Recommended transmission reduction ratio.

[Robert1224]

Ahoy,

I am re-powering my Hunter 30 with a Nanni 3.21 (21hp) diesel. This comes with a Technodrive TMC 40 transmission. I have an option with reduction rations. 2:1 is what I am used to, so I am likely to stay with this.
I do have the option to change to a 1.45:1 or a 2.6:1. Is there any reason anyone can think of to choose one of these over the 2:1?

Cheers,
Bob

 

[kloudie1]

Lots of complex interplay, but no huge advantages.. slower shaft speed (in the 2.61:1) at a given boat speed makes for a more efficient propeller (slower rotating speed and more pitch than the 2:1) When sailing in neutral with engine off, probably less boat drag for the 2.61:1 case.... probably can be measured under lab conditions, but probably not noticeable in a sailboat.

 

[Benny17441]

If you are keeping the same propeller stay with the closest gearing to what you have. The Nanni 3.21 is rated for 21 HP at 3600 RPM which is the same RPM range for the Yanmar 2GM. The gain in HP will enable faster acceleration.

 

[Steve Dion]

I am curious on why you decided to go with the Nanni. My only concern would be parts availability & technical assistance if/when they are needed.

 

[Robert1224]

I am curious on why you decided to go with the Nanni. My only concern would be parts availability & technical assistance if/when they are needed.

Steve,
They have really been outstanding. In fact, their technical staff is the best I have dealt with. Outstanding, and parts are very easy to come by and much less expensive then other brands.
Regards,
Bob

 

[kloudie1]

The Nanni folks use a Kubota engine, so parts shouldn't be a concern.