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
Model  Ratios Pleasure Light





















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.
Service Classification Definitions - Pleasure

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 PRM150 according to this classification for any commercial boat is not approved by PRM Newage Ltd.

Service Classification Definitions - Commercial

PRM Newage Ltd recommends that when considering the PRM150 in boats of whatever hull form used in commercial applications, and semi-displacement hull boats for pleasure applications, these boats should be classed as commercial duty and the gearbox selected accordingly.

Important Note
  1. It is essential for the engine, transmission model, reduction ratio and propeller size to be correctly matched so that the engine can attain its rated speed appropriate to the relevant service classification without labouring.
  2. It is also necessary to ensure the torsional compatibility of the complete propulsion system from engine through to propeller, since disregarding this may result in gear noise, particularly at low speed operation, and may even result in damage to the engine as well as the transmission components.

PRM Newage Ltd will provide all possible information and assistance to help find solutions to potential torsional problems, but it is the ultimate responsibility of the person assembling the drive and driven equipment to ensure that they are torsionally compatible.

Operating Pressure

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.

Oil Cooling

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 ¼" 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
Oil capacity 1.4 litres (2.5 pints) plus the amount necessary to fill the oil cooling circuit.

Flexible Input Coupling for PRM150
Part Number Outside Diameter Mounting Hole Pattern Remarks
in mm No. Diameter Pitch Circle Dia.
in mm in mm
MT4904 8.50 215.9 6 0.344 8.74 7.875 200.0 SAE 6 1/2 in
MT4905 9.50 241.3 8 0.344 8.74 8.750 222.25 SAE 7 1/2 in
MT4906 11.75 298.5 6 0.320 8.13 7.875 200.0
6 0.320 8.13 9.843 250.0
6 0.320 8.13 10.625 269.9
6 0.320 8.13 10.75 273.1
MT4907 6.12 156.0 5 0.250 6.35 5.593 142.1
MT4908 5.965 151.5 8 0.256 6.5 5.512 140.0 Hawker Siddeley Marine
MT4909 10.50 266.7 6 0.32 8.10 9.625 244.5 Mitsubishi
MT4910 7.48 190.0 6 0.32 8.10 6.693 170.0 Nanni/Yanmar

Adaptor Flanges For PRM150
Part Number Description Weight
kg. lb.
MT4902S/A Special SAE4 adaptor, Volvo Penta 2000 series 10.0 22.0
MT4901S/A SAE5 adaptor 7.5 16.5
MT4903S/A Special SAE5 adaptor, Volvo Penta 2000 series 2.7 6.0
MT8083S/A B/W ( Velvet Drive) adaptor 1.4 3.1

Other Accessories For PRM150
Part Number Description Weight
kg. lb.
MT0149 Oil cooler, complete with pipes and bracket 1.5 3.3
MT3054 Tailshaft half coupling ( pilot bored) 1.3 2.9
MT3056 Tailshaft flexible coupling 0.7 1.5
MT5036 Oil pressure gauge, direct mounting 0.1 0.2
MT0156 Neutral safety start switch 0.04 0.1