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PRM 90D Drop Centre Marine Gearbox (Ahead Ratio 2.50:1)

Part No. PRM-90D2-5

£691.70 You pay £691.70 Incl VAT You pay £576.42 Excl VAT

RRP £886.80 £739.00

Save £195.10 (22.0%) Save £162.58 (22.0%)


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Brand PRM
Country of Origin United Kingdom
Gearbox Manufacturer PRM
Construction Heavy Duty Aluminium Gearcase
Hydraulic or Mechanical Mechanical
Gearbox Model PRM 90D
Ratio Ahead / Stern 2.50:1
Shaft Arrangement Drop Centre
Nominal Power Rating Pleasure 1.10 BHP / 100 RPM
Nominal Power Rating Light Commercial 0.73 BHP / 100 RPM
Approximate Dry Weight 11.25kg (24.5lbs)
Capacity Oil Capacity: 0.3 litres (0.5 pint)
Gearbox Spline 10 teeth B10 x 23 x 29mm DIN 5464
Gearbox Coupling 4", 4 holes, 3-1/4" PCD, 2-1/2" female register
Warranty (Years) 2
Replaces PRM-80D2-5

Simple mechanical operation, lightweight, compact & rugged.

The PRM90 gearbox is designed for use in pleasure craft where a simple lightweight transmission is required.

The cone clutches for both ahead and astern are mechanically operated and require no adjustment.

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.

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.

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.

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

Propeller Free Wheeling
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.

PRM90 Gearbox spline: 10 teeth B10 x 23 x 29mm DIN 5464. PRM 90 Gearbox coupling: 4", 4 holes, 3¼" PCD, 2½" female register. Oil Capacity: 0.3 litres (0.5 pint).

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FAQ & Technical Information

  • Do you have the Manual for the PRM90D? +

    Yes, please see attached document for the Product Manual.

    PRM90D Workshop ManualDownload
  • Technical Article - Gearboxes & Spares +

    The technical article for gearboxes & spares is here:

    Technical Article - Gearboxes & SparesDownload
  • What are the measurements of the PRM90D? +

    Yes, please see attached technical drawing for full dimensions and specifications.

    PRM90D Installation DrawingDownload
  • Which PRM 90 Model is right for my application? +

    Nominal Power Ratings for PRM 90 Marine Gearbox

    Model Ahead Ratio Pleasure Light Commercial
    BHP kW BHP kW
    90D2 2.04:1 1.26 0.94 0.83 0.62
    90D2.5 2.50:1 1.10 0.82 0.73 0.54
    Max Input Power 50 37 33 25

    Maximum operating speeds: 5,000 rev/min

    Note: These powers are expressed in BHP and kW per 100 rev/min engine operating speed, and are 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 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.

    Service Classification Definitions - Light Commercial
    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.

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