Crow’s Nest on Ships

A crow’s nest is a structure in the upper part of the ship, especially old-fashioned ones. It is used as a lookout point and positioned high above to increase visibility over the curvature of the Earth.

On the deck of a ship 4 m (13 ft) above the surface of the ocean, an observer can spot a 20 m (66 ft) high ship from at most ±25 km (16 mi). On the other hand, from a 35 m (115 ft) high crow’s nest, an observer will be able to spot the same ship from ±40 km (25 mi) away.

On modern ships, the role of a lookout is replaced by radars. And for the same reason, a radar is positioned in the upper part of a ship.

Simulated Observation from a Ship’s Deck (4 m above sea level)

Observer height 4 m — Object distance 20 km
Observer height 4 m — Object distance 35 km

Simulated Observation from a Crow’s Nest (35 m above sea level)

Observer height 35 m — Object distance 20 km
Observer height 35 m — Object distance 35 km

We are using the curvature simulation app from Walter Bislin with these parameters:

  • Refraction k = 0.17 (standard atmosphere)
  • Object 1: Ship, 20m
  • Views: view angle: 0.35°

References