25' Double Eagle aluminum build (placing stringers)

Discussion in 'Metal Boat Building' started by Northeaster, Mar 10, 2014.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    That reflection fooled me.
     
  2. Northeaster
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    Northeaster Senior Member

    Hi Folks - hoping for a bit more advice from the experienced fokks here.

    I will finish tacking the 2nd topside on this weekend, and hopefully the transom the following week, before flipping it over to weld the inside seams of keel and chines - then flipping back upside down to backcut and weld outside of same seams.
    I have a couple of questions though:
    - transom - I have never seen mention of transom welding (in sequence of other welds), so when is it best to weld inside and outside of transom to bottom plate (fillet welds) and transom to topsides outside corner joints)?

    - Should I tack on long pieces of angle temporarily on outside of keel and chine seams before flipping over to do inside welds? If so, I could then leave them on to do outside welds of same seams, if placed a few inches from joint - it does make backchipping of outside tacks and seams with skillsaw more difficult though - doable, just more difficult.
    What is normally done?
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Are you tacking one side only..then flipping...or fully welding one side then flipping. Not 100% sure what you're saying here....as it is conflicting.
     
  4. Northeaster
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    Northeaster Senior Member

    Tacked on one side only- The outside of keel and chine seams are tacked every 6 inches now, and I had planned on flipping it (merely for easier welding and less fumes accumulating) and then fully welding inside of same seams. Then flip back upside down, backcut to good root and fully weld outside keel and chines, starting with the keel and working from midship towards bow and stern, alternating.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Ok i understand now.

    You should fully weld one side before flipping.
    Also you need to break/grind the spot welds out before welding over them. You should never weld over a spot weld.

    You should also have the transom in before flipping. Since this helps to hold the hull together too. If you flip without welding the transom, you'll most likely end up needing to do a bit of cutting fairing in after! As the hull will move if not stiff enough!
     
  6. Northeaster
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    Northeaster Senior Member

    I apprecate the advice!

    re: needing to fully weld one side before flipping - is this still necessary if I am not actually lifting or putting any weight on the hull itself?

    It's hard to see in the pics, and the boat jig is not raised to flip in the pic either.... but the heavy duty jig connects via a sliding tube inside a sleave attached to a tripod at each end (aft one is not in place in pic).

    I should be able to jack the jig up slowly, until the center of gravity (of the jig and boat combined) is level with the rotating sleeve on the tripod, and the whole mess should be able to be spun around like a chicken on a rotisserie. I have large bolts that thread into nuts wleded onto the sleeve, to act as a break / position stop - not to be used without other safety steps..., but I should be able to position the boat at any position, around 360 degrees.

    I copied the concept from pics Kevin has posted in other forums- he calls it the Davis jig. You can see parts of it in pics below.

    The hull sheet is tacked in a dozen places to the stem and a few frames, and I would put a few large straps around to alos hold the hull to the jig - the hull only weighs about 1000 - 1500 lbs at this point.
     

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    Last edited: Mar 18, 2015
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Well if so, why ask:

    Thus is everything secured or not? Doesn't sound like you're convinced yourself.

    If it is secured...why the straps?....that should answer your question!
     
  8. Northeaster
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    Northeaster Senior Member

    sorry, The tacks are not really there to hold the boat, while right side up.i.e. when the hull is hanging frames, which securely bolted to the jig - so therefore I think it is reasonable to have a few straps around it as well.

    My question is - do you only suggest to fully weld one side before flipping when builders actually out weight on the frame (on old tires for example) or lift directly on the hull to flip?

    |In my case, do you think tacks only on one side are enough, or would you still recommend fully welding one side?
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Whenever we have flipped boats we fully welded everything. Reason being is that the weight of the boat needs to go somewhere. No matter how you turn it...how is it being supported? Thus you need to cater for movement, no matter how small or large. Best way is fully weld. But this is inside and out, not just one side!

    Without knowing how much or little is tack welded and the arrangement of the structure internally, to say definitively is hard to advise.
     
  10. Northeaster
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    Northeaster Senior Member

    Ok - I understand it is hard to advise with all of the variables- thanks for taking the time to respond!


    The main thing I would like to know now is if folks think I need to temporarily tack long angle or flatbar sections, on edge, along one side of the keel joint, or along the chine (either a couple of inches onto topside or a couple of inches onto bottom plate) - in order to control warpage while welding the inside of these joints - they are currently tacked on one side only - the outside.
    If so, should it go the entire length of these joints, or only on the more flat areas, where the plates do not form a nearly 90 degree outside corner joint for example.
    Input appreciated!
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    The reason why it will warp/buckle is 2 fold:-

    1) Incorrect weld sequencing
    or
    2) Insufficient stiffness of the joint

    or both.

    There was an article in professional boatbuilder magazine recently on the welding sequencing that may be of use for you. EDIT...It is in the Oct-Nov issue of last year (2014).
     
    Last edited: Mar 22, 2015
  12. Northeaster
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    Northeaster Senior Member

    I will try to mitigate warpage by following recommended sequence as well as using temporary stiffeners.

    Not sure if I should make a new thread, as really ot to do with stringers any longer -

    Anyway, progress report - finished flipping boat over using jig based on Kevin's "Davis Jig" pictures. Worked well and I lucked out and was very close to center of gravity on first try, as it turned by hand (with long board as a lever)- with safety lift line in place in case it wan't well balanced.
     

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  13. Ad Hoc
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    Ad Hoc Naval Architect

    Nicely done :)
     
  14. Northeaster
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    Northeaster Senior Member

    Thanks AdHoc!

    Finished welding the inside seams of keel and chines ,and took about an hour to flip the boat back upside down working alone.

    I will start on backchipping the outside of same seams tomorrow and welding them up, starting with the keel, then chines ,working from midships towards ends.

    Also, while right-side up I placed the transmission in it's rough place, going from my full size drawing/ sketch of hull, frames ,CB of boat and CG of engine/gearbox.
    Then drilled small hole through keel seam for prop shaft mockup and tacked temp brackets to hold the mockup shaft in place at transmission coupler and at strut / cutlass bearing location. I only used a couple of 1/8" tig welding rods end to end for the mock-up shaft for now.
    I didn't want to enlarge the hole in the hull until the gear and engine are more mocked up for real, in case I am able to modify frames or location slightly and get the engine even lower in the hull.

    I am still debating between a full keel, per plans with a skeg bar to the bottom of rudder post or a partial / lower keel (as in poutboard version) and then a more exposed strut, prop and rudder. An owner of the same design told me he would go with a small keel, as the full keep version stayed too upright (no lean) during turns and he thought a small keel would be a good compromise, although it would be difficult or impossible to have a skeg bar, unless the small keel took a depe dive with a piece of flatbar for example, just before the prop.....
    The plans had called for a single plate keel but Kevin talked me out of that, dues to multiple repairs he has made in the past, and he advocated a box keel. So, that is the route I will likely go, incorporating the shaft tube/ cutlass into the aft end of the box keel, rather than requiring a separate strut to hold the cutlass bearings.
    Will post pics/ plan drawing when I have time.
     

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    Last edited: Apr 4, 2015

  15. Ad Hoc
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    Ad Hoc Naval Architect

    I agree with Kevin a stiffer (box) keel is better. Single plate will get bend easy in a grounding and do major hull damage.

    I see you decided not to sequence the welding as per that Proboat article.
     
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