The gearbox is purpose built to operate with standard rotation engines i.e. providing a clockwise rotation of the gearbox input shaft when viewed on input. In forward drive the output shaft rotates opposite to input shaft therefore requiring a right hand propeller.

The reduction ratios offered are 2.04:1 and 2.50:1 with a common astern ratio of 2.5:1

The heavy duty aluminium gearcase is externally ribbed for strength and heat dissipation and therefore requires no oil cooler.

Direction actuation is by a lever with positive detent positions for ahead, neutral and astern. It is suitable for use with proprietary remote control operating systems which must be of the single lever dual action type, i.e. MORSE MT3 or SL3 which operates the engine throttle in conjunction with the gear lever.

The normal operating temperature should be in the range 50° to 95° using a good quality Automatic Transmission Fluid.

The PRM90 output shaft can be rotated continuously with the gearbox in neutral.

It is therefore not necessary to fit a propshaft brake when running with the engine shut down, for example when sailing.

Approximate dry weight: 13kg (28.7lb)
Oil Capacity: 0.3 litres (0.5 pint)

Limited to craft used exclusively for pleasure boating; operation at full engine throttle should not exceed 5% of total time, with balance of usage at 90% of full throttle engine speed, or less. Maximum operation 500 hours per year. The selection of PRM90 according to this classification for any commercial boat is not approved by PRM Newage Ltd.

Planing or semi-displacement craft used in pleasure or commercial applications may qualify for light commercial rating if annual usage is less than 1500 hours and full throttle operation is limited, with most operating time at partial throttle.