Correct RPM for M25-XPB

[David]

On our maiden voyage this past weekend, we were making approx. 6.2 knts with the throttle open full and the RPM at approx. 1400 RPM.I beleive I should be crusing at 2000-2500 RPM.We have a C30 SR with a 12x12 3-blade prop.Does that sound like the speed we should be getting at that RPM? In other words should I check the tachometer calibration?If I increase the idle speed, will that increase max RPM as well? Should I do that?Thanks,Dave

 

[Gary Kunkel]

RPM

David:If I remember correctly (that means w/out looking it up) our prop is also a three-bladed 12X12. We have a Catalina 30 w/ Universal M25-XP engine and typically achieve something like 5 KTS or slightly over with the throttle around 2,000 to 2,200 RPMs. My guess would be the tach calibration. I think there is an easy method to check using a flourescent light if you search the archives for tach or tachometer. In our case, we also calibrated our knot log using muliple runs up and down a measured nautical mile. If you haven't done that, it's worth doing and will confirm your log's accuracy (or need to calibrate it). It was easy to calibrate and really did need it. Doing both those things will give you confidence in both the knot log and tachometer readings.Regards,Gary Kunkel

 

[Tom Soko]

Tach Adjustment

David,Adjusting the tach is very easy. Get a flourescent light and a piece of tape, and you're ready to go. Put a piece of tape on the front engine pulley. When you start the engine and hold the light near it, the tape will appear to 'freeze' in 4 places on the pulley at exactly 1800 RPM (for instance at 12, 3, 6, and 9 o'clock positions). You can adjust the tach to that known RPM. I think you'll find you're actually cruising at 24-2500, with a max RPM of 30-3100 in neutral.