Updated: Apr 14
I used to think of the relationship between the hulls and the platform as one of three parameters we work through in the design process to determine the sailing characteristics of a new design, the other two parameters being the displacement to length ratio and the power to weight ratio.
I now see the relationship between these parameters very differently, largely due to the way the modern cruising catamaran has evolved and continues to evolve. The displacement to length ratio and the power to weight ratio are both outcomes from a long and complex process of experimentation and decision making. They could both be the starting point for a new new design but in most cases they are not.
The relationship between the hulls and the platform on the other hand is deterministic in that it's the foundation around which the concept is resolved.
In the past I've referred to this relationship between the hulls and the platform as a ratio, but ratios are mathematical constructs. The relationship between the hulls and the platform can be quickly assessed by comparing their relative lengths but otherwise allocating a numerical value to this relationship is not easy and it's not really necessary.
For one thing there is no clear delineation between the hulls and the platform and that's as it should be. It is sufficient to say that the hulls are everything below the height of the cross structure and the platform is everything above and including the cross structure.
There is no pressing need to make the distinction. If the displacement to length ratio is high the first pace we're going to look for a culprit is the bulk of the platform.
And so given that most designs begin life in the context of a single determining parameter; the length overall, the importance of the configuration of the platform comes clearly into focus. That a large platform will contribute weight and windage is obvious but solutions that we find in the configuration of the platform have far reaching consequences for the rest of the design as I will explain in a series of posts to come.
Above: Cutloose has a modest platform in relation to the hulls