Cost Versus Gain
The use of carbon for rigs gives superior performance over Aluminium for all the reasons above. How much of each advantage is incorporated into a rig depends on how much you want to spend.
There are a number of different manufacturing methods for carbon tubes.
The more expensive tubes will have the majority of the carbon fibre hand layed up and oriented at zero degrees to the spar. They will be cured at high pressures with an accurate control over the amount of resin through the use of pre-preg resin systems.
Less expensive manufacturing methods, like filament winding, is unable to lay enough fibres at zero degrees and may have more variation on resin content. These will be slightly heavier and not have as good dynamic response as the pre-preg spars.
However, methods like filament winding in our Sri Lanka facility still produce spars superior to aluminium and are cheaper than the hand layed up pre-preg spars. This will suit the class that wants to have some performance increase, without increasing costs too much.
Generally, high performance classes will choose to use the hand layed up pre-preg tubes.
Design & Optimisation
The quality and amount of design for each rig will provide a big difference in performance.
Aluminium masts are made from fixed specification extrusions whereas carbon masts can be engineered specifically for each boat. The more accurate information the mast designer has on the boat allows for better optimisation of the rig design.
It is very easy to model a carbon tube based on the equivalent aluminium section for that boat, but experienced designers will be able to provide a design which will out perform the aluminium mast through being stiffer and having local reinforcements in the correct areas to ensure the mast bends and responds optimally.
There are generally two stages to the rig design. The first is an engineering study based on the geometry of the boat and it’s sailing loads. This will provide the EI or stiffness values required at various heights of the rig, plus the rigging loads and sizes needed. Southern Spars uses proprietry software called Rig Calc to perform this study. This package has been developed to provide the optimum answer for all masts and spars from America’s Cup and Super Yachts, down to Performance Sport Boat rigs like the Melges and Mumm.
The second stage is a finite element analysis of the entire rig.This is done using North Sails proprietry software, Membrain.
The exact geometry and material properties of the mast, rigging and sails are used to develop a “sailing” model of the rig and hull.
The complete boat can be analysed in different sailing conditions, sail and rig trim can be varied to understand how the rig will react and perform.
The result from this is that owners can be provided with the correct loads to set up the rig when on the dock and the sailmakers can use the result to better match sails to the rigs.