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Island Time

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Posts posted by Island Time

  1. 2 hours ago, Fish said:

    Errr, you've not been to Westhaven lately ay? the whole new promenade is made of a steel structure, with steel piles into what ever is beneath it, a fair bit being seawater and sedimentary sludge's etc.

    I'm pleased you also question this, as its been bugging me ever since they built it, how you can put steel in sludge and not have a problem. Thought I just didn't know what I was talking about.

    Some of those posh new houses just across from you IT have steel piles in the reclaimed GH sludge. 15 m deep, went in like a hot knife through butter. All the digger had to do was hold the I beam up, and in it slipped... They are tied into the concrete floor pad for the house. Which all sounds well and good, but you'd never guess how they get an earth spike in for the electrical supply of those houses.... Tied into the reho of the floor slab. Apparently the building code only requires 50 yrs durability for these things, including piles and floor slabs?

    Have been to Westhaven, just busy with work and did not pay much attention to it.  Sounds like a right shambles!

  2. Yep, knew about the ones in  GH. Still dumb, imo, but they are not directly in the water. Possibly not quite so dumb. Time will tell.

    Theoretically, if the steel bits are all connected, they have the same potential, but immersion in anything acidic at multiple points is asking for trouble. Yes, I know two types of metal and acid make a battery, but guess what - the earth wire is copper....

    Directly in sea water, which is slightly acidic, is a recipe for disaster. 

  3. Got any pics of the new structure KM? Surely they were not stupid enough to have exposed metal in the sludge? This is why wharf piles are timber, or special concrete and prep to ensure the reinforcing is protected from the liquids. Two exposed metal pylons could indeed form a battery, and if your boat is between them, or nearly so, it could be part of a circuit.

    The boat must have two exposed bits of metal, or something long and conductive. The pitted area is where the current leaves the boat.  There must be an entry point, maybe rudder pintles or shaft? 

    I do understand that in some circumstances damp timber can conduct as well,  but don't know much about that.

  4. OK, Yep that is uncommon.

    How about a bonding system? Metal thru Hulls?

    I'm thinking that the boat might offer less resistance than the water, and a stray current might by running thru it as part of a circuit.... If the centreboard is pitted, then that's the exit point. There must be an entry point somewhere. Current can't flow without a circuit. 

    So, does the corrosion occur at coating imperfections, and have a dimple in the center - like this;


    This is an example of AC corrosion - Ive never seen a boat suffer from that, but this is an unusual case. Really requires a corrosion specialist (not me!!) to identify, but it would be good to understand the mechanism once it is found.

    Most boat issues are DC.

  5. 2 hours ago, KM... said:

    The boat is 108 years old, she was perfectly fine in October, not a single thing has been changed on the boat since before then. There has never ever been any item of any form that connects her to Westhaven bar 3 mooring ropes and the water. The 3 mooring ropes are connected to fittings both ends that terminate in wood, it has not changed for at least a decade possibly closer to a century.

    But Westhaven HAS changed a LOT, all within metres of her, since Oct last year.

    To suggest the boat has very suddenly decided to change 107 of history at the exact same time the environment she lives in had some very large dramatic changes defies logic.

    Well, if the boat has no other connection to the dock, the marina is not at fault. The most common issue I find doing corrosion surveys is a bilge pump with failed insulation, standing in bilge water. To say nothing has changed is stretching it a bit. Things corrode, insulation fails, sometimes circuits are left powered on, or switches/circuit breakers fail. Shorts etc happen. All these things are fine until they are not.

    The easy path is to blame the marina - which almost all owners try to do. Remember than stray current corrosion is really a DC phenomenon  - the reason that the AC ground matters is because it is connected to the boat DC. Whatever you think, you can't change physics. If the boat is isolated from the dock electrically, the issue is on the boat.

    Anyway, don't guess. Use a ref electrode, and measure. It's normally not too hard to find.

  6. 56 minutes ago, CarpeDiem said:

    Can you get stray current corrosion from other boats if you're not connected to shore power and don't have a DC system?

    Or are you saying that if you're not connected to Shore power then any stray current corrosion is due to your DC system.

    I understood that you had to be either connected to the shore power, and/OR have a faulty DC system...

