Plywood: fasten to frames or stringers?

Discussion in 'Wooden Boat Building and Restoration' started by troy2000, Dec 8, 2009.

  1. troy2000
    Joined: Nov 2009
    Posts: 1,743
    Likes: 170, Points: 63, Legacy Rep: 2078
    Location: California

    troy2000 Senior Member

    Years ago I read a piece on building boats out of plywood. I don't remember who wrote it or where I found it, but I do remember the author insisting that plywood sides and bottoms on a boat should never be fastened directly to frames or bulkheads. According to him, the only proper method was to run stringers fore and aft, and fasten the plywood only to the stringers.

    I wouldn't guarantee it, but it seems to me he was writing back around the early sixties. And I believe there were photographs of a fairly small motorboat under construction.

    Does anyone agree...disagree...think it doesn't matter?:confused:
     
  2. gonzo
    Joined: Aug 2002
    Posts: 14,509
    Likes: 660, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    There have been a few boats built like that. However, saying that it is the only method is rather fanatical.
     
  3. troy2000
    Joined: Nov 2009
    Posts: 1,743
    Likes: 170, Points: 63, Legacy Rep: 2078
    Location: California

    troy2000 Senior Member

    I wish I could remember who the author was. He was quite insistent about it. I think he believed fastening to a frame concentrated the stresses, or some such thing.

    For some reason, I always thought I had read it in a Glen-L Marine how-to. But I just went and looked at their website, and that isn't what they say.
     
  4. boat fan
    Joined: Sep 2008
    Posts: 717
    Likes: 17, Points: 18, Legacy Rep: 435
    Location: Australia

    boat fan Senior Member

    They ( Glen - L ) say this ...

    There was a builder of high end Italian power boats that said he would never do it ...stress risers .
    He also said not to notch stringers into frames for the same reason.

    Don`t remember who he was either ...
     
  5. troy2000
    Joined: Nov 2009
    Posts: 1,743
    Likes: 170, Points: 63, Legacy Rep: 2078
    Location: California

    troy2000 Senior Member

    Then maybe it was a Glen-L publication I read it in, way back when. But if I remember right, the recommendation at the time was quite a bit stronger than "preferably.":)

    I don't think I'll be building with plywood thin enough, or fastenings spaced closely enough, to worry about it.
     
  6. wardd
    Joined: Apr 2009
    Posts: 897
    Likes: 37, Points: 0, Legacy Rep: 442
    Location: usa

    wardd Senior Member

    build the skin then fit the frame to it

    the basket approach appeals to me
     
  7. boat fan
    Joined: Sep 2008
    Posts: 717
    Likes: 17, Points: 18, Legacy Rep: 435
    Location: Australia

    boat fan Senior Member

    Troy ..these guys don`t like it either .....

    Personally , I would build this way.

    [SIZE=+1][​IMG]Nexus Marine Corporation

    http://www.google.com.au/url?sa=t&s...n_mHCg&usg=AFQjCNG24fBe-lI3X1fbrxztWeoCZt061w

    The chine and all stringers have now been installed. All these members were precoated with epoxy resin before they were installed. The stringers have been glued and screwed to the outside of the frames. The stringers are not notched into the frames. This prevents "hard spots" in the planking. It's stronger this way. The aft cabin bulkhead and engine room bulkhead have to be watertight, so we have blocked between the stringers just on those bulkheads.
    [​IMG]

    [/SIZE][SIZE=+1]Here we are looking at the inside of the transom, portside. Again , with the bottom stringers passing over the aftmost frame and notching into the transom frame only.[/SIZE]
     
  8. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Everything depends upon the design, the type of boat, size, etc.. Plywood is manufactured in several ways that vary in cross-grain stiffness. Imagine building a house floor using the plywood with the grain running parallel to the joists below. I've done this with plywood that had poor cross-grain strength and within a short time it sagged from normal loads.
    A flattish hull shape with wide panels (such as a jon boat) could really use some cross-frames in contact with the plywood. On the other hand, a more curvacious hull like a nutshell pram is plenty strong enough with no cross-frames. It also matters, as said, if the plywood is stiff across the grain seen on the outside plys. It matters how robust the plywood relative to the boat's length. Nothing is as simple as to state all boats benefit from frames set in from the stringers.
     
