Working out my gear ratio - Borg Warner velvet drive 71C

[Jules W]

Hi All
I have a velvet drive 71C in my Moody Grenadier. I have had lots of issues with it (have had it rebuilt three times in 16 years) and would love to get another so I have at least a spare on board.
Trouble is that the plate is horribly tarnished / damaged and almost impossible to read and I just cant make out the gear ratio.
I can see the following info:
2501005
81-01-002
37786650/4
A.O.C.2.6/77
10.17.006
71C
Ratio 1:

I am hoping that someone who knows more than me about this (it cant be hard) can see from this information a way to tell what the ratio is.
The only other info I can offer is that the prop is 3 bladed and 20inch diameter and she cruises along at 6knots at 1500RPM.
Any help would be greatly appreciated. I have tried the Moody Owners forum (of which I am a member) but the Grenadier was a rarity and so was the use of this set up in the Moody boats

Many thanks
Julian

 

[rogerthebodger]

https://velvetdrive.com/files/7172.pdf

Does this spec sheet help

 

[burgundyben]

10.17.006 tells you, google to confirm for yourself, I think its 1.52:1 reduction

The 006 last 3 digits are the reduction.

 

[Jules W]

Thankyou both for your replies. 1:1.5 sounds right based on my own calculations of engine horsepower and prop size.
Many thanks

 

[gordmac]

Get a non contact tacho, measure engine and shaft speeds, divide to get ratio.