In boats, a worm gear shaft is typically used in the steering system. Here's a more detailed explanation of its role:

1. Steering Mechanism: The worm shaft is a key component in the steering gear of a boat. It converts the rotational input from the helm (the steering wheel) into a linear or reciprocating motion that is used to move the rudder left or right, thus controlling the direction of the boat.

2. **Reduction Gear**: The worm shaft is often part of a reduction gear system. It allows for a high reduction ratio, which means that a small rotation of the steering wheel results in a large movement of the rudder. This is important for precise steering control.

3. **Load Distribution**: The worm gear and shaft help distribute the load evenly, which is crucial for smooth and reliable operation, especially in larger vessels where the rudder can be quite heavy.

4. **Durability**: Worm shafts are designed to be durable and withstand the harsh marine environment. They are typically made from materials that can resist corrosion and wear.

5. **Maintenance**: While worm shafts are designed for long-term use, they do require regular maintenance to ensure they function correctly and to prevent any issues that could affect the boat's steering.

6. **Safety**: In boats, the reliability of the steering system is critical for safety. The worm shaft plays a significant role in ensuring that the steering system operates smoothly and predictably.

In summary, the worm shaft is an integral part of the steering system in boats, providing a reliable and efficient way to control the direction of the vessel.