Threefold 6 Builders' Notes


The Threefold 6 uses stitch & glue details for joining the hull panels at the chines but is built over permanent frames, as used for conventional boatbuilding. The basic steps of the hull constructions are as follows:-

1. Make the frames, bulkheads and wing boxes for the main hull and set these up on building stocks by normal boatbuilding methods. The wing boxes must be supported by the frames and bulkheads.

2. The keel and stem must be added next and the stem planed to the right shape. This is done by clamping pieces of stringer to the first few bulkheads and frames and using these as a guide to show the angle that the plywood will lie against the sides of the stem.

3. Next the stringers and sheer clamps must be added.

4. After that, start on the hull skin. Use the methods described below to establish the panel shapes. They are glued to the longitudinal framing and joined at the chines by the stitch & glue method described in the specification.

There are various ways to transfer the shapes from the framing onto the plywood. The bottom panel is easy because the plywood sheet can be clamped in place and marks made on the plywood at the chine corner of each bulkhead. The plywood is then removed from the boat and the marks joined by a curve using a batten (flexible length of wood or plastic) held with weights or panel pins. Draw the curve along the batten then cut along the curve. The same method can be used for most other parts of the skin. If you are building accurately, you will be able to use the cut panel as a template to mark the matching panel for the other side. First check the fit before you mark it though, so that you can make any adjustments that are necessary.

In places where it is not possible to clamp the plywood sheet in position, it is necessary to use other methods. This may apply for the side panels against the wing boxes. One way is to cut cheap hardboard into 50mm wide strips. Cut the strips into pieces and position them along the edges that the new panel must fit. Staple or screw the ends of the strips together to hold their shape and add diagonal strips to brace them so that they cannot move when you remove them from the boat. The end joins between strips should coincide with the bulkhead chine points to give accurate reference points. Move this pattern across to the plywood sheet and mark the shape onto the plywood. As described in the previous paragraph, use a batten to draw the correct curve.

The amas (outer hulls) also need the bulkheads to be set up on building stocks and the sheer clamps added. After that the skin panels can be marked in the same way as for the main hull.

The rest of the construction is pretty standard boatbuilding. As with all multi-hulls, performance will suffer if you build it too heavy. Always keep weight in mind while you are building. Use okoume marine plywood, it is much lighter than fir, meranti or other plywoods. Don't use heavy timber species for framing.


I drew the Threefold 6 a long time ago. In the years since then, much of the hardware has changed or phased out. The following is a list of alternative items that can be used to replace the ones that you find on the drawings and in the specification. The new hardware references are in red and all are to the Ronstan catalogue.

Ronstan RF1266 Fiddle block = RF51500
Ronstan RF1275 Clamcleat fiddle block, swivel snapshackle and becket = RF51530/RF6170
Ronstan RF1350 Block = RF51100
Ronstan RF1351 Block with becket = RF51110
Ronstan RF1366 Fiddle block = RF51500 but change to 10mm rope
Ronstan RF15 Turning block with clamcleat = Use RF58 swiveling deadeye with camcleat
Ronstan RF179 Blocks = Use RF185
Ronstan RF241 Rudder fittings = RF2505
Ronstan RF288 Block = RF467
Ronstan RF298 Cleat = PNP7
Ronstan RF299 Cleats = RF523
Ronstan RF47x8" Chainplate = RF47
Ronstan RF518 Bow fitting = Use RF417 Chainplate with RF416 padeye behind it
Ronstan RF595 Mast step = Ask you mast builder to supply a rotating step
Ronstan RF648 Superston open barrel turnbuckles = Turnbuckles from their new range
Ronstan RF905 Gudgeons = RF2505
Ronstan RF980 Genoa track 3 = RF980 still available
Gibb 1031 Cleat = Any 150mm aluminum mooring cleat
Gibb1055 Fairlead = Any small aluminium mooring fairlead
150 mm Screw down access hatch = PNP40
Gibb 528KPS Shackle = RF1032
Clamcleat CL211 = RF5106
Clamcleat CL229 = RF5106
K-158 Compass = Any suitable deck-recessed compass
Clamcleat R374M = RF5106




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This page was updated 5 March 2009

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