ADVANCE CARBON STRUCTURE
INTRODUCTION
As production begins for each of the major molds of the 1370 (hull, deck, hardtop) our design team has now progressed to the finer details of the internal moldings and the general assembly and production processes. With significant demand for the 1370 the brief for our internal design team has expanded to enable faster production times and enhanced repeatability and quality through more defined tolerances and strict build processes and jigs. This involves more upfront planning, investment and development but will enable the production of a superior vessel whilst also making a higher production rate possible.
The brief, in simple terms is to enable a higher rate of production whilst either maintaining or even further reducing the weight. So, to achieve this we have developed an assembly using a modified version of the Seawind modular furniture system. The system will encompass 4 large furniture modules, offering both a lightweight internal arrangement, finished surfaces and structural reinforcement, though unlike the other Seawind models the 1370 will use this technique paired with a one piece main bulkhead made from a glass/carbon hybrid, and an innovative carbon fiber structural grid arrangement tying the furniture into the hull structure below. The combination of these techniques has enabled us to save hundreds of kilos when compared to traditional construction materials and techniques, we’ll cover both of these structural elements in more detail below.
STRUCTURAL CARBON GRID
The lightest hull structure possible is one with maximum reinforcing bulkheads and stringers, and reduced laminate of the hull plating itself. Think of a commercial aircraft, its plating relies on thin aluminum, however it gets its structure from a sophisticated framework of longitudinal and transversal frames. The same principal proves true in boat building and if weight was the only important factor, this would likely be how all boats are built. Weight however is not the only factor as we also need to maximize the usable space inside the vessel and we must design a structure that is easily produced and repeated with consistency and accuracy. For these reasons, composite builders tend to opt for thicker laminates and minimal internal frames and stiffeners. To obtain the aggressive performance characteristics we demand from the 1370, the underwater sections below the cabin floors required additional longitudinal stiffeners and athwartship bulkheads. Traditionally, Seawind would make flat bulkheads and glass these into the hull, one by one after measuring up the hull and marking locations and alignment for each of these itels, much like the process of a one off build.
This would however extend the time required for the hull to remain in the mold, and with mold turnaround the major limiting factor in our ability to speed up production a solution was sought out to streamline this process. Now a structural grid is no new technology on its own, most production powerboat builders and most monohull builders use a similar process, we have however avoided this in the past as traditionally these grids are heavy. Our solution therefore was to design a grid system that would be as light as a one off built structure, whilst offering the advanced turnaround time and consistency of a molded grid. The solution employed, was to replace the fiberglass laminate with a full carbon laminate, having a dual advantage of offering much less weight whilst also improving stiffness. While carbon for e-glass replacement varies depending on the area applied, typically when used in a high load structural item, we expect a fiber to fiber weight of 1/3 the original laminate. Add to this the reduced resin weight (typically around 1:1 fiber/resin ratio) for a direct replacement of glass to fiber we expect to save around 670g per kg. With such a significant saving, you may ask why we don’t just use carbon everywhere. Well, for one, carbon is expensive. And more importantly, this formula does not hold true for all areas of the boat. For instance, due to minimum skin thicknesses determined by ISO and other governing bodies, a swap to carbon, does not actually allow us to reduce the fiber weight despite the additional strength added. Additionally, typically we don’t find significantly advantageous savings when swapping out woven or biaxial cloths, the main savings are possible when replacing directional fibers. It is these areas we focus on to obtain optimum cost/weight ratios.
ONE PIECE CARBON/GLASS HYBRID BULKHEAD
Rather than building the bulkhead into the furniture on the 1370, we have chosen to construct a one piece bulkhead which spans from port to stbd beam uninterrupted. This allowed the carbon fiber directional reinforcement to span full width, offering supreme stiffness and load distribution. Why hybrid? Well as discussed earlier, the gains to be made in replacing woven mats with carbon are minimal, and therefore we have focused only on reinforcement patches and directional reinforcement for the high cost carbon fiber materials to produce an optimal structure, conscious on strength, weight and cost. Actually we have applied this philosophy to the entire 1370 structure, currently we have over 270kg of carbon fiber designed into the hull/deck/bulkheads of the base 1370. To emphasize just how much of a big deal this is, these carbon areas alone, once infused would have a weight of around 540kg. In comparison, a fiberglass only structure would weigh 1,620kg.
By manufacturing the bulkhead in one piece, we are able to bond it to the hull and to the structural carbon grid, before the furniture’s are installed. This allows us to not only glue the bulkheads in but also fiberglass them into the hull for a belts and braces, approach to this major structural area.
As you can see, we are very focused on optimizing the build and performance of the 1370. Despite originally not intending for such significant use of exotic fibers, we are confident that these continued improvements will be hugely favorable when the boats begin to hit the water.