Understanding the CAPAC

jralbert
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Re: Understanding the CAPAC

Post by jralbert »

Jeff: weigh in on the question of a change in Capac reading when boater plugs into shore power. I used to know this stuff but it escapes me. Shore power is AC and shouldn't affect CAPAC which is reading DC potential. If there is AC grounding/short issue should that bleed over into hull stuff??

And on the range question, I used to run at .6 (brackish water - partly salty/partly fresh) and at first it scared me but I didn't see any corrosion and learned to live with it. Your mileage though may vary
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Fastjeff
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Re: Understanding the CAPAC

Post by Fastjeff »

Shore power should NOT change the CAPAC readings. If it does, there's something wrong with your isolation unit (and that needs to be corrected).

Okay?

Jeff
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frederickunltd
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Re: Understanding the CAPAC

Post by frederickunltd »

I looked at a 32 over the weekend, Fresh water, in Tennessee. CAPAC was .04 I know that is low, but what causes it to be low, and what might the ramifications of that be?
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Busia
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Re: Understanding the CAPAC

Post by Busia »

Just means it doesn't have enough anode. They are probably just worn out and need to be replaced.
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Re: Understanding the CAPAC

Post by Fastjeff »

In fresh water, you might need to add a block of magnesium to your regular anodes. I used a bread loaf sized chunk bolted to the starboard trim tab and it got my readings where they should be. Lasted a few years then had to be replaced. Got a photo of this if you're interested.

Jeff

PS: My regular anodes where changed regularly as well.
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bcassedy
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Re: Understanding the CAPAC

Post by bcassedy »

A question / observation...

I know that the waters in Tennessee have more clarity to them than the Ohio River where I boat and moor our boar. BUT... could the issue being experienced by Frederick (in post above) be due to water getting between the anodes / bolt points and hull, building up a layer of "stuff" that would diminish the metal to metal contact AND/OR a buildup on the Capac sensor itself - the end result being an incorrect reading?

A suggestion would be:
- how long has the boat sat idle?
* long idle time might mean there's been time for buildup to take place.
- What are the bottoms of boats near the boat he's looking at look like through talking with marina operator or the owner's themselves - boat pulled out and observations made?
* giving Frederick some insight on what might be a contributing factor.
- A little expenditure... Seems I remember Jeff may have mentioned (years ago) that he had purchased an "over the rail" unit <magnesium or aluminum> unit that was suspended/attached to the railing with wire and down into the water. Using this provided a connection to the boat's hull and could improve the Capac reading and could help isolate the cause of the lower reading.
https://www.boatzincs.com/corrosion-ref ... gLcXPD_BwE

Jeff (or anyone knowledgeable...) is the above correct?
If the surface of the Capac sensor is compromised, pulling the boat might be the only answer so that it can be inspected and/or cleaned (GENTLY!).

Bill
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Busia
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Re: Understanding the CAPAC

Post by Busia »

The first thing I would do is check the reading using a digital VOM from the sensor to the hull. Set it on millivolts DC. The meter in the boat is old and not accurate. Then go from there.
BUSIA
located in Ketchikan, Alaska. Gods country
32 foot Marinette express. (no fly bridge)
twin 350 Crusader (Chev 350) engines
1:1 Borg Warner velvet drive transmissions
Closed cooling (antifreeze in the engine)
Proud to be retired IBEW
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GB49
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Re: Understanding the CAPAC

Post by GB49 »

I use a multimeter every year to check/calibrate the capac needle. It can be adjusted with a small blade screwdriver.

Also check the coupling butt connector that connects the Capac to the sliver chloride electrode. The plastic capsule that protects the butt can get wet and corrode.
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Re: Understanding the CAPAC

Post by Fastjeff »

At first, to correct the CAPAC reading (boat in fresh water) I used a magnesium 'guppy' with a wire that clipped to the railing. That brought the readings up to snuff. Tossing it out all the time (and occasional forgetting to) got to be a pain, so I added the block of magnesium to the trim tab.

You can buy a mag guppy on the web, which would solve the problem for now.

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington
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