Follow the Designer's Plans

There are many types of personality that get involved in boatbuilding. We each do it for our own reasons. Most are not qualified to design that boat, so buy a set of plans that comes closest to meeting their needs, from a designer of their choice.

I have a question for you, as an amateur boatbuilder preparing to start a new project or already into it. It is a rhetorical question, so please don't bombard me with responses. The question is this. If you selected your plans from a reputable designer who knows his craft, why are you wandering off the path chosen by the designer and building it differently, why are you changing important aspects of the design?

You may think that the change that you make is of little consequence but can you be sure? You may be placing the whole project at risk, also jeopardizing the time and expense that you invest in it.

I have been working with a client who can serve as example. He is building a dinghy, of stitch-&-glue construction. Simple enough, in fact so simple as to be the simplest form of boatbuilding. He is an engineer and engineers readily admit to the tendency to redesign anything and everything that they can lay their hands on. It is the difference between a tinkerer who must fiddle first before getting on with the job at hand and a person who just gets down and does what is needed without fuss. It is seeking perfection beyond the point of perfection, where it sometimes becomes so complicated that it no longer works.

In this case he has seen the beveled chine details that are commonly used by another designer and has applied them to my design, which uses square edges on the panels. The wheels came off when the bulkheads didn't fit correctly because the hull panels were narrower than they should have been, due to the loss of width to two bevels at each chine. I referred him to my chine details, clearly shown on the drawings. He had not considered that the change would affect the panel widths of the CNC kit that had been supplied to him.

Another issue developed at the same time, in attempting to fit the bulkheads into the hull. As an engineer, he had meticulously measured the bulkhead locations on my construction drawing and attempted to set them up in those positions. But they didn't fit. I referred him to the building instructions, which clearly tell exactly where to place the bulkheads, without measuring from the drawings. He admitted to having not read the instructions and was working only from his measurements from the drawings. The problem is that this was a hand-drawn design from more than 30 years ago, before CAD, and designed from a small cardboard model that I built by trial-and-error then dismantled to measure the panels and transfer them to the drawing. Somewhere in that process the drawn transom angle differs from the boat that results from the hull panels.

I have gone for more than 3 decades not knowing that the transom angle was wrong and many hundreds of boats have been built to the design, with the builders happily following the instructions to build boats slightly different from the drawings but all very much the same as each other. If this builder had read and followed the instructions I may never have realised that the transom was drawn at an incorrect angle on that drawing. The drawing will stay as it is and boats will continue to be built that way, following the instructions.

I drew this design primarily for first time amateurs, with basic woodworking skills and no knowledge of intricate boatbuilding. My advice to that builder was to take off his engineer's hat and to replace it with the amateur boatbuilder's hat.

There are, of course, ways that a builder can modify the boat from what is shown on the drawings. Simple ones like changing a rubrail detail don't need to be cleared with the designer. Speaking larger boats, anything major, like an interior layout redesign or anything structural, should not be changed without first getting agreement from the designer that you can make that change. Something that may appear to you to have little significance may actually have structural, stability or other implications. Extending the stern or increasing the freeboard changes the distances that structural components have to span and may invalidate aspects of the designer's structural calculations.

Most of my larger monohull sailboat designs have the engine located in the middle of the boat, where it has the optimum location for stability, trim and pitching characteristics, with a galley counter built over the engine. Modifying the interior layout has to be done around that engine location because moving that heavy weight will change the trim of the boat.

I had one client who had the unbalanced skeg-mounted rudder modified by a builder who thought that he knew better and said that a balanced rudder would be an improvement. Yes, a balanced spade rudder will give a lighter helm due to reduced loads. But, and it is a very big but, don't place a balanced rudder behind a full skeg or a full keel unless there is a lot of separation between them, to allow the water to close properly behind the skeg or keel and give the rudder clear flow onto its leading edge. The result of this bad modification is a rudder that pushes its leading edge into the water flow to one side of the obstruction when the helm is turned but has it hidden when on centreline. The result is unpredictable rudder response because the flow onto the rudder blade is very disturbed and irregular.

The unbalanced rudder before modification

The rudder and skeg after modification. Don't do this.

Another engineer client added many fancy features to his boat, features that would help a very expert sailor to draw more performance from his boat, as well as some intended to make the boat easier to sail. He is the ultimate tinkerer and the boat looked very impressive when completed. But so many of the changed details just did not work. I had designed for him a boat with relatively simple rig that would be easy and efficient to sail. The boat that he launched was much more complicated and difficult to sail. The extra features have gradually been removed and he is now unmodifying (the spell-checker says that I can't use that word, it clearly doesn't understand) his deck layout to bring it much closer to my design.

Builders of my boats will know that I am very supportive of their projects and am freely available to advise on changes that they may want to make. If they heed my advice we are good. If not, they are responsible for the results themselves. The designer of your boat certainly knows more about the design and what you should be doing with it than you, as the owner or builder. The best option is to work together with the designer to adapt the boat and your needs, rather than your wants, to produce the most suitable boat.

