Welding a steel craft whilst afloat - electrolysis?

Discussion in 'Metal Boat Building' started by LittleVlet, May 6, 2010.

  1. capt littlelegs
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    capt littlelegs New Member

    Yes of course AC, DC is safer but even so appropriate safety recommendations should be followed.

    http://www.lanl.gov/safety/electrical/docs/elec_hazard_awareness_study_guide.pdf
     
  2. CDK
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    CDK retired engineer

    troy2000:
    Of course you wear gloves when welding, if not for the electricity then certainly for the hot sparks. But I was remembered by the sting of a new electrode numerous times whenever I had forgotten to wear gloves.
    You cannot hold a cigar with these thick gloves on.....

    Now that I use a DC welder with argon or CO2 it is more important than ever to wear at least one glove if you have to position the workpiece. It has a 2500 V trigger voltage to start the arc: if the workpiece is not in good contact with the bench, that sting really hurts!
     
  3. capt littlelegs
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    capt littlelegs New Member

    An anology for both an earth wire and an RCD is a parachutists main and reserve shutes. You can get by with just one or the other but who in their right mind would?

    An RCD should in all cases, and as far as practicable, be in addition to the main earth wire, it is not a substitute and only 97% reliable in good conditions.

    Relying on an earth through water is not only instrusive and dangerous to anyone or thing in the water but it is unreliable. Your measurements were not taken by the correct earth loop impedence tester and will change at different locations and there can easily be insufficient current flow to operate the RCD when many in Europe are rated at 30 milliamp. You cannot assume that your readings are good for anywhere else that you moor or any good for anyone else. It is not an earth!

    The current will flow in the path of least resistance to the nearest supply earth point, this can mean through the water not to the ground. It also relies on a poor paint covering and will be affected by other boats nearby properly connected to earth and also affect them. Using the water for your earth is anti-social like dumping sewage, it affects other people. Even small leakages will cause problems.

    3 amps through the water will kill someone outright and if the RCD fails to trip the 3 amps will remain flowing because it is insufficient to blow any fuses. It will also kill anyone steppind aboard the boat the same as if out of the water. An earth wire properly sized will give the least resistance to any fault current and the quickest disconnection time even if the RCD fails to trip.

    You stated that an RCD needs no earth, I think we have established it does!

    If your boat is affected by electrolysis there are a number of steps you can take that are far safer than removing the earth. If your boat is fibreglass or wood there is no need for any problems if you do not connect the onboard earth to the battery neg and the machinery or any under water fittings, there is no point. Neither is there any point in bonding all the different hull fittings as it is just completing the electrolytic circuit.

    A metal boat is different and poses more possible shock problems so it needs to be earthed but here you can disconnect the boat when not occupied or supply through an isolation transformer. A galvanic isolator might work if substantial enough for full fault currents but they are easily bypassed even by slight AC fault currents.
     
  4. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The analogy eludes me. Unless proven otherwise the earth wire may not be a reserve chute but a time bomb.

    There is a 5 mA RCD on board and a mechanical, 30 mA one in the shore power box. Please calculate the statistical chance that both fail simultaneously. I can also advise you to disassemble an RCD and see the powerful spring that tries to pull the contacts apart as soon as the wedge is pulled away by a solenoid. Anything can fail, but this is a safety device, designed not to fail.

    "instrusive" is not part of my vocabulary so I cannot judge that part.
    You have no right to question my figures because you haven't seen the test equipment I used. I think it is safe to assume that an electronics engineer/designer with over 40 service years knows how to measure.

    Of course the resistance will change with the location, but only marginally. There may be slight differences in salinity and depth but these do not change the order of magnitude.
    That's wrong! The current doesn't flow in the path of least resistance but is distributed (1:Reff = 1:R1 + 1:R2....+1:Rn). For the correct representation of current distribution in a conductive liquid I need signs that are not on my keyboard; look it up in your study books.

    The earth electrodes from the power grid also rely only on water only, stone and sand do not conduct. They are impotent midgets compared to a metal hull in the water. A path from the hull to nearest supply earth point exists only if the distance to the hull is much smaller that that to the bottom. And even then, the current conveyed is only fractional.

    The 3 amps apply to my boat, which as I wrote is a poor example because it doesn't have a large conductive area. A metal hull or even a GRP hull with more conventional propulsion would have a much lower resistance so would draw enough current to blow any fuse (with both RCDs bridged). The resistance of a metal hull in seawater beats any earth rod in the power grid.

    We have established no such thing. An RCD functions without an earth wire.

    It is of paramount importance that all metal parts are bonded, not only to reduce corrosion but also to avoid cross-talk between RF sources like radar, depth sounder and VHF radio. Even the RF signals may cause corrosion if there is no central ground.
    Zinc electrodes must also be part of the grounding system; their surface area must be large enough to keep the hull at a positive potential under all circumstances.