    No, because you are not connected to them with a circuit. The only common path is the water.

  7. Corrosion;

    OK, let me make this real clear. For a boat to be damaged by corrosion it has to be part of a circuit. That circuit can be via the water, and out of and back into  (via the water) different bits of immersed metal on the boat. The least noble bit of metal will corrode. That's why anodes are sacrificial anodes, so nothing important is trashed.

    You are electrically linked to all other boats on the dock (thru the water), and to the dock itself if it has metal immersed. That is one arm of a potential circuit. The other common arm, completing the circuit, is often the shore power cable earth, hence causing issues when plugged in. This is not necessarily a problem on the dock, but it can be.

    If you have no shore power lead, or are protected with a working galvanic isolator or isolating transformer, and you still have corrosion issues, the problem is on your boat as  there is only one connection to the shore (the water), not a circuit.

  8. 41 minutes ago, KM... said:

    Just got back from the job of fixing the result of Westhavens latest free bonus for it's berth holders, rampant and very aggressive electrolysis.

    Hmm, electrolysis. Beware of anyone who uses that term! It's either stray current corrosion, or Galvanic Corrosion. There are big and important differences.

    In a marina the size of Westhaven, there WILL be multiple boats leaking electricity into the water. Mostly it will be DC, but although the DC is the issue for corrosion, the AC is worse because it can kill.  Read up on electric shock drownings if you wish.

    Of course all electricity requires a circuit to do anything.  This is why you need a galvanic isolator or isolating transformer on your boat, so your neighbor's crap boat does not use up your zincs, then eat your underwater metals. Either isolator  blocks the circuit to the mains earth so that you are not part of the circuit shared with other boats thru the shore power lead. The safety earth still works. 

    Cheap insurance, and can pay for themselves in zinc savings. Stray current corrosion is what can rapidly remove your underwater metals. Galvanic corrosion is slow.

    True "Hot Marinas" are very rare in NZ, almost always an issue on a boat is from that boat.....



  9. Yes, but I knew it was somewhere. As the standard does not explicitly say it IS retrospective, it is not;


    For those who dont want to follow the link, but are interested, here is the basic stuff.


    Fundamental constitutional principles and values of New Zealand law

    This is a single section from Chapter 4. Read the full chapter here.

    PART 7

    The presumption against retrospectivity

    Legislation should not affect existing rights and should not criminalise or punish conduct that was not punishable at the time it was committed.

    This presumption is part of the rule of law. The general rule is that legislation should have prospective, not retrospective, effect (Chapter 12 provides guidance on legislation that has a retrospective effect).


    SO, if your gas man or electrical inspector is insisting on changing something that is safe, just old, and not compliant with current regs, find another inspector! Or quote them this....

  10. 14 hours ago, marinheiro said:

    reminds me to read the text rather than just the file name of my extract 😄

    OK, any idea where in the electrical regs the same statement (or similar) is made? I've been looking for it....


  11. Agreed MH, it's a RORT!

    But it's section 1.5;

    The requirements of this Standard shall be used in conjunction with, but do not take
    precedence over, statutory regulations that may apply in any area. Where no requirement is
    given, good practice shall apply. In a matter of uncertainty, advice should be sought. This
    Standard applies to new installations, alterations and extensions commenced after its
    publication date or the date of adoption by the relevant Technical Regulator. It does not
    apply retrospectively to existing installations
    but any repairs or modifications to existing
    installations shall comply with the requirements of this Standard.

  12. It can track thru ply a long way. Ideally you need to cut it out as far as it is wet/rotten/soft. Then it must dry before repair. You need a moisture meter to test when it's dry enough, and it can take a long time to properly dry. You can buy a moisture meter (stanley) from bunnings for a reasonable price if you can't borrow one.

    This is why fixings in or on ply hulls should be drilled oversize, filled with epoxy, cured, then drilled to suit fittings. But usually they are not.....

  13. Just to be pedantic.

    Be careful of the "chopping board" solution. Some use them for backing fittings, and they often slowly migrate from the load. depends what they are made from. There are plastics that can do this, semi crystalline engineering thermoplastics, but you need the right one. 

    You'd probably get away with it though!

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