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Why do English builders-Princess/Sunseeker install 2 large zincs right on the hull bottom?

Discussion in 'Props, Shafts & Seals' started by Capt J, Mar 30, 2020.

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  1. bayoubud

    bayoubud Senior Member

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    We have four zinc plates on the transom with shaft and rudder zincs. Last summer our diver said our zincs were inactive. Our electrician took readings and determined we were over zinced. We pulled the shaft zincs and saw some activity. Just was in the boat yard and left the shaft zincs off and plan to monitor, may need to remove rudder zincs too? Our dock is not near another dock with a in the water boat. Never experienced having to remove zincs.
  2. olderboater

    olderboater Senior Member

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    I still think it's likely a MAN thing as they are the predominant engine in the boats mentioned and so think likely designed for them, then used also for the CAT's.
  3. Capt J

    Capt J Senior Member

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    It's neither. These are the only zincs for the entire vessel (aside from swim plaforms which only zinc the platform). So the entire vessels bonding system is tied to these 2 transom zincs which they decided to mount on the hull bottom instead of on the transom. Perhaps it is a MAN thing where the zincs have to be submerged all of the time, and that's where they mounted them and just use that spot for all engines.
  4. olderboater

    olderboater Senior Member

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    That's exactly what I said. Designed for MAN, so just used for all. It's like when Sunseeker uses IPS and they get none of the space benefit.
  5. PacBlue

    PacBlue Senior Member

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    How can it be an engine thing when the engine is inside the boat and the shafts, struts, propellers are outside? What is the zinc sacrificing to ? Bonding systems and sacrificial zincs are two different things.

    Like to see a MAN spec that requires it?
  6. cleanslate

    cleanslate Senior Member

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    Can't electrolysis travel up through the shafts to the engine and/ or seawater through the raw water intake into the engine , especially if there is always a solid fill of raw sea water from the intake into the motor?
    . I always thought that would make a good path for electrolysis to follow and get into the motor and cause problems. I guess it added extra protection for the motors. I assume they have pencils links within the engine at critical spots.

    I know for a fact mile Detroit diesels are connected to the bonding system that was done by ocean yachts back in 1981....Uhm they are connected to the old bronze grounding tubes. Not the zincs.

    Seems to me big whopper zincs are doing all the work on the sun seekers I assume they have no grounding plate for other things such as the motors.

    I have the old Drag-O- tubes; Sun Seaker has the new Drag-O-Mongo Zincs!
  7. PacBlue

    PacBlue Senior Member

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    The engine is usually isolated by the transmission fluid or a viscous coupling. Your Detroit blocks are part of the boats Ground System connected by bonding all the metal components you can under reason or requirements. Not all engine makers recommend this connection for their own reasons.

    But metal wear is different and simply put depends on different metals coming in contact through an electrolytic medium. Modern engines have titanium heat exchanger plates, stainless, copper nickel, cast iron and other metal parts connected to bronze fittings by raw cooling water , but those are not being wear protected by two zincs in the stern underwater imo because of where the raw cooling water exits the system.

    Hear is a brief read for starters: https://www.proboat.com/2015/04/the-mysteries-of-bonding-systems-revealed/
  8. bayoubud

    bayoubud Senior Member

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    Years back my Man mechanic told me their engines had isolated grounds. Nothing electrical grounds to the engine block. Everything in sea water is connected to the bonding system and transom zincs. The shafts and rudders need zincs if not connected to the bonding system.
  9. cleanslate

    cleanslate Senior Member

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    Oh boy now I'm more confused than ever ! Lol..
    Just kidding , thanks for the read. I will have to read it just a few more times to get it through my thick tired skull. Lol.
  10. mapism

    mapism Member

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    PB, to my knowledge, MAN engines always relied on a bonding to large external zincs also for the protection of the internal components which must go in contact with raw water, and which don't have any specific zincs.
    That's a different approach vs. say Cat engines (at least traditionally - not sure about the latest common rail like the 12.9 that CaptJ mentioned), which rely on specific, engine-mounted anodes.

    Ref. MAN specs, below you can see the relevant page of an installation manual.
    With a disclaimer: this is pretty old, meant for their pre-common rail engines - cue: Morse control cables.
    But interestingly, while looking for this page among my old files in order to (hopefully) clarify your doubt, I only just noticed that in their drawing, awful as it is, the shape and placement of the external zinc reminds the one in the Princess 62 photo.
    On the other hand, I'm pretty sure that most if not all yards who adopted mechanical MAN engines used to fit transom anodes, like the one which you can (barely) see in the second photo, in between the trim tabs plates.
    And I'm equally sure that MAN never argued with any boatyard against that solution, which aside from being equally effective at rest and at low speed, is undoubtedly more hydrodynamic, though as I said I wouldn't be concerned by the other alternative. Surely not in a 30 something kts boat, anyway.

    Now, this is as far as I can go with facts.
    But all considered, bearing in mind also what I already mentioned about CR engines using components with several dissimilar metals, I believe it's reasonable to assume that in recent years MAN became more strict about the placement of engines-relevant anodes in a position where they can be effective also at planing speed.
    I would just be curious to understand if the same principle applies also to the latest CR Cat engines, regardless of the fact that they are actually designed and built by FPT, or if it's just a matter of standardizing the production of boats available with different engines.
    If nobody knows better, there is a very good engines specialist at the yard where my boat is stuck at the moment who probably knows the answer. Hoping that the conditions for releasing this lockdown thing will materialize, possibly sooner rather than later...

