On Fri, 20 Jun 2008 08:49:34 -0400, Rosalie B.
wrote:

We are back home because we have an intermittent problem and decided
to come back to deal with it rather than wait and be stuck somewhere.

What is the problem?

Bob has his idea, but I'd like any alternate opinions.

We were motor sailing along, as the breeze basically died (although it
was from the predicted direction), and I was in the aft cabin when
suddenly it sounded to me as if the engine was running away. I went
up into the cockpit and said to Bob "What is that noise", and he said
there was someone coming up behind us. (We can't see directly behind
us due to stuff on the aft deck.) But I looked and there was no one
there. Bob slacked off the throttle and then cautiously came back to
speed and the noise was gone.

This happened about twice more. The gauges never moved during this
time - RPMs were the same, oil pressure normal, engine temperature
normal (and Bob checked that with the infrared gauge), engine charging
as normal. Bob checked the bilges and looked in the engine
compartment and saw nothing amiss. The engine continued to run as
normal between times.

We got to Crisfield just after 7 and tied up and went to dinner at the
Cove (wonderful dinner) and then we had a thunderstorm.

So yesterday, we were planning to go down to Cape Charles and decided
that was too far under the circumstances and were going to divert to
Deltaville. This happened once more, so we came home instead.

So what do you think this is?

Too bad you didn't record the sound. Since you said the gauges all
read no change in engine operation (boat speed didn't change?)
what could account for the sound?
I don't know boat drive trains, but have run across something similar
in a car. Traveling on the highway, there were occasional times when
something close to an "engine racing" sound would occur. Speed and
normal engine operation said otherwise, and the sound emanated from
the right side of the engine compartment. It was very obvious and
accompanied by some vibration. I suspected the CV joint.
I was wrong. Soon after the noise started occurring, the alternator
failed, and when it was replaced the noise was gone permanently.
Hopefully, it's something so minor for you.
You really have to pinpoint the source of the sound.
Again assuming engine operation remains steady, the exhaust system is
another place to look at.

--Vic