Systems and methods for controlling movement of drive units on a marine vessel

1. A system for controlling movement of a plurality of drive units on a marine vessel, the system comprising:

a control circuit communicatively connected to each drive unit in the plurality of drive units;

an operator input device for inputting a desired steering angle to the control circuit;

a speed sensor for inputting a speed of the marine vessel to the control circuit;

wherein, when the marine vessel is turning, the control circuit defines one of the drive units in the plurality of drive units as an inner drive unit and another of the drive units in the plurality of drive units as an outer drive unit;

wherein, based on the desired steering angle and the speed of the marine vessel, the control circuit calculates an inner drive unit steering angle and an outer drive unit steering angle that will cause each of the inner and outer drive units to incur substantially equal hydrodynamic loads while the marine vessel is turning;

wherein the control circuit subsequently sends steering control signals to actuate the inner and outer drive units to the inner and outer drive unit steering angles, respectively; and

wherein an absolute value of the outer drive unit steering angle is less than an absolute value of the inner drive unit steering angle.

2. The system of claim 1 , wherein the control circuit sets the inner drive unit steering angle equal to the desired steering angle.

3. The system of claim 2 , wherein an amount by which the absolute value of the outer drive unit steering angle is less than an absolute value of the desired steering angle is directly proportional to the speed of the marine vessel.

4. The system of claim 2 , wherein an amount by which the absolute value of the outer drive unit steering angle is less than an absolute value of the desired steering angle depends on trim angles of each of the inner and outer drive units.

5. The system of claim 2 , further comprising an additional drive unit located between the inner drive unit and the outer drive unit;

wherein the control circuit determines an additional drive unit steering angle; and

wherein an absolute value of the additional drive unit steering angle is less than an absolute value of the desired steering angle and greater than the absolute value of the outer drive unit steering angle.

6. The system of claim 1 , further comprising a plurality of steering actuators, each steering actuator in the plurality of steering actuators receiving one of the steering control signals and actuating a respective drive unit in the plurality of drive units to its respective drive unit steering angle.

7. The system of claim 6 , wherein the plurality of steering actuators comprises a plurality of hydraulic steering actuators.

8. The system of claim 1 , wherein the plurality of drive units comprises a plurality of outboard motors.

9. The system of claim 1 , wherein the control circuit sends control signals to actuate each drive unit in the plurality of drive units in the same rotational direction so as to turn the marine vessel.

10. A method for controlling movement of a plurality of drive units on a marine vessel, the method comprising:

receiving a desired steering angle with a control circuit that is communicatively connected to each drive unit in the plurality of drive units;

receiving a speed of the marine vessel with the control circuit;

defining one of the drive units in the plurality of drive units as an inner drive unit and another of the drive units in the plurality of drive units as an outer drive unit when the marine vessel is turning;

based on the desired steering angle and the speed of the marine vessel, calculating with the control circuit an inner drive unit steering angle and an outer drive unit steering angle that will cause each of the inner and outer drive units to incur substantially equal hydrodynamic loads while the marine vessel is turning; and

sending control signals to actuate the inner and outer drive units to the inner and outer drive unit steering angles, respectively;

wherein an absolute value of the outer drive unit steering angle is less than an absolute value of the inner drive unit steering angle.

11. The method of claim 10 , further comprising receiving an operator input for the desired steering angle and setting the inner drive unit steering angle equal to the desired steering angle.

12. The method of claim 11 , further comprising determining, based on the speed of the marine vessel, an amount by which the absolute value of the outer drive unit steering angle is less than an absolute value of the desired steering angle.

13. The method of claim 11 , further comprising determining trim angles of each of the inner and outer drive units, and based on the trim angles, determining an amount by which the absolute value of the outer drive unit steering angle is less than an absolute value of the desired steering angle.

14. The method of claim 11 , further comprising calculating an additional drive unit steering angle of an additional drive unit located between the inner drive unit and the outer drive unit, wherein an absolute value of the additional drive unit steering angle is less than an absolute value of the desired steering angle and greater than the absolute value of the outer drive unit steering angle.

15. The method of claim 11 , further comprising actuating each drive unit in the plurality of drive units in the same rotational direction so as to turn the marine vessel.