1969 Chris Craft Roamer 46 refit

[q240z]

So this is an impressed current system, right?

Yes.

The Engelhard manual for the unit is linked from the blog article.

[Captain Ralph]

Relax
You have an epoxy sealed bottom beyond the technologies from when this equipment was originally designed.
And were not sure the meter is zeroed when not conducting.

You can always find a silver test plug and with a DVM (digital volt meter) to check current from your boat the old fashion way.

Oh, one more thought; Unplug your shore power cable. Any change in the system meter display?

[q240z]

Oh, I'm not in a panic or anything, and I wondered for a bit if perhaps the barrier coat is making it difficult for the system to find much bare metal to polarize. Then I remembered that, for example, the inside of the propeller shaft logs aren't coated beyond the point where I could apply epoxy, so roughly 3' of bare aluminum inside the log pipes. The inside of the OEM raw water standpipe inlets for the toilets were also inaccessible and almost certainly bare aluminum. Also, the system is ideally protecting metals in the raw water circuits of the main engines and (soon, hopefully) air conditioners. So I do want it to do the job it's intended for. I don't think it would be wise in the long term to rely on epoxy barrier coat alone.

With the 12vdc, anode, and reference cell disconnected, the meter drops to zero. With the reference cell attached, it climbs to 4.5-5 IRRC. With all wires attached and the breaker flipped on, it goes from 5.5 to 7.5 and fluctuates constantly, but spends most of its time at 6-6.5.

When we take the boat out for a cruise and come back, the meter doesn't change. The anode runs off the battery, and shore power is filtered through two Bridgeport Magnetics torroidal isolation transformers. The neutral and ground wires never enter the boat. My shore power system has no way to leak. But it's safe to say that disconnecting shore power makes no difference.

I've been giving the greasy eyeball to the blue wire that connects R4 and DR1 to R14 potentiometer. If I'm reading the theory of operation section of the manual linked from my blog correctly, that blue wire should be feeding constant 0.7v to R14. But I'm seeing 0.000v on my Fluke meter. A guy who reads my blog suggested that could mean DR1 died. So I'm going to pull one pin from the board tomorrow and see what my Fluke tells me about that diode.

[Dan Mapes]

Just curious if something like someone flushing a toilet (illegally) nearby could affect the salinity of the water around the transducer?

[q240z]

Interesting that you should mention changing salinity.

One of my early theories was that I'm in brackish water and the tide coming and going is why I'm seeing needle fluctuation. But, as to possible unsanctioned toilet flushers, I'm the only one on the dock from Monday to Thursdays, excluding holiday weekends, and most of the boats are pontoons that aren't even connected to shore power. I'm seeing this pattern every day that I'm there.

That blue wire that connects R4 and DR1 to R14 potentiometer showing 0.000v instead of 0.7v is my primary suspect now. I had a mere inkling before, but a retired Navy electronics specialist who kept lots of 1950s and '60s electronics alive reads my blog and he raised that issue, too.

Regardless, I appreciate all suggestions. If the blue wire turns out to be a dead end, I'll start paying more attention to who's onboard and possibly flushing illegally.

Q

[yachtsmanbill]

BOND BOND BOND. PERIOD. Smart "Y" work? Check these guys too...https://www.boatcorrosion.com/ This is the best bang for yer buck too! https://www.ebay.com/itm/40386248351...Cclp%3A2047675

[q240z]

It's a welded aluminum hull. Everything that's welded together is bonded. But you know that, Bill.

The "smart Y" smoked itself the first time I plugged it in. I cut off the "smart" part and remade it into a dumb Y that works without getting so hot it smokes my deck paint.

I have Bridgeport Magnetics isolation transformers. There's no shore neutral or ground that comes aboard, so the magic boxes would serve no purpose on my boat.

[Captain Ralph]

Separate from your original concerns, but from your text, Neutral and fault current are always connected to your hull? None shunted to shore service?

[q240z]

Correct. The green and white shore power wires stop at the shore power cords. There's nothing to connect them to on the isolation transformers.

[q240z]

Back to the settee, I reused some of the mahogany and Douglas fir marine plywood that was original to the boat to make the HVAC duct top, with a removable sections for maintenance. It's turning out pretty well.

1969 Chris Craft Roamer 46 Refit: Remaking the Salon Settee III

Cheers,
Q

Before


After