MAIN MAST SCARF REGLUE

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Comment by bob mitchell on September 7, 2016 at 8:56pm

    FOUR IMPORTANT COMMENTS ON MAST EPOXY REPAIR: I have gotten serious on the main mast repair in the last few days, doing one side a day (based on how much sanding I can stand, and how fast epoxy drys). So since I got focused there are four comments I would like to make - two specifically on mast repair and one on epoxy in general.

     1) My masts came from Gaffney's boat Le Bateau Sans Souci (the boat with no worries). Sans Souci was a West Coast boat, which means it was early in the production cycle. Anyway, the masts had been worked on some. The lumber itself was in good shape except for mast heads, but some of the seams and scarfs were exhausted. It did not help that a hot rod fork lift operator bounced hard across the pot holes - I saw some of the seams fail on that trip to the flat bed. I don't regret that though because I have gained really valuable mast rebuilding skills and I am confident my masts are strong (knock on wood).

        My first point is that though the repair scarf appeared good, the lumber they scarfed in was plane sawn instead of quarter sawn (definitely google if you don't know the difference), and in the five or so years the mast has been drying out the plane sawn replacement boards checked significantly, while none of the original quarter sawn checked at all. An alternative explanation was that the lumber was not dry. Regardless, if I were building or repairing a mast I would use quarter sawn dry lumber. Originally the mast were made of Sitka Spruce, which might not be available, or  if so prohibitively expensive. Don't just abandon old masts - there may be some good lengths of salvageable Sitka for scarfing in. Second choice would be Douglas Fir. 

          The second point is that though the scarfs looked ok, if you tapped really carefully it felt and sounded like there was some space between the staves - something wasn't right. They had added some 5/8" oak dowels, and I suspect they had smeared epoxy along the edges, but they had not gotten epoxy inside. It is an easy matter to use a large plastic syringe without a tip (got mine from Walgreens) and inject epoxy into the scarf. Drill  3 pairs of I/8" holes at a shallow angle, paying attention to the varying depth of the scarf joint to determine how deep, ie try to end each hole on the varying depths of the scarf plane. You definitely do not want to run out of the scarf and into the hollow of the mast because that is where all the epoxy will end up. If you try to inject the epoxy and none will come out, fine. But what I found was that in several cases the epoxy went in and eventually came out other of the drilled holes. So I would go ahead and inject all holes, then put a piece of plastic on top and clamp the scarf with a few clamps.

      The third and fourth point have to do with mixing epoxy. I have had very few batches that did not go off correctly, but being overconfident after 20 gallons and 7 years, I had 2 failures in a week. The first was carelessly mixing a 30 cc batch, which is very small. The smaller the batch the easier it is to mess up the proportions. Small batches MUST be measured really carefully.

     The second mistake occurred when I was mixing a normal three squirt batch (2 to 1 - total 3 ounces), and added too much hardwood dust as filler.