Light saves ships from ice damage

17 Jun 2002

An array of laser beams can protect a ship's propellers from damage caused by large pieces of ice.

The optical load-deflection system (OLDS), designed by engineers at Canada's National Optics Institute (INO), is based on three-dimensional laser triangulation and monitors the deformations of each propeller blade in real time to an accuracy of 0.5 millimetres at distances of greater than three metres.

Three laser beams are aimed at the ship's propeller blades and the distance of each beam from the blades is calculated from the intensity and position of the scattered reflections. The emission and collection optics of the system are underwater in a watertight housing filled with air. This housing also contains a low-light CCD camera to record images of interactions between the propellers and the ice. The lasers are located on the ship and the beam is delivered to the underwater optics by optical fibres.

Propeller damage by ice presents major problems for navigation in Arctic waters. This device provides an early warning of potential problems, so avoids the risk of propellers breaking and leaving a ship stranded in a remote place.

The project was carried out for the Transportation Development Centre of Transport Canada, and INO subcontracted some of the work to MetriComp Systems of Calgary, which specializes in installing instrumentation on ships.

Andre Morin, the project leader for this system, says that it is a development of a previous device, tested in Antarctica in 1995, which used fibre-optic strain gauges and white-light interferometry. The earlier device was effective but very expensive.

The new device was described at the Electronic Imaging '99 conference earlier this year and an initial phase of testing was carried out in October 1999 on an icebreaker in the Lancaster Sound, Canada.

SH