Letting Stringers & Chines "Stand Proud" from Transverse Frames

Discussion in 'Metal Boat Building' started by timgoz, Oct 2, 2006.

  1. timgoz
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    timgoz Senior Member

    Is the amount you let the chine/stringer project from the frame dependant on the stock thickness?

    I will be working with 1/4" stock, 1/8" topsides & 3/16 bottom plate.

    Of course the above depends on the called for welding schedule. Mine does not call for the frames to be welded to the hull plate, but to the stringers & chines (intermitant).

    Thanks all.

    TGoz
     
  2. marshmat
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    marshmat Senior Member

    Can't suggest any dimensions, I've never done that either. I do like how you plan to weld the hull plate to the longitudinals but not the frames; indeed, the gap you describe would be a good thing. If you scrape a rock this way, you would likely get away with a long dent; hit a rock with a metal hull where the frames touch the plating, and you'd probably get a puncture where frame and rock meet.
     
  3. timgoz
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    timgoz Senior Member

    Marshmat,

    Several of the books I have recommend the above. Gotta reread the pertinent parts but I think the distance involved is approx. 1/8" or less.

    If memory & common sense serve me correct the technique also helps to avoid the "starved" horse look.

    Hopefully a smallish (28-30') steel displacement hull at normal cruising speed could survive a high percentage of collisions with most anything. That excludes the involvement of large breaking seas & large vessels.

    Take care.

    TGoz
     
  4. MikeJohns
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    MikeJohns Senior Member

    Presuming you are slotting the longs into the frames

    It is common for straight flat bar frames to stand off the plate some distance with chine construction since the cross section of the plate particularly lower fwd is not straight so variable projection of the longs past the frame allows for the transverse plate curvature.

    The frames only need to touch the plate where they are required to be welded eg tank ends and bulkheads.

    Hope this helps
     
  5. timgoz
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    timgoz Senior Member

    Thanks Mike.

    TGoz
     
  6. Thunderhead19
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    Thunderhead19 Senior Member

    You could figure out how much stretch or flex you'll get in the plating, and make the gap wide enough to prevent clicking and rattling when the hull sheet flexes enough to contact the transverse frame. Typically in longitudinal framed design, you're only using the transverse frames to hold the hulls cross sectional shape so that the longitudinals can do their job. As long as they can do that, its up to you how much room you want to take up indside the hull with those frames. You can notch them so they don't stand too far proud of the longitudinals, or you can sit them right inboard.
     
  7. tom kane
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    tom kane Senior Member

    To me,good bottom skin drainage makes a boat easy to keep clean and dry and safe, so stringers should not be notched into frames but contact with the bottom plate stringers only from stem to stern.Nothing worse than having a boat devide up into many sections that retain water.
     
  8. timgoz
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    timgoz Senior Member

    Thanks guys.

    Tom,

    Would not well thought out & placed limber holes facilitate drainage?

    Take care.

    TGoz
     
  9. Wynand N
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    Wynand N Retired Steelboatbuilder

    Timgoz,

    Letting the stringers stand proud from the transverse frames can also be termed "longitudinal framing".
    This is an excellent way to build a strong and fair hull. The way you go about is to slot your frames, fit the stringers loosely into the slots and only tack welding this to the frames. Plate your hull and fair the plates so you have a smooth hull. Now push the stringers tight against the hull plating and tack weld into place. Check fairness of hull and make adjustments if needed, and only now weld the longitudinal stringers to the frames and start the welding up everything.

    I include two photos showing this type of method and it was of a Dix 65 hull I had built. It is a raduis chined hull and was build upside down. Note that the frames in the keel area actually touches the hull to strenghten that area for the keel loading.
    The gap between the plating and transverse frames is 20mm
     

    Attached Files:

  10. jehardiman
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    jehardiman Senior Member

    Start with 3 times the diameter of the rod you are going to use to wrap the ends then do a mock-up weld with that rod. That will tell you as this is generally more of an access issue than a flex issue. Otherwise, do quick beam deflection calculation to 1/2 yield in the maximum length longitudinal using 10t of skin plating for the flange. If that is greater than the access use that.
     
  11. timgoz
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    timgoz Senior Member

    Wynand,

    Thanks for the help. I hope to get going on a Thom Thumb soon. My plans are getting quite old (bought them in 1991) so I plan to loft the boat instead of using the patterns as they may have shrunk, ect...

    Bruce Roberts recommends the patterns ,but all I have read otherwise calls for lofting from the lines & off-sets table. What do you think?

    I ask because I see in previous posts that you have built several Thom Thumbs.

    Also, as to letting the stringers proud from the frames. I assume with the thinner plate and framing materials that I will be working with a somewhat smaller gap than 20mm? Maybe 8-10mm. Is my thinking in line?

    Take care.

    Thanks again to all who have helped.

    TGoz
     
  12. origamiboats
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    origamiboats Junior Member

    The 36 foot steel yacht design I am building to uses no transverse frames, and does not require a strongback to build. With the right design you can dispense with use of most transverse members and keep a lot of weight out of your boat, which allows you more carrying capacity for water, fuel and stores. No need to put limber holes, as all framing runs for an aft. My boat does have longitudinals, which some might call longitudinal framing, plus some transverse framing (4 webs) in the keel area to spread loads there. There is more information about my style of boat in the Yahoo group, "Origamiboats" (link below).

    Alex

    http://groups.yahoo.com/group/origamiboats
     
  13. timgoz
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    timgoz Senior Member

    Thanks Alex,

    The Tom Thumb can be done "frameless" but requires a strongback. I think Wynand has done one or more this way.

    Frameless would have to make sandblasing less problematic & time consuming I would thing.

    I'm gonna take a look at the link you have provided. Thanks again.

    Take care.

    TGoz
     
  14. Wynand N
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    Wynand N Retired Steelboatbuilder

    Tingoz,

    Yip, I had indeed built a few (seven) TT24's, all of them of frameless construction. The plating have been done over a "former" with the longitudinal stringers fitted and the stringers come off with hull.
    BTW, the complete hull and deck plating is 3mm mild steel.

    Here are a few pics, one of plating in process, hull removed from "former" and my own TT24 nearing completion in my backyard,
     

    Attached Files:


  15. timgoz
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    timgoz Senior Member

    Thanks Waynand,

    Do you lift the hull off of the former & cross brace ASAP for roll over, or do you keep the former in for roll over & then lift it out of the hull?

    How does the Tom Thumb motor? Where I hope to be located will result in alot of motoring as the winds can be quite light & currents heavy. What would you recommend in the way of horsepower, 15hp? Could I expect 5kts. at approx. 1/2 gph with a Yanmar or similar diesel engine of the above size?

    Did you loft the boat, or use the patterns provided?

    It looks like you did a real fine job on your Tom Thumbs.

    Thanks again.

    TGoz
     
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