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Thread: Fastener for steam bent frames

  1. #1
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    Default Fastener for steam bent frames

    I am building Assassin by Wes Farmer. I am strip planking with 1/2 inch cedar . I plan on using 1inch #8 silicon bronze screws to attach the 5/8 thick white oak frames. What spacing for the screws should I use?

  2. #2
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    Default Re: Fastener for steam bent frames

    Quote Originally Posted by Pete H View Post
    I plan on using 1inch #8 silicon bronze screws to attach the 5/8 thick white oak frames.
    This? https://duckworks.com/assassin-plans/

    OK, but what are you attaching said frames too?

    Or did you instead mean to tell us you're going to be screwing your 1/2" cedar (red? Alaskan yellow? Atlantic?) to those 5/8" white oak frames?

    I'd ask:

    - how wide are your cedar strips?
    - are you beveling each then edge-gluing them together during your build?
    - will you be beveling each strip then leaving a caulking gap?
    - you going with traditional hull finish or plan on covering with fiberglass bedded in epoxy?

    Screw spacing depends on what your answers might be, maybe more.

  3. #3
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    Default Re: Fastener for steam bent frames

    I would probably think about copper rivets.
    The spacing should be "just right"

  4. #4
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    Default Re: Fastener for steam bent frames

    I will be attaching the cedar strips to the oak frames, My strips are 3/4 inch wide, I am beveling each strip ,glue with titebond 3, edge nailing every 4 inches with 1 1/2 hot dipped galvanized finish nails, then fiberglassing the exterior with epoxy

  5. #5
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    Default Re: Fastener for steam bent frames

    Then 1 screw per strip at each frame, pre-drilled to avoid splitting plank or frame and countersunk into plank. Not much material to counterbore then plug screw holes in 1/2” thick cedar.

    I’m not sure why you want to edge-nail too… real chance of splitting strips even if you pre-drill pilot holes. Lot of work for not much additional strength given your plans for glass & epoxy. With frames on 8-3/4” centers at most you’d need just one nail kinda ‘more or less’ centered between each frame. Try not to have all those nails lined up in a tight row too, there’d be a weak spot in your planking running in between every frame otherwise. Better to offset each nail 1/2” or 3/4” alternately left/ right of dead center instead.

  6. #6
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    Default Re: Fastener for steam bent frames

    Are you really sure about edge-nailing? What benefit are you trying to achieve? Glue is strong enough, and that's before the fibreglass.

  7. #7
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    Default Re: Fastener for steam bent frames

    By my arithmetic, there will be over 2000 edge-nails. Some fraction of those will be off-center and really F&*K up fairing.

    Myself, Id use strip composite construction, with glass inside and out and no ribs. We did a 17 fantail launch this way and it worked out well.

  8. #8
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    Default Re: Fastener for steam bent frames

    I'm with Jim on this one. If you are going to use glass at all, go all in. Those oak frames will just get in everything else's way, add no extra strength, and then rot out from under you.
    Looking at the design it was probably for carvel construction, so the frames would have been integral to the design.

  9. #9
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    Default Re: Fastener for steam bent frames

    Quote Originally Posted by Slacko View Post
    I'm with Jim on this one. If you are going to use glass at all, go all in. Those oak frames will just get in everything else's way, add no extra strength, and then rot out from under you.
    Looking at the design it was probably for carvel construction, so the frames would have been integral to the design.
    Exactly.

    The dialogue describing the original Assassin build makes mention of 5/8" planking, 14 strakes per side, as well as hollowing the backsides to best fit the frames. That extra 1/8" is to allow for hollowing on the insides and fairing on the outsides.

    Changing planking to 1/2" may fit the frames more easily, permit strips to bend to fit. If the ultimate goal is to add fiberglass and epoxy on the outside, internal bent frames, at the spacing indicated, are mostly unnecessary.

    Same for edge-nailing planking strips together when bent frames will be taking so many screws (three, maybe four where a single plank would have required just one or worst-case two rivets) they'd be markedly weaker than if built as designed.

    Taking a traditional design then changing aspects of construction to fit a more appealing method isn't a recommended path for any but the Very Experienced Builder.
    Last edited by sp_clark; 07-29-2021 at 06:55 AM.

  10. #10
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    Default Re: Fastener for steam bent frames

    I think my strip planked ketch has a screw in every other plank. They're also edge nailed.

  11. #11
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    Default Re: Fastener for steam bent frames

    My primary guidance in building this boat has been Paul Fisher's book on strip plank construction. Several Selway Fisher boats are constructed the way I am building. He recommends frames instead of fiberglass on the inside when building a steam boat. He feels it is stronger to handle the weight of a steam plant. My boiler is only 140 lbs so that is not a issue but I do like the look of bent ribs in a boat. I think it is a a more classic look. I am edge nailing because nailing does contribute to the strength but the main reason is it eliminates all those clamps and having to wait for the glue to dry. S o far I am a couple thousand nails into the job and have only about a dozen nails poke thru on the inside. Getting back to my original question about screw spacing, I was thinking about 4 inches apart .

