Aluminum "Shoal Sailer"

Discussion in 'Sailboats' started by KVA, Aug 15, 2020.

  1. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Assume that the top view looking down on the water line of the boat when heeled is an oval. Any protrusion, ie the curved pipe that you have suggested, will offer resistance to the forward motion of the boat. Ahead of the midship point, this
    will be in essence a scoop. Your curved protrusion could offer resistance to lateral slip without increased drag, only at the mid point, apex, point at which the tangent of the curve in the water line to the keel, at all other times ahead and behind of the midpoint, the protrusion will mainly produce drag in the direction of travel.

    You do not need tabs to locate plate to plate in the proper location. Depending where you have the sheets plasma, waterjet, laser cut, they will more than likely be able to etch corresponding points on adjacent sheets.
    If not an etch a simple kerf cut at 90 degrees, say 1/8 of an inch into the plate periodically would do it as well. The 1/8 inch cut will be filled with the weld bead

    There has been quite a few responses regarding the welding. I do not see the focus on sticking flat bar into spaces between butt joints. This will add at least two further full length welds into each joint.
    If you weld along one side of say the flat bar in post #55, 4 times, the flat bar will bend upwards, ie make the bottom concave and it is unlikely that you will be able to straighten this after welding.

    If you are trying to make the joint "stronger" than the surrounding plate, you can stitch weld in the flat bar after a proper joint has been made up.

    Our boats were built to resist non intentionally "grounding " 4000 pound boats, 30 mph, hitting rocks. Our bottoms, 1/4 inch, stringers 2 1/2 x 5 x 1/4 angle on 12 inch centers. We welded the angles in after the shell was welded. A stitch weld,
    6 inch bead, 8 inch skip, 6 inch bead, etc welded both sides, opposing beads, and the stringers would always make a slight curve due to the shrinking of the angle at the weld beads.
    A strategic application of heat on the top flange after welding, and the stringers would straighten themselves out.

    Along the keel, on the inside received an additional layer of 5 x 1/2 inch flat bar, both sides of the keel line, then a 1/2 by 5 inch flat bar on end as the keel often took the brunt of any impact forces plus we needed to ensure that the plate etc ahead of the jet intake would not flex upon intake. (certainly under load, everything stretches under tensile loading but we needed to ensure that the intake platform where the jet intake was bolted to would not deform the intake)

    There is no need to provide additional support at the plate butt joints within the joint.
     
    Last edited: Aug 31, 2020
    A II and bajansailor like this.
  2. KVA
    Joined: Jun 2020
    Posts: 9
    Likes: 1, Points: 3
    Location: Spain

    KVA Junior Member

    Thank you for sharing the construction details!

    What would be bad about tabbing all the sheets together?
    (assuming that no crevices remain after welding)
     
  3. A II
    Joined: Jun 2020
    Posts: 176
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    Location: Belgium ⇄ the Netherlands

    A II no senior member → youtu.be/oNjQXmoxiQ8 → I wish

    My guess is the form would be forced by the tabbing, and not forming a gentle curve.
     
  4. KVA
    Joined: Jun 2020
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    Location: Spain

    KVA Junior Member

    Sure, I could see that if there is only one tab every meter or more..
    I was thinking more like 20cm tabs every 10cm, same sort of pattern as an intermittent weld, and with the slots curved per desired form.. so the thing seriously locks together before welding and ideally without any/much fixturing.
     
  5. A II
    Joined: Jun 2020
    Posts: 176
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    Location: Belgium ⇄ the Netherlands

    A II no senior member → youtu.be/oNjQXmoxiQ8 → I wish

    Re post #61:
    Yes, the post #45 and #55 suggestions are doubling the needed welding length, and also the position of the 4 longitudinal welds will deform the added flat bar like crazy, the flat bar's mid section will bend upwards, and the flat bar's ends will bend downwards, pulling the hull panels along with them, and so badly deforming the hull sides into concave shapes.

    Indeed, if added strength at the joints is desired than better add longitudinal stringers above the joints in the way you've suggested after the hull panels are welded together inside and outside.

    very poor chine stringer suggestion for flat bottomed boat, from post #55:
    4 x weld instead of 2 x.jpg

    The below quoted and originally very ill placed text in post #48 fully applies here, so I don't have to type that up myself, thanks for that buddy.
    see post #51 for info
     
    Last edited: Sep 2, 2020

  6. A II
    Joined: Jun 2020
    Posts: 176
    Likes: 65, Points: 28
    Location: Belgium ⇄ the Netherlands

    A II no senior member → youtu.be/oNjQXmoxiQ8 → I wish

    With that kind of tabbing my argument against it, in post #63, is indeed no longer valid.
     
    Last edited: Sep 1, 2020
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