This is an Oppikat 9ft junior catamaran. The builder launched it for his children and test-sailed it himself first. He emailed me to say that the boat is dangerous and he cannot let his children sail it. I asked for the measurements of his mainsail and he said that they had intentionally made it a ‘bit larger’. I found that it was approximately 65% larger than my designed mainsail, which is a massive increase. After remaking the sail to the correct size the boat is sailed safely by his children.
Most of the boats that are built to my designs are amateur projects. Amateur boatbuilding is in my origins for both building and designing, from very early in life. I watched my dad building boats when I was hardly more than a toddler. My first boat, built with the help of my dad, was a tin canoe. The first more serious boat that I built was a 4.5m tortured plywood catamaran that I designed as well. It was a very rudimentary design, drawn when I was absolutely clueless about boat design. Thanks to a good eye and more by luck than any other factor, I built a fast and well-mannered boat that was also exciting to sail. It had some structural issues with the trampoline frame that I was able to remedy by trial and error but I raced it, I surfed it and I cruised it. Both the boat and I survived our many experiences together. When I moved on to bigger boats I sold it to a friend and a few years later he sold it to another mutual friend. Built before epoxy became the standard boatbuilding resin, it eventually succumbed to rot after many years.
After that I built my first big boat, which was when I experienced the value of good drawings. I was building to the design of a top-level international designer who was known for his plywood designs for amateur and professional builders. It was to compete in a trans-ocean race and I intended it to be true to the design. Then a rumour started that the rules for the race were to change, with minimum size increasing enough to render my boat ineligible. My yet-to-be-built boat had to grow in length to meet the new minimum for the race.
The result was that my boat morphed into something rather different from the designer’s drawings. I did this in full cooperation with the designer. I first got his permission to make the changes and he provided new drawings for important aspects. They were for the new ballast keel, rig and rudder. He also advised me on scantlings. I had technical drawing training at both high school and university level, so I drew the new profile, interior layout and deck for myself, as well as the engine installation. That process got me interested in boat design and put me onto the path to study and eventually graduate with a Diploma in Yacht Architecture. So, I know all about boats built differently from what is shown on the drawings. Been there, done that.
In retrospect, it would have made more sense for me to have traded in my drawings with the designer for the next boat up in that design series. That one had very similar styling and would have been big enough for the race. However, without being involved in that redesign process I would not have started on the road to yacht design.
All of us who enjoy making things like to personalise what we create, to make each into something special, fine-tuned aesthetically to our personal style or preferences. It works with boats, making the personalised boat stand out from the crowd, giving character to something that might otherwise have been no more than just another boat among the fleet of look-alike cruiser/racers. That is good for both the builder and the boat.
Customising should not be taken too far though; it should be limited to aesthetic aspects or minor detail changes and not a lot more. For bigger changes you should liaise with the designer on what they will allow you to do and what you must not change. Designers have different policies about changes to their designs, some totally disallow deviating in any way from the design, under pain of disowning the boat. Others allow limited changes but only with permission.
There is, of course, a lot of variation of detailing standard between designers. Some provide little more than very basic drawings showing lines, offsets, rig, and interior layout, with scantlings and not a lot more than a hint at the structural detailing. If the design that you are building fits into that category then you have a lot of scope to use the detailing that you want. Many professional boatbuilders prefer this type of design to one that is comprehensively detailed because it gives them freedom to use detailing that they have used before and which they like.
At the opposite end of the detail scale are those designers who draw almost every detail of the entire structure. If your plans are very detailed then it probably means that the person who drew them knew the alternatives and drew those details for good reason. Even on my own designs I sometimes wonder, when working on completing a drawing that has had a lengthy delay, why I drew a particular detail. Then, when changing it, I come across the same issue that was part of the earlier decision and have to change it back again. I have also sometimes drawn a detail that works well. Then, when I start building it, I think of a better, quicker or easier way to do it, so the drawings get changed to match the experience. All of those experiences are in the background of all designs that follow, giving good reason for the details as drawn.
If you have confidence in the designer of your boat then you should have no problem sticking to the design and liaising about any changes that you want. If your ideas are not good or at least acceptable changes then the designer will tell you to stick to the drawings. If you still want to depart appreciably from the drawings against the designer’s advice because you feel that you know better than the designer, then why are you buying plans from a designer? You should design your own boat to have control over the structure and details.
If you don’t have confidence enough in the designer to follow the drawings then maybe you should not have bought the design. Did you possibly buy that design because the plans were cheaper than a better design? Whatever your reason for building that boat, if you think honestly that the designer has made an error and the drawing should be changed then you should bring this to the attention of the designer, for confirmation whether it is an error that needs correcting or the drawing is correct.
Changes will often have unexpected consequences. For example, a builder of one of my stitch-and-glue dinghies contacted me to say that he could not get the bulkheads to fit in the correct positions. He was building from a kit that had proven success by many other builders. It took awhile and a few emails back and forth before I figured what the problems were.
