PRM 750C hydraulic marine gearbox, gear ratio 2.57:1

Description

PRM750C In-Line Hydraulic Marine Gear, gear ratio 2.57:1

The PRM 750 In-Line marine gearbox’s dual-shaft design and separate, identical friction plates for forward and reverse operation enable full rated power in both directions. The output shaft (flanged shaft) is aligned with the input shaft. The splines on the input shaft are the same as those on, for example, the Velvet Drive marine gearboxes in the 71C and 72C series.

The inline version of the PRM750 gearbox is designed to directly replace the Velvet Drive 72C gearbox. With the PRM MT5030 adapter flange, the total installation length of the marine clutch remains the same as that of the original 72C gearbox. The SAE mounting is the same B/W as on the Velvet Drive 72C gearbox.
This solution enables direct interchangeability of gearboxes without any modifications to the existing installation.

Technical Specifications:

• Gear Ratio: 2.57:1
• Power Rating (Recreational Use): 9.48 hp / 100 rpm
• Power rating (light professional use): 7.85 hp/100 rpm
• Output shaft rotation direction during forward drive: RH or LH
• Input shaft splines: 26 TEETH, 20/40 DP
• SAE mounting: B/W (Borg Warner) housing Ø 209.5 mm / PCD Ø 234.95 mm
• Maximum permissible instantaneous rpm: 4,500 rpm
• Maximum permissible continuous rpm: 4,000 rpm
• Weight: 93 kg
• Gearbox oil capacity: 3.0 liters + capacity of the heat exchanger and hoses
• Heat exchanger connections: 1/2" BSP x 16 DEEP

The gearbox’s hydraulic system quickly transfers the control lever’s movement to the friction plates, and the gearbox responds rapidly to changes in direction, which is important for good boat handling.

Operation and Propeller Rotation

The gear can be used with both right- and left-hand propellers, making it particularly suitable for twin-engine installations. The housing is made of high-quality cast iron. The oil pump and hydraulic control valves are mounted externally for easy access.

Reliable
The gear is extremely durable and reliable; it is also equipped with a mechanical locking device in case of a hydraulic failure. In such a case, the gear can be locked in the drive position, allowing the boat to be safely returned to port.

Operating Pressure
Minimum – 30.34 bar (440 lb./in²), maximum – 33.44 bar (485 lb./in²). The top of the valve block has a 1/8" BSP hole and the side has an M18x1.5 threaded hole for installing a pressure gauge, if one is needed.
Oil cooling
The normal operating temperature of the oil should be 50–80 °C, and the temperature must not be allowed to rise above 90 °C. An oil cooler is required to maintain the correct operating temperature. The valve block has 1/2" BSP connections for installing an oil cooler.
Propeller Thrust
Propeller thrust, whether forward or reverse, is transmitted to the output shaft bearings. The force exerted on the bearings is sufficient for all power ratings approved by the manufacturer.
Propeller Free Spinning
The output shaft of the PRM750C marine gearbox can be rotated continuously when the gearbox is in neutral. For this reason, a propeller shaft brake is not required, for example, when sailing.

PTO Installation Option
A distinctive feature of the PRM750 marine transmission is the direct-drive power take-off (PTO), which is available as an option. It allows the use of a Type B hydraulic pump compliant with the SAE J744C standard, providing an economical and space-efficient way to power the vessel’s hydraulic machinery and equipment.