Electrolysis in fresh water - Update

[Dunaruna]

I'm getting conflicting ideas about mounting aluminium pontoons to a steel framed boat - insulate them from the frame, don't insulate them from the frame.<br /><br />The lake has a high mineral content, apparently this can act similar to salt water in regard to electrolysis. <br /><br />I've googled this subject for weeks now and can find scant little info on the subject. One idea I found was to insulate the motor frame from the boat frame (mount the motor on nylon and run the bolts through nylon tube). The idea is to not use the boat frame as a common earth.<br /><br />I want to do this right the first time - any thoughts.<br /><br />Aldo

 

[JB]

Re: Electrolysis in fresh water - Update

Many chemicals can make water into an electrolyte.<br /><br />I would proceed as though I was building the boat for salt water.<br /><br />Good luck.

 

[18rabbit]

Re: Electrolysis in fresh water - Update

Aldo, anytime you have dissimilar metals you have a difference in electrical potential. Given the opportunity, electrons will travel. We see the process as corrosion. You can exacerbate the transfer of electrons by introducing ions. Negative ions are like democrats; they will pick up a freeloader anytime they can. In this case, an electron from the aluminum alloy. You can think of pure H2O as an insulator and thus not a problem. Any water other than pure H2O has ions suspended in it. But the further you move away from ‘pure’ the bigger the problem will be. Salt water is ion–city! If your floating paradise will be exposed to anything other than pure H2O, do not allow steel and aluminum to be joined. If anyone tells you different, walk away. As far as insulating the two metals, don’t know; sounds like a hassle and something that would require regular inspecting. Alternative idea: is it possible to use an aluminum frame joined to the aluminum pontoons?

 

[Dunaruna]

Re: Electrolysis in fresh water - Update

(If your floating paradise will be exposed to anything other than pure H2O, do not allow steel and aluminum to be joined.)<br /><br />O/K, so even if the motor creates a common earth through the frame I'm o/k if I completely insulate the alloy toons?<br /><br />Insulating the pontoons isn't a big problem, nylon tube with flanges for the bolts to go through. (not unlike shock absorber rubbers). The nylon is very tuff unlike rubber or polyeurothane. I am also having kamakazi anodes fitted, haven't decided yet between zinc or magnesium. <br /><br />18rabbit, I always tend to overthink problems but these toons are costing me the GDP of a small country - I want to understand all this and make the correct decision. <br /><br />The motor is a 2004 50HP EFI Bigfoot, apparently it uses a frame earth to run the rudder angle gauge. I am also fitting a garmin FF, the transducer will be mounted on the toons, is that another earth connection? I should know all this but I just can't get my head around it.<br /><br />EDIT: Just thinking out loud - the toons will be half submerged, the only part of the metal frame that is underwater is the motor leg, doesn't that mean that its impossible to keep both metals out of the electrolyte? (mineral laden water)<br />Aldo

 

[18rabbit]

Re: Electrolysis in fresh water - Update

Aldo, I was just watching a show on fast boats. The big boats have steel hulls for strength and aluminum topsides to reduce weight. To join the two metals they use a special bi-metal that is aluminum and steel fused together. They said this avoids corrosion issues. Don't know where you get it, probably not cheap but you don't need much. The joining of aluminum to steel on big, fast boats was common in the program.

 

[Dunaruna]

Re: Electrolysis in fresh water - Update

JB & 18rabbit, thanks for the help. I'm starting to get a handle on this now. Thanks again.<br /><br />Aldo

 

[rodbolt]

Re: Electrolysis in fresh water - Update

you must electrcally bond the two. insulating wont work as the water will be a conductor. the US navy tried aluminum super structures on steel hulls with limited sucess and finally gave up.<br /> good luck and keep posting

 

[OBJ]

Re: Electrolysis in fresh water - Update

Aldo...give this site a check out....<br /><br /> http://www.yandina.com/electrolysis.htm <br /><br />Maybe ya' already did....dunno.

