Last week the builder of one of my boats asked me about painting the interior of his boat, what should he paint and what shouldnt 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 doesnt 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 doesnt 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, dont leave it unpainted either. These sealed compartments must be coated inside with three coats of epoxy but you dont 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 dont 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, dont 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/
After a 5 coats of clear epoxy it was time for varnish of the deck and sides. I have completed 4 coats of varnish and the amber tint has given a nice ivory color to the white stripes and toned them down a bit. Looks better I think. As stated on the varnish can (Epifanes), the first coat was thinned 50% with mineral spirits. I used a foam trim roller to put it on quickly and a wide foam brush to tip it off. The first couple of coats were sanded with 220, but I could see scratches, so I have now been using 320 and then 400 between coats. Thinning is about 25%. I have been rolling on half of the forward deck and then tipping off, then do the same on the other side. If there is any imperfection, I have learned to ignor it because there is no going back, it only makes an issue worse. I was hoping to be done after 4 coats, but there were a couple of dry/missed spots so Im on for at least 5. I hope to be done before the boating season is over.
This is clearly an honor for us and its also been fun to see the parade of Champion Boxers, Fashion Models and Movie Stars who have had their photos taken in front of our "little boat" as they attended the Opening Gala of the brand new IWC Boutique at 535 Madison Avenue which was dedicated to the Great Muhammed Ali.
We then had to design the model according to the specifications of a design team in Switzerland. Our plans and samples of materials to be used were all submitted to New York, from where they were sent on to Switzerland for approval. The model needed to be relatively lightweight, but would clearly be much larger than most model boats of the class. It was to be of a particular raceboat that is a prominent contender in the Volvo Ocean Race, which is a grueling race around the world involving 70 sailboats that are as "state of the art" as anything currently made by human beings. 
We were not able to procure drawings of the boat, so we used photogrammetry to develop the lines. You will find that they are quite accurate. The hull body was to be a little over 48" LOA (53" with bowsprit and radar arch). We decided to cut the hull from machinable foam, a material that is epoxy based with additional constituents to give it a density between pine and maple wood. It is preferable to machining wood because it is infinitely stable and there is no grain, which tends to cause print-through and does not take details as well. We have a small CNC machine that can cut a piece of material to a maximum length of 12". In order to cut the hull, we thought that we would have to farm the job out to someone with a much larger machine than ours. 
We found that, for too many good reasons to elaborate on here, most CNC cutting companies did not want our job. Thus, we had to cut it ourselves with our small machine. This is actually good, because it allowed us to adhere to our rule of making every single part of the model ourselves.
We accomplished this by splitting the hull form into 3 two inch thick parts, divided along the buttock lines. The longest; the one closest to the centerline, required 5 operations in which an area was cut and then, using special alignment pins, the adjoining area was cut. In all, the hull body alone took 14 separate operations involving 64 hours of cutting. In order to keep the machine from binding an elaborate counterweight system was used. The hull could have been ruined at any stage for a variety of reasons, but we were able to keep problems under control. In order to reduce weight further, large holes were drilled into the hidden parts of the hull in much the same way as is done in the construction of aircraft parts. The 3 long parts were laminated with very slow epoxy and filled with a phenolic balloon/epoxy compound. When the surface was ready, it was finished with spray lacquer. 
The backing board presented a different set of problems to overcome. In the interest of keeping weight down, it was decided to make the backing board from two 1/2" thick layers of Gatorfoam, a material that consists of a light foam core sandwiched between hard facings. The resulting one inch thick backing board might seem very sturdy until you understand that the panel is 54.73" wide by 121.65" tall or a little over 101" tall. Rigidity was enhanced by using cherry and baltic birch plywood in strategic locations so that they not only strengthen the backing board, but they strengthen the model structure and provide a hanging mechanism as well. Thus, the face of the backing board is only 1" proud of the wall.
Getting such a large piece from the Chesapeake Bay to 535 Madison Ave. looked like a logistical nightmare, but with over a week put into the creation of a very special container and good freight handlers, it made the trip in great shape. 
