Electrolysis check for Swift Trawler Owners

AC imposed stray current while not a problem for the boat (no anode/cathode to shed material as the current reverses 60/50 times per sec.) it can injure and kill someone in the water. DC imposed stray current can and will cause significant damage to your boat in a surprisingly short amount of time.

Bonding as FF said can be good or not needed depending. Some boats have no bonding (mine) and are just fine. Test with a silver/silver test cell to be sure.

I recommend an electrical survey every few years. I just did one and it cost me $180 bucks and found another boat nearby with 6.8 Amps worth of leakage into the water due to a ground and neutral connected at a GFI, remember the grounds on a boat are common and should never be connected to the AC neutral.

DC wire laying in bilge water connected to battery is a very big problem looking for a wallet to happen in.

How did this seacock get to this condition?

To me it looks like the bilge has no natural ventilation and the metal had water condensed on its surface 24/7.

If so, it is remarkably poor work for a "name " brand cookie.

SCOTTEDAVIS said:

DC imposed stray current can and will cause significant damage to your boat in a surprisingly short amount of time.

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Yep.

This happened in a matter of weeks. The cause was found (broken insulation on a bilge pump wire) but the damage was done and the prop eventually fell off anyway.

The question of whether to bond various pieces of metal gear and underwater metals in a circuit or leave them isolated is a subject that's sure to generate heated debate. If the argument could be made for one approach or the other without regard to other related grounding issues, then isolation would surely win out. However, other grounding considerations-including electrocution prevention, the mitigation of damage from lightning strikes, and the need to provide a safe path to ground for short circuits in the AC and DC electrical systems-argue in favor of an overall grounding system. Moreover, if done properly, this system helps to minimize stray current corrosion that can affect any node on the circuit.

To make an already complex topic simpler, let's limit the scope to fiberglass boats. The bonding of various metals, such as the stainless steel of rudder stocks, the bronze of seacocks and through-hull fittings, the Aquamet alloy of propeller shafts, and the aluminum of tanks and spars, may seem like an invitation for corrosion. Every effort typically is made to keep dissimilar metals apart, especially those that are far apart from each other on the galvanic scale, such as aluminum and copper alloys.

The key difference with a comprehensive bonding system is that all of these dissimilar metals are part of a circuit that also includes a sacrificial anode, typically made of zinc. Because zinc is especially galvanically ignoble, when it's connected to the DC bonding system, it affords galvanic protection to all other metals above it on the galvanic scale.

Not bonding underwater metals does not eliminate the potential for in water AC current flow, and electrocution, the engine will by default be part of the DC negative system, and the AC safety ground must, for electrocution prevention, be common with it, which gives stray AC leakage current a path to the water. Ideally, an AC fault to a bonded object will cause the source circuit breaker to trip, rendering the fault safe. To make this system safer, ELCI shore power circuit breakers (essentially a GFI for the whole boat, albeit with a higher trip threshold) are now commonly installed on new and refit vessels.

Finally, linking the DC bonding system with the AC safety ground (and the lightning-grounding if present) systems means that most metal masses on board are part of the grounding system, offering both electrocution protection as well as corrosion mitigation. And to protect all the elements of this boat-wide circuit, diligent attention should be paid to the sacrificial zincs that will prevent galvanic corrosion. Frequent inspection and replacement of the zincs when required is a small price to pay in exchange for protection against potentially harmful or life-threatening electrocution scenarios or short circuits from any of the electrical sources aboard boat.

In this case, corrosion of an alloy that contains high levels of zinc may have been staved off for some time by sacrificial anodes as long as they and the bonding system were maintained. The threshold for resistance in the bonding system, between zinc anodes and the protected metal, is very low indeed, it cannot exceed one ohm. Therefore, a little corrosion or a loose or poor connection (using a hose clamp for instance) can easily create enough resistance to block protection otherwise provided by a zinc anode.

