Tips on building the strongback

Discussion in 'Boatbuilding' started by mariobrothers88, Dec 3, 2020.

  1. mariobrothers88
    Joined: Sep 2020
    Posts: 117
    Likes: 6, Points: 18
    Location: San Diego, CA

    mariobrothers88 Senior Member

    Hi guys, the woods catamaran strongback plan calls for 2 long 2"x5" timbers spaced 600mm apart and 2"x2" timbers to support the bulkhead pieces. I am planning to use a laser level to make sure everything is level and square, do I also need to use the plumb bob/spirit method (as detailed in the Gourgeon brothers book) or is the laser level enough? Also to tie down the strongback so that it doesn't move, I'm planning to use 10" steel tent states (from Harbor Freight) at each station (1o on each side). Is that overkill or not enough? I understand that it's really important that the strongback not move throughout the process, so I'm actually thinking maybe I should put more stakes.

    Also I was planning to use low quality/cheap pine timbers to build the strongback, would there be any issues with that?

    Thanks guys for any tips or advice!!
     
  2. gonzo
    Joined: Aug 2002
    Posts: 15,150
    Likes: 910, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    What are you attaching the stakes to, soil?
     
  3. mariobrothers88
    Joined: Sep 2020
    Posts: 117
    Likes: 6, Points: 18
    Location: San Diego, CA

    mariobrothers88 Senior Member

    yes, soil!
     
  4. wet feet
    Joined: Nov 2004
    Posts: 663
    Likes: 101, Points: 43, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    As fond as I am of laser levels,I have a natural suspicion about their use as a sole determinant of accuracy.Consequently I also use a water level at the outset to mark a line at both ends of the workshop,as well as both sides.This way I can occasionally check the laser against the reality of the water level and it also makes it easy when marking a waterline on the hull.I know it isn't strictly related to the strongback but I find it a useful piece of insurance.

    What hasn't been described is the size of the boat in question or which way up it will be built.If building upside down I like the top surface of the stongback to be at least 22 inches off the floor for allowing relatively easy access under the boat.A large hull with a strong sheer will need more.On an earth floor I would plan on using a good size plywood pad under each leg of the strongback and the use of few stakes will do no harm.When setting up the moulds,don't skimp on diagonal bracing and finally,don't forget that when the hull is planked (or skinned) you will need to extract the moulds and sawing them apart in situ isn't particularly efficient.
     
    bajansailor likes this.
  5. hoytedow
    Joined: Sep 2009
    Posts: 5,767
    Likes: 350, Points: 93, Legacy Rep: 2489
    Location: Quam prospectum!

    hoytedow wood butcher

    Even small earth anchors would be far superior.
     
  6. gonzo
    Joined: Aug 2002
    Posts: 15,150
    Likes: 910, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

  7. hoytedow
    Joined: Sep 2009
    Posts: 5,767
    Likes: 350, Points: 93, Legacy Rep: 2489
    Location: Quam prospectum!

    hoytedow wood butcher

    These hold very well.:
    20201204_100342.jpg
     
  8. mariobrothers88
    Joined: Sep 2020
    Posts: 117
    Likes: 6, Points: 18
    Location: San Diego, CA

    mariobrothers88 Senior Member

  9. gonzo
    Joined: Aug 2002
    Posts: 15,150
    Likes: 910, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    That should be enough to secure it. Make sure the soil is compacted enough so the jig doesn't start settling and bending. It would be better if you rent a vibrating compactor for half a day and compact the soil.
     
  10. mariobrothers88
    Joined: Sep 2020
    Posts: 117
    Likes: 6, Points: 18
    Location: San Diego, CA

    mariobrothers88 Senior Member

    Thanks for the reply! I will be building the woods flica 34' catamaran with a beam of about 18'. I plan to build the exterior hull upside down, then flip it to do the interior.

    Why the plywood pad? Could I use tarp instead? I was thinking of laying down gravel and a tarp underneath the entire strongback, should I also do a plywood pad underneath each leg?

     
  11. wet feet
    Joined: Nov 2004
    Posts: 663
    Likes: 101, Points: 43, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    The plywood pad is to spread the load from the weight of the strongback plus the ever increasing weight of the hull.A decent size pad at each leg ought to be enough.You really don't want the legs of the strongback sinking into the ground and my earlier recommendation about marking the waterline on the workshop wall does give you a reference to verify that it isn't or that sadly,it is.I used to work near a building on marshy ground that moved a bit at one end when the tide was in or out and keep the possibility in mind.
     
  12. fallguy
    Joined: Dec 2016
    Posts: 4,302
    Likes: 742, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Post anchors 24" are good enough if you have wind protection from concrete barn walls, provided a dry site and no freezing as you have.

    I like 2x10 or 2x12 kiln dried lumber for the strongback on edge. Choose lumber that is straight. If you can purchase floor joists and get them to the site; even better, but the 2x lumber in 12' allows you to have some error in the anchors without shimming to straight. The strongback needs to be level mosty. A degree of difference in width matters not.

    The tack life lasers are really decent. Be careful buying cheaper lasers. I was on a jobsite one time doing siding work and the laser was not making any sense. I looked at the manual and the laser has a 3% error rate. 3 percent in 34 feet is really terrible...

    You can tarp the ground, but only if you are dried in from rain.

    As I said before, sun in Tijuana will be your biggest enemy and you will want to take your work to paint quickly.
     
  13. mariobrothers88
    Joined: Sep 2020
    Posts: 117
    Likes: 6, Points: 18
    Location: San Diego, CA

    mariobrothers88 Senior Member

    Hi guys, even though the plans call for 2x5s for the strongback, I am going to use 2x12's based on all the amazing advice and tips! Do you guys recommend using 2x2's for the cross timbers that join the 2x12s, or bigger timbers like 2x4s?

    Thanks for all the help guys I really appreciate it!!!
     
  14. mariobrothers88
    Joined: Sep 2020
    Posts: 117
    Likes: 6, Points: 18
    Location: San Diego, CA

    mariobrothers88 Senior Member

    Hi guys how important is it for the lumber for the strongback to be kiln dried given the climate here in Tijuana is pretty dry with average humidity ranging from 33-66% most days? The reason why I ask is that most of the local wood in Tijuana is not kiln dried. If I want kiln dried I would have to buy it from the USA which means a lot of hassle at the border crossing. Can I just buy local even if it's not kiln dried giving the humidity is pretty mild here?

    Thanks guys!!
     

  15. fallguy
    Joined: Dec 2016
    Posts: 4,302
    Likes: 742, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    It would be very foolish to build a strongback from wet timber. If you can find timbers that have been around awhile drying all summer; or you can use a moisture meter; you will want moisture of below 10% to avoid significant movement. Once you setup the strongback and start sheathing, you really can't make changes or adjustments. Most lumberyards know which 2x material is older in the yard and has had plenty of time to dry, but a meter is best.
     
Loading...
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.