We have a very wide range of designs, covering many styles, materials, aesthetics and capabilities. See them on our main website or our mobile website.

To Paint, or Not to Paint

Last week the builder of one of my boats asked me about painting the interior of his boat, what should he paint and what shouldn't he paint? I had not really thought of it before, that there are different thoughts about what to paint and why. Before I answer, I will tell you of my experiences on a wide range of boats, those built by me and those built by others.

On all of the big boats that I have built (they were all for my own use), people who visited the boats or sailed with us often commented about how fresh they were down below compared with their own boats or others on which they had sailed. I had observed this as well. There was never any diesel smell, never any dank, damp odour and never any need for air fresheners on my own boats. In contrast, many of the other boats were oppressive as soon as I went below, with some rather bad smells.

Most of these boats had been owner-built or owner-completed and they all had large areas of plywood that were unpainted, left as raw timber, under berths, in the bilges etc. My own boats had no exposed timber, not inside lockers, under cabin soles, inside the lazarette, under berths, not anywhere.

So, how does this make such a difference? A boat lives in a wet environment and most are closed up the majority of the time. When the sun is shining, the inside of a boat is much warmer than outside and that warm air soaks up moisture from any water that is in the bilge or elsewhere. Humidity builds up and creates an ideal atmosphere for mould to grow. Mould spores are in the air all around us and waiting to proliferate.

When the air cools in the evening the moisture is wrung out of the air again. It settles as condensation on hull, deck and joinery surfaces throughout the boat. It doesn't care whether they are exposed surfaces that you see whenever you are on the boat or hidden ones that you seldom see. The humidity is everywhere in the boat when it is hot, so condensation settles everywhere when it cools.

The unpainted wood surfaces absorb some of this moisture and hold onto it. It becomes that ideal environment for the mould spores to settle and grow. Once it starts, if left unchecked, the mould will spread throughout the boat and can also be the start of rot problems.

Mould inside the boat can be difficult to kill off. It needs to be killed everywhere and the surfaces must be thoroughly dried then sealed with epoxy or paint so that the cycle doesn't start again. It would have been so much easier to have just painted everywhere when the boat was being built. Sure, painting everything will have added a few weeks to the build time but it will have been worth the extra effort to save the hassles of the future.

The same principle applies to preventing diesel smells. Every big boat has a diesel or oil spill or two in its life.That liquid will soak into any raw timber that it contacts. Once into the surface it is impossible to remove and it will result in diesel or oil smells inside the boat for the rest of its life. If those surfaces had been painted then the problem would never have arisen.

So, what coatings should you use? All surfaces of the hull and deck skins, as well as all associated timber framing (stringers, backbone, beams, sheer clamps etc) must be protected by three coats of epoxy. This should include the perimeter of bulkheads against hull and deck but you may prefer to coat all bulkhead surfaces as well. The epoxy needs to be protected from the attack of UV (even below decks) so I recommend painting over the epoxy with a prime coat, followed by undercoat and finishing coat of paint.

Elsewhere, coat with primer, undercoat and finish coat. That means every timber surface, whether you will see it again or not. If it is a sealed compartment, e.g. inside a swim platform, don't leave it unpainted either. These sealed compartments must be coated inside with three coats of epoxy but you don't need to paint them.

Aside from mould, smell and rot prevention, there are other reasons to paint everywhere. 

• Painted surfaces are very easy to clean. You can throw a bucket of water in the bilge or a locker, swill it around and then pump it out, no harm done. Or you can wipe it down with a damp cloth or sponge rinsed in a bucket, very easy.
• Light-coloured paint reflects light, unlike raw timber that absorbs it. The painted compartments are bright and make it easier to find things that have gone astray. A fully painted lazarette is not a dungeon that swallows up tools and other things that will not be seen again until you build up the courage to dive into that dark place in search of lost treasures. That also applies to cabins in the ends of the boat, which are much more bright and habitable if painted in light colours. Clear-finished okoume plywood becomes quite dark, has uninteresting grain patterns and is not as attractive as you might imagine, not by a long way.

This problem is not limited to owner-built plywood boats either. I have seen this regularly when poking around inside boats displayed on boat shows in London, Annapolis and other places. Many production builders don't bother to protect the timber surfaces inside lockers, lazarettes, berths or the bilge. It costs them labour and materials to do so and it costs the owner down the line to sort it out or live with the results.

So, don't bother to argue with yourself over which surfaces to paint and which to leave raw, just get down to it and paint them all. You can thank yourself later when you reap the benefits.

Allied to this is the need for good ventilation. Strategically positioned ventilators will help to keep the air fresh inside your boat, removing excess moisture and making it a much more pleasant environment for people instead of mould.

Dudley Dix
Dudley Dix Yacht Design
http://dixdesign.com/