A MODERN SOLUTION - Ted Van Dusen

Composite Engineering built their first carbon fibre mast in 1978. That was also the year that Woody Stoddard and I joined two businessmen to start US Windpower, which was to become an early leader in modern wind turbines. Woody and I had just completed our PhDs in ocean engineering and had designed and built what is generally recognised as the first modern wind turbine to demonstrate the feasibility of renewable energy as an alternative to fossil fuel and nuclear power plants. Both Woody and I also specialised in computational fluid dynamics; however, Woody had experience with wake modelling of helicopter rotors so he worked on the turbine aerodynamics. I had experience with advanced composites, so developed a computer code to model the turbine blade structure and determine the stress, deflection and dynamics. Composite Engineering produced the first run of production turbine blades before US Windpower and Pearson Yachts subsequently formed the joint venture TPI, to manufacture the blades.

From here it was a simple matter to analyse sailboat masts using the turbine blade program. With the addition of a program to calculate the load on sails we soon had a design package to predict the deflection of a free-standing mast, determine the stress anywhere in the structure, and optimise the mast diameter and wall thickness to minimise the weight aloft.

The first step in designing a mast is to determine the stability of the boat. We use the maximum righting moment to determine the highest loads the mast can experience and then use the righting moment at the heel angle for optimal beating in a good breeze to determine the luff curve which the sailmaker then uses to design the sails. 

Composite Engineering use both pre-preg laminate and tri-axial braiding in fabricating their hulls and spars. Most of our spars are braided with about 75% of the fibre along the axis of the spar, 12% at +/-45°, and the rest wrapped around at 90°. We braid over a rigid mandrel with as many layers as necessary to obtain the desired wall thickness to form a seamless woven structure. After curing in our autoclave the mandrel is then pulled out...

View the entire article, "Middle Ground," by Nigel Irens and Ted Van Dusen -- from the October 2011 issue of Seahorse Magazine.