Reverse-Reduction Gearboxes
In-line gearboxes giving ahead, astern and neutral with a fixed reduction ratio, for shaft-driven vessels from small workboats upwards.
Features
- Hydraulically actuated clutches for ahead and astern, with the control head and cable or electric actuation specified alongside.
- Ratio selection is the main decision, and it is made from the propeller calculation rather than by matching the box that came out.
- Oil cooling through a dedicated cooler on higher-powered boxes, with its own plumbing to design into the engine room.
- Monitoring of oil pressure and temperature gives early warning of clutch wear, which otherwise appears as slip under load.
- Ahead and astern ratings can differ, and the astern figure matters on vessels that manoeuvre or tow astern regularly.
Specifications
| Figure | Typical range | Unit | Why it matters |
|---|---|---|---|
| Reduction ratio | 4.05 : 1 | the propeller match depends on it | |
| Rated input power at speed | 450 at 1 800 | kW at rpm | the rating is the pair, not the power alone |
| Astern rating | 70 - 100 | % of ahead | relevant on towing and manoeuvring duty |
| Oil cooler required | yes, freshwater | adds plumbing and a cooling load to the design | |
| Control actuation | electric with single lever head | has to match the wheelhouse arrangement |