How Boats Sail

Understand the science behind how boats sail and why they can sail into the wind

Test Summary

Difficulty:
410 Number of times this test has been taken.
73% The average score for this test.

Lift

Explaining how a boat sails downwind is fairly straight forward, you open the sails as far as possible and the wind pushes the sails, moving the boat along...simple. Explaining how a boat sails upwind is a little harder, after all, you're sailing against the only apparent force (the wind) that you have to push you along. However, the force of the wind on a sail works exactly in the same way as a wing on aeroplane, air moves across the surface of the wing and creates a force called lift. Lift is created by the following:

  1. Air travelling around the outside of the curve of the sail takes a longer path than the air around the inside of the sail. This longer path means the air travels faster around the curve of the path, causing a lower pressure than the air surrounding it.
  2. Inside of the sail, the air has a shorter path to travel so travels at a much lower speed and has a lot more pressure.
  3. This difference in pressure between the inside of the sail and the outside of the sail causes lift, a force that helps push the boat through the water.

Keel / Centreboard

Lift isn't the only force required for a boat to travel upwind, keels/centreboards prevent the boat from being pushed sideways through the water by the wind. The force applied by the water on the keel acts in the opposite direction to the force of the wind, these 2 forces squeeze the boat, pushing it forwards through the water, similar to when you squeeze a bar of soap in your hands.

How Boats Sail - Keel / Centreboard
Why Doesn't The Boat Drift Sideways? Well actually boats do drift sideways ever so slightly, however the water pushes against the keel when the boat drifts and it is this force that prevents the boat drastically drifting.

Tests

Taking a test can be a great way to build on what you have learnt already and build confidence before taking a formal qualification test. The How Boats Sail test consists of 3 questions randomly chosen from a selection.

410 Total Tests Taken
73% Average Score
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Terminology

Here's a list of the sailing terminiology used within this theory