Designing our boat: how it works

Si’s now almost at a stage in his boat design where he can start to make a scale model of our boat and use this to assess the shape and fairness of the computer model of the boat that he has been working with up until now. Once this is done, we can start building! So I thought it might be interesting to talk about what Si’s done so far and why, and what is still to come before we start on the build.

I sat down to write about the design and realised that for all the time I’ve spent sitting next to Si while he’s been drawing and designing, I actually had very little idea of the specifics steps of designing a boat. So I made Si sit down and take me through the process of design from the first little lightbulb moment to the swanky roll of paper at the end with borders and numbers and names and ‘build me’ written all over it. This is a condensed version of our conversation:

1. You get the brief, or the idea. You sit down and scribble down anything that comes to mind. Your take on the concept and your initial idea of how the boat will look, how long it will be, what it will be made of, what kind of rig it will have.

2. You do a parametric study of other boats within a broadly similar category. This allows you to specify the design criteria and constraints, and is a massively good excuse for wandering around boatyards and perusing boat magazines.

3. With this information, you go back to your original sketches and start to revise them. You outline the features you want your boat to have, its general dimensions, and you make initial decisions on things like hull materials, rig, sail area and weight.

4. Once you’ve done this, you produce a model. In the past, boat builders would always produce a half model of the boat, by carving a lump of wood into a scale version of half the hull. Some boat builders still do this, but in general nowadays the process happens on a computer screen using three dimensional modelling software.

5. With a first draft of your design on the computer, you run through a series of checks and calculations to tweak your design and ensure that it fulfills the aims stipulated on the brief. Inevitably, changing one element of the design has a knock-on effect on all the other elements, so you go round in series of cycles, adjusting and honing everything until you arrive at your final design. This process includes everything from calculating the boat’s stability, working out how to make your design comply with regulations and coding, to adjusting the length to fit the location the boat will be used in, and deciding on what colour you’re going to paint the seats. Si is nearing the end of this process right now. All in all, the process looks something like this (except hopefully less wonky):

6. Once everything has been accounted for and checked, and you are happy with your final design, you produce a solid half model of the boat, cut from either foam or timber. This gives you the chance to show a customer a tangible representation of their boat, and allows you to appraise the shape and fairness before committing to building your boat. In the past, at this stage, the boat builder would have finished shaping and carving the original half model based on the decisions made in the previous step. The easiest way to get a half model cut these days is by sending digital files of the design to a cutting company, who will be able to use a three axis router to automatically cut the shape directly from your design.

7. What you do next depends on the hull material and method of building. Si’s decided to build our boat out of strip planking which will then be epoxy sheathed. So with this method, having cut your half model, and made any necessary adjustments, you start on the process of making the design into a plywood kit to build with. By doing this, you produce a design that can be built quite quickly and cheaply as a one-off boat, but with a design that can be digitally cut and replicated any number of times.

8. The plywood kit will form the skeleton of the boat, over which we will fasten the planking. Si will convert his digital design into a series of pieces that can be individually cut and put together. The file he produces will look something like a flat packed pop-out kit for making a toy model with. Think Airfix. Before sending the file to be cut at full scale, Si will make a tenth scale model out of card or thin plywood to check that all the pieces of this skeleton fit together as they should. This also gives you a good idea of how the build itself will work, and is a last minute chance to make any changes. Once this is done, you send the file off, get the pieces cut at full scale, and start building!

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