For the record, Electric Shock Drowning (ESD) is almost unheard of in saltwater. It happens almost exclusively in freshwater. I have been diving in Bay Area saltwater marinas for 21 years and in that time well over 1,000,000 in-water hull cleaning events have taken place here. To my certain knowledge, no hull cleaner has been injured or killed here due to ESD. That's a pretty good indication that electrical problems (while not to be ignored) do not present a signifcant danger in saltwater, IMHO.

From the BoatUS web site. Maybe not the most technically correct explanaition, but will give you the general idea:

Why fresh water and not salt? Salt-water is anywhere from 50 to 1,000 times more conductive than fresh water. The conductivity of the human body when wet lies between the two, but is much closer to saltwater than fresh. In saltwater, the human body only slows electricity down, so most of it will go around a swimmer on its way back to ground unless the swimmer grabs hold of something — like a propeller or a swim ladder — that's electrified. In fresh water, the current gets "stuck" trying to return to its source and generates voltage gradients that will take a shortcut through the human body. A voltage gradient of just 2 volts AC per foot in fresh water can deliver sufficient current to kill a swimmer who bridges it.

Electric Shock Drowning (ESD) Explained - Seaworthy Magazine - BoatUS

Brass thru-hulls

Here is an article on this topic: http://michel-christen.com/2T-H.pdf
It explains in very good detail what the problem is right down to metal composition. I like (sarcasm) that in the EU they specify an underwater thru-hull is to withstand at least five years of use without deterioration that compromises its condition. Not a very high bar to jump...

fstbttms said:

For the record, Electric Shock Drowning (ESD) is almost unheard of in saltwater. It happens almost exclusively in freshwater.

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Correct, ESD is a fresh water issue. I had the great good fortune to take the ABYC Corrosion Analysis course taught by Kevin Ritz. Kevin is the "discoverer" of ESD and his story of losing his 8yr. old son, Lucas to the phenomena is heart breaking. Take the time to watch Kevins' youtube video on this issue. youtube video

This has been an interesting thread. Several posters identified stray current corrosion as a possible cause (probable in my view). I didn't see any discussion of causes and remedies. There are two:


One is internal. The most typical is a bilge pump wired backwards or a bare terminal lying in bilge water. That will supply DC voltage to the underwater metals and eat them away quickly whether they are really bronze or just crappy brass. Note the picture of the folding prop above.


The other is external. An adjacent boat has a similar DC to ground problem and that DC voltage comes over to your boat on the shore power ground. It will do the same thing to your boat. A good galvanic isolator will stop most ground leakage. An isolation transformer is even better. Or just keep your shore power unplugged.


David

djmarchand said:

One is internal. The most typical is a bilge pump wired backwards or a bare terminal lying in bilge water. That will supply DC voltage to the underwater metals and eat them away quickly whether they are really bronze or just crappy brass.

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Never seen a true bronze seacock damaged by galvanic or stray current corrosion.

CeeBee, thanks for the thread, I have 2015 Jenneau Velasco 43, I imagine all the fittings are the same, I checked everything after reading the thread, and see no evidence of anything like this, we love the boat and although everything is not up to mega yacht perfection, for the money, room and s
peed it is hard to beat. Will keep an eye on this, but I agree with many of the posters it would appear to be something local to the slip, and not a boat issue.

fletch said:

CeeBee, thanks for the thread, I have 2015 Jenneau Velasco 43, I imagine all the fittings are the same, I checked everything after reading the thread, and see no evidence of anything like this, we love the boat and although everything is not up to mega yacht perfection, for the money, room and s
peed it is hard to beat. Will keep an eye on this, but I agree with many of the posters it would appear to be something local to the slip, and not a boat issue.

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Although I've never seen a Velasco, the 37 and the 43 definitely fill that same area of the market Swift Trawlers do. Also, the Jeanneau NC's fit the market well, just don't have the flybridge.

djmarchand said:

This has been an interesting thread. Several posters identified stray current corrosion as a possible cause (probable in my view). I didn't see any discussion of causes and remedies. There are two:


One is internal. The most typical is a bilge pump wired backwards or a bare terminal lying in bilge water. That will supply DC voltage to the underwater metals and eat them away quickly whether they are really bronze or just crappy brass. Note the picture of the folding prop above.


