A boat with two engines can do something a single-engine boat can't: turn almost in its own length without moving forward or backward. Put one engine in forward and the other in reverse, and the boat pivots like a tank. Once you get the hang of it, twin engines make tight marinas far less intimidating. Until you do, they can feel like twice as many things to go wrong.
This article explains how twin engines steer a boat at low speed, the basic moves every twin-engine skipper uses, and how to practice them.
Why twin engines can turn without the wheel
On a twin-engine boat, the two propellers sit side by side, one on the port side and one on the starboard side of the centerline. Each one pushes or pulls the stern on its own side.
- Both engines in forward: the boat moves straight ahead.
- Both in reverse: the boat moves straight back (more or less).
- Port forward, starboard reverse: the port side is pushed forward while the starboard side is pulled back. The boat rotates clockwise, turning its bow to starboard.
- Starboard forward, port reverse: the boat rotates counterclockwise, turning its bow to port.
Because the engines are offset from the centerline, they create a turning force, or moment, even with no rudder at all. That's why twin-engine skippers often say to leave the wheel centered and steer with the shifters at low speed. The rudders need water flowing past them to work, and at docking speeds there isn't much. The engines turn the boat regardless.
An easy way to remember which way it turns: the boat turns away from the engine that's in forward. Port engine forward pushes the bow to starboard.
The basic moves
Pivoting in place
Put one engine in forward and the other in reverse, both at idle. The boat spins roughly around its middle. Because propellers usually push harder in forward than they pull in reverse, the boat may creep forward slightly as it turns. You can balance that by giving the reversing engine a touch more throttle, or by shifting the forward engine to neutral for a moment.
Pivoting is what lets twin-engine boats turn around in a narrow fairway between rows of slips.
Steering with one engine
With one engine in gear and the other in neutral, the boat moves and turns at the same time. Port engine alone in forward moves the boat ahead and swings the bow to starboard. This gives a gentle, controlled turn and is useful for small adjustments while creeping toward a dock.
Correcting your heading
While moving slowly forward with both engines in gear, you can straighten out by briefly shifting one engine to neutral. Want to swing the bow to port? Briefly take the port engine out of gear, so the starboard engine pushes the bow over. This is the twin-engine version of a small steering correction.
Backing straight
Backing with both engines in reverse tends to wander, because each propeller also pushes the stern sideways a little (see prop walk). On a twin, the two propellers usually turn in opposite directions, so these effects largely cancel. Fine corrections come from briefly shifting one engine to neutral, or putting it in forward for a moment.
Walking the boat sideways
An advanced twin-engine trick is moving the boat sideways, toward or away from a dock, without moving forward or back. It combines opposed engines with the rudders:
- The opposed engines produce a turning force.
- The rudders, turned hard over, deflect the prop wash from the engine in forward, adding a sideways push to the stern and cancelling the rotation.
The result, when balanced correctly, is a boat that slides sideways. It takes practice, it depends heavily on the boat, and on many boats it only works in light conditions. Boats with joystick systems, which control the engines and drives together through computer control, can do this automatically. Thrusters make it easier too, as described in Bow and Stern Thrusters.
Docking a twin-engine boat
Here's a typical approach to backing into a slip, one of the most common twin-engine maneuvers:
- Center the wheel and leave it there.
- Idle down the fairway past your slip, using short bursts of power to control speed.
- Pivot by opposing the engines until the stern lines up with the slip.
- Back in slowly with both engines in reverse, using short bursts.
- Correct with one engine at a time: if the stern drifts to port, a brief burst of forward on the port engine (or reverse on the starboard engine) swings it back.
- Stop with a short burst of forward on both engines, then secure the lines.
Throughout, keep the throttles at or near idle. Twin-engine boats respond strongly to throttle, and adding power to fix a problem often creates a bigger one. Short, gentle shifts, with pauses to see what the boat does, are the key.
Integrated vs separate controls
Twin-engine boats come with two main control styles:
- Separate controls have a shift lever and a throttle lever for each engine, four levers in total. Many experienced skippers prefer them for docking because you can shift in and out of gear without touching the throttles, which stay at idle.
- Integrated controls (single-lever controls) combine shift and throttle in one lever per engine: push forward from neutral to engage forward gear, then further for more throttle. They're simpler to use, but it's easier to accidentally add throttle when you only meant to shift into gear.
Whichever you have, the habit to build is the same: gear in, pause, gear out, watch. Use your hands on both levers so you can respond quickly.
Common mistakes
- Using the wheel at low speed. Turning the wheel when the boat is barely moving does little. Steer with the engines.
- Too much throttle. Idle is usually enough. More power means more momentum to stop.
- Holding a shift too long. The boat keeps turning after you shift back to neutral. Shift early and let it carry.
- Losing track of which lever is which. Under pressure, it's easy to grab the wrong one. Practice until it's automatic.
Practicing in The Boat Docker
The Boat Docker offers twin-engine inboards with either integrated or separate controls, and the physics model differential-throttle turning: run one engine forward and the other in reverse, and the boat pivots with no rudder input at all. Rudder steering, on the other hand, scales with water flow, so it's weak at docking speeds, exactly as it is on a real boat.
A good exercise is to try docking with the wheel centered the whole time, steering only with the shifters. Then add a crosswind and see how much harder it gets. The Throttles & Steering training page shows the controls for each setup, and changing the tonnage lets you feel how a heavier boat carries its momentum through every shift.