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Cheechako · 08-10-2009, 08:28

Not being plugged in to shore power should help alot. Green is not an issue. It should be a fairly thin layer of green. Are they flanged seacocks? or just ball valves threaded onto thru hull fittings?

Solitude · 08-10-2009, 10:03

I have 5 holes in the bottom. 3 with ball valves,a speedo and a stuffing box.

Stuffing box: (bronze)? Green, moist, leaks 1 drop every 10 seconds (not a problem for me but I may snugg it up a little this winter)

Engine intake: Bronze, through hull, ball valve, green, moist (raw water cooled)

Head: in and out ,Bronze through hull, ball valve, not green, not moist
Speedo bronze dry not green.

I guess it comes down to the two broze fittings with the most moisture are turning green. Common ? As you said green alone isn't an issue.

I will take a picture tonight. Just to be sure.

Do shaft zinks protect the stuffing box? I dont think there would be a connection because of the packing. Then again if its not in the water except for the wet packing there wouldn't be a connection to worry about?

BTW thanks for your help.

osirissail · 08-10-2009, 19:30

If the thru-hull is pink then it is ready to fracture and fail. If the salt builds up each night then either the thru-hull is porous or leaking at the threads, or has a fracture in it underneath the stainless strap. Replace it as soon as possible.

Solitude · 09-10-2009, 09:15

I didn't get pictures but the thru hull comes straight up with a straight ball valve with a hose attached to a threaded in barb connector and hose clamp.

The green is least at the bottom by the thru-hull and greatest at the top on the barbed connection (flakey). The hose clamp needs to be replaced as it shows some corrosion. The barbed connector is covered in green and white.

I will replace the hose clamp and clean up the corrosion with a wire brush and monitor it for a week or two. I scraped and tried to dig the end of my screwdriver into the pieces but it seemed solid. Because the hose clamp is a little rusty it is hard to tell if the reddish colour is coming from the hose clamp alone.

Would just some leakage from the hose connection be enough to create the green with flakey white powder (Im thinking salt) ?

I purchased a zinc plate yesterday and drilled a hole to attach a wire and clamp. I’ll monitor how quickly the green comes back and attach the cable to it if it needs it.

Thanks for your help!

Chief Engineer · 09-10-2009, 19:40

There are some spots in Annapolis that divers won't go into the water because of the stray current.

Quote:

Originally Posted by GordMay

I suspect you may have a problem with Stray Current corrosion, the result of a ground-fault on your own boat, or perhaps a hot marina.

Stray current corrosion involves the same electrochemical reactions as simple and galvanic corrosion except the reactions are driven by higher DC voltages from sources such as batteries, battery chargers and alternators. Stray currents (or interference currents) are defined as those currents that follow paths other than their intended circuit. The conditions causing this type of corrosion require an electrical fault, along with a problem somewhere in the bonding system of the vessel (the system designed to keep all underwater metals at the same potential to prevent this form of corrosion). The externally induced electrical current, that attempts to flow between the objects, causes one object to give up ions to the other object, and corrode. Stray current corrosion can strike hard and fast, often resulting in damage in weeks, days, or even hours.

Galvanic corrosion occurs when dissimilar metals are placed in the same electrolyte (like water) and are connected electrically. The transfer of current from one metal to the other, in the completed circuit, results in the corrosion of the more anodic metal and the protection of the most noble of the two. This form of corrosion takes on the order of many weeks to months to manifest itself in a visible manner.
A common example of galvanic corrosion can be seen when a stainless steel fitting is attached directly to an aluminum component, such as a spar. Over time, the aluminum will corrode in the area around the fitting.

Check out some of our earier discussions:

http://www.cruisersforum.com/forums/...sion-2469.html

http://www.cruisersforum.com/forums/...odes-8773.html

http://www.cruisersforum.com/forums/...tion-2043.html

http://www.cruisersforum.com/forums/...rina-8445.html

Solitude · 10-10-2009, 21:06

I´m not quite sure if the past threads refer to bonded boats that are plugged in? I have no AC or DC (not plugged in or bonded). I put a grouper anode over the side and took the folowing meausurements.

