Thansmission advise?

[drs3317]

What transmissions are available to econimally replace straight Velvet Drives 2 to 1 ratio? I need reversable transmissions because the new engines are not counter rotating and I would like to stay with a straight drive to avoid any further modifications. They will be connected to 320 hp gas mercruisers. Thanks for recommendations!
Dan

[jav]

I presume you have the 72c and not the 71c? If so, ZF 63 (or 630 is the old ZF/Hurth designation) is a decent choice. It can supply full engine power in either rotation. It has the same Borg Warner shaft, spline and face mounting but keep in mind that the tranny length and height offset on the output flange are different.

[drs3317]

Not sure if the old velvet drives were 71 or 72 but they were trashed when I bought the boat. The ZF 63 spec sheet only shows them available in a 1 to 1 and I need near 2 to 1. I was told the velvet drive 72 series in 1.88 ration can run in either direction but the other transmission would have to be 2.10. Can this work? I don't like the idea of two different ratios.

[jav]

I'm not sure what spread sheet your looking at but the ZF 63 is available in 5 ratios including 2.037:1. As far as running 2 different ratios, I'm sure it could function with the appropriate adjustments in the props but it would be quite unorthodox and I wouldn't do it. The dynamics of trying to produce equal thrust from 2 different setups at all different speeds and sea states is questionable and not recommended. Trying to explain that setup if you ever sell the boat could be colorful too.