Motion-induced interruptions aboard ship: Model development and application to ship design

Abstract

The most severe direct motion induced effect on the ability of an individual to work in a moving environment probably occurs in gross body tasks requiring balance and co-ordination, be it the crew trying to undertake their task effectively or the passenger trying to walk around the vessel. During rough weather working in the ship becomes more difficult and even the most experienced sailor will experience events where they must stop their activity, be it a specific task or merely standing, and hold on to some suitable point to minimise the risk of injury; these events are called Motion-induced interruptions (MIIs). MIIs were recorded during the performance of a series of tasks on board a ship at sea in rough weather. The tasks were: standing facing aft, walking athwartships, a simulated weapon loading task, standing facing athwartships and a simulated fire-fighting task.

Complex mathematical models of postural stability exist but currently lack the fidelity to accurately predict MIIs. This paper presents data from an empirical study in which MIIs experienced by subjects on a ship at sea were logged by an observer. Measurements of lateral and vertical acceleration of the deck immediately prior to the MII were made and thresholds of acceleration for undertaking task were determined. These so called tipping coefficients are presented for use with predictive tools in ship design.