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Thread: Delignification around propeller stern tube in shaft log

  1. #36
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    Default Re: Delignification around propeller stern tube in shaft log

    I'm pretty sure I have the same issue happening around the rudder tube in Petrel. And Skookum Maru had her horn timber completely replaced a few years back. Now I'm wondering whether that repair was due to similar problems. Judging from the comments here I expect she's over-zinced...



    That's not counting the hefty zinc on the rudder which is not visible in the photo. She's also fastened with galvanized screws, and we refastened with the same, but there is not much I can do about that.

  2. #37
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    Default Re: Delignification around propeller stern tube in shaft log

    No one has mentioned bonding in this discussion.
    There is very good evidence that bonding between metal components on or in the hull cam also contribute to delignification.
    The Cheoy Lee has evidence of bonding on the outside of the hull - what has it inside?
    Is the Petrel bonded internally?
    Remove the bonding if you want t sort out this problem for ever.

  3. #38
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    Default Re: Delignification around propeller stern tube in shaft log

    I mentioned bonding in post 3 . The first reply .

  4. #39
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    Default Re: Delignification around propeller stern tube in shaft log

    I don't think this is a "fix" but seems to be an improvement at least - I had been monitoring a few areas around fasteners that grew that alarming white fuzzy stuff. About a month ago I installed a 'galvanic isolator' and the fuzzy stuff has stopped. Or been reduced so much that I don't see it anymore, at least.

    It's wood, it's going to decay. But I'll be a lot happier if that takes another thirty years

    op, go to the rotdoctor site and look at the photos of their horn timber. Freddy Krueger nightmares in wood

  5. #40
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    Default Re: Delignification around propeller stern tube in shaft log

    Not to drift the thread too far from the OP's question, but neither Petrel nor Skookum Maru is bonded. However I'm not sure how much that helps. Both boats:

    - Have stainless propeller and rudder shafts, steel rudders and steel bottom plates supporting the rudder, bronze propellors and shaft logs, and zinc anodes all in proximity or actually in contact with each other.

    - Contain a combination of bronze, iron and galvanized fastenings below the water line (!)

    - Use the engine block as the negative ground for the starter motor and all engine senders. Since the prop shaft can carry current to the gear housing and then to the engine block, effectively this setup ties most of the metal in the boat together through the DC electrical system. (This is the first thing I'm planning to change).

    I don't think it's much of an exaggeration to say that they are basically huge batteries surrounded by wood, and the wood will lose out eventually for all the reasons that Chris M. has outlined in detail here and elsewhere. I am planning to do what I can to improve things by following as many of his recommendations as possible. There is nothing I can do about the ferrous fasteners but I take some comfort in knowing that Skookum Maru went for 50+ years on her original iron nails before she needed to be refastened, so she should be ok in that area for the next few decades at least.

  6. #41
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by cstevens View Post
    - Use the engine block as the negative ground ...
    This just came in today .... it's not as sexy as putting the ground on a solenoid but simple and pretty fool proof (I need that )
    Attached Images Attached Images

  7. #42
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    Default Re: Delignification around propeller stern tube in shaft log

    You gonna put that on a boat ?

  8. #43
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by wizbang 13 View Post
    You gonna put that on a boat ?
    Good point. While working on marine electrical systems we were looking at plating buss bars to keep them from corroding which causes high contact resistance. While heavy high phos electroless nickel wasn't the best on a new contact, it was the best after a month or so. You might be able to protect the switch contacts with No-al-0x an aluminum filled contact protection grease. post #4 of 18
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  9. #44
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    Default Re: Delignification around propeller stern tube in shaft log

    Why not use a marine battery on/off switch? Just got a 600 Amp one from Hamilton for $30US.
    "If it ain't broke, you're not trying." - Red Green

  10. #45
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    Default Re: Delignification around propeller stern tube in shaft log

    The goal for Favorite's switch is to isolate the engine from the DC ground. My plan for that same requirement has been to install one of these on the ground cable to the engine:



    https://www.bluesea.com/products/901...12_24V_DC_250A

    and wire it to the engine start switch so the only time the engine block is connected to DC wiring at all is when the starter is being cranked.

  11. #46
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by cstevens View Post
    The goal for Favorite's switch is to isolate the engine from the DC ground. My plan for that same requirement has been to install one of these on the ground cable to the engine:



    https://www.bluesea.com/products/901...12_24V_DC_250A

    and wire it to the engine start switch so the only time the engine block is connected to DC wiring at all is when the starter is being cranked.
    Hi Chris -

    1) Why? & 2) what happens with the alternator & no ground? How does it charge the batteries?
    "If it ain't broke, you're not trying." - Red Green

  12. #47
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by Garret View Post
    Hi Chris -

    1) Why? & 2) what happens with the alternator & no ground? How does it charge the batteries?

    1. Because, as I understand what Chris M. has outlined in other posts, the connection between the engine block and the DC ground has the potential to include all of the big metal bits in the boat in an electrical circuit, which is one of the factors that causes deterioration of the wood.

