Hello all -- If there is a prior thread, please feel free to cross-post. We have searched the forum, spoken to yanmar, and other vendors and keep hitting a wall.
Our 2009 Hunter 45DS has a Yanmar 4JH4TE (the 75 hp turbocharged diesel) and a KM4A2 transmission with a 1:2.63 gear ratio. The prior owner replaced the factory prop with an 18.5" diameter 4-blade max prop that has a ring on the forward (transmission side) edge that allows us to "dial" in the pitch. We believe that our divers may have inadvertently changed the pitch as we have inexplicably lost ~30% of our power: we normally travel at 6 kts at 2,600 RPMs (our max as the engine was previously abused so we are going easy on her) and now we travel at 4 kts at 2,600 RPMs. For reference our normal cruising range is 2,200 RPMs to 2,600 RPMs.
I am given to understand that there is a relationship between RPMs and inches of pitch but I cannot tease out why that matters or how it works. Further, I cannot track down what the optimal pitch is for our boat, engine, and transmission. Can anyone direct me to either a resource and/or tell me about their setup?
Thank you in advance!
Sean
Our 2009 Hunter 45DS has a Yanmar 4JH4TE (the 75 hp turbocharged diesel) and a KM4A2 transmission with a 1:2.63 gear ratio. The prior owner replaced the factory prop with an 18.5" diameter 4-blade max prop that has a ring on the forward (transmission side) edge that allows us to "dial" in the pitch. We believe that our divers may have inadvertently changed the pitch as we have inexplicably lost ~30% of our power: we normally travel at 6 kts at 2,600 RPMs (our max as the engine was previously abused so we are going easy on her) and now we travel at 4 kts at 2,600 RPMs. For reference our normal cruising range is 2,200 RPMs to 2,600 RPMs.
I am given to understand that there is a relationship between RPMs and inches of pitch but I cannot tease out why that matters or how it works. Further, I cannot track down what the optimal pitch is for our boat, engine, and transmission. Can anyone direct me to either a resource and/or tell me about their setup?
Thank you in advance!
Sean
