The first of the new Carkeek-designed CF520 IRC/ORC racers is now nearing completion at Fibre Mechanics in the UK
A new and better world
Building a racing yacht today is a very different experience from how it was 25 years ago and it’s not just due to advances in materials. In fact, the basic materials and techniques have hardly changed. The resins are tougher, the carbon is stiffer, and the honeycomb is now made of Kevlar not Nomex. But compared with the materials revolution that took place between 1980 and 1995 you’d have to say that the development of race yacht building materials has plateaued. Nonetheless, things are very different
now for two reasons. First, developments of the 1980s and 90s left us with materials that have more predictable properties, and this allows composite engineers to design far more sophisticated structures. The laminate ply books we work with today are a great deal more complex, precise and optimised; and since materials properties are more reliable, engineering safety factors can be reduced. Second, non-destructive test apparatus
and techniques have improved greatly and become far more available to the marine
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industry. And alongside that evolution there are some highly experienced operators specialising in yacht structures, who can give very reliable information about a laminate or a structural bond quality. Both of these are major advances, but
from a builder’s perspective more optimised laminates allow less room for error; and better NDT means that errors are more likely to be detected. Taking both together, we are left with a set of technical issues to resolve and also some issues of engineering philosophy to wrestle with. We’ll look at the philosophy first, and if you’re still with us after that we’ll look at some of the technical issues…
Whose fault is it anyway? Architects and engineers design boat structures to withstand loads agreed with the owner. Though in deciding what those loads should be, most owners will put the question back to the engineer. At the design stage the owner will ask for the lightest solution possible, and in most cases engineers will rely on one or other classification authority or standard (CE, DNV/GL, ISO and so on) to set the appropriate strength level. Once sailing, it is the owner’s
responsibility to make sure the boat operates within the limits agreed, though exactly how sailors should recognise the point at which a boat is being overloaded is another matter (on which we have views…). Bearing all that in mind, who is to
blame when a boat breaks? l Did the owner overload the boat?
l Were the maximum loads assumed by the engineer too low? l Did the designer make a calculation error? l Was the builder issued with drawings that reflect the engineer’s calculations? l Was there a critical flaw in the composite laminates? It is hard to quantify what actual loads
were applied at the point of failure unless the boat has instrumentation designed to do that job onboard, so the owner will typically look to the builder and engineer for answers. Barring errors, the engineers can usually demonstrate that a composite laminate meets the design brief. And the classification authorities who set the brief do not warrant that their scantlings are adequate for specific boats, they can only confirm that specific designs meet their standards… All of which leaves the builder in a weak
position because, in stark contrast to the position of the designer, owner and class authority, it’s very easy to identify minor flaws in practically any laminate, leaving the builder trying to argue that, for example, the porosity in a laminate is at such a low level that it should not have caused the boat to break. And that is why building boats today is
so different. As builders we need to go about the business of building yachts in such a way as to eliminate errors and avoid pitfalls at every stage. There are a number of strategies that we employ to do that. First, where practical, we prefer to take responsibility for the structural engineering.
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