🔍 Key Concepts

• Twin-screw vs single-screw maneuverability and control if one engine/shaft is lost • How bollard pull (pulling power) relates to total horsepower and number/size of propellers • Effects of having two propellers on exposure to damage from debris

💭 Think About

• Think about whether simply adding a second screw automatically increases bollard pull if total horsepower stays the same. • Ask yourself: does having two propellers in the water make you more or less likely to suffer damage from floating debris? Why? • Consider what happens to control of the tug and tow if you lose one engine on a twin-screw boat compared to losing the only engine on a single-screw boat.

✅ Before You Answer

• Verify how bollard pull is usually determined for a tug (total horsepower, propeller design, and thrust efficiency). • Check which statements are clear advantages of twin-screw tugs that are commonly accepted in practice. • Identify the choice that makes a claim about performance that is not automatically guaranteed just because the tug has two screws.