Best wood for laminated frames?

Discussion in 'Wooden Boat Building and Restoration' started by bntii, Feb 21, 2012.

  1. bntii
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    bntii Senior Member

    Restoration work- 35' sloop with plenty of cracked frames.

    The plan is to sister frames and glue up in situ.
    Boat is in North America, but most any wood species can be sourced for the job.
    Full complement of milling equipment available to bring boards down from plank to laminates.

    Thanks all
     
  2. michael pierzga
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    michael pierzga Senior Member

    First choose the peice of wood with that can be machined with the least amount of grain run out.



    Best species...Hmm...careful you dont get into the Ford Chevy argument.

    Best ? Are these bright finished frames ? Is weight an issue ?

    Mahogany and ash was popular on the racing boats.

    Oak is classic


    If glueing with epoxy not too much clamping pressure
     
  3. bntii
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    bntii Senior Member

    Thanks Michael-this is just a poll of sorts as I was asked for advice from a person restoring the boat with a slew of cracked frames.
    I know how I would proceed but figured it wouldn't hurt to ask & see if I am steering them in the right direction.

    thanks again
     
  4. Petros
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    Petros Senior Member

    I would think that you should use the same wood, or at least one with similar properties, as what the original frames are made from.

    Different types of wood behave differently, elastic modulus, stength, etc. If the sistered ribs are very much stiffer than they will take all of the loads as the hull flexes cocentrating the stress at the glue or fastener joints, leading to early failure (the connection will get overloaded). With the same properties the loads will be shared, the glue joint will flex together, and the hull should maintain its load carrying properties.

    Simple answer is when you put a stiff piece of wood along side a not so stiff one, when loaded the stiff one will carry almost all the load. Use the same wood if possible, or one with the same elastic modulus, shear strength, compression strength, etc.

    Make sure you get the hull back into its original shape before you reinforce the ribs.
     
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  5. Boston

    Boston Previous Member

    in terms of native hardwoods that have good to excellent rot resistance, I'd start by seconding Petros, If thats not an option I'd go with the most similar characteristics, otherwise you might just end up breaking more stuff in the not to distant future.

    Black locust has tremendous rot resistance but its not a typical rib material
    white oak
    black walnut
    cherry

    all have very good rot resistance and are local woods you can find cheap.
     
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  6. michael pierzga
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    michael pierzga Senior Member

    Springback is also an issue. If you use a really stiff wood you need to cut the laminations thin....takes time , plenty of epoxy and turns a board into a pile of sawdust To conserve oak the local shop cuts thick , steams the oak, then laminates 2 or 3 sticks together to make a frame.
     
  7. Boston

    Boston Previous Member

    saves on glue as well.
     
  8. michael pierzga
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    michael pierzga Senior Member

    Thin sticks of wood are easy to steam ...they use a big PVC pipe with metal rods driven thru from side to side to form a rack, rags plugging the ends and a simple tea keetle type rig on an electric hot plate.
     
  9. Boston

    Boston Previous Member

    some people might use a PVC pipe but I prefer to stay away from polyvinyl-chlorides, bad for the ole health


    [​IMG]

    This system is sectional so I can fit just about any length board I need to. At the time it was steaming sills for a historic restoration. They needed to have the same twist and warp as the original or the hysterical society wouldn't be happy.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Whoa !!! Heavy caliber !

    I suspect the local gang .. err emm, " Borrowed " the PVC pipe a few years ago when the port laid drainage pipes for a new charter fleet shower house.

    Other good things to borrow are those do not enter steel crash barrier stands...make great saw horses and mini scafolds
     
  11. PAR
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    PAR Yacht Designer/Builder

    Petros is correct, you need to select a species that is similar to the original in physical properties.

    Some woods tolerate steaming better then others, which is why you don't see much mahogany, but do lots of oak. Select a species that can bend without high breakage percentage.

