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CONSTRUCTING A PLY ON FRAME BOAT |
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INTRODUCTION Traditional ply on frame construction consisted of making quite a heavy framework which was usually a combination of transverse frames and longitudinal stringers, hog etc on a flat building berth and then putting on the ply hull skin oversize and trimming it back. The word 'traditional' here is a bit of a misnomer as plywood suitable for marine use has been available for less than a 100 years. The framework was heavy because it was made up of individual pieces of solid timber traditionally jointed - this frame work served 2 purposes - first to provide the correct shape for the craft and secondly to give athwartship and longitudinal strength and stiffness to the hull structure. Once the hull was complete, the first purpose was complete and no longer required which meant that much of the structure was actually redundant. Modern computer software means that the plywood frames and girders can be developed very accurately before construction begins and the advent of modern epoxies means that much of the wood filleting and framing can now be omitted. So, instead of constructing a framework of many bits and carefully erecting each component onto a flat building berth/floor, we can now cut out computer generated shapes which slot together and which automatically align themselves correctly, even if the building space does not have a flat surface to work on. This modern "egg-box" type construction also means that the hull frame work can be "unitized" into pre-fabricated building blocks constructed in a small space and ready for assembly together elsewhere. At the chines, the normal stringers can be fitted or, the ply hull panels can be developed by the designer and cut out and attacheed over the framework in stitch and tape style so combing both stitch and tape and ply over frame methods. This is a good compromise - on larger craft, the frame work gives points of reference to work to and the panelling can then be fitted using quick, modern stitch and tape methods. The ply framework can either be joined to the hull panels with epoxy fillets or attached using wood fillets/cleats. We now have a Manual which covers Ply on Frame Construction and it's variants :- |
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| THE MODERN PLY ON FRAME
METHOD
For this, we will use a couple of different Selway Fisher Designs as examples - the Ailsa, 22' Black Swan, Shanghai and CR25 designs.
A. The above is a picture of the aft section of the Ailsa 22 - she has a flat bottom, flat topsides and rounded strip planked bilge area - in this case her framework was built in 3 pre-fabricated sections and assembled later - note that the ply fore and aft girders and ply bulkheads are slotted together and the joins made up with wood fillets.
B. A Black Swan out in Saudi Arabia - again the ply components are slotted together - note the transverse bottom floors slotted in place ready to accept the first plank.
C. Subtle differences - this is another Black Swan, this time by Uri Fischer in Israel where more epoxy is going to be used - in this case as fillets to join the ply components together.
D. A Shanghai framed up and with longitudinal stringers fitted and planed ready to take the plywood planking.
E. Another Black Swan, this time by Henner Ostermeyer in Germany with the flat bottom panel fitted - in this case the chine seams are going to be epoxy/taped rather than have wood stringers.
F. Above - Uri's Black Swan with most of the the pre-shaped planks fitted - again the seams are to be epoxy/taped.
G. Henner's boat fully planked and looking good with the coachroof going on.
H. Sam watt's CR25 - the stringers can be clearly seen fitted into slots cut in the plywood bulkheads and the first planks fitted.
I. A second shot of the aft end - the fore and aft girders form bunk fronts and merge into cockpit seat fronts.
J. All planked and in the process of being turned up right ready for fitting out.
K. Finished and launched. |
