Drilling A Hole

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  • Drilling A Hole

    I want to install a brass garboard drain plug on my Stainless Marine outboard bracket and have a few questions for you guys.

    First, will the brass and aluminum and stainless screws cause any corrosion?

    Second, can I use a unibit on the aluminum to enlarge the existing 5/8" hole into 1"? Looks like 1/4" thick. Normally if I wanted to drill a hole I'd use a hole saw, but that's not really an option when trying to enlarge an existing hole.

    Thought about using a jig saw but due to the location it's not doable. Currently using a rubber flip down type of drain plug and everytime I get back from a day on the water I pull the plug and it seems like I have a gallon or more water in the bracket.

    Plus, I also fear that one day the plug I'm using now will fail and fall out although it never has yet.

    TIA guy's.


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  • #2

    you can use a hole saw if you make a jig. Pre drill a 1" hole in a board, clamp the board to the work, use the hole to guide the hole saw.

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    • jmike
      jmike commented
      Editing a comment
      Good idea except there's no real way to attach clamp's. I could make a template and attach it with two self drilling screws but then I'd have two holes in the bracket below the waterline. I might be able to wedge a template between the ground and the bracket.
      I have the lumber to do it. Now you got me thinking...

  • #3
    Yes, dissimilar metals is a concern due to galvanic corrosion. I'd use a 'Marelon' plug by Forespar Marine:

    "Marelon® is a proprietary formulation of polymer composite compounds using composite reinforced polymer and additives to produce a superior marine-grade product. It is ideal for use below the waterline.

    The Forespar Garboard Drain is a drain and plug assembly that fits up to 1-3/4" thick transoms. It has 3/4" male threads with a screw plug and is made of precision molded, lightweight high strength Marelon with carbon reinforcement."


    To avoid issues with the SS hardare into the aluminum bracket, use Tef-Gel or cover the screw threads with a good adhesive-lined heatshrink, plus a marine goop. Tef-Gel was made fo the US Navy to isolate the SS from the tin and allow the use of SS hardware to hold items in place, yet also be electrically isolated from bulkhead/deck material.

    Click image for larger version

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    Life is too short for an ugly boat!

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    • #4
      Going the opposite way of Bill. Use a hole saw to make a 5/8" Dowell just a smidgen longer than the depth of your 1" hole saw. Insert in over the pilot bit inside of the 1" bit and insert the Dowell into the 5/8 hole. It will keep your 1" bit steady.

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      • #5
        Thank you guys! Once again BOB rules the day!!

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        • #6
          You could have phrased your thread title a little differently.
          jus sayin 😀

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          • jmike
            jmike commented
            Editing a comment
            Did it for attention?

        • #7
          There is an special bit that allows you to use a smaller hole saw as guide to for a larger hole saw. McMaster Carr sells one and does Bosch: HE1 Hole Enlarger Kit. If you can get the right size hole saws.

          This example/explanation of how to use it is from another website:


          “You use the 1 inch hole saw basically as the pilot with this and then cut your new hole opening with the desired 1 1/4 inch saw. Should easily get you out of a jam. Both hole saws fit on the arbor at the same time giving you your pilot hole size along with your new hole size to be cut in.”

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          • #8
            Originally posted by jmike View Post
            First, will the brass and aluminum and stainless screws cause any corrosion?
            ​​​​​​
            Yes, go to "Plan B".

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