The other is external. An adjacent boat has a similar DC to ground problem and that DC voltage comes over to your boat on the shore power ground. It will do the same thing to your boat. A good galvanic isolator will stop most ground leakage. An isolation transformer is even better. Or just keep your shore power unplugged.


David

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So I'm thinking of wiring a sump pump in my bilge for my AC to drain into. Do I need to do something special with the wiring so I don't cause a DC voltage "leak"?

There are some terminals available high in the bilge that supply the bilge pump that I was thinking of tying into. Will that be OK?

If you are using a packaged sump, pump and float switch for the A/C drain, wire the pos DC to the switch and the negative to the motor. I suspect that the wire to it will be color coded red and black, so just follow that. Crimp the connections with heat shrink connectors and by all means keep them up high out of any bilge water.


David

Wiring a bilge pump "backward" i.e. reverse polarity, will not necessarily cause stray current corrosion per se (interestingly, the pump, if of the submersible variety, will often still work if running in reverse, just not very efficiently).

Wiring a bilge pump so the negative lead is wired to the float switch, on the other hand, can allow current leakage, as carbon trails within the pump motor create a path to the motor's shaft and into bilge water. This practice gained some popularity in an effort to mitigate the possibility of stray current corrosion, in the belief that the float switch and its wiring were more likely to be a source of current leakage. While that may be true, the scenario sets up the pump to become an almost certain source of leakage, making this wiring approach the greater of two evils. If positive power is supplied to the pump at all times, with the negative lead switched, it does so even when the pump isn't running, offering up this leakage path 24-7, vs. only when the pump runs, which is why the positive lead must be wired to the float switch.

Bilge pump, and more specifically float switch, wiring is among the most common source of stray current. Every effort should be made to ensure connections remain above normal bilge water levels. My recommendation is to make connections 18" above the base of the pump (good quality pumps and switches are made with leads much longer than this). If this isn't possible, ensure butt splices are waterproof/submersible by using heat shrink butt splices (take note, it is very easy to pierce these with overly aggressive crimping dies, the pierce expands when the terminal is heated, so inspect yours carefully after heating, pierces can be "fixed" with silicone sealant) or by adding resin style heat shrink tubing over a conventional butt splice. Avoid having two wires travel into one end of a heat shrink connection as it's difficult to make a good watertight seal when doing so, if you must, knead the heat shrink around these wires while it's still warm to work the resin into the gap, or again, seal with silicone. Corrosion aside, bilge pump connections should be robust and watertight so that pumps will continue to work in the event of a flooding scenario, if the pump quits as soon as the connections are submerged, it does little good in an emergency such as this.

Ok. Thanks David and Steve. I figured I could screw this up somehow. I would have not thought through the possible electrolysis effects of wiring the positive to the motor.

I really need a boat electronics class.

Good grief. Confused again. Instructions in the package are vague.

Opened up the package and found three wires. Black, solid brown and brown/white. The brown/white is the switch wire and solid brown is the positive pump wire, from what I can tell?

Steve should write a book, clean, concise easy to understand and spot on.

Thanks for your contributions!

While it is true ESD is essentially a fresh water issue, it must still be taken seriously (especially for marine industry professionals) even in typically saltwater regions. In certain parts of the country, where boats are kept in estuaries such as the the Seattle Area, portions of SF Bay, Chesapeake Bay, and in any harbors or bays into which rivers flow, the salinity can change dramatically seasonally and after heavy rainfall, and even with tidal fluctuations. Where I live on the Chesapeake Bay, into which several large rivers flow, this is very noticeable.

Additionally, any electrical fault aboard a vessel that can cause ESD, can potentially cause an onboard electrocution or electrical fire.

