RE powering

[windstalkers]

Hi, I recently repower my boat from a 2qm20 Yanmar to a rebuild 3gm30f Yanmar, do I need to change the propeller to.

I don't have speed comper to my other motor any idea why?

thanks

[Tomodore]

Conventional wisdom dictates loading the engine at max rpm. If you don't have proper load on engine it will cause issues. The exact pitch or diameter of prop is part science part art. It took 2 tries when we went from a tired 28 hp Volvo to a 38 hp Beta. Been 7 years and 3000 hours and still runs great. I understand project creep and just wanting to be done but treating your new engine well will pay off in my opinion. Been there.

[FlightPlan]

You can go to boatdiesel.com, and they have a calculator that takes in the boat particulars engine model and HP, etc. It's $50 to join for a year, but worth it in regards to the blog inquiries and answers. I used it in my re-power project and it nailed it in 2 degrees of pitch.

[Compass790]

Originally Posted by windstalkers

Hi, I recently repower my boat from a 2qm20 Yanmar to a rebuild 3gm30f Yanmar, do I need to change the propeller to.

I don't have speed comper to my other motor any idea why?

thanks

try this website for a free prop calculator
https://vicprop.com/free-propeller-sizing-calculators?


It seemed to nail it for our boat. IIRC the 2qm20 is a lower revving motor than the 3gm30 so you definitely need to change props. Think the 2qm20 is 2600rpm & the 3gm30 is 3600rpm. Not sure of the rotation direction but check the CF library for manual & that will tell you.
Hope that helps