Electrolysis

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    Posted: 30 May 2007 at 9:09am
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I know its probably been covered before but....

Have almost finished assembling a 4M alloy pontoon boat. I used polyprop bushes and a piece of vibra stop pad to isolate the motor. I also isolated the steering and remotes from the hull. Using a multimeter there is no conductance between the motor, or any cable components/steering components and the hull.

All stainless bolts used to fit other components, seats, electronics brackets etc have been isolated from the alloy using bushes/shrink wrap/plastic washers  (I'm a fussy  bugger). All alloy joins that are not full-length welded will be siliconed.

Anyhow I was surprised to read on the vibra stop website that they recommended fitting an earth strap between the motor and the hull to avoid electrolysis?

What precautions or measures are people taking to avoid electrolysis in tin boats?

Also when pressure testing pontoons and a sealed floor how many psi do you use? Do you just paint some soap suds over all the welds to check for leaks?

Cheers in Advance
Lurch
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Post Options Post Options   Likes (0) Likes(0)   Quote bustedoff Quote  Post ReplyReply Direct Link To This Post Posted: 31 May 2007 at 6:42pm
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Don't you need the different metal parts to be all at the same electrical potential? I think this will stop the battery effect (electrolysis). On aircraft they do it by earthing all metal parts to the main frame.
 
Pressure testing, I reckon about 4 psi?
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Post Options Post Options   Likes (0) Likes(0)   Quote Rockhopper Quote  Post ReplyReply Direct Link To This Post Posted: 31 May 2007 at 9:49pm
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Electroysis will occur when two dissimilar metals ( in your question ali in your boat and ali/steel of the motor) are both placed in an electrolyte (conducts electricty for the sake of argument) which in this case is salt water.
One of the metals will be more "positive" than the other and will turn to a salt under the right conditions.
The trick is to make the metal that disolves not your expensive outboard so people add zinc which are way more "positive" electrical current flows then flows from the zinc , dissolving it in the process.
 
By electrically straping it all together the electrical difference between boat and motor is removed. You have not completely removed the problem as seawater itself is a path to earth (or seabed) , the zincs will still do the same job but now the whole boat is covered.
Why does the answer to all government problems involve taking more of my money ?
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Post Options Post Options   Likes (0) Likes(0)   Quote Rockhopper Quote  Post ReplyReply Direct Link To This Post Posted: 31 May 2007 at 9:53pm
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As an aside, is a pontoon boat more bouyant if the pontoons under pressure ???
Why does the answer to all government problems involve taking more of my money ?
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeP Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jun 2007 at 11:19pm
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Originally posted by Rockhopper Rockhopper wrote:

As an aside, is a pontoon boat more bouyant if the pontoons under pressure ???
 
The opposite would be true.  More bouyant if they contained a vacuum.  However this would not be so smart as you wouldd need them to be much stronger (thus heavier) in order to withstand the vacuum, and if they developed a leak below the waterline they would suck in the seawater.
 
Regards,
Mike P
"Sumfin Fishy"
Lotus 1900 (19 ft) with 135HP Mercury O/B
"My greatest fear is that, when I die, my wife will sell all my toys for what I said I paid for them".
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Post Options Post Options   Likes (0) Likes(0)   Quote Almo1960 Quote  Post ReplyReply Direct Link To This Post Posted: 20 Apr 2023 at 2:30pm
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I’m wondering if someone can shed some light on this.
I have a small modern aluminium boat fitted with a Yamaha F50. When I put a multi tester between the boat & trailer I get a voltage reading of 0.17volts. Disconnect the battery and it’s still there. (Safety chain off)
Remove battery and connect tester to positive lead & boat, same reading.
Disconnect everything from distribution post, same reading.
Connect tester between negative battery terminal with battery leads connected 0.00 volts. Have I got an issue or is this small voltage (0.17 volts) acceptable? Could such a low voltage be caused by the 30 odd stainless screws holding various things in place?
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