Design Contest Entries  


Duckworks/Small Craft Advisor
- Design Contest #7 -

Class IV Everglades Challenger

ENTRY #3

P52

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P52 Statistics

LOA
-
22'-11 1/2"
LWL
-
21'-6"
Beam (hull)
-
19"
Beam overall
-
10'-8"
Beam trailering
-
6'-8"
Draft hull
-
6"
Draft float
-
12"
P.C
-
0.635
#/" immersion (includes float)
-
160#
Displacement solo
-
620#
Displacement tandem
-
840#
Trailering weight
-
300#
 
Sail Area
-
163 s.f.
Bruce # solo
-
1.49
Bruce # tandem
-
1.35
SA/WS solo
-
3.52/1
SA/WS tandem
-
3.13/1

A proa produced primarily from 5.2mm underlay (with a nod to the P51 Mustang, an icon of straightforward practical design).

This particular design exercise is constrained by the fact that it’s going to be built and campaigned, albeit loosely, by yours truly. Added constraints include a fairly tight budget both in dollars and time plus the significant trailering distance.

A class 4 EC challenger is by definition primarily a sailboat with human auxiliary power. Got to be light enough to get off the beach at the start, narrow/low enough to get under the bridge at Placidia and sail in the shallows.

A proa will provide the longest waterline for a given amount of material and has a tradition of seaworthiness combined with shoal draft and beachability. Besides the whole proa concept is what I’m enamored with at the moment.

A few general comments and then I’ll hit the highlights of the various sections. Time and money constraints dictate a stitch and glue approach. 5.2mm underlay is more a ‘stabilized sheet material’ than plywood and the design tries to take this into account. Material choices are influenced by what’s at hand particularly a lot of rough sawn 2x12 cedar 14-16’ long and a partial roll of 17oz biaxial e-glass. Overall length started out at 24’ (3-8’ lengths) but dropped back to 22’11-1/2” (6.99 meters) to avoid dealing with bi-directional navigation lights. There’s an elegant solution with switched LED’s but no time.

Hull
Simple long skinny dory, trapezoidal cross section makes a concession similar to its semi-namesake losing a couple of percentage points in wetted surface/volume ratio while gaining simplicity of construction, beaching and trailering. The ¾” T&G plywood bottom is the only significant deviation from the material usage statements, the extra twenty or so pounds being well worthwhile in peace of mind credits during beaching and fast runs in shallow junk laden water. Extra ¾” plywood handy for miscellaneous connector bits, oar sockets, mast tripod pivots and the like. Initial stitching and lamination would be done with the gunnels over spread to get a bit of compounding/prestressing in the 5.2mm hull sides.

Float
Straight 5.2mm with a touch of cedar at the gunnels, pretty simple and quick. The triangular profile should provide vortex lift and the configuration has just enough buoyancy to support fully loaded craft in two-man configuration. The trapezoidal fin tip may or may not be necessary for hydrodynamic efficiency but it’s a handy step getting in and out of the water plus keeping the tip from digging into the sand. Trials may show a need for a daggerboard or similar fin but my experience with ACDC2 leads me to believe P52 will be able to sail well even to windward in 12-16” water, though the extra shallow water drag will play havoc with leeway angle. If by chance you fly the float, leeway resistance drops and the boat will slide to the lee until the float takes another bite. Remember, this is a fast cruiser not a racer.

Pod/Superstructure
A fairly rigorous attempt was made to keep it simple and usable. Seating can be up on beam or drop down to pod with feet down in hull as conditions warrant. Pivots were analyzed for leeway force and backwinded conditions. When trailering, main weight of float is taken by extension on trailer. Classic parallelogram geometry lends itself to trimming the CLR if needed, hopefully not. In any case the nylon rope X braces should absorb some shock if contact is made with a fixed object.

Oar(s)
AKA rudder on a stick. The first time I twisted the grip on ACDC’s rudder was a revelation, far better to twist than to push/pull. The whiffle-ball universal joint shown allows the pivot point to slide up and down the oar to transition from steering rudder to sculling fin in seconds. The sculling arrangement is untried as yet, but it's simpler with a smaller parts count than any alternative I could come up with including a fairly neat ‘side saddle’ prop assembly which would probably be the fall back drive if the scull fails miserably. Trials will determine whether both oars should stay deployed for shunts or one oar moved from side to side. Second oar is necessary as a spare in any case and there are times when deploying both oars can allow you to maneuver in ways foreign to more conventional craft. A “duckfoot” attachment would be used for poling in shallows.

Rig
“Conventional” Florida Crab Claw a la Commodore Monroe (1890s). A bridle on the upper yard allows a fixed central mast without binding problems while shunting. The tack is attached to a shuttle that slides on a piece of plastic pipe on the leeward gunnel. The brailing lines are essential for depowering sail in high wind shunts and putting some camber in the sail during lighter winds (windward brail only). Construction wise it’s a lot of birdmouth cuts but I’ve got all that cedar and a drill press jig with shaper bits. Fortunately a crab claw works well flat cut so a reinforced piece of polytarp is the sail with two reefs as shown with no change in CLR unless you need to lower CE of reefed sail by which time a storm triangle or a drouge might be more appropriate.

Accommodations
Cavernous in the sense of two very small caves. For casual cruising some sheltering fabric bits tied into the mast support tripod seem inviting.

Conclusion
A lot of mental, and now manual, effort has gone into this venture and it has and continues to be both fun and challenging, a fitting prelude to the event itself.

Postscript
Time flies. Boat is maybe 67.3472% (+/-) done, lots yet to do. Boat currently (12-19-06) weighs 235# without main hatch, a-arms, rig, or finish (but includes bottom glassing/graphite). So it appears the design weight is doable. Here’s hoping the balance of design intent works as well.

Addendum:

Addendum to building P52 for the adventurous, intrepid or plain foolhardy.

First you are on your own, particularly regarding rigs, P52 ended up fairly well sorted out hydro ynamically, less so aero wise.

Major changes:

  • Telescoping beams rather than swing arms.
  • Three planks rather than trampoline.
  • Quarter rudders rather than steering sweep/oar.
  • Added buoyancy to float by skinning outside with ½" foam and glassed.
  • I'd also extend hull to 3 full sheet lengths, trying to stay under 7 meters to avoid nav lights is silly considering the speed potential.

Worth a quick look: Click HERE

Best Wishes,

Skip

 

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