 

[Dunaruna]

Re: Electrolysis in fresh water - Update

OBJ, your a life saver!<br /><br />Haven't seen that site before - and its in non technical english!!!<br /><br />Thanks heaps.<br /><br />Aldo<br /><br />EDIT: Still reading 18rabbit, gimme time to digest all this. One point though - my marina does not have shore power facilities, the only potential problems will come from other boats with bad generator wiring or my own boat (no gen for me - 12volt solar all the way). I can't do anything about other boats but I can make sure I've got mine right.

 

[18rabbit]

Re: Electrolysis in fresh water - Update

I have an issue with the DIY galvanic isolator on that web site. It is functional but not safe. I do not recommend builting it as shown.

 

[BillP]

Re: Electrolysis in fresh water - Update

You are fighting electrolysis. Bond (connect all metals systems with a common wire)together and connect to a MAGNESIUM sacrificial if in freshwater and zinc sacrificial if in saltwater. The sacrificial has to be in contact with the water to work.<br /><br />ZINC is used for saltwater and if used in freshwater on aluminun the aluminum will be the sacrifical anode.

 

[Dunaruna]

Re: Electrolysis in fresh water - Update

This is my dilemma, conflicting opinions. I'm back to square one when I take BillPs' post into account.<br /><br />Bill, many people on the lake have told me to use magnesium (a friend of a friend is one of those braniac types, he explained it to me but all I heard was blah,blah,blah - way to technical for my little brain).<br /><br />So I bond all metals, the toons will be bolted on with 48 SS bolts (I can also use serated washers for 'bite') - I assume this negates the need for wires. Do I use the frame of the boat as a common battery earth (12volt)?<br /><br />Aldo

 

[Dunaruna]

Re: Electrolysis in fresh water - Update

Check me if I'm wrong but I think my confusion comes from not understanding the terminology used here. <br /><br />Bond - electrically connect dissimilar metals using straps.<br /><br />Insulate - Don't allow dissimilar metals to touch.<br /><br />So I can actually bond & insulate. Yeah?<br /><br />This is what I will probably do (next weekend). Mount the toons insulated and run earth straps between the toons and the frame - the frame will be a common earth but I will run earth wires to all electrical appliances/lights etc.<br />Use magnesium anodes underwater on the toons. What about the anode already fitted to the new bigfoot?<br /><br />Any final words of wisdom?<br /><br />Aldo

 

[rodbolt]

Re: Electrolysis in fresh water - Update

hello<br /> yep yopu got it. bond and insulate <br /> and the bigfoot has magnesium anodes avalible <br />and we thought you downunders were still on the evelutionary ladder

 

[Dunaruna]

Re: Electrolysis in fresh water - Update

Eureka! It only took me 2 weeks <br /><br />I have finally realised that insulating prevents "galvanic corrosion" and bonding helps to prevent "electrolysis" . Two different processes with similar visible damage. <br /><br />At first I couldn't understand why I would insulated the toons and then join them with a cable - seemed counterproductive.<br /><br />Thanks guys. You da men (& gals).<br /><br />Aldo

 

[Dunaruna]

Re: Electrolysis in fresh water - Update

Just an update with a couple of pics if anyone is interested. Bit of a delay getting the pontoons built but they are finally done and I'll be fitting them next weekend. <br /><br /> delivery <br /><br /> delivery2 <br /><br /><br />Almost a shame to get um wet <br /><br />Aldo

 

[burp]

Re: Electrolysis in fresh water - Update

Aldo, Those are some BIG pontoons!

 

[18rabbit]

Re: Electrolysis in fresh water - Update

Aldo...you been ripped off! Those aren’t pontoons, they’re grain silos!

 

[Dunaruna]

Re: Electrolysis in fresh water - Update

I must admit that when I saw them they looked bigger than I envisaged, they looked a lot smaller in the drawings <br /><br />Good to carry 18 ton - conservatively.<br /><br />Aldo

 

[BillP]

Re: Electrolysis in fresh water - Update

NICE! You got a project man, but I'm a little worried about having only a 50hp x 4s bigfoot...my 20' pontoon boat has a 50hp x 4s! Take big anchors for when the wind blows.