QB - a 21’ cruising schooner proa

17 October 2023     Editor    13 Comments.

A 1:12 size model in corrugated cardboard, illustration board, the old gold standard isn't readily available here in the hills of Oklahoma.
Surprisingly the model weighed in matching the design displacement. The mannequin however was seriously underweight hence the bolt style pfd.
Layout table under construction. Three H.C. door panels 36
Assembly. Hull sides are 24
Bulkheads, berth flats and ring frames installed.
Hull has been flipped over and the bottom glassed, lapped over the bottom to just over the waterline for an 18 oz bottom.
Assembly continues. Hull now in a cradle with rollers so boat can be moved around a bit.
Shunting day.
Back in the shop.
Boat is now off the rollered cradle and sitting on 2 2x4’s at about where the sliding beams will be.
Interior is painted Gripper primer and polyurethane porch enamel.
Current state, deck with a coat of primer.

GALLERY | Click images to enlarge

Skip Johnson is building another proa! An avid contributor to the old Proafile forum(RIP), Skip has built some truly radical proas in his day. Toning down the rad half a notch for his latest, QB is a well-proportioned pocket cruiser, using a novel construction method of Gpet sheet foam core and fiberglass. Much thanks for the building report, Skip! -Editor

QB Design and Construction Report

By Skip Johnson

QB aka “Questing Beast” from T H White’s The Once and Future King. Questing Beast is a nigh on perfect name to describe the fool’s errand I’ve traveled for some time now.  Unfortunately the phrase doesn’t roll off the tongue smoothly so QB it is. Parenthetically a version of the phrase worked perfectly for my attempt decades ago to build a sub ten pound sit on top, stick and frame with clear winter window shrink film skin. Leastie Beastie was a twelve pound unique marvel until the UV rather quickly destroyed the skin.

QB is a 21’ proa schooner with cambered panel staysails and end mounted rudders. Construction is foam and glass, foam is primarily ½ inch, 5 PCF (pounds per cubic foot) Gpet foam (10 sheets) with one sheet of 12mm Corecell M80 for bottom panels and some scraps of 12mm Corecell M200 bought from fallguy over at Boatdesign.net. Fiberglass is primarily 9 oz tooling cloth with 12 oz biaxial taping and some 22 oz unidirectional tape spot reinforcement. The 9 oz tooling cloth was a mistake; I should have used 12 oz biaxial throughout. The tooling cloth worked fine when vacuum bagged but contact wet out usually required some remediation no matter how careful I was. And the stuff was terrible for shedding where cloth was cut. Virtually all fiberglass work was topped off with a layer of peel ply.

Design weight light is 320 lb which now seems possible, hull weighed 170 lb prior to painting, float is also slightly under the estimated weight but still needs some remediation and fairing.

Other random notes about the boat. Float is based on a Speer P30012 section stretched to about a 7.5% section. Rudders are straight P30012 section. Sliding beams are 3” x 1/8” wall 6061 aluminum tube sliding in HDPE bushings. Masts are sectional step tapered aluminum flagpoles 3” diameter base, 2” diameter cap. Sails are 4 oz Dacron with a leading edge luff of seat belt webbing. Battens are 3/8” c.f. tubing. Auxiliary power is an A.D. style scull with fiberglass blade and aluminum tubing shaft. A number of bits; navigation lights, ball and socket set for scull and ratchet mechanisms for roll up sail reefing are 3D printed pieces.

