Strange behaviour, going in circles

[rsn48]

So was out yesterday, early November in the Powell River area of British Columbia burning off fuel before the boat went on the hard today. My friend was at the helm while I was below in the galley getting a water, when the boat began to go in circles. We were on a fairly strong in coming tide with moderate winds in the same direction. When it happened, I thought something had snapped in the steering mechanism. I took over the helm and throttled back from full speed (11 knots) down to 2 knots. When I slowed the boat down I got back control and the boat performed without problems for the rest of the way back to the marina in Comox.

This is an I/O motor, single leg with a Chevy 350 cubic inch motor. The leg on this thing is incredibly large, larger than modern ones. The boat was built in 1969 as an express cruiser. The leg turns the boat.

Any theories as to what happened?

[ShellBack89]

Do you have trim tabs on the boat and if so could one had been in the full down position?

[rsn48]

Assuming you are correct, wouldn't the behavior occur again? I did look at the trim tabs today as the boat is on the hard now for a long refit. They appeared to be in synch.

[SV_Harbinger]

Could you possibly have fouled one of the tabs on something in the water, if the leg is fine and they are both in sync and the behavior inproved with a reduced speed that seems to make sense to me. It wouldn't have to be very big either for it to have an effect on steering if it was considerably away from the centerline of the boat, if you were around here I would suspect that a stray lobster pot bouy got you..or perhaps a line in the water.....

[Dave_S]

Do you have autopilot ? could that have been accidentally set to calibrate itself ?

To calibrate mine you find a clear space and set it start and it goes around in circles and in figure 8's until it's happy.

Don't ask me too many questions I've never done it but apparently that's what it does.

[rsn48]

This boat doesn't have autopilot, what I tell my guest when they take the helm - "you're my autopilot."

Its possible we snagged something, but we were in 300 feet of water so no mooring bouys around.

20 NM's earlier we heard a very soft kind of thud, hard to describe, a sound I've never heard before, I've hit a few dead heads so I know what that sounds like. There was a lot of whale activity around us with tail fin breaching, I kind of half wondered if a tail fin had some how brushed the boat.

If you take a look at this pic, you'll see the 1969 outdrive and it is massive: [Go to the second picture]

https://www.facebook.com/marketplace...22498835044761

[Sea Q]

could have been a tree root ball a lot of stuff in the water with all the rain lately
when you slowed down the thing came off I would check it out when on the hard

[rjash6666]

About 10 years ago no matter whether I steered north or south my boat went west with the tide.Eventually we foun that a long sheet of plastic had caught on my keel. it resulted in my rudder being totally ineffective..
Bloody plastic or fishing nets. Perhaps something similar.

[cruising_ollie]

Check the chart to see if you were passing over power cables or power cables on a bridge. Had a nasty experience on Patuxent River, MD close to one of the bridge pylons.

[rsn48]

Told my buddy, a retired BC Ferries captain, about my experience. He told me a similar experience happened to him with the Queen of Surrey many a year ago, he felt it was the combination of tidal currents and wind affecting the ferry and feels the same happened to my boat.

The next day after this experience, my boat was put on the hard for a long refit and the first thing I looked at was leg, nothing seemed out of ordinary. I will be having the steering mechanism examined, for more reasons than just this event, and possibly something will come to light.

[thruska]

Airpockets in your hydraulic steering ?
Leg doesn’t cooperate with helm sometimes when that happens ...

[rsn48]

While I have it on the hard, I'll have that checked out.

[rsn48]

I think I'm getting close to the answer - cavitation. I think the boat turning in a tight circle created a cavitation situation where the prop lost bite in the water.