120 series saildrive ratios

[geoff]

In the workshop manual for the saildrive 120s series all models  have the same gear ratios [forward ], 2.2 /1 .However having just replaced my rather tired 120 SE with a much less used 120 SD I find that the data plates suggest otherwise  2.2 for the SE and 2.47 for the SD.  Having a variable pitch prop I think I am ok but I am confused. Next obvious question do I increase or decrease pitch ? Geoff

[Symphony]

The difference in shaft speed is approx 200rpm (lower). I had this when I replaced a 120 with a 130 on a 2030. We reduced the pitch by 1" on a 16" prop. When you say you have a variable pitch prop do you mean a Bruntons Autoprop or a prop where you can adjust the pitch like  Maxprop or a Featherstream? If the former then talk to Bruntons. If the latter, I would try it as it is and see if you get near maximum revs. If more than say 300 down then reduce the pitch by 1".

[geoff]

Thanks Symphony, It is a kiwiprop  18in 3 blade. My intuitive reaction is that if the prop revs are lower the pitch should be higher, but thats why I asked the question ! Geoff