The pinnate propeller is a programmable pitch propeller. It has an even number of blades, and the opposing blades are assembled in pairs on axles which pass through the hub. These axles, called pinnate axles, can be turned by a mechanism and give the blades a programmed pitch variation when the propeller rotates.

The principles of the pinnate propeller and results from model tests were presented in a paper at the Propellers 81 Symposium (1).

In October 1982 tests were begun with two pinnate propellers in a Swedish Navy patrol boat. In this paper the tests are described, and some of the main experience is presented.

* The tests confirm the technical feasibility of the concept.

* They show a remarkable reduction of the intermittent cavitation when a suitable pitch program is applied and a reduction of pressure pulses at the hull above 'the propellers.

* Despite the lower pressure pulses, the vertical acceleration in the hull above the propellers increased, whereas the transversal acceleration was diminished.

* The highest cavitation-free speed was increased.

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