plywood on frames versus S&G

Discussion in 'Wooden Boat Building and Restoration' started by fabrice, Mar 29, 2010.

  1. fabrice
    Joined: Mar 2009
    Posts: 54
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Poitiers, France

    fabrice Junior Member

    Hi there,
    I'm sure it's been asked before but can't find the answer :
    what will be heavier ?
    plywood on frame with stringers, or plywood S&G ?

    I read a lot of reports on S&G building : It seems from time to time that the weight bill comes awfully over expectations, so I'm trying to figure out if it's worth building carefully and skillfully on frame, instead of gluing insanely thick plywood like a mad monkey :D
     
  2. hoytedow
    Joined: Sep 2009
    Posts: 5,627
    Likes: 256, Points: 93, Legacy Rep: 2489
    Location: North of Cuba

    hoytedow Wood Butcher

    You don't have to use a thicker plywood with stitch and glue than you do with frames. Frames would be heavier and less "comfortable" than the streamlined interior of a stitch and glue creation.
     
  3. jehardiman
    Joined: Aug 2004
    Posts: 2,735
    Likes: 340, Points: 83, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Actually, it will depend on the size of the boat/panels and the amount of curvature. For narrow panels with lots of bulkheads like a small kayak, Hoyt is correct, you don't necessarily need thicker panels or stringers. The larger the boat/panel becomes, and the distance between frames/bulkheads, there comes a break point where you can start putting in stringers and reducing skin thickness.
     
  4. fabrice
    Joined: Mar 2009
    Posts: 54
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Poitiers, France

    fabrice Junior Member

    Yes, this makes sense to me.
    plywood is a great asset, if only you understand well how it bends, and why.

    Fortunately building small canoes and kayaks one only needs small widths.

    So, asking again while being a bit more accurate in my terms :
    Doing the same small boat, assuming we choose the panels right thickness in both construction (shouldn't be the same I guess), which "program" will be lighter ?
    which one will be easier to keep in boundaries of a weight bill without drifting too much ?
     
  5. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    Generally S&G will be lighter depending on how thick you make your fillets, the weight of the cloth, what type of cloth used (dynell will suck up much more resin and so be heavier in combination). Generally a fillet thickness (from corner of joint to closest surface on the inside of the fillet should run about the same thickness as the thicker plywood used. So using 5mm bottom and 3mm sides the fillet depth should be 5 mm and taper around double the depth (10-12 mm) to nothing on each panel. Best way is to boarder tape the fillet area with painter's tape and do your fillets then pull the tape...like so:

    [​IMG]

    To give you a fillet that looks like this:

    [​IMG]
     
  6. fcfc
    Joined: Feb 2005
    Posts: 779
    Likes: 29, Points: 28, Legacy Rep: 399
    Location: france,europe

    fcfc Senior Member

    I do not thing there is a true answer

    English reply :p

    Technically, the plating is the same thickness for the same panel size. There is absolutely no reason to have it different.


    I fear the biggest problem is the designer/builder self confidence.

    For a framed construction, the plating is often bonded AND fastened. Kind of belt and braces, because the bonding only should be enough. If the plating is debonding, and need the fastening, there is something catastrophically wrong in the design or building.

    In a stich and glue, there is ONLY the bonding. So, there is a human tendancy to do a overkill bonding and filleting, just in case.

    There is also a severe lack of data for stitch and glue design for fillet size / epoxy charge to use and reinforcing tape with/weigth to use for S&G. In fact, I have not found engineering and design information on epoxy filleted T-joints for plywood.

    microfiber charge only, glass bubble charge + woven tape, phenolic bubble charge + biaxial tape, radius, tape width and weight :?: :?: :?: :?: :confused:
     
  7. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    OK...so I will go with Empirical data...I ain't never broken anything yet with the fillet I describe! I have used it in 8+ boats without a problem...no cracks, leaks or other structural failures. One fillet, one layer of cloth inside and one outside for anything under around 12 ft/ 700 lbs displacement (canoe/kayak style excepted...up to around 18 ft length for those). Over that add layers of cloth.
     
  8. gonzo
    Joined: Aug 2002
    Posts: 14,462
    Likes: 644, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    It can be either way depending on design.
     
  9. fabrice
    Joined: Mar 2009
    Posts: 54
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Poitiers, France

    fabrice Junior Member

    lewis, I'll stick to that (what an accurate word in the context :D )

    I wander on forum looking esentially for this kind of answer :
    Experience, helping me to figure out what I really need or want.

    BTW, your pics show a really clean job, congrats !

    FCFC : j'ai rien compris ! :D
     

  10. hoytedow
    Joined: Sep 2009
    Posts: 5,627
    Likes: 256, Points: 93, Legacy Rep: 2489
    Location: North of Cuba

    hoytedow Wood Butcher

    Fabrice,

    Vous comprenez plus que vous dire.;)
     
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.