Chine logs cut to shape vs bending

Discussion in 'Wooden Boat Building and Restoration' started by bkwk, Aug 9, 2012.

  1. bkwk
    Joined: Aug 2012
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: usa

    bkwk New Member

    Is it ok to cut chine logs to shape rather than bend them?


    New to boatbuilding and had this question about chine logs. I dont know if the bend is important to a boats structure/integrity or not. Im working on a small 8ft jon boat with internal chine log construction if it matters. Laminating and steaming are not options for me.



    thanks to all assistance
     
  2. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 474, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Bending permits the grain to follow the load paths, while cutting allows the grain to run out of the edge of the stock, making for a considerably weaker chine log. Jon boats don't have much bend to them in the chines. How big a piece are you trying to bend? An 8' jon boat would likely use a 1x2 chine log, which is pretty flimsy stuff. Use a heat gun on the hardest part of the bend, after soaking this area with water for a day or two.
     
  3. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Unless the designer of your boat was a comedian, all chine logs should bend naturally to the curves required. Relatively straight-grained wood maintains its strength when bent (to a point).
    Steaming can be nothing more than wrapping a very hot wet towel around a piece of wood for a minute.
    Wood tends to settle or relax into the shape it has been forced into over time. This means the tendancy to snap from extreme bending diminishes as time goes on, especially if the wood is wet and warm.
    Build your boat as drawn. A proper chine log will have been proportioned to allow the bends required. No steaming or laminating should be required.
     
  4. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 139, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    I have never heard this to be a problem, is there something unusual about this particular jon boat? or are you using some very stiff and brittle wood.?

    I have built 18 or 19 small boats (I loose count), all wood, never has this been an issue.

    Please explain why you can not just bend it to follow the chine. Post pictures of the design.
     
  5. tunnels

    tunnels Previous Member

    Chine logs !! wow i havent heard of that exspression !! but i understand what is being refered to !!
    1984 when i worked in Tahiti the wood boat builder next shed to where i was used the branchs of trees that they had a great pile of all laid out and dry as a bone they had a plywood pattern of the rib shape and laid it on the branch till they found the right shape then band sawed two 1.5 inch thick strips off the branch !!that way the trees grain followed all way through from top to bottom

    Cutting a whole series of thin batterns and epoxy laminating them together around the rib shape is the next best thing !

    In fibreglassing can use a simular principle but using layers of unidirectionall glass and foam with double bias glass all done in combination .

    Right at this moment i have draw up a life saver for the designer that had spec-ed window mullions to small in size and have to carry not only the window glass where it get stuck to and joined but the whole weight of a cabin with a small flybridge on top .
    The size makes it seemingly impossible but its how its constructed thats the key . this is what i came up with !!
    The mullions are just where the internal foam glass frames carry on from and go across an opening where the screen glass goes then convert back into frames again .
     

    Attached Files:

    • 002.jpg
      002.jpg
      File size:
      254.1 KB
      Views:
      811
  6. bkwk
    Joined: Aug 2012
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: usa

    bkwk New Member

    Thanks for the responses so far.

    Today I played around with the chines again. I origionally had cut a 1x12 down to a 1x2 for the chine. Which was really a 3/4 by 2. Then thought that a 1x2 is usually a 3/4 x 1 1/2 so I cut the chine down to a 3/4 x 1 5/8 today and was able to bend one side close enough to make it work. Im going to chaulk up my lack of experience to this bending problem. I had an 8ft chine and had used an 8ft piece of wood so I did not have much leverage to help with the bend. I scaled down a 12ft model to an 8ft model but I think the bend was a little to abupt for the scaled down version. I was able to get one side close enough and screwed down. I am working on the other side which is currently clamped in a bend but hasnt quite bent far enough yet. I think with a little help from an assistant I can get it close enough to work.
     
  7. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Are you using the same dimension chines on the 'scaled down' boat ?

    I know you said that laminating wasnt an option, but ff your chines are two hard to bend, its not that hard to saw them in half lengthways, and bend one half in place, then epoxy and glue the other half on top with a bunch of clamps to hold them in place.

