It’s a bit of a long post, but I think weighted-sums as a decision making tool is awesome! I would whole-heartedly recommend it to anyone who’s has to make a complicated decision.
With so many options at hand which more or less matched the design brief, and so many factors to consider, I was going to need a structured approach to have any chance of arriving at a conclusive decision. My dad lent me a book “Contemporary Management Science with Spreadsheets“, and recommended that I read the chapter on multi-criteria decision-making. Being in a bit of a state of despair, but determined to resolve the issue, I flipped open the book and started reading. The chapter featured two techniques, weighted sums and the more complex analytic hierarchy process, which relies on a very large number of pairwise decisions. I chose weighted sums because it’s the simpler method of the two.
Method – Weighted Sums
Pick out clear candidates (decision alternatives) for the process
Decide which criteria are relevant for your decision
Give each criterion a relative weight, for how important it is to you
For each candidate, rate how well it satisfies each of the criteria
Calculate rating x weight for each entry, and then add those up for a total score for each candidate
When I started my quest to find the right design over Christmas, I had a few things going for me: I had a clear design brief, I’d also spent a good deal of time looking into the possibility of building a somewhat smaller trimaran in the weeks before, and had done some rough calculations showing that a tacking outrigger, even if it’s only 7m long, is actually viable option. The solution space is enormous though. Overall I considered everything ranging from modular hulls, to smaller proas, tacking proas, a small trimaran such Newick’s Tremolino design (where you take the rig and floats of a large beachcat and build a central hull yourself), an i550 (a small and very neat monohull sportsboat), to even a simple open sailing & rowing dory or perhaps something like a Goat Island Skiff.
I’ve finally got some more current renderings, which show what I have in mind for my boat. It’s still a work in progress, and there are still a lot of details to work out, but it’s getting there! I’ve put a lot of work into thinking over the size and underwater shape of the hull, how to best mount the beams onto the main hull, and also what the coachroof and companionway is going to look like. I’ve also worked out a scheme to (hopefully) keep condensation on the cabin walls from becoming a major problem in cold weather.
The overall size of the boat is back up to just under 9 meters, I’ve finally figured out a way that I can build the boat with the available space (garage), and also how to keep the costs down enough so that I can actually pull this off. My estimate is that I need another 8000€ to complete it, from where I am now (tools bought, ama built, and some raw materials already on hand), so I’m going to have to work quiet a bit to get it all together. 😉
It’s been a while since my last post, exams and a few other things kept me busy, but I’ve still been working on the design now and again. Over the last few days I’ve really gotten back to boat-design and actually building something again! Today I built a quick 1:1 mock-up of the middle 1.5m of the cabin, to check on the ergonomics of the current design. That was my third mock-up overall, and I got it done in just over three hours, which is incredibly quick considering that the first one I ever built took more than three days. I’m getting faster at this prototyping business. 😉 You can definitely trade a lot of the accuracy for flat out construction speed, and there’s plenty of tricks to help speed things along as well.