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
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  2. KVA
    Joined: Jun 2020
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    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
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    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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    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
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    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
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    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
  7. KyleA.
    Joined: May 2018
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    Location: Canada

    KyleA. Junior Member

    Hey it's been awhile, finally got back to it a bit today.
    I have been playing with the 'scow' style, and think that something like this both looks nice and might work alright in terms of shallow draft.
    upload_2020-11-21_15-40-54.png
    The narrower end is the bow.

    Basically turned into some sort of barge.

    Looks like this heeled 15 deg, 5 deg yaw, 1 deg pitch forward, 1360kg disp.. draft ~ 0.33m
    upload_2020-11-21_15-43-28.png

    I was playing with flat, wedge, and round ends and the round ends definitely suit appearances the best. The round entry might make it a little easier going with head-on waves.
    It also seems like a manageable shape to construct; almost flat panels etc. The ends can be rolled.

    Also thinking that this sort of shape will lend well to water ballast tanks along the sides..
     
  8. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

  9. KyleA.
    Joined: May 2018
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    Location: Canada

    KyleA. Junior Member

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  10. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    Looks like a Humber keel which has been slightly tapered.

    It also looks quite narrow.

    I was thinking of something a bit more beamy, about 2.4 M, and about 8.0 M long.

    It would have side panels that are about 1.0 M high, which would be slightly flared, so the bottom plating could extend past the chine without the boat being wider on the bottom than at the top. When sprung, the tops of the sides would curve upward as will the bottoms, which would give you a natural sheer and bottom rocker (more may need to be cut in to get adequate rocker depth).

    Plan veiw wise, I would divide the hull into three lengthwise segments which would be nearly equal in length. The first would be the bow, which would come nearly to a point. It might have a stem-transom, which is defined by being taller than it is wide.

    Next would be the center segment, in which the chines run absolutely flat an parallel to one another. This would be the segment in which the roughly 6 mm thick bottom plate will extend roughly 20 cm past the chines. The chines would be about 2.0 M apart there.

    Finally, there wold be the stern segment, in which the sides curve back to a transom which is half the width of the boat.

    The sides would have no twist.

    I envision a twin rudders with one on each end of the transom. I also see a long, shallow box keel which would be about 20 cm deep, which could be water filled.

    The idea here is to have a heeled draft roughly equal to the level draft.
     

  11. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    I decided to do a straight-line representation of my idea to see how it would look.

    (see thumbnail)

    The basic idea is that the chine-runners act as a second keel.

    As the boat heels, the windward chine comes out of the water, and the leeward one immerses. The center keel becomes less and less effective, as the leeward chine and runner become more effective.

    This may seem similar to the chine-runner system on the Paradox one. It is. But it is not the same. With the Paradox system, the rudder is relied on to provide most of the lateral resistance. The beauty of that system is that the rudder can be short and deep, and can provide a nice lifting foil to lift the boat to windward. The catch is that you need a short, deep rudder with considerable area to do the job. In chronically shoal waters, this will not do. The rudder would be constantly hitting bottom and likely being ripped off the boat as a consequence.

    With my system, the runners and the long, shallow keel provide the lateral resistance, and the rudders (not shown) simply steer the boat.

    The consequence of this, is that this system has no real efficient foil to lift the boat to windward, but has two relatively inefficient long, shallow keels. It won't go to windward like a Paradox will. But it will go to windward in very shallow water, as the actual sailing draft is likely to be around half a meter deep. It will likely be more than its level draft. This would be good news in a grounding situation. By simply easing the sheets, you may be to get the boat free.

    The center keel serves three functions:

    1.) It helps guide the boat onto the trailer and helps hold it high enough, so the chines clear the fender tops. The bunks will serve mainly to keep the hull level.
    2.) to provide the initial lateral resistance to get the boat to heel rather than simply slide off to leeward.
    3.) to serve as a bumper to hit the rocky bottom first. This could be useful especially when motoring. The ends of the keel are designed to deflect and stop the boat when it hits the bottom, instead of jamming itself into crevasses.

    If the boat rode deeper, the center keel could probably be eliminated.

    But this would mean: decreasing the Beam, shortening the Length, or greatly increasing the rocker. All but one of these possible changes would shorten the sailing Length.
    Decreasing the Beam would also decrease the livability of the boat, not to mention limit its sail carrying power.

    The extreme Beam forward plan form is intended to cause the bow to lift, as the boat heels, rather than burrow. It also provides more internal volume.

    Trikster428.png
     
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