PRM marine gear ratio 1.46:1

Description

PRM 500D Hydraulic Marine Gearbox, Gear Ratio 1.46:1

The PRM 500D marine gearbox is suitable for both recreational and commercial vessels. The gearbox is a Drop-Center model, in which the output shaft is 126.7 mm lower than the input shaft. The gearbox’s dual-shaft design includes separate multi-plate clutches for forward and reverse operation. This design enables continuous transmission of full rated power in both directions.

The PRM500 is also available with the following gear ratios: 1.935:1, 2.565:1, and 2.904:1. All gear ratios allow the propeller to rotate either clockwise or counterclockwise when moving forward, making the PRM500 particularly well-suited for twin-engine installations.
Robust Construction
The gearbox housing is made of high-quality cast iron, and its internal ribbing increases rigidity and strength. The housing consists of two separate halves to facilitate maintenance. The oil pump and hydraulic control valves are mounted outside the housing, making them easily accessible.
Hydraulic Operation and Lubrication
The hydraulic drive system operates on standard lubricating oil with the same viscosity as the oil used in the engine, so automatic transmission fluid (ATF) is not required. The system ensures a quick response to control lever movements and, consequently, excellent boat handling. The control lever has a clear mechanical neutral lock position and is compatible with manufacturer-specific remote control systems.
Safe to Use
The hydraulic system is robust and reliable in design, but to further enhance safety, it also includes a mechanical locking device. This ensures that, in the unlikely event of a hydraulic system failure, the vessel can be safely steered back to port. The lock is accessible through a removable cover located on top of the main gearbox housing.
Option for PTO Installation
A special feature of the PRM500 is the direct-drive power take-off (PTO), which is available as an option. It allows for the use of a Type B hydraulic pump compliant with the SAE J744C standard, providing an economical and space-efficient way to operate the vessel’s hydraulic machinery and equipment.

Technical Specifications:

• Gear ratio: 1.46:1
• Power rating (light commercial use): 6.19 hp / 100 rpm
• Drop-Center model, drop 126.7 mm
• Output shaft rotation direction during forward travel: RH or LH
• Input shaft splines: 17 TEETH 16/32 DP
• SAE mounting: SAE2, SAE3, SAE4, and B/W adapter plates available
• Maximum instantaneous speed: 4,500 rpm
• Maximum continuous RPM: 4000 RPM
• Weight: 68 kg
• Gearbox oil capacity: 2.5 liters + heat exchanger capacity
• Heat exchanger connections: 3/8" BSP

Operating pressure
Minimum – 18.27 bar (265 lb/in²), maximum – 22.06 bar (320 lb/in²). The top of the valve block has two 1/8" BSP threaded holes, and the side has an M18 threaded hole for installing a pressure gauge, if needed.
Oil Cooling
The normal operating temperature of the oil should be 50–80 °C, and the temperature must not be allowed to exceed 90 °C. An oil cooler is required to maintain the correct operating temperature. The valve block has two 3/8" BSP connections for installing an oil cooler.
Propeller Thrust
Both forward and reverse propeller thrust are transmitted to the output shaft bearings. The force exerted on the bearings is sufficient for all power ratings approved by the manufacturer.
Propeller Free Spool
The output shaft of the PRM500D marine gear unit can be rotated continuously while the gear unit is in neutral. Therefore, a propeller shaft brake is not required.

Definitions of operating categories – Pleasure craft use Limited to pleasure boats with a planing hull; operation at full throttle (maximum RPM) must not exceed 5% of the total operating time. The remaining operating time must not exceed 90% of the engine’s maximum RPM. The maximum permitted operating time is 500 hours per year. Selection of a PRM marine transmission in accordance with this classification for commercial use, sport fishing boats (for rental), or long-distance pleasure cruisers is not permitted.

Definitions of Usage Classifications – Light Commercial

Vessels with planing or semi-planing hulls used for recreational— or for commercial use may meet the requirements for light commercial use if annual operating hours are less than 1,500 and full-throttle operation is limited, such that the majority of operating time is spent at partial throttle.