I've seen stray current corrosion consume AQ22 (the most corrosion resistant shaft alloy) shafts, stainless steel swim platform supports, silicon bronze through hulls and struts and manganese bronze (this is actually brass since it contains zinc) propellers with astonishing rapidity. I know of no metal that is immune to this phenomenon.

While shore power connections, specifically the AC safety ground, or inadvertent onboard neutral to ground connections, can complete a galvanic cell and lead to galvanic or even stray current corrosion, except in very rare cases, those with very high current density and with aluminum hulls or outdrives, Shore/AC power is not a common corrosion source; which is why the "hot marina" theory holds little water. Boats can be "hot" leaking stray DC current into the water, but that rarely lasts for long as they typically consume their own underwater metals pretty quickly, however, and again with rare exceptions, a marina's own AC power typically isn't the cause of the problem.

Galvanic isolators, a corrosion prevention tool, and a veritable requirement for any vessel with shore power, blocks only DC voltage for this very reason, it's the source of the most common type of corrosion, galvanic, while permitting AC voltage to flow in the event of a fault. Galvanic isolators typically cannot block stray current corrosion caused by a nearby vessel that shares the same shore power source, as they are limited to blocking about 1.4 volts. Galvanic corrosion is slow and is typically less than a volt, while stray current corrosion is battery derived and therefore is much greater, up to 24 volts.

Dude, black wire connects to ground.
Brown wire connects to the Manual side of the three way switch.
Brown /White wire connects to the Automatic side of the three way switch.

HopCar said:

Dude, black wire connects to ground.
Brown wire connects to the Manual side of the three way switch.
Brown /White wire connects to the Automatic side of the three way switch.

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Light bulb! I savvy now. Forgot about the bilge pump switch with the manual activation side. I think I killed one too many brain cells New Years Eve. ?

So If wire this into my existing bilge pump switch, if/when I hit the manual switch for the bilge pump then this little sump will also get energized. What if there's no water in this sump tank? Will that ruin this little pump. It's a very cheap sump pump.

Steve DAntonio said:

While it is true ESD is essentially a fresh water issue, it must still be taken seriously (especially for marine industry professionals) even in typically saltwater regions. In certain parts of the country, where boats are kept in estuaries such as the the Seattle Area, portions of SF Bay, Chesapeake Bay, and in any harbors or bays into which rivers flow, the salinity can change dramatically seasonally and after heavy rainfall, and even with tidal fluctuations. Where I live on the Chesapeake Bay, into which several large rivers flow, this is very noticeable.

Additionally, any electrical fault aboard a vessel that can cause ESD, can potentially cause an onboard electrocution or electrical fire.

I've seen stray current corrosion consume AQ22 (the most corrosion resistant shaft alloy) shafts, stainless steel swim platform supports, silicon bronze through hulls and struts and manganese bronze (this is actually brass since it contains zinc) propellers with astonishing rapidity. I know of no metal that is immune to this phenomenon.

While shore power connections, specifically the AC safety ground, or inadvertent onboard neutral to ground connections, can complete a galvanic cell and lead to galvanic or even stray current corrosion, except in very rare cases, those with very high current density and with aluminum hulls or outdrives, Shore/AC power is not a common corrosion source; which is why the "hot marina" theory holds little water. Boats can be "hot" leaking stray DC current into the water, but that rarely lasts for long as they typically consume their own underwater metals pretty quickly, however, and again with rare exceptions, a marina's own AC power typically isn't the cause of the problem.

Galvanic isolators, a corrosion prevention tool, and a veritable requirement for any vessel with shore power, blocks only DC voltage for this very reason, it's the source of the most common type of corrosion, galvanic, while permitting AC voltage to flow in the event of a fault. Galvanic isolators typically cannot block stray current corrosion caused by a nearby vessel that shares the same shore power source, as they are limited to blocking about 1.4 volts. Galvanic corrosion is slow and is typically less than a volt, while stray current corrosion is battery derived and therefore is much greater, up to 24 volts.