    If laminating, you usually don't need to steam the pieces, unless there are some really quick curves, such as those seen on powerboat hulls in the aft quarters. Decreasing the thickness of the pieces within the laminate can sort this out usually.

    If gluing (epoxy or other wise) use 30% thinner stock if bending hardwoods, compared to softwood counter parts, with the exception of the really dense softwood, such as SYP.

    Epoxy would be my first choice in a laminated bent frame, regardless of wood species. The oily or tannin contaminated woods, such as oak and teak can receive a surface prep, that will eliminate any bonding issues. If electing to use oak (a common choice) then use live oak, rather then white oak, if you have to option. Live oak has an interlocking grain so it doesn't split, check or "burst out" like white oak can in the bending process. It's also a fair bit stronger and more rot resistant.
     
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  12. bntii
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    bntii Senior Member

    Thanks Par.
    That is the approach I had passed along so I am near the mark then.
    They are perhaps too close to getting in over their heads on this one and I am reluctant about laying out procedure.

    The frames I have done were all in white oak @ 1/4" bent to forms and sided in the surfacing planer. I take off bevels & cut in on the frames after the come off the form. I have always used epoxy- wet out neat then syrup consistency to glue up.

    The owner wants to laminate in situ but I don't know how that job is ever run with all the mess made and how bevels are dealt with.
    My take is that the fasteners will work if the frame is not held close to the hull & this needs the correct bevel.
    I don't know how the laminates can be rolled into the hull to take the bevels if laminated on the boat.
    Perhaps I am over stating this?
    I don't want a bit of friendly advice to get me pushing tools :), but at the same time I think any work should follow best practice if possible.

    Edit- She is a Cheoy Lee Rob: teak plank, steamed white oak 8" on center. She has 1/3 of frames cracked, or about 30 or so..
    The procedure they are taking is to sister everything, not replace.
     
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  13. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I used to own a 35' Choy Lee in Maryland. It was the offshore Robb design (Lion class sloop, but yawl rigged to take advantage of the CCA rules). I sold her back in the very early 1990's. Choy Lee did the yawl conversion. She was named Falcon originally and I kept the name, not to piss of the boat naming gods. Does it still have the builders plate (usually mounted on the center of the bump up in the cabin or the forward bulkhead). If it says Falcon, I'll bet it's the same puppy. Comfortable boat in a blow.

    I wouldn't sister her, as the frames are fairly dainty and all the additional fasteners will just ruin whats there. Fastening good to bad is never a wise move. Yes, you can laminate in place, but this is usually reserved for repaired ribs, rather then wholesale replacement. If repairs you can save some trouble by using a stepped scarf, instead of a straight scarf (12:1). The usual places for these girls to break frames is, aft from the engine. If she's bashed into something then you'll get breakage forward to the mast step or around impact locations.

    If replacement is desired, get her on the hard, remove the engine (Atomic 4?) and other heavy items, to relieve her burden, then pull every third frame. This leaves enough structure in place so she'll hold her shape, while you replace the ribs. With every third one replaced, move down one rib and do the same again except every other set can have two replaced. In other words, remove one then skip one, then remove 2, then skip one, then remove one, then skip one, etc., etc., etc. Once this is done, you only have the odd ones you skipped, which can be pulled wholesale and replaced, knowing the hull will hold her shape. Check for hogging, especially aft and good luck, if you have to replace frames at the aft end of the LWL.

    As to the actually process, well this is an entire volume of information and everyone has their own method, including me. It's a lot easier if you're also doing deck work.
     
  14. bntii
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    bntii Senior Member

    Thanks Par- I will pass that along but I think the work load will be beyond what they are up to.

    They have presented a 2 week schedule which can run to 6 if required....
    I have not been on the boat- If I am asked to take a peek, I will pass along what I find.
     

  15. ancient kayaker
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    ancient kayaker aka Terry Haines

    FYI springback amount for unsteamed laminations is 1 in (n^2)-1
     
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