A motion analyzing system based on stereo vision technology to measure the motion of ship model during towing tank tests is developed. The non-contact optical measurement system has a characteristic pattern installed on the upper deck of the ship model and two high resolution cameras fixed separately in front of it to take behavior of the pattern from two different angles. Two sets of digital images are then introduced into a motion analyzing program to calculate motions of the ship model. The outcomes of this system are compared with those that obtained by gyroscope/laser sensor. The test results show that motions of the ship model derived from two methods have the similar tendency, however the proposed method is too sensitive as to that the data fluctuate violently, a process to filter out the high frequency part is necessary for practical utility.
Benefit from the highly progress of simulative technology, it becomes much faster and easier in designing the shape of ship hull. However to decide the power of a new ship is still a difficult issue. In practice, resistance test and self-propulsion test which carried out in towing tank are the most common method to conduct power estimation. During these tests how the attitude of the ship model would vary is very helpful for ship motion performance evaluation. Moreover, in sea-keeping test the movement of ship model under the action of wave is more complicated and measurement of six degrees of motions of the ship model are essential.
In general, the devices used to measure the ship motion are laser sensor and gyroscope sensor depend on how many freedom of motions are going to measure. In our 8 meter width, 165 meter long, 4 meter depth towing tank, laser sensors is used in heave and surge measurements, and gyroscope sensor is used to measure roll, pitch and yaw. Because these devise are expensive and the installation process is very complicated, hence a simple and low cost system is required.
