Hi

We have on our 21ft trailer-sailer a new yamaha 8hp 2-stroke fitted with a charging coil for battery charging. Whilst cruising the Zeeland area of southern Holland this summer I noticed that whilst the engine was running the depth sounder (NASA Clipper Duet) became very inaccurate initially in that the shown depth increased significantly but seemed to settle down after a while.

Do I need some kind of a capacitor somewhere to stop the engine affecting the sounder or display?

 Secondlly, is it possible to overcharge the battery using this sytem, or is it self-regulating?

Hi Jan

I'm not sure I have the answer to your depth sounder problem, but could it be that the magnetic field set up by the charging coil or in its cables of the outboard is effecting things?  

This is most likely to be the case if any of the cables from the outboard to the battery are laying close to, or in the same harness as the depth sounder cables.  Perhaps if the cables and depth sounder inside the boat were screened from each other or if in the same harness/loom they were separated it would help. (?)

Thanxx.

That's certainly a possibility I hadn't considered, but I am fairly sure that they are not close to each other. I will of course check.....

Thanks again.

Jan

I assume that you have a matched regulator to the engine ? I only ask because the electrical output of an outboard is usually termed "lighting" and is AC, not DC - requiring the magic box to convert to suitable DC. One engine I had the box wasn't matched and caused a "dirty" half-sine wave voltage form lower than optimum.

The other factor of course is that most o/boards only supply limited charge capability and switching on items can pull voltage down drastically ....

I have checked the output and it is certainly rectified DC. The spec says it is a six amp charging rather than lighting coil, so it should do the job.

Whilst running the engine (and indeed at other times!!) we keep the current draw to a minimum. The depth sounder/log and the VHF are generally the only electrical items switched on and the draw of these is minimal.

Jan

Have you considered where the transducer is situated?

Is it possible that when the engine is running there is a lot of caviation or air around it? Guessing that you don't travel very fast with that combination but if you did either could be a reason for in accurate readings.

W.

How is the transducer for the echo sounder fitted to the hull?

If it is in one of those silly tubes full of oil, it could well be that the vibration of the engine running is affecting the transducer.

Before you start fidling with the electics, just put a volt and ampmeter on the battery and see what is actually going on with it.

The best way to fit in hull transducers is to put a big splodge of sikaflex on the hull , making sure there are no air bubbles in it and then push the transducer into the sikaflex so it is nicely buried in it but not actually touching the hull, this works beautifully on anybodies kit. Never epoxy them in, you get too many air bubbles.

There are various reasons for using the oil tube method. main one being that Transducer is removeable anytime you wish. If you use correct sized tube for transducer head - it should be close fit but enough spare to allow the fluid to flow past while slowly pressing transducer down. The transducer should also have the top nut fitted to stop it hitting the hull and also swinging around in the tube.

I have 4 boats, 2 of which fitted with transducer in-hull Echo-sounders. My weekender which is usually powered by outboard and transducer is very close to o/board mount has it epoxied to the hull. Easily done without air bubbles - I mix the epoxy on the head itself and then quickly place against hull pushing only enough to lightly squeeze epoxy out the sides showing complete contact. Do not push or twist hard - this can create cavities in the epoxy.

Epoxy - contrary to what you'd imagine as loong as it's not excessive and up / over sides of transducer head is easy to break seal. Careful pressure to one side will remove transducer leaving the epoxy behind.

My main motor sailer has oil-filled tube next to engine bay. In 10 years I have only had to check / top-up once. I use Castor Oil as it's thick and environmentally friendly.

Sikaflex is more permanent than epoxy - surprise but true. I would be reluctant to use it. A lesser bond silicon or similar product maybe.

Transducer is fitted on centreline of hull about six feet or so in front of outboard, so cavitation or air etc is not a problem.

Unsure how the transducer is actually fitted to the hull, but I think epoxy.

Have you tried it without the engine running? If so does the intereferance stop?

Just a thought as the neighbour's BIL hairdrier moped plays havoc with all our radio and televisons here and that is I assume still 2 stroke?

W.

That'll just be the voltage drop as the engine starts, it does it on most boats if the starting battery is the service battery

I have my boat rigged that way, and everytime you start the engine all tjhe low voltage alarms go off on GPS Plotter etc etc.

I just switch the alarms off & all is fine.

Engine is pull start not electric!

Then I would hazard a guess that the Alternator in the outboard has a protective device to protect its diodes when the engine is running and there is no battery attached (as is often done without boards) Then as the voltage is produced as the engine starts running and it discoveres a battery attached, I'd put money on it that it transmits tiny bursts of current in each direction to determine the battery is there and which polarity it is! These bursts will be causing the issue.

But I'm sure someone can explain this process it more scientifically.