Electrolysis - what to look for?
Printed From: The Fishing Website
Category: General Forums
Forum Name: The Boat Shed
Forum Description: Discuss all things boating.
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=106009
Printed Date: 01 Jun 2026 at 6:08am
Topic: Electrolysis - what to look for?
Posted By: FizFisho
Subject: Electrolysis - what to look for?
Date Posted: 14 Dec 2014 at 7:01pm
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I thought it might be a useful topic for guys new to tin. When viewing a boat, what do you look for, is it pitting? Where are the most common places for it to occur?
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Replies:
Posted By: Space Invader
Date Posted: 14 Dec 2014 at 7:19pm
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Mmmmm... good topic. Lots of guys wont admit to having it, but I will. At first I knew NOTHING about it until i bought my first big alloy boat, which happened to have it. (I dont feel the brand is important in my case). Anyways, I identified it by small foaming spots on the inside of the hull, mainly forward, near the keel, which would come back a in a few days after being wiped clean. I've since replaced the battery cables, washed the inside of the hull with a mix of water & diluted white vinegar, attached an anode to the outside of the hull(Near the worst spots) & tossed a couple of lose anodes into the hull where the worst corrosion was. So far I've had a marked reduction in the foaming spots, but not quiet completely stopped it. I'd be interested in others experiences too. |
Posted By: FizFisho
Date Posted: 14 Dec 2014 at 7:22pm
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Ok thats great which brings another question, how to treat it and how to keep it at bay. My understanding is its loose or poor shielded wiring and a lack of anodes. Is that correct? Suffice to say an anode on the leg of your donk isnt enough to protect a boat, where else and how should they be placed? Lets say in a small boat like an fc430 or other dinghy, whats the safest way to wire to avoid it? |
Posted By: Tzer
Date Posted: 14 Dec 2014 at 7:52pm
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It might pay to have your service agent do a electolysis test to see if the anodes already on engine is enough. I have been told too many anode blocks can have the reverse effect and actually create rather than prevent electrolysis or something like this, dont really understand the effects. Just had my boat tested as Im now leaving it over weeknds on a berth and although what was on the leg & transom sheild was just within paremeters we added couple small anodes opposed to one large one. |
Posted By: nzmuzza69
Date Posted: 14 Dec 2014 at 8:32pm
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If you earth your boat out when not using it it helps a lot ,put an earth peg in the ground and run a wire attached to a clip and hook on to you hull ,remember to remove before heading out fishing. |
Posted By: Don18025
Date Posted: 14 Dec 2014 at 9:24pm
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Fiz, there is an excellent page by Nautech Marine with links to the scary phot album. http://www.nautechmarine.co.nz/corrosion.html My experience is that alloy corrosion starts in a number of key places. Under paint - blisters and when it lifts white chalky deposits. Note many workboats are left unpainted. Close and adjacent a to dissimilar metals - using stainless, steel chrome alloy fittings in alloy hulls. Also remember different grades of alloy have the potential to cause corrosion. I have seen a nasty hole on an old stabi caused by a metal knife ( cheap SS) forgotten in the corner of a hull, which had been allowed to fill with rainwater, which eventually emptied itself. There was enough salt on the boat to carry a circuit, after the boat had been drained but not cleaned and parked in an old shed with a leaky roof and left for a few months! Stray electrical currents - major cause bad circuit construction and design. Tzer is correct, the anodes on the engine are there to protect the engine and not the boat, so he is smart adding some more anodes to the hull.
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Posted By: Space Invader
Date Posted: 14 Dec 2014 at 9:56pm
I've seen lots of info & sites identifying electrolysis (as above), but very few seem to actually offer many real world solutions.
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nzmuzza69 wrote:Posted By: Garry 23041
Date Posted: 15 Dec 2014 at 6:48am
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It is important to keep the inside dry between trips. I mean down in the bilges, shouldn't have water sitting. Someone gets a pin hole along the keel someplace and lookout, the thing is often riddled. Try not to weld bits on your boat or add fittings etc unless you are sure you need to do it. I know it's a big deal in moored ali boats where they are exposed to all that stray current in marinas and around moorings. It's a very bad thing to have.
