Full hydraulic operation, lightweight, compact & rugged
The PRM150 marine gearbox is purpose built for use with both pleasure craft and commercial boats; its twin countershaft design provides separate oil-operated multi-disc clutches (which need no adjustment) for ahead or astern drive allowing full rated power to be transmitted continuously in either direction.
The reduction ratios offered (1.53:1. 2.09:1 and 2.82:1) are all available for left-hand or right-hand propeller rotation in “ahead”, making PRM150 particularly well suited to twin engine installations.
The heavy duty aluminium alloy gearcase is internally ribbed for rigidity and strength and consists of two separate halves to facilitate servicing.
The hydraulic operating system functions on normal multigrade engine oil, avoiding the need to use automatic transmission fluid, and ensures rapid response to movements of the operating lever for good boat handling. The operating lever has a positive neutral detent and is suitable for use with proprietary single lever remote control operating systems.
Robust and reliable, the hydraulic system is nevertheless provided with a mechanical lock up device for added security, so that in the unlikely event of a hydraulic failure the boat can be brought safely back to port. Access to this device is via the detachable manifold on the rear of the gearcase which also houses the hydraulic control valve.
Nominal Power Ratings, PRM 150 Marine Gearbox
Maximum operating speeds: 5000 rev/min intermittent, 4500 rev/min continuous
Note: These powers have been measured at the engine flywheel. Ratings have been established to ensure the long trouble free life of the gearbox which should not, therefore be used at powers in excess of those shown.
Minimum – 25.51 bar (370 lb./in²), Maximum – 28.96 bar (420 lb/in²). A tapped hole 1/8″ BSP is provided in the rear manifold so that a pressure gauge can be fitted if required.
The normal operating temperature of the oil should be in the 50°C – 80°C range and should not be permitted to exceed 90°C. An oil cooler is necessary to ensure that correct operating temperatures are maintained, and the gearbox is provided with two 1/4″ BSP connectors to allow it to be fitted. The size of the cooler depends on a number of factors including the transmission horsepower, operating speed, duty cycle, inlet water temperature and ambient temperature.
Propeller Free Wheeling
The PRM150 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, e.g. in multi-engine installations or when sailing.
Approximate Weight & Oil Capacity
Approximate dry weight:
21kg (46lb) excluding drive coupling, adaptor flange and oil cooler
1.4 litres (2.5 pints) plus the amount necessary to fill the oil cooling circuit.