You are now entering: The two-length zone

The two-length zone is often a critical factor in the rules and tactics that apply when you are rounding or passing a mark or obstruction, so let's look at how the rulebook defines it (see box}.

The two-length zone is an imaginary area on the water surface with its center at the mark or obstruction and a radius of two boat lengths. Locating the zone can be a challenge because, obviously, you can't see it, and also it's not a fixed area.

The size and shape of the zone vary according to the length of the nearest boat and the shape of the mark or obstruction. For example, if the boats that are rounding the mark are different sizes, the radius of the zone is two hull lengths of the boat that is closer to the mark. Also, if the mark or obstruction is not circular in shape, the perimeter of the two-length

When you are sailing in a fleet with boats of different lengths, you form the two length zone by using the hull length of the boat that is closer to the mark or obstruction. In this example, the Green boat is closer so the zone has a radius of two of her hull lengths. Even though the red boat is within two of her own hull lengths from the mark, she has not yet entered the "zone."

The zone will not be circular either. Instead, it will have an irregular shape that is two lengths from every point along the outer edge of the mark or obstruction. The good news is that. unlike the point at which boats are 'about to round' a mark, the two-length zone does not change according to the wind and sea conditions.

The two-length zone is not necessarily a circle. It's an area around a mark or obstruction that is less than two hull lengths from the perimeter of that object. Here's what the two-length zone looks like around a 'race commjtee boat.


Definition:  Two-Length Zone - The area around a mark or obstruction within a distance of two hull lengths of the boat nearer to it.

David Dellenbaugh, former starting helmsman for America3, publishes Speed&Smarts, a monthly newsletter of how-to information for racing sailors. For subscription information call: 800-356-2200. To order a new subscription, click