Scaling the Bolger Single-handed Schooner

Discussion in 'Boat Design' started by lboatman, Jan 2, 2012.

  1. lboatman
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    lboatman Junior Member

    Happy New Year all!

    I was interested in building the Bolger Single-handed schooner, but it's too big to fit in my garage. So I've scaled the design to 94% (in all 3 dimensions to preserve the lines), converted it to stitch & glue from plywood on frame and designed carbon fiber masts. For those interested in the project, I've put up a website at http://www.morocz.com/BoatBuilding/SchoonerBuild.htm documenting the design rationale and the build. Expected launch is Spring 2012.

    Cheers,

    Laszlo

    PS - click on the picture for a larger image

    [​IMG]
     
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  2. marshmat
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    marshmat Senior Member

    She's looking pretty nice, Laszlo :) I'm looking forward to hearing how she turns out once you have her in the water.

    Phil Bolger did a few designs in stitch-and-glue that came out to about the same scantlings you chose for this one. As long as you don't take her out in a gale or drop her on rocks and reefs, I'm guessing it'll work just fine.

    Carbon masts on something like this seems a bit luxurious, but who am I to stop you?
     
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  3. Perm Stress
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    Perm Stress Senior Member

    Chopping off the pointed stern to make a tombstone transom would much simpler.
     
  4. Perm Stress
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    Perm Stress Senior Member

    http://www.morocz.com/BoatBuilding/SchoonerBuild8.htm
    The "braces" you did omit are necessary to strengthen the hard spot where box for keel and rudder end. You NEVER end anything stiff (like keel box or a bulkhead) in the middle of plain bottom, side, bulkhead, whatever.
     
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  5. marshmat
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    marshmat Senior Member

    Good point PermStress, I missed that page earlier....

    Yes, braces at both ends of the daggerboard box and rudder box are necessary; joining it to only one bulkhead is not sufficient. The bottom is not stiff enough to resist the moment of the keel without a bulkhead or frame to spread those loads.
     
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  6. Perm Stress
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    Perm Stress Senior Member

    Even if the box is properly supported by the bottom/bulkhead/deck combination, what is the case here, for bottom plate end of box is still the hard spot.
     
  7. lboatman
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    lboatman Junior Member

    True, but then it wouldn't have the same lines. Bolger seemed pretty specific in his original description that the pointiness would help out if the stern dragged. But you'e right, it probably would have been simpler otherwise.

    Laszlo
     
  8. lboatman
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    lboatman Junior Member

    The wooden braces are gone, true, but they've been replaced by the taped seam. The glass tape and fillet spread out and transfer the load to the bottom.

    Also, the box goes through the bottom, rather than sitting on it, and the bottom is 1/2" thick. Nor are the boxes in the middle of an open area. They are next to bulkheads and fairly close to the bottom seams, with the distance less than what Bolger originally specified, so the flexibility of the bottom is well controlled.

    The predominant forces will be a static downward force from the net weight of the ballast and the dynamic left/right forces when heeled. The static force will be resisted by the epoxy glue in the 1/3 square foot of bonding area against the bulkhead, the taped joints and fillets against the bulkhead, the taped joints and fillets against the bottom and the water pushing against the bottom itself.

    The left/right dynamic forces will be resisted by the taped joint and fillets against the bottom and by the lateral post formed by the bottom from where the boxes bear against the edges of the holes to where the bottom intersects with the sides. That's 10 square inches of bearing area backed up by at 18 inches of wood depth, the equivalent of a 3"x3" post a foot and a half long. The half inch thick wood is attached on 3 sides (hull, bulkhead, box), so it's the equivalent of a 1/2 thick, 18" x 20" plate. It won't be flexing.

    I don't mean to drown you in numbers, but I wanted to share my design calculations to show why I felt no need for the braces. This is not a heavy thwart resting on a flimsy hull panel. The support structure is still there, just not in the original form.

    Laszlo
     
  9. lboatman
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    lboatman Junior Member

    I respectfully disagree, see my post to Perm Stress. And, in the Spring, the water will be the ultimate judge and we'll see who's right. I hope you're not, I'm not fond of swimming in cold water :D

    Laszlo
     
  10. Perm Stress
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    Perm Stress Senior Member

    There is NO support structure to spread the stress created by rigid end of box in the middle of plain bottom. Consider water pressure, occasional wavelet slap, global deformations (bend, torsion) of hull, not only keel loads.
     
  11. lboatman
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    lboatman Junior Member

    Actually, there is - the composite joint. There's 160 square inches of area to spread the stress. That's over double the surface area of the braces specified by Bolger. In addition, there's the more than 22 square inches of area where the bottom rests against the boxes, plus the 33 square inches where the bottom cloth overlaps onto the bottom of the box. That's a total of 215 square inches of area to spread the stress.

    The support is there, it just doesn't look the same as in the original boat.
     
  12. Perm Stress
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    Perm Stress Senior Member

    Do you have any extension of keel box forward to the next bulkhead or frame?
    Do you have transversal member, like the deck beam at for end of keel box?
    What support structure you talk about?
     
  13. lboatman
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    lboatman Junior Member

    1. No, but neither does Bolger's original design. Please contact him for further explanations.;)
    2. Yes
    3. The composite joints and the wood-on-wood bearings surfaces (as described in the previous posts and pictured on the website).
     
  14. upchurchmr
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    upchurchmr Senior Member

    Iboatman,

    This looks like a really nice adaptation of an old fashioned heavy design. Everything I have seen makes sense. Pity others don't get it. But I am sure you were prepared for the typical average attitudes.

    I had a couple of those at work today, just thought I would offer some support. Too bad you can't immediately continue, I want to see the next steps. I had a friend with a Bolger Black Skimmer an I really wanted to see it built as you are doing.

    Nice job.

    Marc
     

  15. Perm Stress
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    Perm Stress Senior Member

    well, it is too difficult for to contact Bolger just now.... maybe some decades later....
    I did not buy the plans for the singlehanded schooner, I have plans for light schooner I built a few models (with mods) from. In those plans there are full bulkhead either end of daggerboard box. And boat is not out scale bigger.

    In study plan "http://www.instantboats.com/instantboats_cake/img/study_plans/13-2-large.jpg" I see at least small extensions of keel box forward at the bottom. (or what they are?)
    So may be, Bolger considered 12mm ply on such small a boat could handle stress concentration I talk about, but still some "spreading" of stress point IS here. ;).
     
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