  12. #12
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    Default Re: Fastener for steam bent frames

    ya got a wonky recipe for this boat construction, thats fer sher

  13. #13
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    Default Re: Fastener for steam bent frames

    There is a detail about strip planked boats... they tend to expand as they take up moisture. When this happens they pull away from the frames, especially at the turn of the bilge.
    Every strip planked boat that I ever looked at had a gap between the frames and the hull at the turn of the bilge. Fiberglassed or not.
    John's suggestion above to omit the frames and just use glass cloth inside and out is a good one.

    (Rivets can be a smaller diameter than screws for a given holding power and need no counterbore. I would offset each one as you work your way up the frame)

  14. #14
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    Default Re: Fastener for steam bent frames

    Quote Originally Posted by Canoeyawl View Post
    There is a detail about strip planked boats... they tend to expand as they take up moisture. When this happens they pull away from the frames, especially at the turn of the bilge.
    Every strip planked boat that I ever looked at had a gap between the frames and the hull at the turn of the bilge. Fiberglassed or not.
    John's suggestion above to omit the frames and just use glass cloth inside and out is a good one.

    (Rivets can be a smaller diameter than screws for a given holding power and need no counterbore. I would offset each one as you work your way up the frame)
    I have never seen a strip plaked boat do that.Have a gap 'tween the frames and skin at the bilge turn, or anywhere else .

  15. #15
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    Default Re: Fastener for steam bent frames

    I think every one I ever inspected was that way. The hull planking expands with moisture across the grain like any other piece of wood, but the frames don't change length, something has got to give.

  16. #16
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    Default Re: Fastener for steam bent frames

    Get some G-Flex and glue the frames to the planking, then you can place the screws wherever you want, they will be only clamping aids. Even better, fiberglass the inside and glue in cedar frames just for show.

  17. #17
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    Default Re: Fastener for steam bent frames

    Quote Originally Posted by Canoeyawl View Post
    I think every one I ever inspected was that way. The hull planking expands with moisture across the grain like any other piece of wood, but the frames don't change length, something has got to give.
    If the skin of the hull is pulling way from the frames and causing a gap it would seem to me that there has been a fairly significant failure somewhere, no? Either fasteners have failed or been pulled through the planks or the frames.

  18. #18
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    Default Re: Fastener for steam bent frames

    If you'd have included in your first post those other details about your build (steam power over original specs for 2- or 4-cycle engine, that you've already been edge-nailing your strip planking) or done the math with that "... about 4 inches apart" comment on screw spacing... in strips 3/4" wide... meaning if you center screws in strips then every fifth strip would put a screw 3-3/4" from those above and below you'd have answered your own question.

    I wouldn't myself trust 1/2" of screw penetration every 3-3/4" to hold those bent oak frames against your hull during installation, drying or over time.

    I'd use G-Flex myself, maybe laminate the frames in place after the hull's been sheathed over removable frames mounted to a strongback.

    And bump up the scantlings for frames taking on steam engine & boiler mountings. Be a lot more weight aft than building to the original specs would leave you with.

  19. #19
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    Default Re: Fastener for steam bent frames

    Thanks to everyone for your response to my question. After reading all these posts I believe I should epoxy laminated frames to the planking and use the screws to clamp them in place while the g-flex cures. Should I screw them from the inside of the hull or the outside?

  20. #20
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    Default Re: Fastener for steam bent frames

    However you like. I would laminate the outside before turning, so that would only leave me the option of fastening from the inside, and I would simply use staples or nails. Fastening from the outside means you have to turn the boat twice, or laminate right side up.

  21. #21
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    Default Re: Fastener for steam bent frames

    You want your hull finished ‘bright’ on the outside? I’d think renewable paint-over-epoxy’d be a more practical choice.

    Which would leave me choosing screws into frames from the outside, later to be removed and the resulting #10-size holes filled with thickened epoxy, or drilled out to a slightly larger diameter then plugged with ‘trenails’ epoxied in place then trimmed flush.

    This all with hull upside-down if your comfortable making patterns from your finished hull while it’s still on the building frames so you only have to turn it once.

    If you’re not put off by turning it three times, add a single layer of ‘glass before turning it upright to then add frames. Most of the screw holes could be filled before turning it over again to fill the rest, then add additional layers of ‘glass & epoxy. Then paint.

    Then turn over once more for fitting out.

    Screws run through cedar into oak have vastly more holding power (purchase) than the same screws run through oak into cedar. You can use cheap steel pan-head sheet metal screws this way, with small scraps of strips under their heads to avoid impressions on your fiberglass or cedar if raw. And whatever choice of screw you use be sure to lube their threads before screwing them through a layer of G-Flex so they’ll come out with little effort… unless of course you choose to leave them in place. In which event flatheads set into countersunk holes are more appropriate.

  22. #22
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    Default Re: Fastener for steam bent frames

    I plan on painting the planking inside and outside. My planking is not clean enough for a clear finish plus I think paint will be lower maintenance. Other interior parts will be finished bright. Screws installed from the outside will be my choice then fiberglassing outside after frames are done.

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