The Construction Process

See photos above

  1. A 1:12 size model in corrugated cardboard. Illustration board, the old gold standard isn’t readily available here in the hills of Oklahoma.
  2. Surprisingly the model weighed in matching the design displacement. The mannequin however was seriously underweight hence the bolt style pfd. Not really visible in the photo is a chunk of XPS foam on the lee side of hull with the same scale volume as a 9” diameter 60” long inflatable beach roller/fender.
  3. Layout table under construction. Three H.C. door panels 36"x 80” with a supporting lightweight framework. Table weighs around 100 lb and is easy to set at different heights depending on needs of an old man that tries to avoid much bending over.
  4. Assembly. Hull sides are 24” wide panels 20’ long. Bottom plank is a parabolic curve with an exponent of 5. Sheer is a more rational 3. The prismatic coefficient is 0.76. The split piece of lightweight pvc pipe was trough to wet out ½” unidirectional tape along gunnels held in place by wood strip covered with packing tape.
  5. Bulkheads, berth flats and ring frames installed. Trammeling from several different points hull seems to be symmetrical within an 1/8” or so.
  6. Hull has been flipped over and the bottom glassed, lapped over the bottom to just over the waterline for an 18 oz bottom. While still upside down the bottom was coated with a thick graphite/epoxy bottom coat.
  7. Assembly continues. Hull now in a cradle with rollers so boat can be moved around a bit. The 2x4 frame on leeward side makes it easy to tilt the boat over for easier access to inside and the underside of seating pod.
  8. Shunting day. Until now it’s been advantageous to work with weather pod towards the right side of shop. Eventually the boat will need to go on the trailer with weather pod to the other side (passenger’s side of vehicle). Power boat has been pulled out and move was easy on roller equipped cradle.
  9. Back in the shop.
  10. Boat is now off the rollered cradle and sitting on 2 2x4’s at about where the sliding beams will be, boat rolled over on side for better access to interior and underside of seating pod.
  11. Interior is painted Gripper primer and polyurethane porch enamel. Horizontal surfaces get an extra coat with non slip additive.
  12. Current state, deck with a coat of primer.

 

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13 Comments

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  • Looks good, Skip. I like the cockpit/deck to windward. Lots of places
    to sit. Looking forward to seeing it sailing.

    2023-10-23 07:31 | by Curtis Patzer

  • Thanks, it’s predecessor, P52, was quite comfortable and QB expands
    on that configuration. A surprise was the utility of standing on the
    end of the berth flat in light conditions minimizing wetted surface
    and was a good place to exercise the AD scull.

    2023-10-23 11:10 | by Skip Johnson

  • Skip! It’s great to see your latest project taking shape!  I’m excited to see the
    rig.  I’ve been thinking about the fat head lateens that the Rocket Interceptor
    and other hot rod sunfish use.  Looks like a pretty sweet proa schooner rig. 
    Or any canoe, really.  Your basic dory formula makes so much sense.  How
    much rocker are you using?

    Looking forward to the rest, Skip!

    2023-10-24 20:07 | by Chris Luomanen
    • Nice to hear from you Chris, thought of you while recently finishing a tensegral stool for youngest granddaughter. Rocker is established by wrapping the parallel sided side panels around shaped bottom and flared gunnel planform. Works out to ~ 2-3" each end, quite flat through middle 70% arcing up from there.
      2023-10-25 06:14 | by Skip

  • Hi Skip, this looks great. I am intrigued by the bow rudders. How do
    they pivot, through what maximum angle, and how do you keep them
    from flopping over when they are at the front?

    The cockpit seat looks very comfortable. The side deck to leeward, is
    that to keep the water out if he heels over?

