An Attempt to Measure the Blade Stress of Controllable Pitch Propeller of an Actual Ship

Abstract

On the occasion of the building of new training ship "FUKAE MARU" of Kobe Mercantile Marine University, an attempt was planned to measure the blade stress of her controllable pitch propeller. She has the overall length of 50 meters, the displacement of 449 tons, and the CPP with diameter of 2.1 meters and with skewed angle of 40 degrees. The propeller and the shaft were designed and constructed to be able to install the measuring apparatus, which consists of the data processing component, the frequency-multiplexed telemeter kit, the cables through the propeller shaft connecting the leading wires of strain gauges with the telemeter kit, and the strain gauges put on the blade surfaces. The most sensitive parts of the apparatus are the gauges and the flexible cables crossing the boundary between the movable blade and the propeller boss, those whitch are exposed to the severe water flow. Much laborious efforts were payed to search the appropriate the sticking and coating materials of gauges, and the durable flexible cable. Measurement trials were carried out over the certain ranges of blade angle and propeller revolution number. According to the trial results, (1) the blade stress of CPP can be measured reliably by the method developed here, (2) the blade stress varies corresponding to the wake distribution, so that it fluctuates cyclically with the propeller revolution, (3) the mean stress changes in proportion to the mean propeller thrust, on the other hand, the fluctuating amplitude shows the different behaviour from that of the mean stress.