My project requires a DC motor for mobility, very similar to an RC car. If precision isn't critical, can I use a solid state relay instead of a motor driver? If the vehicle moves an extra inch on the ground, I don't really care.
For a DC motor, you can use a relay instead of a motor controller if you aren't too concerned about precision. Be careful to account for the inductive surge in current, and ensure your relay can handle the peak current. You'll also see a reverse current if you stop the motor abruptly, so flyback diodes are a good idea as @hauptmech indicates.
If you want to use a relay in your airboat, use flyback diodes, otherwise you might get stuck with the gators.