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Posted By: FizFisho
Date Posted: 15 Dec 2014 at 8:08am
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thanks don mate, ok so now i know what it looks like, its a pitting kind of corrosion by the looks. can this be somewhat avoided by wiring a boat with proper shielding?
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Posted By: Bigfishbob
Date Posted: 15 Dec 2014 at 10:29am
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I also look for dark grey spots underneath the hull up to 5 mm diameter usually accompanied by some pitting or porous looking metal. When I pull up the floor board I find much bigger pitting across an area up to 20mm diameter or more. ------------- www.waikatosportfishing.co.nz |
Posted By: FizFisho
Date Posted: 15 Dec 2014 at 10:39am
| its a bizarre corrosion type. almost looks like a pitty mould and can appear in a big bunch which I can only imagine weakens that entire sections (like osmosis in a glass hull)? |
Posted By: outback
Date Posted: 15 Dec 2014 at 9:21pm
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Does everyone wash out the sealed underfloor chamber (as best you can) and leave bung out to drain or just leave the bung in and check occasionally for water? I wondered whether leaving a small amount of salt away in there to slosh around would be a good idea? |
Posted By: Garry 23041
Date Posted: 16 Dec 2014 at 6:48am
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We have an old tsunami (It's old as) we use to dive out of and it's always wet on the deck when we use it. It tends to hold water in a space in the center of the boat under the floor. The floor is not welded. We always take out the lower bung as well and put a stick under the front of the trailer so it is drained and dry. I can't speak to leaving salt away in there but i would put water and salt away in and rinse it for a bit and drain and dry if it was me guessing. This boat is still mint in terms of holes or white powder, as to the rest she is not the bell of the ball any more that's for sure! |
Posted By: MacSkipper
Date Posted: 16 Dec 2014 at 6:58am
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Garry 23041 can you post a couple of photos? Thanks. ------------- Good fishing trip nothing breaks, great trip catch fish. |
Posted By: Garry 23041
Date Posted: 16 Dec 2014 at 7:44am
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What do you want photo's of skipper? I bet you worry about electroysis.........yeah right.
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Posted By: MacSkipper
Date Posted: 16 Dec 2014 at 8:23am
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Garry 23041 - photos of outside of boat and floor - like to see rig and compare outside and inside - also wondering if you are right and no issues - seems like a bit of care and no worries? Wish I had realised this with my trailer - plastic boat is fine but trailer is getting sad - only really started looking after trailer once it was to late - has anyone tried fitting anodes to boat and trailer and does it help? ------------- Good fishing trip nothing breaks, great trip catch fish. |
Posted By: Garry 23041
Date Posted: 16 Dec 2014 at 8:43am
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Next time I go to the barn I will take some snaps. It's raining and blowing here and it seems so very hard to go outside. Trailers are temporay at best wouldn't you say....... I was interested to read on here the other day that some are sealing the box sections with lindseed oil in them to preserve the structure you can't see. Sounds interesting.
