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Corroded Trim Tabs

Discussion in 'Stabs, Tabs & Gyros' started by CR CRUISER, Feb 14, 2013.

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  1. CR CRUISER, Feb 14, 2013
    #1
    CR CRUISER

    CR CRUISER Member

    Joined:
    Dec 18, 2009
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    Location:
    Campbell River, BC
    I sent a customer's 245 Grady White to the dealer to have its annual service. They called me and said that they found the Bennett trim tabs to be severely corroded with some holes right through the SS trim planes. Sure enough, when I went to check it out, along the front of the tabs closer to the hinges, they were rotten. As well the hinges and backing plates were also severely pitted. The zincs on the tabs were still functioning but due for replacement.

    This boat lives all year in saltwater at their private island. There is no hydro to the dock and no metallic structures in the area. When tied up, the outboards are tilted up out of the water with the battery switches off. There is no other metal in the vicinity. The only possible cause that we can see is that the trim tabs were installed on top of an existing layer of bottom paint. They are going to sand off this paint and leave a 1/2" border of bare gel coat around the tabs to provide isolation from any galvanic activity.

    Any other thoughts as to why this happened? We want to correct the cause before putting the baot back in the water.

    Thanks for your suggestions.
  2. Beau, Feb 14, 2013
    #2
    Beau

    Beau Senior Member

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    Location:
    Beaufort, NC
    CR

    Sounds like galvanic decay, SS doesn't just rot? I'd be surprised to hear that the problem was caused by the fact that the tabs were mounted over existing bottom paint. I've painted mine for the last 14 seasons and the boat stays in the water year round. Vital to make sure that the zincs are metal to metal on the tabs, though. Even with the engines up, there will be some galvanic current in the water.
  3. Capt Bill11, Feb 14, 2013
    #3
    Capt Bill11

    Capt Bill11 Senior Member

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    First thing I would do is contact Bennett and run it by them.
  4. Capt J, Feb 15, 2013
    #4
    Capt J

    Capt J Senior Member

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    I agree, Bennett is usually very good about standing behind their products. I have seen thousands of trim tabs that were bottom painted and don't think that has anything to do with it.
  5. T.K., Feb 15, 2013
    #5
    T.K.

    T.K. Senior Member

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    Jan 31, 2007
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    Location:
    Cairo - Egypt
    Use an Ohm meter and measure continuity between the stainless steel ram and the sacrificial anode. If there is no continuity, the trim tab ram is not grounded and will suffer from galvanic corrosion.

    Ensure that you have fitted salt water anodes, zinc or aluminum and not magnesium anodes.
  6. CR CRUISER, Feb 15, 2013
    #6
    CR CRUISER

    CR CRUISER Member

    Joined:
    Dec 18, 2009
    Messages:
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    Location:
    Campbell River, BC
    I've already talked to Bennett and they have no ideas either. It seems that all we can do is repace them and install new zincs.
  7. Capt Ralph, Feb 15, 2013
    #7
    Capt Ralph

    Capt Ralph Senior Member

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    Bond them to the boat. Make one of the attaching screws a machine screw bolt thu the transom and bond to your boat system inside the transom.