Shaft 55.8 mv
Stuffing box 46.5 mv
Thru hull 85.5

The measurements were dificult Thats an average. From the posts I was expecting 10 times the value.
multimeter in DC mv
anode in the water
8 gauge wire to the clip
connected to multimeter probe

Why so low... Does it make sense?

osirissail · 11-10-2009, 07:38

Solitude
>>>>> I have no AC or DC (not plugged in or bonded).<<<<<<< You have an engine and therefore you must have a battery to start the engine. Therefore you have a DC system. The battery negative terminal system is either connected to a grounding plate under the outside of the hull or to the engine which is grounded to seawater via the propshaft and propeller. Normally any AC system also has its "ground wire (green)" connected to the ship's ground system or the engine.
- - In the USA boats are built to comply with ABYC standards which is then used by the insurance industry to evaluate compliance with accepted norms for a "safe vessel construction". ABYC has historically required all vessels to have a bonding system which is a continuous loop of wire connecting all metal parts of the boat to each other and then to a "ground." This is to prevent an electrical shock from injuring any people on the boat should they touch a lifeline stanchion or other metal part of the boat. The bonding system is also used to take all metal parts that touch seawater to the same electrical potential and thirdly to help with dissipating lightning strike energy.
- - It was found that bonding bronze thru-hulls/seacocks was causing accelerated electrolysis in the bronze and even more importantly in a lightning strike the bronze thru-hulls were passing too much of the lightning power causing them to heat sufficiently to allow them to melt their way out of the hull. Despite ABYC standards boaters were cutting the bonding wires to their thru-hulls for either or both reasons.
- - Then Marelon (reinforced fiberglass) thru-hulls/seacocks came on the market (They are sold in the USA by Forespar) and solved that problem. Manufacturers flocked to Marelon as they were electrically inert (FRG) and could not corrode and were as strong as metal thru-hulls/seacocks.
- - The readings you posted are of no value. You cannot use a multimeter to measure electrolysis - the reading you are getting are most likely residual stray or induced voltages from your body or the batteries inside the meter. You need an Electrolysis meter which has no batteries and two long cables - one of which has a silver anode which is dropped over the side into the seawater. The other cable is attached to the part being tested. The millivolt meter will then read any voltage potential between the seawater and the metal part. The meters have scales on them for each type of metal and yellow and green zones to guide you to understand if you have too little, just right, or too much zinc protection.
- - Unbonded bronze thru-hulls/seacocks have a problem. Bronze is an alloy of tin and copper and some minor other stuff. Unbonded, which means not connected to a zinc, allows the tin to leach out of the bronze and the remaining copper is brittle and porous. The bronze will turn pink when sufficient tin has been leached out. That process is effectively stopped by a bonding system but then you have the possibility of a lightning strike melting the thru-hull out of the boat and 1.5" holes admitting seawater. Several boats have sunk that way. So it is 6 to1, half dozen to the other whether to bond or not to bond. Replacement with the Marelon system solves that problem. But sometimes that is neither cost-effective nor possible without major de-construction of the inside of the boat.
- - Bronze in the presence of water will corrode to a green "patina" - you will see this on those heroic statues in the city parks. The white stuff is from pigeons. Back to the boat - salt deposits however, mean either salt water is dripping onto the parts or there is a leak allowing salt water to pass through the metal of the thru-hull/seacock. Determining which it is - is important as you may have severely thinned or weakened metal which can break easily or just a leaky thread joint. As others have suggested make sure you have soft wood cone plugs that fit, attached by a string to the thru-hulls/seacocks so if one breaks you can shove the "plug" into the hole and keep your boat from sinking.
- - Old fashioned "stuffing boxes" are usually attached to the boat by a rubber hose and the prop shaft is electrically isolated from the stuffing box by the packing material. So the stuffing box is not in the "bonding" system and will turn green by the normal reaction of bronze to water. Not a problem.

Solitude · 11-10-2009, 08:05

Hi
Yes of course I have both an AC and DC system in my boat! I dont plug in to shore power (no AC) I disconected the battery teminals (no DC).

According to others on the site you can use a multimeter so I tried.
Please read "Hot Marina". Here are the instructions I used... see below.
I´m not sure if I followed it correctly IE is this test only valid with DC connected or AC connected. I should have (and will) take measurements with DC connected.

I agree that it is logical that the stuffingbox would be isolated from the shaft by the packing.

Now if the test from the Hot Marina, thread is garbage please someone else let me know as well! It was suggested to me from some people have alot of respect for on this site! My results were 10x lower but maybe I performed the test wrong.

