A sailboat turns to port by herself under motor

[tomaz_423]

Hi,
I noticed that a sailboat started to turn to port when I released the wheel and autopilot was off.
The sea was flat and there was practically no wind.
She started to turn slowly, but developed a sharp turn - the rudder all the way, so she circled in small circles.
Is this normal or it indicates a bent rudder?
The boat was a Beneteau Oceanis 473.
Now I can not remember if other boats did the same or I just never let the wheel free under power.
I did not notice this under sail.

[smackdaddy]

I don't know anything about the design aspects of the question, but that could potentially be a good safety feature. That is, that if you happen to fall overboard while motoring it would circle.

Of course, you might lose a leg while trying to re-board the motoring boat - but hey, at least the boat is still around. Alternatively, you could just dog-paddle for four days and wait for it to run out of fuel.

Interesting question.

[Matvolver]

Originally Posted by smackdaddy

I don't know anything about the design aspects of the question, but that could potentially be a good safety feature. That is, that if you happen to fall overboard while motoring it would circle.

Of course, you might lose a leg while trying to re-board the motoring boat - but hey, at least the boat is still around. Alternatively, you could just dog-paddle for four days and wait for it to run out of fuel.

Interesting question.

That's assuming he doesn't run himself over with his own boat

[Jeff_H]

The answer relates to whether you are motoring or not, and whether the helm actually turned or the boat simply turned. In a general sense, most boats will turn slightly to port when they are motoring due to prop-walk. it can be more pronounced on some boats more than others. (Our 1939 Stadel Cutter was really bad in this regard).

On the other hand, this should not happen when in neutral and the rudder should not turn.

Jeff

[tdw]

Originally Posted by tomaz_423

Hi,
I noticed that a sailboat started to turn to port when I released the wheel and autopilot was off.
The sea was flat and there was practically no wind.
She started to turn slowly, but developed a sharp turn - the rudder all the way, so she circled in small circles.
Is this normal or it indicates a bent rudder?
The boat was a Beneteau Oceanis 473.
Now I can not remember if other boats did the same or I just never let the wheel free under power.
I did not notice this under sail.

what Jeff said.....

[Faster]

If under power the propwash will often impact on the 'balancing area' of the rudder and tend to push it to one side or the other depending on rotation. The effect is most pronounced on balanced spade rudders, and pretty much non existent on unbalanced rudder designs, which have easy helms under power and sometimes brutes under sail!

You won't notice it under sail, or if it's a situation where the prop is aft of the rudder, such as many cruising cats and boats with outboards..

It's quite normal in our experience.