rpm

[Ken Juul]

This one has got be stumped.  Came to the boat yesterday, plug in shore power overnight.  Batteries full when we left the dock.  On the way to a 3 hour sail, max rpm is 2700 going out the channel, normal is 2900, so suspect some fouling.  Anchor out for lunch, 2 fridges running, navigation still on, ice maker running off the inverter for 2-3 hours.  Coming home motoring into the wind max we could get was 2500 rpm.  Alt belt is in good shape and proper tension.  Wires off the alternator are clean and tight. This is the second time in the last couple weeks this has happened.  Pretty sure it is an indicator problem, not mechanical, what am I missing, not sure where to look?  Alternator is the OEM 55 amp motorola, maybe it is giving me hints that it is dying

[KWKloeber]

Fouling would lower the speed, not the rpm, right?

Does seem like a tach or AC signal issue. How old is the tach?

-kk

[Noah]

Sounds like time for laser tach test and a helper while underway.

[Jim Hardesty]

Ken,
You didn't say that your speed was down.  When my max RPM and speed has dropped like that it's always been the fuel filters.
Jim

[Ken Juul]

speed seems about normal.  It has been a bad year for barnacles in my part of the Chesapeake, so prop fouling is an issue, but the prop was just cleaned a couple weeks ago so I don't that is the issue.  Laser tach is a good idea.  The alt and tach are original, neither has given me any reason to suspect they are dieing.  If it was the fuel filter, why ok in the morning and not in the afternoon?  More investigation to do.