The gearcase is constructed of high grade cast iron, internally ribbed for rigidity and strength, and consists of two separate halves to facilitate servicing, the oil pump and hydraulic control valves being externally mounted for easy accessibility.

The PRM280DP live PTO gearbox specifically designed for driving hydraulic pumps to SAEJ774C series B specification. The maximum power which can be transmitted is 22kW (29.5hp) per 1000 rpm.

The hydraulic operating system functions on normal lubricating oil of the same viscosity as that used in the engine, 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 hydraulic failure the boat can be brought safely back to port. Access to this device is via a detachable cover located on top of the main gearcase.

A trolling valve can be fitted. This is electronically operated which allows variable speed of the propeller to zero whilst allowing a maximum engine speed of up to 1200 rpm.

Minimum - 20.00 bar (290 lb./in²), Maximum - 22.06 bar (320 lb./in²). Two tapped holes 1/8" BSP on the top, and M18 on the side of the valve block are provided so that the 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 valve block is provided with two 3/8" BSP connectors to allow it to be fitted.

Both ahead and astern thrust is carried by the output shaft bearings which are of adequate capacity for all factory approved ratings.

The PRM280 output shaft can be rotated continuously with the gearbox in neutral. It is therefore not necessary to fit a propshaft brake in such applications.

Approximate dry weight: 63kg (138lb) excluding adaptor, drive coupling and oil cooler.
Oil capacity: 1.7 litres (3.0 pints) plus the amount require to fill the cooling circuit.

Limited to planing hull pleasure craft; 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 PRM marine transmissions according to this classification for any commercial boat, or in sport-fishing charter boats or in long range pleasure cruisers, is not approved.

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.

PRM Newage Limited recommends that all displacement and semi-displacement craft used for commercial applications should be classed as heavy commercial duty. In vessels of this type (including trawlers, purse seiners, lobster and crab boats, tugs, ferries, offshore supply boats etc.) the marine gearbox is expected to work at full governed engine speed. The power setting of the engine must be known and must be within the gearbox's permissible heavy commercial rating.