the starboard engine forward means that the boat will automatically turn to port. Astern, a ship has even more resistance from the water. That’s because the stern isn’t as hydrodynamic as the bow. The resistance force going astern is therefore stronger and so the boat turns even faster. The rotation by this torque is therefore stronger going astern than when ahead.

Torque

Propwalk twin engines

Another advantage of two screws is that you can take advantage of the prop walk to both port and starboard. Ships with two engines usually have a right-hand propeller on the starboard side (sailing forward) and on the port side a left-hand turning propeller (sailing forward). In other words the propellers turn forward sailing outwards. It is possible to make use of the propwalk when maneuvering, sometimes almost comparable to a stern thruster.

Propwalk twin engines
Propwalk and torque

Watch out, because on some ships it’s the other way around. It is sometimes more economical in terms of fuel consumption to let the propellers turn inwards sailing ahead. In the examples below, I assume that screws rotate inwards going astern.

If we put the starboard engine in reverse, that engine will of course turn counterclockwise and the stern will walk to port. The propwalk in reverse is always considerably stronger than in forward. That’s because the shape of the screw is designed for sailing forward and in reverse the shape is actually not good. We can create propwalk to port or to starboard. We do this simply by engaging 1 engine astern and the other neutral. By putting the other engine in forward and using the prop wash on the rudder blade, we can move the stern almost perpendicular aside. Just like having a stern thruster.

Mooring with twin engines

Prop-walk to port or starboard and the fact that the screws are next to the center line of the yacht gives extra possibilities. Docking and undocking is different compared to yachts with a single screw.

Mooring astern to the shore

Mooring on an windward shore (seen from the ship) can be done by going in reverse to the shore and stopping it. You are in full control because the bow will be blown away by the wind, but that does not matter because you focus purely on the stern. Then someone first secures the stern line with a double line on the ship. Then you can slowly engage the screw on the outside (so not on the side of the shore, but on the sea side) so that the bow also comes along the quay. If you are afraid that the forces on the stern line will become too great, you can put the other engine (on the shore side) slightly in reverse. The speed of this pivot can be accelerated by turning the rudder blade / steering wheel towards the shore.

Mooring ahead to the shore

You can also sail at an angle of 45 degrees to the windward shore. You then first throw the bow line from the foredeck around the bollard. Then put the screw on the sea side so not on the side of the shore, in reverse. Due to the prop walk, the stern walks towards the shore. Engage the engine on the side of the shore to reduce the tension on the line. To speed up the turn, you can turn the rudder/steering wheel away from the shore.

Docking with twin engine

Undocking with twin engine

You can also use the previous principle when undocking. For example, if you are moored on a shore with a light wind and ships are moored in front and behind you, you can get out more easily using one of the following two ways.

Springing Off: Pivot (in reverse with stern spring) cast off and sail away (ahead)

Remove all lines except the stern spring. You then put the engine on the sea side, so not on the shore side in reverse. As soon as the ship has pivoted enough, cast off and sail away ahead and take in the stern spring. If you are afraid that there will be too much tension on the stern spring, engage the engine on the shore side in forward. To speed up, turn the rudder blade towards the shore until the angle between the shore and the ship is large enough for you to sail away. This method is also used on ships with a single screw, but the torque with two screws is much stronger because the screws are next to the keel line.

Use the prop-walk and bow line

Another way is the following. You take away all lines except the bow line. You engage the engine on the shore side in reverse and now take advantage of the prop-walk that walks the stern into the wind. If you are afraid that the forces on the bow line will become too much, you can engage the other engine ahead. Keep the tension on the bow line. This method only works with light winds, if it is windy you will probably have to spring off.

Undocking with twin engine

Conclusion

The use of bow thruster, stern thruster and steering wheel sometimes does not make it any easier. Usually it is better to focus only on the two throttles. When sailing on engine in harbors, the speed is relatively low, so that’s why the rudder blades don’t do much anyway. With two engines, bow and stern thrusters are only for minor corrections and emergencies, but try to do as much as possible with the two main engines.

Twin engine maneuvering course

Would you also like to spend a day or two maneuvering in the harbor on your motor vessel or catamaran with two engines in the harbor with an instructor, please contact me. I can offer these anywhere in Europe. I will be happy to practice with you the docking and undocking. We pivot the yacht around it’s center point in narrow harbours, drive astern in the harbour, practice man overboard, going through locks, line handling, etc. We practice until you and your crew have become a real team. That way you will avoid stress in marinas and avoid too much burst, smoke plumes from the exhaust and unnecessary use of the bow thruster.