Full hydraulic operation, lightweight, compact & rugged.

PLEASE NOTE: The PRM260D gearbox has been replaced by the PRM280D gearbox. The PRM260C in-line gearbox is still available.

The PRM260C marine gearbox is purpose built for use in both pleasure craft and commercial boats; its 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.

The PRM260C is supplied in an in-line configuration.

A choice of 1.96:1 and 2.94:1 reduction ratios is available; each will provide left-hand or right-hand propeller rotation in "ahead", making the PRM260C particularly well suited to twin engine installations.

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 PRM260C input shaft, spline, adaptor flange and mounting pads are as used on Borg Warner (Velvet Drive) 71C and Paragon P23 & P25 gearboxes.

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.

Nominal Power Ratings, PRM 260C Marine Gearbox

Model  Ratios Pleasure Light Commercial


260C2  1.96:1 2.72 3.65 2.51 3.36 2.31 3.08
260C3  2.94:1 2.72 3.65 2.51 3.36 2.31 3.08
Maximum operating speeds:
4500 rev/min intermittent, 4000 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 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.

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 - 18.27 bar (265 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.

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 valve block is provided with two 3/8" BSP connectors to allow it to be fitted.

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

Propeller Free Wheeling
The PRM260C 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 Weight & Oil Capacity
Gearbox Approximate dry weight Oil capacity
PRM260C 63kg

excluding adaptor, drive coupling and oil cooler. 1.70 litres
(3.0 pints)
plus the amount require to fill the cooling circuit

Flexible Input Couplings for PRM260C

Part Number Outside Diameter   Mounting Hole Pattern Remarks
in mm No. Diameter Pitch Circle Dia.
  in mm in mm
MT1224 9.50 241.3 8 0.344 8.74 8.750 222.3 SAE 7 ½ in
MT1222 12.375 314.3 6 Multi Punched - Dimensions on application  
8 0.375 9.53 11.625 295.3 SAE 10 in
MT1162 13.875 352.4 8 0.433 10.99 13.125 333.4 SAE 11 ½ in
MT1213 14.25 362.0 6 0.320 8.13 11.625 295.3 Perkins 4-236
6 Multi Punched - Dimensions on application  
MT4911 13.875 352.4 8 0.433 10.99 13.125 333.4 SAE 11 ½ in High Deflection
MT4912 14.25 362.0 6 0.320 8.13 11.625 295.3 Perkins 4-236
6 Multi Punched - Dimensions on application High Deflection
MT4913 12.375 314.3 6 Multi Punched - Dimensions on application  
8 0.375 9.53 11.625 295.3 SAE 10 in High Deflection
MT4914 9.50 241.3 8 0.344 8.74 8.750 222.3 SAE 7 ½ in High Deflection
MT1468 14.25 362.0 6 Multi Punched - Dimensions on application (For 260C)

Adaptor Flanges for PRM260C

Part Number Description


kg. lb.
MT8074S/A SAE 2 Adaptor Flange 13.0 28.7
MT854S/A SAE 3 Adaptor Flange 11.0 24.3
MT1210S/A SAE 4 Adaptor Flange 10.0 22.0
MT1209S/A SAE 5 Adaptor Flange 7.0 15.4
MT1426S/A B/W ( Velvet Drive) Adaptor Flange 4.3 9.5

Other Accessories for PRM260C

Part Number Description


kg. lb.
MT913S/A Oil cooler 1.2 2.6
MT915 Oil pipes (pair) 0.5 1.1
MT784 Oil cooler mounting bracket 0.2 0.4
MT771 Tailshaft half coupling (pilot bored) 2.5 5.5
MT1104 Tailshaft flexible coupling 1.5 3.3
MT0214 Neutral safety start switch 0.04 0.1
MT5036 Oil pressure gauge (direct mounting) 0.1 0.2