    It will be a stronger chine than just one piece of wood. If either of the chines looks like breaking, epoxy some 6 ox glass tape to the outside of the bend. You will find you can then bend it without snapping.
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 474, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    One trick that is often employed on a tight radius is to cut a slot along the greatest area of the curve, so you'll be bending two 3/4" square pieces, instead of a single 1x2. Once you have it in position, you can wedge open the slot, pack it full of thickened epoxy and let this cure. When dry, it'll be one continuous piece of wood again. The slot only runs as far as the hardest part of the bend, then stops, leaving the rest of the chine log intact.
     
  9. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Unless stated (like, "made from one by twos available at your local lumber yard..."), the reduction of 2", e.g., to 1 1/2" as is done in building materials, is not done when shown in boat plans---- so your chines should be a full 1" by 2". This is because sizing is so much more critical when building. You might have, for example, 1 1/4" x 2 3/4" shown. Obviously, if something like 1 1/4" is spec'ed, that's exactly what was required.
    Calling a 3/4" x 1 1/2" a one by two is only a way of listing and buying building materials that are sold that way by long tradition (due to referring to the dimensions prior to planing).
     
  10. troy2000
    Joined: Nov 2009
    Posts: 1,743
    Likes: 170, Points: 63, Legacy Rep: 2078
    Location: California

    troy2000 Senior Member

    I'll take bets that if whoever drew those plans specified 1x2 chine logs, he meant for the builder to use S4S nominal-sized boards.

    The design is most likely for a 'Home Depot special,' to swipe a phrase from PAR... hard to imagine it calling for full-dimensioned wood.
     
  11. bkwk
    Joined: Aug 2012
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: usa

    bkwk New Member


    lol, yes, indeed it is a "Home Depot Special".
     
  12. bkwk
    Joined: Aug 2012
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: usa

    bkwk New Member

    Ok, got the other chine in place this evening with a wrachet strap and a wedge of wood. Put the rear, middle, and front chines in place. Screwed only for now. Will glue and such later. I tried to post pictures but my camera had issues loading on computer. But for those curious it is an:

    8ft jon boat, plywood bottom, 36 inches at rear, 30 inches at front, curved line was drawn from 5 feet at zero to 6 feet 6 inches at minus one inch and front 8 foot at minus 3 inches(this being from both sides of the bottom). Chine log construction, screws, goriila glue, BC exterior grade plywood bottom, select knot free pine for sides, transom, front, and chines. To be primed and painted with exterior paint. No epoxy or fiberglass will be used. This boat to be stored out of weather when not in use. Will be moving post and photos to the building thread when I get camera fiqured out.

    Thanks to all advise posted, this is my first boat build, I wanted to go small and simple first, If she floats I plan on going 12 to 14 foot for the next.
     
  13. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Probably the designer meant 3/4" x 1 1/2" but he must state so on the plans somewhere. If you have to guess, what good are the plans? An experienced boat carpenter would sense which dimension was the correct one but these boats are built very often by novices and they have no experience to guide their guesswork.
    I would say bkwk should read the plans very carefully and see if there is mention of lumber yard sizings somewhere.
     

  14. ancient kayaker
    Joined: Aug 2006
    Posts: 3,497
    Likes: 146, Points: 0, Legacy Rep: 2291
    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    I may be too late with this info but the sharpness of the chine bend (and the stress in the wood) is proportional to 1/L^2 where L is the length. So if you cut the length to 2/3 and kept the beam the same the bend is now more that twice as sharp as before. At the same time the leverage is reduced so the force required is now increased more than 3 times.

    In the finished boat most of the strength comes from the plywood skin, the chine logs mostly provide enough glue width for a strong joint. I once cracked a chine log when bending it so I cut kerfs halfway through on the inside of the bend, every 2 or 3 inches. The logs bent easily after that. BTW this should not be done with a “conventional” build where planking is applied over a frame as the chine log strength will have been factored into the hull by the designer.

    Alternatively, if you reduced the ply thickness for the smaller boat, you can reduce the thickness and width of the chine log by the same amount. I use 3x the ply thickness as the minimum dimension for both width and thickness, extra width is usually specified to reduce twisting and allow for beveling.

    Incidentally; on the camera issue lots of cameras have the same problem; if you have a SD card you can remove it and plug it into a SD card port in one of the USB sockets, this is much faster and safer IMHO.
     
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.