    2. Good question: The full project also includes running dedicated ground wires for every component that would normally be grounded to the engine. One-wire senders need to be replaced with ungrounded two-wire senders, for example. But I'll confess that I have not sourced all of the necessary the components so I don't know if it's possible to completely isolate a Detroit 3-71 from DC ground.

  13. #48
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by cstevens View Post
    1. Because, as I understand what Chris M. has outlined in other posts, the connection between the engine block and the DC ground has the potential to include all of the big metal bits in the boat in an electrical circuit, which is one of the factors that causes deterioration of the wood.

    2. Good question: The full project also includes running dedicated ground wires for every component that would normally be grounded to the engine. One-wire senders need to be replaced with ungrounded two-wire senders, for example. But I'll confess that I have not sourced all of the necessary the components so I don't know if it's possible to completely isolate a Detroit 3-71 from DC ground.
    Wow - that sounds like a ton of work. I built a kit car years ago that had to have 2 wires run to everything (fiberglass body). The term PITA leaps to mind...

    My boat has had a grounded engine since 1941. I think I'll leave it that way...
    "If it ain't broke, you're not trying." - Red Green

  14. #49
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by wizbang 13 View Post
    You gonna put that on a boat ?
    Yes, I am. It's simple. Nothing to break, nothing to fail. The worst it can do is get a bit corroded and need a bit of polishing occasionally. It's a diesel. The only time it needs electric is when starting/running (for the accessories).

    Maybe eventually the engine will get an air start.

    @Chris, concerning gages and alternator, I figured disconnect the engine ground when not running it, but leave it connected in use. The ratio of hours running to hours delignifying is pretty low
    Last edited by Favorite; 03-13-2019 at 06:13 PM.

  15. #50
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by Garret View Post
    Wow - that sounds like a ton of work. I built a kit car years ago that had to have 2 wires run to everything (fiberglass body). The term PITA leaps to mind...

    My boat has had a grounded engine since 1941. I think I'll leave it that way...
    Well, yes - but to be fair there are a lot fewer things that need to be individually grounded on a Detroit Diesel than on a car. Alternator, starter, maybe four or five senders. There just aren't that many wires going to it.

    Quote Originally Posted by Favorite View Post
    Yes, I am. It's simple. Nothing to break, nothing to fail. The worst it can do is get a bit corroded and need a bit of polishing occasionally. It's a diesel. The only time it needs electric is when starting/running (for the accessories).

    Maybe eventually the engine will get an air start.

    @Chris, concerning gages and alternator, I figured disconnect the engine ground when not running it, but leave it connected in use. The ratio of hours running to hours delignifying is pretty low
    That's a good point too. Certainly a lot easier that way.

  16. #51
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by cstevens View Post
    Well, yes - but to be fair there are a lot fewer things that need to be individually grounded on a Detroit Diesel than on a car. Alternator, starter, maybe four or five senders. There just aren't that many wires going to it.



    That's a good point too. Certainly a lot easier that way.
    Most all sensors on engines I've seen ground through the block. How to you ground them without grounding the engine?

    I feel like I'm really missing something here.
    "If it ain't broke, you're not trying." - Red Green

  17. #52
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    Default Re: Delignification around propeller stern tube in shaft log

    Quote Originally Posted by Garret View Post
    Most all sensors on engines I've seen ground through the block. How to you ground them without grounding the engine?

    I feel like I'm really missing something here.
    I haven't done all of the legwork to answer that with specific components. I'm going off a list of recommendations that Chris McMullen posted here:

    https://waitematawoodys.com/2015/05/...f-leaky-homes/

    Specifically:

    Some hints to eliminate DC Voltage Leaks in Boats.


    1. Insulate the negative connection from the frame, on alternators, generators and anchor windless motors.


    2. Use two pole senders on the engine alarms.


    3. Install a solenoid on the starter motor negative so it is only connected as the engine is started.


    4. Battery switch’s can leak. Have a second switch on the negative.


    5. Be sure your bilge pump is wired correctly and in good order.


    6. Use an insulated gearbox to shaft coupling.


    7. A Furuno depth sounder is two wire but the bronze housing (like an alternator) connected to the negative! Sleeve it with plastic so there is no connection to the wood. Leave it, and it is unintentionally bonded and you have a circuit.


    8. If you have shore power, use an isolating transformer.


    9. If you still must bond for safety purposes? Well, accept the fact you have made a circuit and face the consequences, maybe you should not have a caulked wet wooden boat!
    I found his arguments in that article and also on this thread compelling so I have been intending to apply those recommendations to Petrel and Skookum Maru. But I have not yet worked out all of the details. In theory you could replace a one-wire, block-grounded sender with a two-wire, ungrounded sender and run an individual wire from the sender to the DC ground without including the engine in the circuit. However that would require the availability of a suitable part and I don't know that those exist for my application. It might just be easier to leave it as-is but disconnect the engine from ground using a switch or solenoid when it's not running, as Favorite is planning to do.

  18. #53
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    Default Re: Delignification around propeller stern tube in shaft log

    Thanks Chris. I think the negative switch when not running makes sense. Good anti-theft device as well!
    "If it ain't broke, you're not trying." - Red Green

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