Of all the maneuvers that a Captain performs, perhaps the most useful and oft repeated is moving his twin screw vessel sideways. And one of the greatest satisfactions come when an onlooker makes a comment about bow or stern thrusters only to discover the vessel that just slipped sideways so smartly, has no thrusters at all. Most twin screws boats are capable of this maneuver at least to some degree. The following is a simple technique that you can use to master this professional looking procedure. read more about pull push prop
First Visualization: When you turn the helm to Port with power ahead, you are actually telling the stern to move to Starboard, as the prop wash is actually flowing against the rudder and pushing it and the boats stern in that direction. When turning the helm to Starboard with power ahead, the stern moves to Port. Now, imagine then that someone is standing behind you with their hands in both of your back jeans pockets and you are leaning slightly forward. If they move your rear end to the right while pushing you forward the effect is that you are turn to the left. Move the rear to the left and you turn to the right.
Simple, that’s how you steer when going ahead. Note; you can steer a twin screw boat going ahead on one engine alone, if you want to go to Port, engage only the Starboard prop, and turn the helm to Port and the stern moves to Starboard relatively quickly. To turn to Starboard, turn the helm to Starboard, (the rudder actually turns to Port), engage the Port prop and the stern moves to Port. Simple, but it is important that you understand this principle particularly the more rudder degree you apply the more dramatic the movement of the stern. Conclusion: The rudder swings the stern opposite the direction you turn the helm.
Second Visualization: Again someone has their hands in your back pockets and you are slightly bent over. Now imagine that each of their hands is actually a propeller. If they push on your right cheek, (Starboard propulsion ahead), and pull on your left cheek, (Port propulsion astern), it swings your head, (bow) to the left. This is referred to as crossing transmissions, one ahead and one astern. Conclusion: Crossing transmissions swings the bow toward the side of the reverse gear.
Now remember, the rudders are behind the props and vessels stern swing is a result of water pushing against the rudder when the props are engaged ahead. When in reverse the rudders have little effect on the stern unless enough sternway is developed to push the rudders. SO:
The person behind you pushes on your right cheek, (Starboard forward), pulls on your left cheek, (Port reverse), while swinging your rear to the right, (helm to Port). Result: a very dramatic turn to the Port. This maneuver along with throttling each engine judiciously can result in turning the vessel about in its own length. The Port prop is pulling the bow to Port, the Starboard prop is pushing the bow to Port, and the Starboard prop wash hitting the Starboard rudder is pushing the stern to Starboard making the vessel turn very tightly to Port, the Port rudder having very little if any effect because there is not enough sternway developed due to the forward Starboard propulsion.
Turn the helm to Starboard, now the Starboard prop is washing against its rudder pushing the stern to the port side, meanwhile the combination of Port reverse and Starboard ahead is pushing and pulling the bow to the port side. Result: the whole vessel moves sideways to Port.
Reverse the Starboard, forward the Port and turn the helm to Port, the vessel moves to Starboard.
The person with their hands in your pocket can simulate this maneuver very graphically.
Summary: Reverse the side you want to walk towards, forward the other side and turn the helm toward the side in forward gear. Fine tune the maneuver by adjusting the throttles and the degree of rudder.
Now practice. It is advised that you take your vessel into open water and fix points fore and aft of your vessel as a reference point, and practice over and over again until you find the ‘sweet spot’ for your boat. Maybe find a buoy or some other floating object to practice near so you can develop your skill. Remember that all boats vary somewhat depending upon the depth of the hull, keel or whether or not the props are partially enclosed in tunnels. Most boats will require slight adjustments to the above procedure. Start with idle propulsion and practice, practice, and practice. Before you know it you’ll be walking your boat like a pro. Meanwhile your buddies at the marina will be wondering, “Where are your thrusters?”