    [​IMG]

    [​IMG]
  11. Capt J

    Capt J Senior Member

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    None of the MAN's have zincs, they usually separate the metals with saltwater in them via O-rings or other non metallic materials. Maybe the new MAN's require the zincs like that, because there are always 2 of them and they're mounted in close proximity to each engine...….
  12. mapism

    mapism Member

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    Waddumean none of the MAN's have zincs? Engine mounted, yep, they sure don't, as I said.
    But the external zincs bonded to the engines internally have been a strict MAN requirement for more years than I can remember.
    Surely more than a quarter of a century, anyway.

    PS: in other words, the only doubt/assumption is about whether they recently became more strict on a placement under the hull rather than on the transom. But the principle of engine-bonded zinc as such, that certainly ain't breaking news.
    Last edited: Mar 31, 2020
  13. Capt J

    Capt J Senior Member

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    The MAN engines themselves do not have zincs, internally and never have.
  14. mapism

    mapism Member

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    Ok, so we are saying exactly the same thing.
    But don't be mistaken (they usually separate the metals with saltwater in them via O-rings or other non metallic materials):

    The reason why they can do without internal zincs is that they are bonded to the external one, not because they have O-R or whatever separating the components inside them.
    Just as one example, the heat exchanger box is made of aluminum, while the tube bundle inside it is bronze.
    You might have seen its side round cover open, which is necessary for cleaning them.
    And there is indeed a very large O-R pressed by that cover.
    But that's meant to keep the cooling liquid separate from raw water, and does absolutely nothing to avoid the contact between the two metals, which for all intent and purposes are 100% electrically connected.
  15. bayoubud

    bayoubud Senior Member

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    Because of the isolated ground and the engine bonded to the zincs. Older Mans had cupronickel he's and coolers which lasted a longtime. Had an old pair of Man v12's that were setup that way. Don't think you should bond an engine used as DC ground to the transom zinc's.
  16. mapism

    mapism Member

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    Correct.
    In fact, in the previous (awful) drawing, you can see also the dedicated starting battery.
    And the domestic grounding should be separate from the powerplant.
    But I'm saying "should" purposedly, because in practice I've very rarely seen a MAN powered boat whose engines weren't (one way or another, it could be almost impossible to understand how) also grounded to the rest of the DC circuit.

    As an aside, I've never seen a MAN engine whose HE external box wasn't made of aluminum.
    Including the 1991 D2842LZE powered boat from where I'm writing.
    But yes, the tube bundle is very solid.
    I actually believe it's bronze rather than CuNi, but very good stuff anyway, as for the aftercooler.
  17. PacBlue

    PacBlue Senior Member

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    All the connections are of piping systems, no mention of engine
    /block to the bonding system? Just portions from the raw water side feeding the engine cooling side, pretty standard stuff.
  18. mapism

    mapism Member

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    Actually J, the diagram does show that also the engine must be bonded - see below.
    And trust me, bonded they always are for good, also in practice.
    Don't ask me why they show connections for BOTH the block and the gearbox, though.
    As if they weren't bolted together...?!?
    Must be the German way of applying the better safe than sorry principle, I guess! :)
    [​IMG]
  19. PacBlue

    PacBlue Senior Member

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    So this is how Industry will read the diagram:

    MAN has gone to the trouble of identifying 12 items that need to be "earthed":

    1. Copper Bonding Strap
    2. Zinc Anodes
    3. Propeller Shaft thru a Shaft Wiper
    4. Exhaust Gas Pipe if using Sea Water Injection in the Exhaust System (a wet Exhaust)
    5. Exhaust Pipe (kind of confusing for FRP Exhaust Pipe, most won't do this)
    6. Morse Control Cables - Throttles
    7. Morse Control Cables - Clutches
    8. Pipe Connections between Raw Sea Water Pump
    9. and Sea Water Filter/Strainer
    10. and Sea Water Shut-off Valve (Seacock)
    11. and Sea Water Thru-Hull
    12. and Steel Tank (fuel)

    Not one specific mention of Engine or Gear, so the weak lines in the diagrams are not hard/fast requirements but appear to be only suggestions unless specifically called out by the Manufacturer.

    Not all items listed are required for a bonding system, for instance, we never tied aluminum fuel tanks to the bonding system. By doing this, there is no chance for stray current to find a path to the tank and create an issue. Same goes for an engine or gear, if it is not a stone cold requirement, it doesn't have to be part of the "earth' system.
  20. mapism

    mapism Member

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    If that's how Industry would read the diagram, well, "Industry" would be wrong.
    In fact, the connections which I highlighted in the previous post belong to those that the manual describes as "indicated in bold print", and nothing in that page is qualified as a suggestion.
    Let me guess J, you are not very used to deal with Germans, are you? ;)

    No worries, anyway.
    Everybody involved in the installation of MAN engines can access the whole installation manual of course, not just to the page I previously posted.
    So, hopefully they will have read also the page below, before reaching the previous one (the red underline is mine, obviously).

    All that said, I'm frankly a bit surprised that this thing of MAN engines bonded to an external hull zinc seems to be not well known/understood in this forum, considering the otherwise pretty high expertise level.
    This is in fact widely known in Europe even among owners of MAN powered boats, let alone yards (including non-official MAN services).
    If I may give a suggestion, aside from obviously replacing any worn out anodes, in MAN powered boats it's worth including in periodical maintenance also an engine bonding check.

    [​IMG]