I just installed a yanmar 2gm20f. In a 1980 Catalina 30 tall mast. I am not getting the speed that I think I should be getting. I have had the prop. re pitch ed. It is a 12 in 8 pitch. But it has just had another couple degrees added to it . Would a larger dia. Help and if so how big. It is a three blade. Is there any good web sights to help find the correct dia and pitch?
repower
- Thread starter swank
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Is the prop from the old engine, and of so what engine was it? Are you able to reach the engines red line RPM or does it come to a lower speed at full throttle? Related to that, are you sure the throttle cable is adjusted properly and opening the throttle all the way? If you are not able to approach governor speed at full throttle, the prop is too big. If the engine runs right up to governor with unsatisfactory boat speed, the prop is likely too small. You may have added too much pitch to the prop. Larger diameter probably won't help, it's the pitch that makes the difference. There can be a lot of trial and error in getting the mix just right.
You will need to check the clearance to see if a larger diameter is feasible. If I'm not mistaken, there should be no more than 1" clearance between the blade and the hull. Maybe it's 2" ... that dimension should be verified. I think your diameter is pretty small as well. I have a 2YM15 and the diameter of my 2-blade prop is 15" IIRC.
The pitch is a balancing act because adding pitch may be reducing rpms too much. The boat runs alright when it is up to speed, but it has trouble getting there. Aside from that, running at low rpms is generally frowned upon from an engine maintenance standpoint.
If your diameter is limited, you may have to increase the number of blades when you have the pitch determined for optimal running.
Get some professional advise as Ron correctly suggests.
The pitch is a balancing act because adding pitch may be reducing rpms too much. The boat runs alright when it is up to speed, but it has trouble getting there. Aside from that, running at low rpms is generally frowned upon from an engine maintenance standpoint.
If your diameter is limited, you may have to increase the number of blades when you have the pitch determined for optimal running.
Get some professional advise as Ron correctly suggests.