    2023-10-25 13:59 | by Topher Dawson
    • Bow rudders pivot on a vertical axis based on a piece of 3" PVC pipe. Two collars (each side) are cut from a coupling fitting and beveled top and bottom. The collars are attached to the pipe and the assembly serves as a mold for sockets to be built into ends of hull. Layers are initial coat of graphite epoxy, 17 oz biaxial, 3mm core felt, and 17 oz epoxy. The sockets are visible in some of the jpegs. The PVC pipe is visible in the background of "Assembly continues". When the pipe is cut to provide a slot for the rudder cassette The shrinks in diameter a bit to relieve stress and will then freely pivot against the socket. Once rudders are finished they serve as mold for the cassettes. The cassettes snugly fit into the slotted PVC pipe and sides are faired into a hydrodynamically friendly shape. Angle is +/- about 30 degrees. Whole assembly is held into place with a loop of spectra that goes through a pair of plastic tubing bushes and around an internal pair of pulleys that are spring loaded. https://youtu.be/LhMFGKC4mlc previous boat. Tillers are locked into plave when forward.
      2023-10-25 14:55 | by Skip Johnson
      • This is a really interesting solution to the rudder question Skip. Is there any provision for the blade to kick up if it strikes the bottom while down?
        2023-10-26 01:02 | by Topher Dawson
        • Yes the whole cassette/rudder assembly will pop back if struck. The rudders on previous boat, Trivial Obsession (TO), had a few unanticipated contact with a stony bottom without damage. More importantly every outing ended up on a concrete ramp or a rocky shore without damage. BTW I forgot to reply about your question re leeside deck. The primary function is to stiffen cabinside and provide a sheltered space for maps and similar stuff out of the rain. QB should rarely if ever get blown over, it is a cruiser rather than a racer. If we are out in really rough weather there will be a tonneau cover over the leeward half of the opening to help keep us from getting swamped.
          2023-10-26 05:18 | by Skip
          • Looking at your youtube video I see how it works, and I like the way the blade uphaul and downhaul go along the pushrod and down the tiller arm to the side of the blade. Does the cassette kick-up around a pivot near deck level at the leading edge? I take it that all the rudder blade is aft of the steering axis?
            2023-10-26 12:45 | by Topher Dawson
            • Actually the pivot axis about 1.5" behind the leading edge of the rudder with an 8" chord. The up/down line on tiller push rod has worked ok on two boats, TO and the Bionic Broomstick. QB will have a hand cranked drum drum assembly on the deck to raise and lower the rudder(s). I've abandoned the push pull stick to a tiller arm this time for a couple of reasons. 1. Though it has worked ok on both the boats mentioned I still prefer a tiller that is parallel to the direction of travel. 2. With the rudders on the very ends of the boat a tiller perpendicular to the direction of travel is hanging out there in an exposed position just asking to be snagged. In all of the 'conventional' dagger rudder proas (Cheers, Sidecar, Mubuli,........) the tiller arm is tucked back into the hull a bit. The rudder cassette doesn't have any connection to the boat except for the spectra cord. So far the cassette has always popped back into place with the help of the beveled rings. In theory it should work for the forward rudder if it's lowered also but it's an area for further experimentation. TO benefited a bit going to windward in light conditions with front rudder about half way down. Time will tell.
              2023-10-26 14:42 | by Skip Johnson

  • Hi Skip,
    I am interested in building a proa similar to your one-time Nomad
    with Peter Worsley’s wing sails and would like to know how well
    it worked etc.
    How do I get in touch, please?
    I don’t want to hijack space on this QB thread.
    Your QB design fascinates me too; especially your construction
    method, so I am keeping an eye out for your progress reports.
    Henry in Brittany

    2024-02-10 13:07 | by henry shaw

  • Hi Skip,
    Sorry, I’ve got a ton of questions because I really like your design…
    I’m curious to hear about how you will cruise it. Coffin berths in the
    main hull? Tent? Will you actually put gear aboard it and not take
    full advantage of its light weight?
    How about the rig? I sail a Wa’apa with a dipping lug schooner rig,
    which is wonderful for me, but I suspect you might be aiming for
    higher performance/higher tech. What do you roll the sails onto
    for reefing? How much does the CE move in a shunt? Will you
    move the center of lateral resistance to compensate (maybe by
    raising the forward rudder?)

    2024-02-21 21:24 | by John Lazenby
    • Sorry to be late replying, just now saw your comments. QB is being built primarily to sail the Texas 200. Coffin berths indeed; P52 had same turned out feeling was more 'caverness' in the sense of openness with your head at the cockpit area. Was surprisingly easy to maneuver in and out. A dome tent with bottom cut out fits over the cockpit area for camping somewhat mosquitoless, important on a Texas200 adventure. Tent also provides standing headroom albeit only in one little spot. I travel with a backpacking mentality primary weight added is water, hard to have too much. Performance goals are moderate. P52 would cruise at 10 - 12 mph in moderate conditions with a 48 S.F. clubbed staysail. But it was unreefable. Current schooner rig is an attempt to have a reefable low stress rig. There's little movement of CE with shunt, short boom on sails and pivot back from leading edge of sail.. Front rudder will probably usually be lifted though it might be partially deployed close hauled in light conditions. There's a little bit of info on the Texas200 website in the 2009 archives.
      2024-03-17 06:45 | by Skip Johnson