Ship motion measurement using an inertial measurement unit

Traditional methods of measuring a vessel's motion involve the use of bulky sensor units which usually require cables. These devices are not only expensive, but are difficult and time-consuming to install. They are simply not affordable and do not provide owners of vessels with a cost effective way of measuring and monitoring their vessels' motion during operation. Measured vessel motion could be used to deduce the sea state using the wave buoy analogy. This additional information could be crucial in improving operational safety for vessels. If motion monitoring is to be used to help improve a vessel's operational stability and provide operational critical information, cheaper and simpler alternatives are needed. In this paper, we present a novel motion measurement system which uses a Raspberry Pi with a wireless module and an inertial measurement unit (IMU) sensor to measure a vessel's motions. The data collected can either be stored locally on the Raspberry Pi or be sent wirelessly to the user. Compared to traditional devices, the Raspberry Pi is cheaper and easier to install. In addition, due to its computing power, some of the post-processing of data, which is traditionally done on a computer separate from the measuring unit, can be done on the Raspberry Pi. For a practical evaluation of using the Raspberry Pi to measure ship motion, it was placed on a fishing vessel for two hours. The IMU used measured nine degrees of freedom, all of which were recorded at 50 Hz on the Raspberry Pi. Afterwards, the data was taken from the Raspberry Pi wirelessly and analysed using Matlab, firstly to ensure that the right data was collected at the right frequency, and secondly to visualise the data. The evaluation shows that using the Raspberry Pi, as an Internet of Things (IoT) device, is a light-weight, cost-effective, and easy-to-install alternative to traditional devices for measuring vessel motion.