Scarphing DF mast blank

Discussion in 'Wooden Boat Building and Restoration' started by lewisboats, Mar 28, 2009.

  1. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    I am building a 12 ft mast. I bought two beautiful 4x4 12 ft DF posts...both appear on the end to to be quartersawn. Problem is that each has a nasty knot in the last 3 ft of one end and I can't get the full length out of either. I have a couple of questions to pose to those who have had more experience scarphing mast pieces together. To start...scarphing ratio...8:1 10:1 12:1 or more? Next: Scarph orientation...athwartship or fore and aft? Finally... which end or in the middle. The mast is 2.5" sqare for the first 2 ft, then straight taper to 1.5" square at the head. It will have a 75 sq ft balanced lug hanging off of it on a 12 ft by 48" max beam scow hull with a daggerboard. Should the scarph be in the thicker but more stressed step and partner area or higher up? Oh...and one more question...scarph orientation re: grain orientation of the wood.

    Thanks Steve
  2. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Too bad you have to scarf a 12 ft stick. It would be better to laminate two 12 ft lengths together if you can.
    Nevertheless, answering your questions, it doesn't matter where the scarf is located. If properly done, it ought to be as strong as the undisurbed wood.
    You've got a lot of latitude in deciding how to orient the scarf. Make sure the grain (flat or 1/4 sawn) is matched when setting up the scarf. A good scarf is nearly invisible. I think seeing the angle from abeam is better looking.
    If you can make a perfect fit, Gorilla glue (polyurethane) is least visible compared to epoxy, and it will form a good water resistant bond . The ratio should be 10:1. A sloppy fit needs epoxy and it should be thickened enough to fill the gaps that are present. Wood flour will work as a thickener.
  3. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    The proper way to scarf your mast would be to rip the 4x4 in half lenghtwise to get 2 pieces 2x4. Then scarf where the knot is so as to eliminate the knot and match the wood grain of the two pieces. The greater the angle of the scarf the stronger the joint but in no case should it be less than 12-1 on structural members. Do this with both pieces to eliminate the section where the knot is and as much of the adjacent wood around the knot as possible. Then laminate the both 2x4 scarfed pieces together rotating them so the scarf joints are at oposite ends. The result is a far stronger 4x4 than an original single piece of perfect 4x4 with no knots.
    Have a Great Day!
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.