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Posted By: Steps
Date Posted: 16 Dec 2014 at 9:20am
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Trailers... Im pretty sure the open end box section trailer we have is the original for the old sea nymph commander... and just about every other SN C has the same trailer.Other than replaced mud gaurd brackets that get the surface rust kill, seal attention about 2 times a yr its and most the other mint. Im sure not all have been well looked after over the decades. So what is the difference between these and all those rusty trailers around it at the ramp? Even going on trade me.. look up S N C and check out the pics/ trailers....most same trailer, old and in damn good knick. Also late sixties/ early 70s American Chev muscle cars had a sacrificial anode mount up in the rear back passengers pillar frame between the frame and outer skin....Outside this period or muscle car I dont know if did or not. |
Posted By: FizFisho
Date Posted: 16 Dec 2014 at 10:03am
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Ok so for a smaller runabout or dinghy (fc430, f14 etc). What are the main sources of electrolisys? 1. Fish finder 2. Radio 3. GPS 4. Music etc What else? Now can these items be wired so its nie on impossible for them to cause electrolisys? (forgetting degradation to wiring etc)
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Posted By: MikeAqua
Date Posted: 16 Dec 2014 at 10:17am
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It's important to differentiate between electrolysis and galvanic corrosion. Galvanic corrosion happens when two metals/alloys with different reactivity are in contact in a liquid that conducts electricity well (e.g. seawater). This causes the most reactive metal to oxidise. Aluminium and it's alloys are quite reactive. Screw and stainless bolt into ally and you will get galvanic corrosion of the adjacent alloy. To avoid you use plastic screws/bolts if you can or use an isolating compound like duralac. Electrolysis occurs when electric potential exists between dissimilar metals. Electrolysis can occur spontaneously, generating a current or it can be forced by an electrical current. In an alloy boat it can be forced by current from the DC system finding it's way into the hull. Things that help in trailer boats include: - - Fitting isolating switches to batteries, - Fitting rubber/plastic mats under batteries, - Checking bus bars, fuse blocks, switches cables to ensure nothing is leaking into the hull. - Removing batteries when the boat is not being used. - Keeping the boat dry when not in use. In moored boats, you need anodes. |
Posted By: MacSkipper
Date Posted: 16 Dec 2014 at 10:20am
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I use a battery switch - isolates battery from electrics when boat stored - means no possibility of stray currents while boat stored and should help keep battery alive as well. I would have thought outboard main cause as dissimilar metals to aluminium boat - should outboard be grounded to boat and anode on boat as well - to cover off when in water? ------------- Good fishing trip nothing breaks, great trip catch fish. |
Posted By: Lethal
Date Posted: 16 Dec 2014 at 10:28am
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dont wire them to the boat, use a baz bar to attach your wires to and use silicon or rubber washers or even both between hull when bolting any stainless steel to your hull,  how to use a Buz bar, you will need two of them, one Positive and one Earth, run your Positive and Earth from your battery to a Buz bar and all your wire is attached from here to what ever your likely to run... name each wire with what it is attached to, run the fuse between the Buz Bar and what ever your running, can make for quick repairs and peace of mind, helps when it comes to resale as well... ------------- Thanks for everything you did for us Eric. may you rest in peace, You were one of the real legends of NZ recreational fishing |
Posted By: MikeAqua
Date Posted: 16 Dec 2014 at 10:30am
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I forgot to add that I had electrolysis in my boat. It was caused by buoyancy foam inside the hull and presumably some leaky electrics. The foam was retaining a small amount of moisture, and presumably the electricity was forcing electrolysis. It's also possible that the foam mix was slighty acidic, and this was enough to drive the electrolysis in the absence of electrical current. I stripped all the electrics, blasted all the foam out of the boat, acid washed and rinsed the hull twice and redid all the electrics. I was very careful to isolate all the electrics from the hull. No problems since then. |
Posted By: MacSkipper
Date Posted: 16 Dec 2014 at 11:46am
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Geez Mike Aqua think I will keep my plastic boat after all.... ------------- Good fishing trip nothing breaks, great trip catch fish. |
Posted By: MikeAqua
Date Posted: 17 Dec 2014 at 10:34am
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Just don't have two-pot foam in a wet or potentially wet area in an alloy boat - or you will need it. Even 'closed cell' foam holds some moisture. Note my boat was 12 years old at that point and was used >100 days per year. The foam had been in for ~5 years. That was all 15 years ago and no recurrences. |
Posted By: Don18025
Date Posted: 18 Dec 2014 at 9:46am
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If you do cook your alloy boat with electrolysis they are easy to recycle by the scrap metal guys. If you own a wooden or glass hull, then electroloysis is mainly going to attack your engine. Electrolysis can damage wooden hulls at skin fittings and fastenings but those hulls have been in the water for a very long time.
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