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PRM 750A Down Angle Marine Gearbox (Ahead Ratio 2.565:1)

Part No. PRM-750A2-5

£3,787.06 You pay £3,787.06 Incl VAT You pay £3,155.88 Excl VAT

RRP £4,855.20 £4,046.00

Save £1,068.14 (22.0%) Save £890.12 (22.0%)


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Brand PRM
Country of Origin United Kingdom
Gearbox Manufacturer PRM
Construction High Grade Cast Iron Gearcase
Hydraulic or Mechanical Hydraulic
Gearbox Model PRM 750A
Ratio Ahead / Stern 2.565:1
Shaft Arrangement Down Angle
Nominal Power Rating Pleasure 9.48 BHP / 100 RPM
Nominal Power Rating Light Commercial 7.62 BHP / 100 RPM
Nominal Power Rating Heavy Commercial 7.23 BHP / 100 RPM
Approximate Dry Weight 90kg (198 lbs) (excluding adaptor, drive coupling and oil cooler)
Capacity Oil Capacity: 3.0 litres (5.28 pints) (plus the amount required to fill the cooling circuit)
Gearbox Spline 17 teeth 16/32 DP
Gearbox Coupling 6", 6 holes, 4-3/4" PCD, 3" female register
Warranty (Years) 2

Full hydraulic operation: offset or down angle output shaft.

The PRM750D and PRM750A marine gearboxes are purpose built for use in both pleasure craft and commercial boats; the twin countershaft design provides separate oil-operated multi-disc clutches (which need no adjustment) for ahead and astern drive allowing full rated power to be transmitted continuously in either direction.

To cater for the widest possible variety of boats the PRM750 is offered in two different configurations : with offset output shaft (PRM750D) and 8° down angle output shaft (PRM750A). Reduction ratios available are 1.09:1, 1.459:1, 1.935:1, 2.565:1, 2.904:1 and 3.952:1 (3.952:1 reduction is not available on down-angle gearboxes) all of which can provide either left-hand or right-hand propeller rotation in "ahead", making the gearbox particularly well suited to twin engine installations.

The robust and reliable hydraulic system uses lubricating oil of the same viscosity as that used in the engine, and helps ensure good boat handling by its rapid response to movements of the operating lever.

The operating lever has a positive neutral detent which assists the setting-up of the remote control operating unit whilst for added security, to guard against the unlikely event of hydraulic failure all gearboxes incorporate a mechanical lock-up device so the boat can be brought safely back to port.

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.

A special feature of the PRM750D & PRM750A is the direct drive power take-off which is available as an optional extra; this will power a hydraulic pump to SAE J744C type 'B' specification, thus providing an economical and space efficient means of driving on-board machinery.

An electronically operated trolling valve can be fitted, which will allow variable speed of the propeller to zero whilst allowing a maximum engine speed of up to 1200 rpm.

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.

Working Oil Pressure
Minimum - 30.34 bar (440 PSI), Maximum - 33.44 bar (485 PSI). Two tapped holes 1/8" BSP on the top, and M18 x 1.5 on the side of the valve block are provided so that the 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 two 3/8" BSP connections are provided on the valve block to allow it to be fitted. The size of the cooler required depends on a number of factors including the transmitted horsepower, operating speed, duty cycle, inlet water temperature and ambient temperature.

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

PRM750 Gearbox spline: 17 teeth 16/32 DP. PRM 750 Gearbox coupling: 6", 6 holes, 4¾" PCD, 3" female register. Oil Capacity: 3 litres (5.28 pints).

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FAQ & Technical Information

  • Do you have the Manual for the PRM750A/D? +

    Yes, please see attached document for the Product Manual.

    PRM750A/D Workshop ManualDownload
  • Technical Article - Gearboxes & Spares +

    The technical article for gearboxes & spares is here:

    Technical Article - Gearboxes & SparesDownload
  • What are the measurements of the PRM750A/D? +

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

    PRM750A/D Installation DrawingDownload
  • Which PRM 750A Model is right for my application? +

    Nominal Power Ratings for PRM 750A Marine Gearbox

    Model Ratios Pleasure Light Commercial Heavy Commercial
    BHP kW BHP kW BHP kW
    750A1 1.09:1 7.17 9.62 5.68 7.62 5.39 7.23
    750A1.5 1.459:1 7.17 9.62 5.68 7.62 5.39 7.23
    750A2 1.935:1 7.07 9.62 5.68 7.62 5.39 7.23
    750A2.5 2.565:1 7.07 9.62 5.68 7.62 5.39 7.23
    750A3 2.904:1 5.96 8.00 5.60 7.51 5.24 7.02

    Maximum operating speeds: 4,500 rev/min intermittent, 4,000 rev/min continuous

    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.

    Service Classification Definitions - Heavy Commercial
    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.

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