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Ply Proa with rocker

Page history last edited by paul.lis.bowker@... 14 years ago

 Paul Bowker's deranged thoughts..




 It has been suggested that Proas would be better with rocker. This is a few rough sketches and thoughts on how to build an assymetric stitch and tape proa with tortured ply.


This drawing is of building the main waka as a pair of hulls, so that the stresses of bending the curved sides are opposed, the inner seams and bulkheads and transoms would be fixed in place, then the two hulls separated down the centreline.


Each transom would be a mirror image so that the 2 halves are then bolted together to make a 20 ft waka. This would be a good kitset boat??







Refer here as well








Danger here be Tygers,









Figure One



 Step one


Scarf some ply into 10 foot lengths, cut 2 mirror image leeside pieces, with 6 inch rocker, (see figures 2 and 5) fasten back to back with temporary fastenings  and grease proof paper between the ply .. along keel. IF YOU CAN'T SCARF PLY, BUTT JOINT IT, OR GLASS TAPE IT, OR YOU WILL HAVE TO MAKE A 16 FOOT PROA INSTEAD.


 Figure Two


 Support the paired lee sides keel edge uppermost vertically on a strongback. 4" x 2" lumber, rigid on cross pieces as feet.


Make two identical transom pieces (figure 3), with matching bolt holes. Screw and glue bulkhead perimeters on inner side of each transom. Use good quality timber, shaped and finished. These will carry the stresses of the junction between the hulls and the mast support.


Fasten transoms upside down, to strongback at 90 deg to paired leesides, very well braced. Expoxy Fillet and tape inner joins to leeside. 


Figure three


Suggest temporary chipboard bulkheads at bulkhead positions one and two.  Fixed and braced to the leeside.


Glue an inner stem piece of hardwood, wedgeshaped, at bow on both port and starboard hulls. This and the temporary bulkheads will need final shaping when windward hull sheets are offered up.


The stem piece is needed as tape and resin cannot be easily applied inside the stem. The windward hull sheets will need good quality fastenings to the stem piece. Bolts and packing pieces could go right through if needed.  The stem piece could extend above decks to be the "manu" and shroud attachment strong point.


Drill lacing holes through the keel joins, (Shortly we will be turn everything over to fillet and tape the inner keel join).


Scarf up some 11 foot lengths of ply.


Cut  out pair of windward sheets, the sizes on figure six are my best guess. Leave some spare for trimming!!


There are two good winch points at the transom and stem to "persuade" the pair of windward sheets to bend into place.


The temporary bulkheads (patterns) will need further shaping and the stem piece especially where it feathers out at the keel line.


Be careful to work the windward sheets against each other rather than distorting the leesides. Lacing along keel.. cable ties, fishing line, copper wire has to go right through but will need cutting when the two hulls are separated later, so don't use stainless steel or kevlar! This will be fiddly, I can see needing a number of attempts to get the lacing done well.


On figure six note how the keel edge on the windward sheets will need a "pleat" removed gradually from about 6 ft from the stem, increasing clser to the stem.


Having achieved a pleasing shape and fit with the paired windward sheets:- Glue and screw windward sides to stem piece and transom timbers, leave keel lacing/ties in place. Fix Temporary fastenings to bulkheads. (This would be a great time to make a permanent pattern of the windward sheet shape, for all the proas you will make so that you have a fleet out on your local beach/lake)


Build two chip board cradles to rest the paired hulls on.


Turn the hulls over as one piece and rest on cradle.



Double check for twists and distortions and correct. Last Chance.



Expoxy fillet and tape inner keel joins and inner transom.



Use the chipboard bulkheads as patterns.


Fix in permanent bulkheads at 2 ft and 6 ft from stem. The upper edge of these will need to be curved  for a whale back deck. Make sure port and starboard are exactly mirror images. Don't forget drain/limber holes in number 1 bulkhead. This is a good time to put foam in the bow space,  buoyancy hatches, screw bungs.



DON'T COVER UP THE TEMPORARY FASTENINGS HOLDING THE TWO LEESIDES TOGETHER. These can be gradually removed from the more inacessible places.


I suggest some temporary knees and braces to keep each hull stiff.. as we are about to give birth..



Boil lots of water.




Te Wheke ... few hours after birth, has grown whiskers since then.






Turn the waka upside down again, maybe tape the outer windward transom joins.. then remove the last of the temporary fastenings, run a cutting implement through all the lacing/ties..ping ping . Hopefully the grease proof paper has stopped  epoxy leaking between the two hulls and stuffing everything up.


Shape and clean each of the stems keels and transoms, tape them up, as many layers as you choose. Too much tape where the two transoms abutt will spoil the fit.


Now is the time to mate the two halves together. Hopefully the bolt holes you drilled were identical.


Go and celebrate.


Next make some inwhales, (on Te Wheke I used scrap ply strips doubled up glued and clamped on the inside of the hulls, then shaped by eye).


Paint/varnish/seal the inside the buoyancy tanks, if you want fittings screwed on the outside anywhere, place some scrap ply in the right place. You will need a splash guard so put a backing piece under the deck in the designated place.


Screw and glue the whale back decks in place, trim to fit. Glass tape the outer seams. On Te Wheke I now leave the spar heel totally outside the lee hull so don't need anywhere on deck to rest it.


 You will need  shroud attachments, and a turning point for the shunt line.


On Te Wheke I used some 3" x 1" to make some Iako sockets in the cockpit. You will need a cockpit floor on stringers, some scupper holes, decent hatches to store gear under cockpit and to get at the joining bolts. Some permanent knees on the transoms, a mast support.


Some Iako holes in the windward hull just below the gunwhales to match the Iako sockets. (I used 2'diameter bamboo for the iako)


See the pictures of Te Wheke on his page for more info.




Figure 4




Figure 5 Lee sheet



Figure six Windward sheet



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