Boatnerd Discussion Forum

My understanding, and I'm not a marine engineer, is that reduction gears "wear in" over time and a replacement gear would not match the worn gears. Replacing all would be a difficult and expensive task. The production of reduction gears during World War II was a bottleneck in the building of turbine-powered ships and one reason that the Liberty ships were outfitted with reciprocating steam engines.

From the ships I've been on, and I'm not an engineer so forgive the layperson viewpoint, the entirety of the fleet was using Falk Reduction gears on paired diesels, two for the smaller boats and four for the thousand footers. Given their weight, size and location in the hull I'd imagine the only realistic way to replace the gears would be to take it apart in-site and not remove the whole thing unless it was really badly damaged beyond hope of repair. Either way it would be one hell of an expense.

Reduction gears, as the name implies, reduce rotational shaft speed of an engine so that it can be used as a prime mover. The [I]USS Wisconsin[/I] has four GE steam turbines producing 212000-shp and like all steam turbines operate at maximum efficiency at very high rates of shaft speed. The reduction gears of the vessel reduced the each turbine's shaft speed from 2000 rpm to around 200-225 rpm, or a 10:1 ratio. Obviously, 2000 rpm could not be applied directly to the propeller shaft. This makes for optimal turbine and propeller efficiencies. High-speed and most medium-speed Diesels use reduction gears for the same reason. By contrast, reciprocating steam engines and low-speed Diesels provide shaft speeds within the capability of their connected propellers, not necessitating shaft speed reduction.

I have no idea why it was said they could not be replaced (although it would be one hell of a job). The gears operate at very close tolerances and the possibility of a chipped tooth or imbalanced gear is always a possibility, although reduction sets are generally very robust if machined and installed correctly and proper lubrication maintained.

Several questions here,

Do diesel and steam vessels use the same type/style of reduction gears. Was on the USS Wisconsin and a acess cover was off the housing, and you could see the gears. Granted the gears I'm sure are definitely stronger gears as a lot more horse power, and different shaft speed.

The engineer said the reduction gears could not be replaced. Can they be replaced on a great lakes vessel? I would imagine if they did they would come out the side, or on a steamer straight up. Are there predetermined ways to bring something like that out when the ship is built?

Thank you