The worm shaft, also known as the worm, is a critical component in a worm gear system used on boats. Here are the main functions of the worm shaft in a marine context:

1. **Power Transmission**: The worm shaft is responsible for transmitting power from the input source (such as an electric motor or hydraulic system) to the output (like a steering mechanism or winch). It does this by converting rotational motion into a different type of motion (usually linear or rotational at a right angle).

2. **Speed Reduction**: One of the primary functions of the worm shaft is to provide a significant reduction in speed. This is achieved by the high ratio of the worm gear system, allowing for slow, controlled movement of the output shaft.

3. **Torque Multiplication**: Along with speed reduction, the worm shaft also multiplies the torque. This is particularly useful for applications where high torque is needed at low speeds, such as lifting heavy loads with a winch or providing precise steering control.

4. **Direction Change**: The worm shaft changes the direction of the input motion by 90 degrees, which is useful in applications where the output needs to move perpendicular to the input.

5. **Self-Locking**: In some designs, the worm shaft has a self-locking feature, which means it can prevent the output from rotating back when the input is stopped. This is important for safety in applications like winches, where you want to ensure that the load doesn’t slip.

6. **Precision Control**: The worm shaft allows for precise control over the output movement, which is essential in applications that require accurate positioning or movement, such as in boat steering systems.

7. **Space Efficiency**: The worm shaft can be designed to be compact, making it suitable for use in the limited space often found on boats.

8. **Durability**: Worm shafts are designed to be durable and withstand the harsh marine environment, including exposure to saltwater and varying weather conditions.

9. **Ease of Maintenance**: While worm shafts are generally reliable, they can be relatively easy to maintain and repair, which is an advantage in a marine setting where accessibility to specialized maintenance services may be limited.

10. **Load Distribution**: The worm shaft helps in distributing the load evenly across the worm gear, which can extend the life of the gear system and reduce wear and tear.

     In summary, the worm shaft plays a crucial role in various mechanical systems on boats, providing a reliable and efficient means of power transmission, speed reduction, and torque multiplication, all while allowing for precise control and direction change.