    Mercruiser had enormous corrosion problems with their early stern drives until they started to use ground straps between all moving parts. A GRP hull with copperpaint as an anti-fouling conducts almost like a metal one, an untreated hull grows over quickly and also conducts electricity.

    The isolation transformer is a good solution, but impractical for a boat with an electric boiler and a microwave. With just a battery charger you don't need it because the transformer is already installed.

    A galvanic isolator is very useful once it has been established that the marina earthing system does not behave like the cases I've mentioned earlier.
     
  5. capt littlelegs
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    capt littlelegs New Member

    Your comments are becoming so stupid and bizarre as to be quite comical now and not worthy of further comment, you must be living on another planet! I suggest you stick to circuit boards and leave shore supplies well alone and to those that know what they are doing before your anti-social behavior kills someone. Anyone even considering removing the earth wire should consult the regulations for your country and an electrician or electrical engineer for proper advice and remember you are responsible for anyone getting hurt if you make unapproved alterations. I don't propose wasting anymore time with this idiot.
     
  6. CDK
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    CDK retired engineer

    So, Littlelegs, once more you revert to being rude and abusive instead of showing you are able to do conductivity calculations or admitting you lack the education and are only following guidelines without understanding them.

    Your reputation is well deserved.
     
  7. capt littlelegs
    Joined: Apr 2010
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    capt littlelegs New Member

    Anyone interested in the correct procedures for inspecting and testing electrical installations as applicable in the UK and similar in other countries will find the following link very useful although it is now superseded by the 17th edition. You will see it is very comprehensive and thorough requiring some specialised test equipment and not something that a 'know it all' idiot amateur can do with just a simple multimeter and no knowledge of the procedures or even the supply company Ze. :rolleyes: :D

    My real life reputation is pretty good and is what matters to me not revenge rep handed out by expert fools and idiot amateurs on a forum who by their own admission have never done any electrical installation or design themselves but claim to know everything about it! They deserve my comments and really are quite funny, in a sad sort of way! :p :D

    http://www.tlc-direct.co.uk/Book/8.1.1.htm
     
  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    No reasoning, no calculation, just a link to a superseded book and more abusive language, is that the best you can do Littlelegs?

    Here is a quote from your cable-chaser's bible (I bet you never read it):

    "A major consideration here is to ensure that the electrode resistance is not so high that the voltage from earthed metalwork to earth exceeds 50 V."

    And that you have connected to somebody's boat?
    Shame on you!
    You deserve two weeks on water and bread for each time you did that....
     
  9. apex1

    apex1 Guest

    Cornelis,

    is that ******* worth your contribution? He obviously is not noticed by Jeff, Or Jeff has a good reason not to ban him.

    Let it go as it is..............
    dumb ******* is a dumb *******........

    And I disagree with you! He does Not deserve his reputation, he deseverves at least -100 (per posting)

    Regards
    Richard
     
  10. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Richard, see this as an experiment, it was meant that way.
    I was curious about the possibility to influence his opinion by using examples, reasoning and calculation. That was very enlightening.

    If somebody has long ago accepted certain beliefs without truly understanding them, the effects are religion-like. There forms an impenetrable shell around it, so the person ignores all new facts and just lashes out violently while feeling attacked.

    I see exactly the same phenomenon in political debates. You can convince only those who are in doubt, because doubt is a sign of though processes going on. The ones where the thought process has stopped, or never started, just yell and throw mud.

    I tried to stay polite, which wasn't always easy and leave it to other forum members to fire their rep. points.
     
  11. capt littlelegs
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    capt littlelegs New Member

    I never realised some German people could be so funny, keep it up lads. :D :p
     
  12. apex1

    apex1 Guest

    Not the only point you missed. "some people" is plural right?

    Would´nt be gardening a nice hobby for you?:p
     
  13. capt littlelegs
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    capt littlelegs New Member

    Obviously plural but hey you can't even write English properly let alone tell me what I mean! Check your contractions. :rolleyes:

    Gardening? No I prefer to watch the self proclaimed experts wither away, it's much more entertaining. :D

    Anyway, I thought you said I'm not worth a contribution? You must love me really! :)
     
  14. apex1

    apex1 Guest

    Sure I love you! We all do!

    Comments on my English are allowed when you speak at least one foreign language as fluent as I speak several of them!:D
     

  15. capt littlelegs
    Joined: Apr 2010
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    capt littlelegs New Member

    That's nice but quite untrue.

    Fair point, I wouldn't have expected anything less from you but I was really just helping you out on your written English, or do you think I'm wrong about that as well? :)

    Can you speak Welsh?
     
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