Multihull designer Dick Newick is renown for his maxim; low cost, accommodation, performance. Choose any two. You can't have all three.
The truth behind the maxim is obvious. What is not so clear is how to put it to good use. But in fact all three parameters can be quantified reasonably easily to provide highly useful metrics for making design decisions.
1. We can easily define our accommodation requirements. For example: Two double cabins and two bathrooms, plus some occasional sleeping spaces for when more guests are aboard.
We can propose a saloon space and galley space of a certain floor area or volume.
2. We can put a limit on the cost based on the available budget. For example we can price the composite structure fairly quickly once we know the surface areas and preliminary laminates. These can be produced quickly once a preliminary model has been built. The cost of rigs, sails and deck equipment can be estimated from previous projects.
3. We can asses performance potential fairly quickly with just two numbers, the length and the estimated weight. That is; the displacement to length ratio.
By creating measures for these parameters we have a foundation for our design work as the relative values for each of the three categories are assessed and adjusted throughout the design process. And we can look for instances of poor fit where design parameters are in conflict. A generous accommodation space requires maximum usable space for minimal surface area. A sphere provides the maximum enclosed volume in this context, and hence the lowest cost and lowest weight for a given volume. But the geometry of a cube is far more practical as a living space and so we transform our sphere into a cuboid, we stretch it and squash it to find a better fit with the preferred aerodynamic and hydrodynamic characteristics of the vessel.
To achieve our optimal design solution within our chosen context we are effectively trying to marry a sailing hull form which is long and fine for performance with an accommodation space which ideally resembles a cube or a cuboid that doesn't deviate too far from a cube for maximum enclosed space with minimum weight and minimum cost.
If we isolate accommodation space and cost there is no conflict in the preferred form as long as we are happy to allow the form to follow a trajectory towards the cube.
The solution for the hull on the other hand is far more complex. It's already in conflict with itself. Long and fine is good for high speed reaching. Shorter and fatter is preferred for light air performance, less weight and less cost. Isolating and optimizing the hull presents a challenging design exercise on its own.
And so, by breaking down the work of the design into an an examination of Newick's three parameters, accommodation, cost, and performance, we have been able to clearly define the two major areas of conflict that are going to define the challenges in the design program.
Those are the conflict in the length to beam ratio of the hull, and the conflict between the preferred form for the accommodation and the preferred form for the hull, which even if designed to optimize light air performance will still be a poor fit with the preferred form for the accommodation.
How the conflicting requirements are resolved is the work of design and being clear about where the conflicts lay presents us with a powerful tool to optimize our designs and be more creative in the solutions we find.