Clinker built restoration to begin

Discussion in 'Wooden Boat Building and Restoration' started by Proa42, Aug 28, 2009.

  1. Proa42
    Joined: May 2009
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    Location: North Carolina

    Proa42 Junior Member

    I recently purchased a 19' lapstrake sailboat. Without going into a rant about used car dealers being the father of all used boat sellers, I've discovered I am about to begin aunexpected journey restoring this thing. It looks too cool not too. So ,I'm hooked.

    The boat obviously sat too long on the trailer as the gunwales have dropped (evidenced by the warp in the thwarts seats). The bent ribs that failed, seem to have failed because of the strain that created cracks, allowing moisture in. This is a self-sustaining failure - the weaker a frame got, the more strain on the others, and so on.

    Plan "A": Spring the gunwales back to original height by taking the load off the keel and suspending the boat from its gunwales (Good wood there), allowing the weight of the boat to pull itself into position (Wetting the wood to soften it up a bit). Once back as close as possible, replace ribs, and refasten where necessary.

    Question 1: Good or bad iead?

    Question 2: Would it be a bad engineering move to replace the steam-bent ribs with sawn ribs and floors?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    You're suspending the boat from the rails thing is the right idea, but wrong way of approaching it.

    The boat likely has a number of distortions from trailer life, hogging, tension cracks, etc. Each needs to be addressed and ultimately removed, but dangling the boat isn't the way. Usually, jacking, strapping and bracing are the methods, but you have to ask yourself, "when do I stop?".

    Cracked ribs are often what we call tension cracks (or breaks). This occurs when the frames (ribs) swell from moisture, stretch at their fasteners, then dry out, relaxing at the fasteners. This repeated movement eventually does a few things. First is the fastener holes "egg out" or elongate, making the grip each fastener has lessened. With time the fastener lose their grip, but unfortunately, not all of them or not at the same rate, so some are better stuck then others, creating localized "hard spots". This is where things break. The frames can also break from repeated tension (hence the name) from the wet/dry cycling. At some point they just give up, usually cracking perpendicular to the frame at a fastener (a weak point).

    Once things like this occur, the shape of the boat changes. the turn of the bilge sags, because the frames aren't continuous any more. On lapstrake hulls you'll see odd twists and puckers in the planking laps as you eyeball them, which indicate cracked and broken frames. Also the ends of the boat droop down, from lack of support. Additionally the deck can separate from the hull and it's beams adopting a fore and aft curve too.

    It takes a great deal of skill to remove these distortions and get the hull close the where it's supposed to be. The common beginner mistake is to try and force the boat back into shape too quickly and things start breaking wholesale.

    Wood has a memory, in that it will remain in a position, if it's held there for a long time or chemically altered. If forced too quickly, it will spring back (memory) or break from internal stresses. How fast is too fast, well once you break a few pieces, you learn to slow down, but generally it'll take months of jacking, tightening straps, adjusting braces, etc. to twist a boat back into shape.

    Why do all this? well, if you just make repairs, you'll lock in all these distortions and have a pretty, but weird shaped boat when you're done. Sailboats in particular are quite sensitive to shape alterations.

    Sawn frames can replace steam bent ones, but will be much heavier for the same strength. They chew up valuable space inside the boat, because of how much bigger they need to be, so it's best to not use them on this type of hull. Laminated frames are an option that have the same dimensions as steam bent frames.

    It would be unusual for a novice to get a boat like this back into shape. Lap strake is one of the more difficult construction types to repair. Most can't get their head around the way things work, but once you do, it's not as hard as most will have you believe. I do a lot of lap strake work, mostly because the others in the area don't like to do it. It requires different repair techniques, but the wood working is the same.

    How is the boat fastened? Can you post pictures. Do you know what it is?
     
  3. Proa42
    Joined: May 2009
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    Location: North Carolina

    Proa42 Junior Member

    lapstrake repair.

    Thanks, first off, for the quick reply.

    This boat is is one of three, built at a boatyard in Minnesota (Amundsons, White Bear Lake). I've contacted them about getting the offsets and plans.

    She is hogging. I found that out as I removed the floor boards -- they sprung up on the ends as the screws were removed. So, she'll be supported at stem and stern with support gradually removed from the center.

    I've removed floor planks and got a full view of what is going on. Lots of bending to do. (Do you know a good vendor for "green" white oak.)

    I'll be taking PIX as I go. I'm documenting this as I go so the shrink will understand what happened.

    I was planning on placing 4X4s under the clamp and gunwales, with a leg to the keel, leaving just enough gap to start wedges between the beam and leg. Wedes will gradually be driven in to raise gunwales.

    Alignment will be maintained with drylines running stem to stern. Center line and make a triangle from transom to stem. Initially spirit levels will keep me close, avoiding twist.

    If I get the offsets, she gets a custom cradle to mold her back. I may be able to lazer once she gets close -- if she gets close. Regardless, she won't get any new ribs till she's settle in.

    She is pretty, but like they say, "Beatuy is skin deep." If I figure how to attach a picture I will.
     
  4. Proa42
    Joined: May 2009
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    Location: North Carolina

    Proa42 Junior Member

    Pictures, I hope

    Here are pictures (If I did ti right):
     

    Attached Files:

  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 487, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Rather then try to pull up or wedge against the sheer clamp and shelf (which will just test the pull out strength of more fasteners), I'd pull her down and let gravity work for me.

    I'd place her on a strong back with a hefty centerline timber or I beam. I'd remove the garboards and then slowly clamp her down to the I beam. If the keel isn't straight, then I'd pick up the rocker, cut a rough "mold" and pull her keel down to this. The garboards have to come off anyway so it makes things simple. I'd also pull the two planks at the worst portions of the bilge turn (plank 4 and 5 in the aft sections). This is where you'll find lots of tension cracks and these plank locations can make installing sisters of replacement frames a lot easier. I'd also pull the sheer strake or the one below it to make feeding in new frames easier and to get a good look at the shelf and clamp.
     
  6. Proa42
    Joined: May 2009
    Posts: 11
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    Location: North Carolina

    Proa42 Junior Member

    Thanks

    Thanks.

    Now to find the oak.
     

  7. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 487, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    In your area this shouldn't be that difficult. Given a choice, use live oak, instead of white. It's stronger and less prone to checks and splits.
     
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