The first problem was that he had followed the stitch-and-glue details used by another designer, ignoring the details on my drawings. He had trimmed off 3mm on each half of the lower chine joints by bevelling them instead of leaving the edges square as shown on my details. With 6mm missing from those two joints, the panels were too narrow. He hadn’t yet done the same to the upper chine joints, so we were able to recover the situation.
The second problem was that he received the kit and design package, then dived straight into the build, taking measurements off the hand-drafted drawing. When I referred him to the instructions, he admitted to not having read them. He went back to the start and followed the instructions, then all worked out. He explained that he is an engineer and that it is a known compulsion of engineers to redesign to improve anything that they build, before they start the project. Their perceived improvements are often the start of a procession of interlinked problems.
The builder of one of my smaller lapstrake plywood gaffers decided that he would like a reverse transom instead of the designed transom, with the opposite rake. From the photos that I saw, it appears that he kept the transom shape as designed but leaned it forward instead of aft, then modified the hull panels to meet the corners of the transom. The result is awkward and inharmonious as-built lines. His boat still looks very pretty from the front but, as you move past and see it more broadside or from aft, the stern is misshapen and ugly, out of symphony with the rest of the boat. This builder did not discuss it with me, he just went ahead and did it. I heard long ago that he had done this and asked him for photos. He must have known that he had done wrong because he sent me photos only from the front, nothing showing the stern.
Now the builder has ill health and wants to sell his boat. He can expect problems selling it because the stern is so clearly wrong. If any potential buyer contacts me to ask about the boat I will have to tell them that it was modified without permission and is not to my design. I would be dishonest and doing a disservice to the potential buyer to say anything different.
This is the top of a high aspect aluminium racing keel. The broken tube extends to the cabin roof to add rigidity of keel and hull. The design required the keel to be bedded in glass-reinforced epoxy against the V-bottom hull. The builder felt it better to bed it in flexible sealant, so the keel was supported on two flexible rubber wedges. The resulting rocking of the keel broke the tube.
An owner/builder of one of my plywood trailer-sailers contacted me to say that he had run aground with the keel down and damaged the lifting keel casing. He had fractured the joints around the base of the casing against the hull skin and felt that the detail wasn’t strong enough to cope with grounding. I asked for photos of the damage, which he sent a few days later. Based on those I was able to tell him that all of the reinforcing structure around the base of the casing, which doubles the hull skin thickness locally and spreads the loads into the hull skin, framing and bulkheads, was missing from his boat. The local reinforcing is clearly shown on the drawings but was omitted by the builder. With the structure in place he would have bumped the bottom, got stuck, lifted the keel a few inches, then sailed away with only his ego damaged.
Another owner of a boat to the same design, who bought it used, asked me why he could twist the foil of the lifting keel, with the joints between the planks opening up as he did so. The drawings for that keel show it encased in 3mm of unidirectional fibreglass. The glass is the main strength of the keel and the builder simply omitted without discussing with me first. That is a dangerous omission.
The change that I see most is builders beefing up construction in one way or another. Beefing up just for the sake of beefing it up mostly adds unnecessary weight. Strengthening the hull structure to cope with more robust conditions than those for which the design was originally drawn is normally okay but it must be done by consulting with the designer. This is to get the best advice on how to make the upgrades that will be most effective in achieving what is needed, in terms of maximizing the structural benefit while minimizing the increase in structural weight. Simply beefing up framing or skin may not be the optimum way to do it and often results in considerable increase in weight, with the boat floating deep when launched and performing below expectations.
As example, some builders of my larger plywood high-performance monohull or catamaran designs want to strengthen the hulls by adding a layer of biaxial glass over the outside of the plywood hull. To them it is a logical upgrade to add strength in that manner. But it is not the best way to do it, so I advise them differently.
Adding strength to the structure is generally to increase resistance to bursting inward from impact with a log or other flotsam. That needs strengthening on the inside, not the outside of the hull. Adding biaxial glass to the outside will spread the impact load over a larger area but a hard impact will fracture the glass and still burst the plywood behind it. The glass will hold the pieces together but will likely leak badly. If the biaxial is added on the inside, between the stringers, the same impact will dent the plywood but the tensile strength of the glass on the inside will resist the panel bursting inward much more effectively than if it is on the outside. The better upgrade is to add a light layer of glass over the outside to toughen the surface against minor damage, abrasion etc and add the heavier and stronger biaxial glass on the inside, in the impact area of the hull. That is for the forward 35-40% of hull length from centreline up to about 300-500mm above waterline. That will add impact resistance where it is most likely to be needed.
I regularly receive calls or emails from people who are considering buying a used boat that I designed. They ask me if I can impart any background info or history about that particular boat. I pass on whatever I have that is relevant. That would include deviation from the drawings or damage in use, of which I am aware.
Builders must decide individually, of course. If you deviate appreciably in ways not approved by the designer of your boat, expect them to point that out to prospective buyers who contact them prior to buying your used boat. It may affect both the price that you can get for the boat and how long it will take to find a new owner.