The variety of working functions which can be incorporated in a model boat is largely down to the imagination and ingenuity of the builder and the budget available. There are no fixed rules about how these things can be operated, but here are a few suggestions:
Bow thrusters: Often incorporated in models of workboats such as tugs and ferries, these are small electric brushed motors fitted inside a tube which runs from side to side at the bow of the model, below waterline level. Water is drawn into one side and expelled from the other, applying a turning force to the bow (or stern) of the model. Typically the motor will run from 7.2v and needs a speed controller which will give equal power in both directions. Connect it to the channel which is operated by a sideways-movement of the transmitter stick and this is usually the opposite stick to the main steering one.
Working winches: These use a geared motor run either by a speed controller or a 2-way relay-based switch, with or without limit microswitches to prevent over-running. MFA/Como Drills have a very large range of geared motors and also a selection of plastic gears, chains, racks, pinions etc. to make up a drive train.
Doors, ramps, deck lifts, retractable antenna: Either use a geared motor as above, or a suitable servo. ACTion’s P96 ServoMorph is a handy device which can vary the total amount, direction and speed of rotation of a standard servo. Model aircraft retracting-undercarriage servos will turn slowly, have high torque output and will rotate 180 degrees with a normal transmitter signal. Sail winch servos will rotate several times from one extreme of signal to the other. Both types can be adapted for these sorts of function.
Gun turrets: Again, use either a geared motor and 2-way switch or a servo. Technobots have a dedicated Servo Position Controller which can be made to move a servo and stop the rotation at any point by returning the stick to centre without the servo following it. This clever little unit can also increase the degree of rotation as well as adjust its speed. It is only available as a kit to build on stripboard, however. Multiple turret servos can be made to rotate together by interconnecting them using Y-leads. Servo rotation can be reversed by either a controller such as the P96 ServoMorph or a simple and cheap reversing lead (available from Component Shop and others).
Fire monitors, bilge pumps: Use a geared water-pump suitable for the voltage available (Robbe and Graupner market several) and switched by a high-current r/c switch, e.g. ACTion P91. Note that the motors in these pumps are not often rated for running continuously for more than about 30 seconds at a time. Ignore such warnings at your peril!