Sounder erratic when engine running.

[Contest1]

My NASA sounder works great when under sail but rapidly jumps throuh a range of depth readings when the engine runs.
I,v checked connections but no change.
Any thoughts?

 

[Champagne Murphy]

Dry joint somewhere on the wiring?

 

[Sandyman]

Alternator output ? spikes on the DC

 

[causeway]

bubbles over the sounder?

 

[Redwing228]

Alternator probably to blame

My NASA sounder works great when under sail but rapidly jumps throuh a range of depth readings when the engine runs.

We have exactly the same problem and have put it down to 'noise' from the alternator. When doing any depth-critical manouevering I turn the engine key to "off" disabling the alternator excitation (Beta engine keeps on running) and just let the instrument run on battery power - behaves normally then, as it does under sail.

 

[smth448]

Could be electrical interferance. Do you have a ferrite on the cable from the transducer to the instrument?

 

[causeway]

We have exactly the same problem and have put it down to 'noise' from the alternator. When doing any depth-critical manouevering I turn the engine key to "off" disabling the alternator excitation (Beta engine keeps on running) and just let the instrument run on battery power - behaves normally then, as it does under sail.

is it ok to do this while the engine is running, it's just that I have the same problem and this would be an easy fix.

 

[dbentley]

I had exactly the same problem when I fitted a new engine (Beta 20hp with standard alternator) to replace an old Bukh. I solved it by fitting a capacitor across the alternator. As I recall, I bought the capacitor from a motor factor, where they are used to suppress radio interference.

 

[Seajet]

Where is your depth transducer fitted, and is it internal or through a hole in the hull ?

 

[LadyInBed]

It could be that the alternator belt is slipping a bit.

 

[Rigger Mortice]

When I had the same problem it ended up that my solar panel was picking up interference from the engine and feeding it back into the boats wiring (the panel was mounted just above the engine).

I moved the panel. Problem solved.

 

[Contest1]

We have exactly the same problem and have put it down to 'noise' from the alternator. When doing any depth-critical manouevering I turn the engine key to "off" disabling the alternator excitation (Beta engine keeps on running) and just let the instrument run on battery power - behaves normally then, as it does under sail.

Thanks for all the sugestions, going to try this one on the KISS principle then work my way round the others as necessary.
I don,tthink the transducer go,s through the hull.
I,ll report progress.