"If you have a multimeter on board, you can test your boat and your dock for about 7 more bucks. Get a pencil zinc, drill a hole in it for a wire and solder a length of wire to it. Connect that to the black lead of your meter, and suspend the zinc in the water, after cleaning it with a scotch-brite pad. Put the red lead to your bonding system. The meter readings indicate thus with bronze and stainless protected metals:

Reading DC volts on 2 volt scale:
Minimum protection: 500-550 millivolts (0.5V)
Full protection: 430-480 mv
Overprotected: less than 380 mv

An unprotected bronze fitting of reasonable quality by itself will read about 700 mv; Poorer grade materials have lower readings, with protection levels adjusted accordingly. A metal will be fully protected when its bonded voltage reading is 200 mv less than its unbonded reading. Additional zinc pulls the voltage down, additional protected metals loads the system by pulling the voltage up. Stray current that causes electrolytic corrosion pulls the voltage up dramatically. A voltage reading over 750 mv DC indicates stray current, and there should be no AC voltage at all. ( A small AC reading may be picked up by the meter leads inside the boat if the shore power is on, especially if there are any flourescent lights, motors, or transformers on.)"

osirissail · 11-10-2009, 09:10

- - Okay getting more specific - there are two different tests. One is strictly your own boat and any under-zinc-ing or over- zinc. You need only to disconnect your boat from any electrical connection, what-so-ever, from the dock. And better yet go out and anchor away from the dock. There are stray currents running through the water from other "electrical leaking boats and marina systems". You need not disconnect anything in the boat. The tests can be done with the engine off, engine on, and AC generator operating to get possible leakage situations during all three operating environments.
- - If you take a digital multimeter and turn it on - you will see the read-out searching and increasing and decreasing from zero. If you grab the ends of the probes with your hands you will see voltage induced by your own human electrical system (humans are bio-chemical batteries and doctors measure our electrical output to see if we are dead or alive). So using a battery powered multimeter to determine millivolts is subject to many errors.
%0

osirissail · 11-10-2009, 09:25

Oops, ran up against the 30 minute limit on editing - - -
- - Measuring millivolts in an un-bonded bronze thru-hull sitting in seawater does what? Nice information but what can you do with it? The bronze thru-hull/seacock is a unit purchased from the store and you cannot change any of its electrical properties. You can only attach it electrically to a zinc by a bonding wire. But a bonding system is a whole system comprising multiple parts of the boat - other bronze fittings, some iron fittings, some stainless steel fittings, etc. You are wanting to measure the whole system in its various operating states to see if there is excessive currents eating away at the valuable or critical parts. You then adjust the quantity of zincs to decrease damage to these parts or repair leakages so that each part of the whole system is best protected.
- - There are parts such as stainless rudder shafts, or heat exchangers that contain dissimilar metals and they can be individually "zinced" to protect them or they can be electrically bonded to the main bonding system to protect them as part of the whole group.

**GordMay** · 12-10-2009, 05:03

See the Fluke tutorial
➥ http://www.fluke.com/Application_Not...r/B0269b_u.pdf

and Michael Kasten’s articles
➥ http://www.kastenmarine.com/mbqMetRef.pdf
➥ http://www.kastenmarine.com/mbqCref.pdf

osirissail · 12-10-2009, 06:24

Those are some seriously good reference articles - especially the Metal Boat Quarterly ones.
- - Off subject a bit but under the category of corrosion - - Stainless Steel corrodes dramatically if while in the presence of water oxygen is prevented from getting to the surface of the stainless steel - intragranular corrosion occurs. A 1/4" thick stainless chainplate with advanced intragranular corrosion looks somewhat normal but you can take a screwdriver and stab it right through the chainplate in the area of the corrosion. I have seen this done in real life at a major rigging supplier in Florida. It is impressive and a strong reminder that stainless steel needs to be open to the air if in a wet area. If you notice surface pitting occuring you need to keep a wary eye on the part and replace it if necessary. Painting stainless in a wet environment is a big no-no.

karlhead · 12-10-2009, 07:04

It looks like you have 3 different metals involved here. Bronze thru hull, stainless hose clamp and whatever the valve. Get something sharp and scratch the thru hull. If it comes out a pinkish color it is no good and probably was caused by stray current either from something on your boat, or most likley from the marina. Take off the hose clamp and remove the bonding wire or whatever that wire is and clean the area well with vinegar. If the corrosion reappears in the next day or two you have a problem with the marina power. Be sure to do the scratch test on ALL of your thru hulls and check you shaft for what looks like rust.