Reduction drive

A planetary reduction drive is a small scale version using ball bearings in an epicyclic arrangement instead of toothed gears.

Gear-drives can be made to have no backlash by using split gears and spring tension but the shaft bearings have to be very precise.

By contrast, a Rotax 912 has an engine capacity of only 56% of the Jabiru 2200, but its reduction gear (of 1 : 2.273 or 1 : 2.43) allows the full output of 80 bhp to be exploited.

The Midwest twin-rotor wankel engine has an eccentric shaft that spins up to 7,800 rpm, so a 2.96:1 reduction gear is used.

[2] This design helps lower the amount of required maintenance and increase the lifetime of the gears.

After completion of construction and delivery to shipyard it is required that these gears achieve proper alignment when first operated under load.

The shipbuilder must provide a foundation that is sufficiently strong and rigid so that the gear mounting surface does not deflect greatly under operating conditions, a shaft alignment drawing that details the positions of line bearing and the method for aligning the forward piece of line shafting to the reduction gear coupling and the location of stern tube being such that the normal wear down of the stern tube will not induce significant movement of the reduction gear coupling from its proper alignment.

But on smaller reduction drives attached to auxiliary machinery or if the design of the ship demands it, one can find thrust bearings as a part of the assembly.

In order to ensure a reduction drive's smooth working and long lifetime, it is vital to have lubricating oil.

A reduction drive that is run with oil free of impurities like water, dirt, grit and flakes of metal, requires little care in comparison to other type of engine room machinery.