  9. hoytedow
    Joined: Sep 2009
    Posts: 5,658
    Likes: 276, Points: 93, Legacy Rep: 2489
    Location: North of Cuba

    hoytedow Bananas

    One reason not to screw skin to frame is that quite often the frame is nothing more than plywood, which does not take a screw in the edge well.
     
  10. boat fan
    Joined: Sep 2008
    Posts: 717
    Likes: 17, Points: 18, Legacy Rep: 435
    Location: Australia

    boat fan Senior Member

    Yes , quite true.
    Stringer spacing has a lot to do with it also.( more stingers , thin skin ) ?
    or opposite .

    If you look at that power boat , the stringers are wider ( 2x ? ) and more closely spaced on the bottom.
    Makes sense .


    Troy ...your sharpie will have a relatively heavy bottom , no ?

    As sharpies benefit by having a heavier bottom , ( 2 x layers ( or more ?) bottom planking ? ) I don`t believe there would be any issues here , regarding sufficient strength.

    Water would collect easier in the lowest part of the " bilge " to mop up .....

    I would just run the stringers over the frames.
    Easier , faster build.
    Better also for a trailer sharpie I think.

    I noticed that they ( Nexus ) build their dory that way as well.
    Should be good for you too.

    What do you think ?
     
  11. jimm
    Joined: Sep 2007
    Posts: 37
    Likes: 1, Points: 0, Legacy Rep: 23
    Location: us

    jimm designer MID

    In boats I have designed, I am familiar with (30' to !30' range) longitudinal and athrotship frames comprise the structure below the waterline. bulkheads and soles constitute reinforcement to the hull above the waterline and are bonded wherever possible to the hull and deck to reinforce its strength. Ths includes seating structure and counter tops.
     
  12. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Dories are a good example of transverse framing in full contact with the hull. The bottom is very thick and there are no stringers. Not even a keelson. This is true whether of plywood or boards.
    I believe very light structures do benefit from recessed transverse frames and many light stringers. When going very light, such as building a plywood skinned kayak, the web frames are usually recessed. This prevents hard spots and localized stresses. Hydrodynamically, very (1/8") thin plywood would act like a stiff fabric. Cross-framing ridges would not flex inward, whiile longintudinal dishing with recessed frames would have better flow characteristics.
     
  13. boat fan
    Joined: Sep 2008
    Posts: 717
    Likes: 17, Points: 18, Legacy Rep: 435
    Location: Australia

    boat fan Senior Member

    Not on this one Alan :

    No frame contact. Stringers on sides and bottom.

    Like you say dories usually have trans. frames in contact with hull...no stringers ....

    Unusual for a dory , but there it is.

    I think the key here being planing dory.....

    I would not build a sharpie without a keelson.

    [​IMG]

    Custom wood 23' Planing Dory

    [​IMG]

    [​IMG]

    [​IMG]
     
  14. peter radclyffe
    Joined: Mar 2009
    Posts: 1,415
    Likes: 61, Points: 58, Legacy Rep: 680
    Location: europe

    peter radclyffe Senior Member

    it shows how weak plywood is
     

  15. boat fan
    Joined: Sep 2008
    Posts: 717
    Likes: 17, Points: 18, Legacy Rep: 435
    Location: Australia

    boat fan Senior Member

    :confused::confused::confused::confused::confused::confused::confused:

    Huh ?
     
Loading...
Similar Threads
  1. sdowney717
    Replies:
    30
    Views:
    590
  2. Travis Grauel
    Replies:
    26
    Views:
    1,613
  3. Paul D
    Replies:
    13
    Views:
    1,481
  4. Floatything
    Replies:
    0
    Views:
    1,081
  5. juan manuel luna
    Replies:
    21
    Views:
    1,783
  6. Old salty
    Replies:
    4
    Views:
    2,600
  7. Vesimakara
    Replies:
    2
    Views:
    1,676
  8. DSR
    Replies:
    13
    Views:
    1,285
  9. theoldwizard1
    Replies:
    4
    Views:
    2,670
  10. stubbymon
    Replies:
    12
    Views:
    5,269
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.