Calculate the distance to the horizon: visibility and the duty to keep a proper lookout

To calculate the distance to the horizon,

take 2,08 times the square root of your height of eye in metres, with the result in nautical miles.

From the cockpit of a sailing yacht, roughly two metres above the water, your view reaches barely three nautical miles. A cargo ship whose superstructure stands thirty metres high is seen much sooner, because the two distances to the horizon add together. That is precisely why large vessels seem to appear out of nowhere: they have been there all along; it is only their hull that lies below the horizon.

In legal and insurance terms, this is what the duty to keep a proper lookout turns on. A collision in which the lookout was demonstrably neglected raises the question of gross negligence, both in the liability cover towards the other vessel and in your own hull cover.

For your cover the picture is simple: full hull cover pays for collisions, even where you caused the damage, while partial hull cover usually gives no collision protection. Some policies also waive the defence of gross negligence. If you know how far you can see, you are less likely to find yourself having to fall back on that waiver.

Worked out for your type of boat

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