We Found A Broken Bolt – Goody!

Technically, it was a large machine screw.

There I was, scraping bottom paint, and a huge chunk of paint comes off and along with it, the screw head falls out of a thru-hull.

When we first started cruising, Dave and I would have greeted that with dismay – what now? (Some days, I still think that Murphy — ‘anything that can go wrong will” – was an optimist.)

Now, we both had the same reaction: glad it happened now.

I mean, if a thru-hull bolt is going to break, the best place to discover it is when you’re already hauled out and in a boat yard. We’re in the perfect place to fix it (and replace the others in the same fitting and check those on the rest of the boat).

We’d much rather take care of things when it’s not a critical time. When it’s a maintenance task and not a emergency situation.

For those interested, the other machine screws in the same fitting appear just fine although we’re going to replace them just to be on the safe side. Looks like the one was buried in sealant and crevice corrosion got to it right where the head meets the shaft.There I was, scraping paint. And along with the paint comes the head of a large machine screw . . .

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11 Comments
  • Lupari Sue
    Posted at 25 October 2014 Reply

    A stitch in time they say. Always geter to check while out of the water.

  • Becky Croston
    Posted at 25 October 2014 Reply

    I was scraping bottom paint on our sailboat when I saw a drip coming from a circular pattern in the bottom paint –about “thru -hull ” sized. I pushed –and immediately called my husband over to investigate. In horror, we discovered that some worker during construction hsd drilled a hole –found out it was in the wrong place, put normal caulk on the plug and stuck it back in and painted over it! We were the original owners. The hole was 10 in. below water –just below the head. The only thing holding it in over time was the bottom paint!!! If that had failed at sea –no way to get to it from inside! Talk about a “godsend ” finding it in time on the hard!

  • Terri Zorn
    Posted at 25 October 2014 Reply

    Very lucky to have found that . whew !!

  • Ron Newton
    Posted at 25 October 2014 Reply

    Are you going to replace all the thruhulls and fasteners that are below the waterline, was this fitting not bonded?

    • The Boat Galley
      Posted at 26 October 2014 Reply

      On Gemini’s, the fittings are Marelon, so not bonded.

    • Ron Newton
      Posted at 26 October 2014 Reply

      Any idea what happened to the bolt? I figured it was electrolysis when I saw the pic but with no dissimilar metals involved can that be eliminated?

      • Carolyn Shearlock
        Posted at 26 October 2014 Reply

        We believe it was crevice corrosion — a bit of water worked its way in around the head of the machine screw and just sat there and slowly corroded a crack across it.

  • Chip Lawson
    Posted at 25 October 2014 Reply

    Carolyn, I hope you are replacing those stainless machine screws with bronze. If you look at the galvanic corrosion chart ( http://www.corrosionist.com/galvanic_corrosion_chart.htm ) you will see that bronze (almost all seacocks are bronze) and stainless are reasonably far apart on the nobility scale so it is not good to have them on contact, particularly underwater in salt water. So in addition to the crevice corrosion you mentioned, you also have to add in the risk of galvanic corrosion id you use stainless fasteners. WIth bronze you will have no issue with either crevice or galvanic corrosion.

    • Carolyn Shearlock
      Posted at 25 October 2014 Reply

      It’s Marelon — that’s what Gemini (PCI) uses as standard. So stainless is okay. But thanks for the reminder to be on the lookout for such things that previous owners may have done and the link to the galvanic corrosion chart!

  • Colin Mombourquette
    Posted at 09 March 2016 Reply

    I love the positive outlook that you always have; it is certainly a desirable attribute for boaters.

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