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37CC prop size

Apr 16, 2015
9
irwin 37 cc Oriental
Hi, I have a 1980 MKV with a Perkins 4108 engine and gearbox with a 1.56 reduction. The manufacturer tells me I should cruise at 3200 rpm, which is about where I hit a comfortable cruising speed. My prop is 16 X 16 3 blade but when I run the numbers through the Vicprop prop calculator it tells me I need a 13 x 8! The engine shows no signs of being over propped but I am wondering if, however illogically to me, I would do better with the Vicprop recommendations.
So, my real question is... what size props are most common on this boat, and are you happy?
Thank you! I have owned several boats and always cruised at much lower rpms. This just has me second guessing. John
 
Aug 5, 2016
25
Catalina Capri 22 Cambridge
Are you sure the gear is a 1.56:1 ratio? Both those prop sizes make no sense at all. It wouldn't spin a 16 X 16 prop with a 2.5:1 gear much less a 1.56:1 gear.
 
Apr 16, 2015
9
irwin 37 cc Oriental
Thanks for the replies. The gearbox says A: 1.56 B:1.95. From what I read, A: is the forward gear. This is new to me, clearly.