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Great that you're posting here, Steve. Saw you present at Trawlerfest in Baltimore a couple years ago and learned a lot. Thanks for sharing your considerable expertise.

Howdy all! - I'm simply posting to stay up on this thread. Planning to haul our Tolly and do as needed; hopefully can find time in not too distant future.

Carry on... Great info here!

Dude, Yes both pumps would run if you switch it to manual. You can probably get away with it. These type of pumps can run dry for a surprisingly long time. Fuse size might be an issue.

I would install a separate switch for the sump. It's not hard or expensive.

Steve DAntonio said:

Shore/AC power is not a common corrosion source; which is why the "hot marina" theory holds little water.

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So very true.

Literally every one of the many dozens of marinas I have worked in over the years has been described to me as "hot" by someone or other. My response invariably is that rapid anode depletion or corrosion issues are almost always due to a problem aboard the boat in question. The "hot marina" is simply the excuse boat owners use to deflect responsibility.

Example- the pic I posted of the badly corroded folding prop earlier in the thread? The owner refused to take my advice and have an electrician track down the problem. He was convinced it was the powerboat in the neighboring slip that was the cause. It wasn't until his bilge pump failed and he had one of his maintenance guys replace it that the broken 12-volt wire was discovered. And again, it ultimately cost him the prop.

fstbttms said:

So very true.

Literally every one of the many dozens of marinas I have worked in over the years has been described to me as "hot" by someone or other. My response invariably is that rapid anode depletion or corrosion issues are almost always due to a problem aboard the boat in question. The "hot marina" is simply the excuse boat owners use to deflect responsibility.

Example- the pic I posted of the badly corroded folding prop earlier in the thread? The owner refused to take my advice and have an electrician track down the problem. He was convinced it was the powerboat in the neighboring slip that was the cause. It wasn't until his bilge pump failed and he had one of his maintenance guys replace it that the broken 12-volt wire was discovered. And again, it ultimately cost him the prop.

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This is also why I'm so in favor of GCFI at marinas. All the boat owners whining when they can't connect. They are being warned and if they respond they may be avoiding major problems with their own boat. I have known people to have problems from the neighboring boat (remember in FL we have all the double slips), but most often it's themselves. Essentially it serves as a test on the boats. Then owners are forced to find their problems.

Question:


If a boat is not hooked up to shore power at all and it is tied by lines-only in mid slip... can stray electric current from other boats or the dock or nearby land harm that boat's submerged metal items?


Please have the answer include what if in salt water or if in fresh water.


Thanks!

Art said:

Question:


If a boat is not hooked up to shore power at all and it is tied by lines-only in mid slip... can stray electric current from other boats or the dock or nearby land harm that boat's submerged metal items?


Please have the answer include what if in salt water or if in fresh water.


Thanks!

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No. It is the common ground connection between the various boats at the marina that causes problems.

Ken

kchace said:

No. It is the common ground connection between the various boats at the marina that causes problems.

Ken

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Thank you, Ken!

Therefore (and, please correct me per chance I’m incorrect)... if the boat is fully isolated from the dock (as I mentioned in post #57 ) i.e. it touches the water only, and then, as well, all batteries on boat have been fully isolated via tall amp switch (Perko or otherwise) turned off .... then the boat's metal parts will experience no galvanization, current corrosion/electrolysis or other metal destructive electric current effects.

That is how I keep our Tolly when berthed. She has had no metal problems. I learned to do this from boating in NY / LI salt waters during mid 1900’s. I also keep plenty of anodes in the proper locations.

Happy Marine-Metal-Saving Daze - Art

On the boat in question, all those sea cocks were un-bonded, so electrically isolated from everything in the boat. Given that, it's hard to blame the degradation on stray current since there was nowhere for current to flow to or from the sea cocks. It seems more likely that it's just really crappy metal and finally met it's maker. Or am I not understanding this, which is entirely possible......