Did a dirty prop cause this?

[Administrator]

Full disclosure: This is not about an A4:

Today, when we took our boat down the creek to be hauled out for the winter, the RPM's were hunting a bit, up and down, and the speed thru the water seemed quite depressed.

Simply a dirty prop or something more sinister?

The boat won't get pulled until Wednesday, so I am left to stew in my own juices for a couple of days.

Bill

[ndutton]

It will be interesting to learn the condition of the prop but I usually associate RPM hunting in a diesel with fuel quality/air.

[Administrator]

Confession:

Not a diesel. Not gasoline.

Bill

[GregH]

electric?

hamster in a wheel?

[roadnsky]

slaves rowing below deck?

[Al Schober]

No hamsters - they get seasick!
Perhaps a nuclear reactor & a small steam turbine?
Had experience with a larger boat/propeller where divers were cleaning the prop underwater, but knocked off for the day with only half the blades cleaned. Boat went to sea (urgent mission) but aborted and returned to port to complete the cleaning. Vibration was so bad in the engine room that resiliently mounted equipment was hitting the hard stops and jeopardizing the connected piping!

[joe_db]

Originally Posted by Administrator

Confession:

Not a diesel. Not gasoline.

Bill

Electric?
Coal?
Uranium?
Hydrogen?
Propane?

We need more info here to even have a guess.

[Administrator]

Electric. A Duffy 18' Snug Harbor.

Bill

[joe_db]

IMHO:
1. The batteries are low and the motor controller is trying its best to move the boat.
2. The bottom/prop are dirty, the motor controller is trying its best to move the boat, and the motor is drawing too much power because of the foul bottom and the controller is cutting back due to some algorithm designed to protect the system.
3. The motor controller is trying its best to move the boat, but it has a defect of some kind.

[Administrator]

Batteries were fine.

One thing I should have mentioned:

The problem was evident at higher speeds. Not so much at lower.

With this vessel, "higher" means 3.5 knots. "Lower" means 2 knots.

Bill

[ndutton]

I think this may portend a deteriorating electrical condition. Every termination, connection and component is in play.

As for the effect being evident at higher speeds, that is also when the system current is higher and therefore could be aggravating whatever might be going on.

[Administrator]

Originally Posted by ndutton

I think this may portend a deteriorating electrical condition. Every termination, connection, and component is in play.

As for the effect being evident at higher speeds, that is also when the system current is higher and therefore could be aggravating whatever might be going on.

That's certainly plausible, Neil, but I sure hope not.

The prop was pretty/very bad. I guess we won't know more until she goes back home with a clean prop in the spring.

In the meantime, anybody know what anti-fouling paint you put on a plastic prop?

Bill

[ndutton]

Originally Posted by Administrator

That's certainly plausible, Neil, but I sure hope not

As do I Bill. Considering the prop, I could not help but think for it to cause varying RPM it would have to apply varying load. How does that happen? Shedding growth underway? Perhaps but does that translate to both higher and lower RPM?

I'm sorry to suggest it but a deteriorating electrical path fit the symptom better. It's still a guess at this point.