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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. Capt J

    Capt J Senior Member

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    All of the late model Princess' and Sunseekers I've seen in the last few years have these giant zincs (usually 2) mounted right on the running surface, rather than on the transom. I get that transom zincs are generally out of the water when running on plane. But, it seems these 2 giant zincs would slow the boat down .5-1 knots.
  2. AMG

    AMG YF Moderator

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    Could it be the ground plates..?

    Dyna Plate 4006_2.jpg
  3. PacBlue

    PacBlue Senior Member

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    When you are on plane for extended amounts of time, the transom zinc is dry and offers no protection to your underwater running gear.
  4. Capt J

    Capt J Senior Member

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    I understand that. But you're only on plane a smidgeon of the time and how much electrolysis could you possibly have on generator for a day? These are giant transom zincs that are over 2" thick and 2 of them mounted right on the running surface near the stern. Not Hydrodynamic at all. Azimut does the same but therea are recessed into the bottom of the hull.
  5. PacBlue

    PacBlue Senior Member

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    All zincs are “insurance” many paths for stray currents, AC or DC, just depends on how much “insurance” you want to carry.
  6. NYCAP123

    NYCAP123 Senior Member

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    To my thinking the number, location and size of anodes is fairly complex math and engineering. An engineer undoubtedly found a need based on the machinery, but that's not to say they had an N.A. involved in the decision. (Left hand not talking with the right.) I wonder if you couldn't get away with shaving down the leading edge. You may have to replace them more often, but as long as they cover the area I don't see a problem. To buy anodes perfect for the boat could mean special order or changing the hull design, neither of which is likely.
  7. Capt Ralph

    Capt Ralph Senior Member

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    When your on plane, I doubt anything is close enough to share any stray DCv currents.
  8. mapism

    mapism Senior Member

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    Do you possibly remember if the boats where you noticed that were all powered with engines of the same manufacturer?
    I can't remember the type of giant anodes you are talking about (any photo?), but I have a funny feeling that those boatbuilders might have gone that route just to comply with a powerplant requirement.
  9. PacBlue

    PacBlue Senior Member

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    Your shaft wipers are tied to your bonding system, therefore everything below the waterline is susceptible.
  10. Capt J

    Capt J Senior Member

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    It's more than 2 boats. No, Man's and Cat's. They''re the only 2 zincs on the entire boat, aside from bow thruster. I'll try to find a picture and post it.
  11. Capt J

    Capt J Senior Member

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    Yes, they are. However, how much zinc protection do you need on plane? You're away from any marina and any other boat and you have billions of gallons of water passing underneath you? At slow speeds maneuvering around a marina etc., the zinc is submerged. A vessel is only on plane (a Yacht) maybe 0.01% of it's life. I have seen thousands and thousands of boat models and boats, where they only have transom zincs that are out of the water on plane and have never seen any electrolysis issues. Just from memory, Cabo, Hatteras, Vikings sportfish (and many others) all only have transom zincs......
  12. Capt J

    Capt J Senior Member

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    There are always two zincs. Tell me this giant zinc hanging down doesn’t slow the vessel down on plane?
    24AA0F30-A4BE-486E-82EB-195B75B20D85.jpeg
  13. PacBlue

    PacBlue Senior Member

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    It is an engineering choice. Transom Only, Bottom Only, or a combination thereof.

    By putting it on the bottom, they get full function on or off plane. As far as any loss in speed, that is pretty much negligible, especially under 40 - 50 knots.
  14. NYCAP123

    NYCAP123 Senior Member

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    From your description I pictured them near the transom and across. I agree with PacBlue that any loss of speed from those would be negligible and they may even assist stability. I am surprised to not see anodes on the shafts and rudders though.
  15. Capt J

    Capt J Senior Member

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    Rudders and shafts are all tied into those zincs via the bonding wires, so no need to bond them individually.
  16. PacBlue

    PacBlue Senior Member

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    That is the key, no rudder zincs, no shaft zinc collars visible. So the only sacrificial zincs are the two port and stbd zincs located on the bottom. I believe other manufacturers using transom zincs have separate zincs on rudders, shafts, struts, etc.
  17. mapism

    mapism Senior Member

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    I also agree with PB that speed loss can't even be measurable, also because judging from the props and the semi-tunnels that doesn't certainly look like a speed demon of a boat.
    Anyway, the position of that anode confirms my suspicion that the placement has something to see with the engines, because nobody in his right mind would place anodes in that position for protecting the u/w gear only, even if bonded inside.
    MAN was in fact my guess when I asked, because they don't rely on internal anodes, and I was told recently by one of their engineers that the latest common rail engines have many dissimilar metal components.
    Much more so than in the past, in fact - to the point of changing also the specs of the cooling fluid just for that reason.
    Couple that with the fact that electrical potential increases with the water flowing vs. static, and one could guess that MAN is specifically asking boatbuilders to fit anodes under the hull rather than on the transom.
    I'm a bit surprised to hear that you have seen the same solution on Cat powered boats, though.
    Did they possibly abandon internal anodes, in their latest engines? I might well have lost track of that.
    Alternatively, it could be also that boatbuilders are standardizing the anodes placement, even if driven by MAN requirements, to any boat where they offer also the choice of different engines, along the lines of why bother differentiating?
    Anyhow, as I said, I'm just guessing.
  18. Capt J

    Capt J Senior Member

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    The boat in the Picture is a 2018 62' Princess with Cat C 12.9's (but that is a Fiat/Ivesco motor). Their 55' and 62' with Mans also have the same anode position and only other anodes are on the swim platform. A 2019 66' Sunseeker with 1200 MAN's is the same way except those are mounted right in the center between the props. Everything in the boat is bonded to these 2 anodes from both manufacturers, except the swim platforms have zincs.

    The 62's top out at 32 knots +/- and the 66' around the same speed.
  19. YachtForums

    YachtForums Administrator

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    I've got a little experience with drag related parasites, but I don't want to discuss old girlfriends. Obviously the small zincs would have no effect on speed based on their location on a planing hull. The large zinc (assuming there is one on both port and stbd hull bottom) would likely result in a measurable loss of speed, albeit negligible. As PB stated, under 40 knots would be barely discernible, but bump that number up and the speed loss will become more pronounced.
  20. PacBlue

    PacBlue Senior Member

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    Would venture to say the loss of speed issue is less of a concern when they are fitted with stabilizers like this 2019 57' Sunseeker Predator:

    upload_2020-3-31_13-19-51.png