FD CONSTRUCTION
 A Brief History by Paul Hemker

Because of the FD's straight lines and light weight, the boat has always been a challenge for the boat builder to come up with a stiff, minimum weight boat that would be fast, and also convenient to sail. While the very first FD's were of molded plywood construction, there have been plastic boats from a very early point in the evolution of competitive hulls. Just as different techniques for constructing wood hulls were explored in the early days, recently new approaches for building competitive plastic boats have been explored.

Original hulls were built using cold molded plywood and a single bottom layout. Hardware layout was traditional and the rig was set up very loose by present day standards. There are still a few of the first boats on the water. The Doesburg and Schoonevelt hulls were beautifully built and fast. There were several other builders who attempted to produce shells using water-sensitive glue in the laminations. Needless to say, their boats are long gone.

While wood boats have been popular, the idea of building in plastic has been around from an early date. The most popular early plastic boats were Alpa and Dubdam with Tiptree also gaining some popularity. They were built using single skin construction with hat sections for stiffeners along with rolled tanks and double bottoms to help stiffen up the flat sections. For flat water and with the light rig tensions used initially, the boats were competitive if not aesthetically as nice as wood boats.

While the first boats had single bottom cockpits, double bottoms were not far behind. There were two reasons for their popularity; the significant increase in stiffness from the truss formed by the floor and double bottom and the elimination of bailers. The original tube type bailers were much better than a bucket, but they really were not as efficient as the modern Elvstrom bailer. It in turn allowed a return to a deep cockpit in the familiar 11/2 layout (probably started by Alpa). Rig tension and ease of movement for skipper and crew were two design goals for "the 11/2".

There has been steady progress from a "brute force" sort of approach of construction with solid keelsons and frames giving way to molded frames and truss type construction. Using molded tanks - both plastic and wood - to increase stiffness is another example of the finese that developed. Wood hulls developed more rapidly with significant improvements in strength that left plastic hulls far behind. While early development was rapid, there was very little progress made for a long period and it is only in recent years that the use of epoxy glues, the addition of various core materials such as lower density wood or foam, covering with high strength materials and the use of variable thickness ply have been explored to maintain wood as more than an aesthic material.
 While wood construction techniques progressed rapidly, plastics had a slower start. Polyester resin and chopped strand mat were the norm for nearly 10 years. Use of epoxy resins and cloth was very limited, although Mader used both in some early plastics hulls. With the desire for competitive lower maintenance boats, more effort was expended toward applying aircraft techniques to the flat FD surfaces. Initially these efforts were in the area of higher strength reinforcements such as cloth and woven roving but there were also early attempts to use paper honeycomb by Ray Greene in decks. It was not until end grain balsa and urethane and PVC foams were tried that significant improvements in stiffness were noted. The latest core materials to be used are aluminum and Nomex honeycomb, overcoming some of the inherent problems with older cores. Honeycombs provide high shear strength with minimum density. Their disadvantages are a requirement for careful design since shear failure can be catastrophic and careful handling since porosity in the skins can result in water logging and skin failure if the water freezes.


"the boat has always been a challenge to the boat builder"


Fiberglas has been the most common reinforcement for shells and, as noted previously, progress was mainly switching from chopped strand mat to cloth and woven roving. Recent developments of S glass, aramid (Kevlar), carbon (graphite) and a variety of unidirectional glass techniques have made it almost mandatory that a builder have a structural engineer along with a chemist to help make decisions for blending reinforcements to provide optimum balance of properties. It is seldom advantageous to use just one type of reinforcements since tensile, flex and impact strengths need to be considered together.

Resin systems have also been undergoing a great deal of reconsideration with epoxy and vinyl ester resins now being popular because of their improved bonding to aramid, better strength and lower shrink. Isophthalic polyester is another resin that is an improvement in physical properties over the more common orthophthalic resins.

Undoubtedly the FD will see continued evolution. New fabrication techniques being developed in other areas will be applicable. New resins and reinforcements are being developed, but they will probably be far down the road. The changing popularity of various cockpit layouts will certainly continue. The resurgence in double bottom interest will last as long as the fast sailors use this style. Truly the past is prologue. New designs will no doubt incorporate the better ideas that have appeared, disappeared, and reappeared through the past thirty years.