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Fuel Tanks in Ocean's

Discussion in 'Ocean Yacht' started by BJG, Dec 6, 2013.

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  1. BJG

    BJG New Member

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    I am wondering if anyone has had, or has heard of issues with replacing the center fuel tank on oceans... particularly the 63' ??

    My 63' is in the boat yard right now having the center tank replaced. When we finally got it opened up and cut out, we found out that the pickup tube was made of stainless steel, and the tank is aluminum. There was a lot of pitting or 'pin holing' directly below the tube, which we believe was cause from galvanization or form of electrolysis jumping from the tube to the bottom of the tank.

    Has anyone else had similar issues. I believe this is a manufacturer issue, and would love feed back.
  2. Marmot

    Marmot Senior Member

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    Diesel fuel is generally a pretty lousy conductor. That is why it is subject to risks from static charges generated when fueling at high rates.

    I really doubt that the SS pickup tube is responsible for the pitting you see. Is the area under the pickup lower than the tank bottom? Is there a sump there? Did the tank ever sit with a large amount of water in it? How far from the tank bottom is the pickup?

    It is possible that movement of fuel to the pickup leads to water collecting in that area and causing the pitting.
  3. BJG

    BJG New Member

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    The tank is flat, rectangle. 300 gallon tank.
    The tube ends approx. 3" from bottom of tank. the pitting is isolated to just that area, no other area in the tank.
    There are not signs the tank has ever had water in it, and it is not likely as this is the MAIN center tank. All outboard tanks gravity feed to this one, and this is the one the engines pull from.... so this tank would always be full of diesel.

    The outside of the tank was virtually like new... no signs whatsoever of water or corrosion.

    The boat yard agrees they think this is a form of electrolysis.
  4. Marmot

    Marmot Senior Member

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    How bad is the pitting and pin holing around the tank penetration for the pickup?

    You can't have electrolysis without an electrolyte.
  5. BJG

    BJG New Member

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    Well... I am not sure how to answer this one... but obviously bad enough to create a pin hole effect and leak significant amount of diesel.
    Coho Dic-04-2013 001.jpg

    see attached for pic
  6. Capt Ralph

    Capt Ralph Senior Member

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    That's corrosion, not galvanic erosion.
    The pickup tube is bonded to the tank by it's pipe connection.
    Chemicals, decay, water and/or more would cause that damage and leave the tank bottom clean without diesel stains.
  7. Capt J

    Capt J Senior Member

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    Getting 20+ years out of an Aluminum tank that sits a few inches above bilge water is very good. I'd highly consider replacing the saddle tanks at the same time.
  8. Ormond Bert54

    Ormond Bert54 Senior Member

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    I'm sure glad neither of my 3 fuel tanks or water tank leaks after 29 years. That job looks … horrific.
  9. Marmot

    Marmot Senior Member

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    Yep. Notice how clean and pit free it is in the immediate area around the pickup? That's because the higher relative velocity of fuel (because the pickup is so darn close to the bottom) in that area did not allow water to sit on the bottom and create corrosion cells. The general shape, size, and location of the corrosion shows where water migrated toward the pickup and collected. That water fed the bacteria that produced the waste products that ate the aluminum.

    Yards don't think, the people you talk to in a yard think but not always clearly.
  10. Capt J

    Capt J Senior Member

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    To me it looks like a tiny bit of saltwater is getting in through the vents or the fills the way the metal is pitted. That is where it is going to end up from all of the tanks and the other tanks shouldn't have water issues. The 63' Ocean has a large saddle tank on the outbound side of each engine, and both of those tanks have a hose at the bottom that gravity feed into this tank which is in the ER aisle underneath the floor. The top of the tank in question, is below the height of the bottom of the saddles that feed it and everything draws fuel off of this tank.
  11. BJG

    BJG New Member

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    I understand your thoughts about water creating the corrosion... but water would not accumulate there as this is the main pickup for the engines. We use the boat frequently, engines get run every week whether we use the boat or not. We have never had any water in the Racores. I don't see how water could build up there as it would be sucked up and ran through engines.

    As a side note, the yard did clean up that area below with acid as they were trying to find the pin holes... possibly why it looks so clean under the pickup tube.

    The outside bottom of the tank (exposed to the bilge) was in perfect shape... paint even still looked clean... so we don't believe it was sitting in bilge water, and there was no corrosion anywhere else.
  12. K1W1

    K1W1 Senior Member

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    Hi,

    Ferrous material from drilling and cutting that is not removed can also cause pitting when in contact with the tiniest bit of water.
  13. Capt Ralph

    Capt Ralph Senior Member

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    Your the original owner? It could have suffered the blunt of damage years ago and once it starts, it really never goes away (corrosion).
    Can we get some up close pictures?
  14. Marmot

    Marmot Senior Member

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    Excellent point. Aluminum boat owners should be very careful about wire clippings and drill swarf in the bilges.
  15. Capt J

    Capt J Senior Member

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    It does not take very much water to cause that damage over a great number of years......Basically 3 tablespoonfuls is all that would take over years of time, the pickup would never pick that up since it is much higher. Since fuel floats, the water always stays at the bottom, there is also not a big surge or movement of fuel in that tank because the saddles keep it 100% full all of the time, unless you're below the last 300 gallons of capacity on the entire boat.

    And also the comments about pieces from drilling the tank is a valid point. On the 63' Ocean I managed, Ocean drilled the 1/2" hole for the pickup and dropped the bung in the tank. It floated around in that tank for 19 years until it got caught in the very same pickup it was drilled for. We had awesome water pressure for 2 seconds, then it would just barely trickle (it was sucking through the pilot hole), then we inspected the pump and the intake hose was totally collapsed, we tried to blow the pickup out and couldn't and pulled it out and found the piece stuck in it, 19 years later.
  16. BJG

    BJG New Member

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    Interesting about the shavings. My captain said there were particles in the tank that resembled metal shavings.

    I will definitely find out about that, as the boat is actually in Ensenada (Baja Naval).

    Thanks for the info.... We are hoping to have some of the repairs covered by insurance.
  17. Capt Ralph

    Capt Ralph Senior Member

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    Please tell us how that works out.
  18. Danvilletim

    Danvilletim Senior Member

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    I'm unclear under what circumstances the insurance would cover this. I love the concept of buying into coverage that would mitigate major repairs on a used boat. I'd love any help in understanding this.
  19. pprecourt

    pprecourt New Member

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    BJG, going through the exact same challenge on our 63' as we speak. Would love any insite before the saws-all's start ripping in. Not exactly an easy location to excavate a tank out of.
    cheers
  20. K1W1

    K1W1 Senior Member

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    Have any of you guys with these problems looked at fuel tank liners?