This is an extract of the talk I gave at a Wooden Boat Festival, entitled "The Ideal Pacific NW Cruiser", which you can see in the powercats section of this website and in brief in the FAQs. But I thought it was worth posting in its own right.

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I want to digress for a moment and talk about yacht design in general.

Ocean going boats have always done two things. Carry lots of people or carry a heavy cargo. Much of boat's development happened in Europe where generally it is easier to move people by land, not sea. So most boats there were designed to carry cargo. Thus they were big and heavy and relatively slow. Yachts developed from these boats and so also tended to be heavy and slow as that was what people expected from a boat.

The place where it is impossible to move people by land is the Pacific ocean, and it was there that multihulls were developed, as they are ideal people movers with a big level deck space for living onboard and easy beaching anywhere.

People are a light cargo and want to get to their destination quickly, which is still as true today as it was 2000 years ago.

You all know the phrase “it's not rocket science” meaning it's not the ultimate in technology and design. Well I say “rocket science is not rocket science, but yacht design is”

I went to the Kennedy space centre a few years ago and got talking to one of the Saturn rocket designers.

I asked him what he would change if going to the moon today. He said, “only the computer”. The rest was basically just a big fuel tank, while I was surprised at how small and simple the engines were. I believe the Russians still use the same basic rocket that Gagarin used. The space shuttles first flew over 40 years ago, so were obviously designed much earlier. The supersonic Concorde aircraft was designed in the late 1950's

Now think of the changes made to yachts, and especially to multihulls since 1968

It is easy to design something static, like a bridge or a building. It doesn't have to move, or even float. So you can put a steeple in a corner of a church and not worry about it falling over.

Once in space a space ship has no loads, no gravity and only one atmosphere between the interior and outer space. Even a static houseboat is harder to design – it has to float level for a start.

Harder still to design are moving things, like a car or plane. They not only have to keep their shape and support a load, just like a static building does, but they also have to move efficiently.

Hardest of all are what I call “interface vehicles” like boats, that work in two mediums at the same time. Air and water in our case. Planes don't usually fall out of the sky, or break when taxiing on the ground. They have incidents when landing and taking off – just when they become an interface vehicle. Space craft have their problems on re-entry when they reach the interface of the atmosphere.

Everything in design is interconnected. It's what we call the design spiral.

At it's simplest - suppose we want a motorboat to go faster. We put in a bigger engine. But that's heavier, so the hull has to be bigger, so it has more drag, so goes slower, so we have to put in an even bigger engine. That is spiralling up and is the easy option.

An alternative is to make the boat lighter. Then we can use a smaller engine, so the loads reduce, so we can have thinner scantlings, so we can have a yet smaller engine. That is spiralling down and is usually the route I prefer.

Although it is easy to find a solution to a problem, it's much harder to come up with a simple one. Harder still to design something that can actually be built. Hardest of all is to design something that can be built in wood.

It's best to design the whole boat in your head first, only later do you draw it. Even then you can expect several false starts.

The smaller the boat the more you have to compromise your ideas. That's mainly because people don't get shorter when they go on a smaller boat. So, for example, freeboard is always proportionately higher. Furthermore the essentials for living on board weigh pretty much the same for a small boat as a big one.

Clearly when sailing at sea you always need a minimum freeboard for safety and comfort on board. The bottom line is that the bigger the boat the better it looks. Not only that but bigger boats perform relatively better. So it is really hard to make a good looking, fast, small boat. Science and the human anatomy are against you.

Usually professionals draw the lines plan last. For you cannot finalise that until you know, for example, how big the engines must be to go at the required speed. And thus how much space they take up and where the centre of gravity will be.

A good hull shape isn't just a matter of having the right centre of gravity and displacement. It also has to allow the boat to move efficiently through the water. After all, and as an extreme example, a boat might float level and on its marks at rest, but may do 60 knots going forwards and 6 knots backwards. So knowing which end of a boat is which is important!