Borg Warner Gearbox Ratio on Columbia 41

[SanyaYachting]

Hi All,

I recently bought a Columbia 41 of 1974 vintage.
She is a project boat and as such one area she need attention is the propeller shaft and propeller. Doesn't have either.
My problem is the identification plate on the gearbox is missing. Therefore I have no idea what gear ratio the gearbox is. Makes it difficult to get a new shaft and prop.

The engine is a Perkins 4.236 and the gearbox is a Borg Warner 71. Any help you can provide would be much appreciated.

[evm1024]

Originally Posted by SanyaYachting

Hi All,

I recently bought a Columbia 41 of 1974 vintage.
She is a project boat and as such one area she need attention is the propeller shaft and propeller. Doesn't have either.
My problem is the identification plate on the gearbox is missing. Therefore I have no idea what gear ratio the gearbox is. Makes it difficult to get a new shaft and prop.

The engine is a Perkins 4.236 and the gearbox is a Borg Warner 71. Any help you can provide would be much appreciated.

You can check the gearbox ratio with an optical tach. Set the engine to 1000 rpm via the optical tach, measure the prop shaft rpm. Do the math.

The velvet drive on my 4.236 "lost" its data plate. this is how I figured out the transmission ratio.

Regards

No magic in setting to 1000 rpm, just a "nice" number