C flex construction?

[Tim francis]

Does anyone have first hand experience with c flex construction? I found some stuff online. I’m in escrow on a 43 Bruce Roberts mauritius and found the blueprints in some paperwork. Seems like it could be a pretty solid considering done the right way. I’m assuming this would be considered a solid fiberglass hull. I’m also assuming it has to be better than any planking and core construction. Just curious if anyone knows about this type construction method.

[coopec43]

I helped lay-up of a C-flex Roberts Mauritius hull back in about 1975.

It would be considered a "solid" fiberglass hull but as it was not a cored hull it had to have lots of stiffeners. Maybe I am biased because mine is Airex cored but it would be too expensive to use now. Most competition yachts would be cored these days.

Cored vs Solid Fiberglass Structures | Christian & Co.
Jun 21, 2013 - Designers and builders of boats know that cored composite fiberglass structures ... Virtually every high performance racing sail or powerboat is cored. ... Builders began coring hulls and taking advantage of the lighter, stronger ...(marinesurveyors. com)

[roverhi]

IIRC Cflex was cloth with woven in fiberglass rods designed to be laid up over a framework. The rods would support the glass between the frames so you got a relatively fair shape. Believe the first layer was Cflex and then standard glass laminate on top of that. Basically it's a solid glass hull. It has the limitations of solid glass construction as it's not all that stiff and benefits greatly from internal stiffeners like bulkheads and furniture tabbed to the hull, glassed in hat stiffeners and/or a moulded grid glassed in.

Cored construction is lighter and stiffer but not without some big negatives. There have been problems with delamination of the glass from the core in foam cored boats. Then there is the age old problem of core rot if water gets into balsa core. Balsa core can be problem free if built right with ALL hardware that is bolted on is thoroughly sealed. Through hulls and other hull piercings should be preplotted in the layup and the core eliminated where the holes are drilled. Personally have routed out the core around fasteners and filled with epoxy on deck hardware which has been trouble free but time consuming way to protect the balsa.

[SV Windrush II]

With proper scantling (Frame and stringer) placement, C-Flex was really strong but heavy, mostly used for amateur boat building where they were building a 1 off hull that would not need solid a mold. Usually those hulls were over built and very thick solid glass. Just investigate who built it and make sure it was professionally done, some amateur built boats were done very well, some were really bad.

[Lepke]

I built a couple commercial boats with C-Flex in the 1970s. It gives a nice hull depending on the bulkheads and frames. I built upside down, had several frames between bulkheads, and ran stringers like a wood boat. I used a Styrofoam core because these were fishing boats, had an insulated hold, and were much quieter with the foam (based on similar boats w/o a core). While the boats were upside down, I did the underside of the deck so I didn't have to do overhead fiberglass. Then turned the hull over with a couple cranes and did the inside of the hull.
At the time, there were a number of people adding C-Flex to wood boats to extend their life, stop leaks.