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/

Quilting Techniques for Amateur Boatbuilders

Most of us learn boatbuilding techniques and tricks as boys, from our fathers. Michael Vermeersch, builder the Didi 950 prototype, sent me this tip that he learned from his mother. Her hobby was quilting, a pastime that I had never considered to bear any relationship to building boats.

The methods that quilters use to cut through multiple layers of fabrics can be useful for cutting fibreglass fabrics.

The Didi 950 has a structural grid in the bottom of the hull, to carry mast, rigging and keel loads. This grid is an egg-crate layout of plywood members comprising backbone and transverse framing that interlock with each other and are encapsulated in multiple layers of fibreglass. Covering these members involves cutting many pieces of fibreglass fabric to odd shapes and for multiple layers. Mike recognised this as being very similar to what his mother used to do when practicing her hobby.

Quilters rotary cutter and cutting board, with glass fabric and template.

In Mike's own words. "The cutter has a replaceable sharp steel wheel.  The mat has a "self healing " rubber surface that the wheel can penetrate for a clean cut.  This setup is typically used by quilters who need to cut a large number of precise fabric pieces.

I tried it with the 25 oz glass tape as well as the 12 oz 0/90 cloth.  It seems to work well.  There are repetitive pieces in the structural grid.  I made patterns out of rosin paper (used under hardwood flooring, available at Lowes and cheap).  I then stacked layers of the 12 oz and cut multiple pieces in one shot.

It worked with up to 4 layers of 12 oz, probably would work with more.  It leaves a cleaner edge with less unraveling than a shears or scissors.  Since the cutter rolls it doesn't pull strands like a knife."

Having myself cut many yards of fibreglass fabrics and mats, I have experience of the difficulties in getting nice clean edges that don't unravel or drag out of shape. Following this technique from the ladies might make all the difference to the neatness of your glasswork.

To see more about all of our designs, visit http://dixdesign.com/

Water Levels for Boatbuilding

In my recent post about building stocks for wooden boats I mentioned using a water level for getting things aligned on the building stocks but I didn't explain how it works.

A water level is the most basic of measuring instruments and is very easy to use. Properly used it is very accurate but there are some principles that need to be taken into account in order to achieve that accuracy. If you ignore them then you can work on blindly assuming accuracy that is not really there.

A water level works on the basic principle that water will always find its own level; it will flow from where the surface of the water is highest to where it is lowest, until the two are equal. It is a simple tube with water inside it, open at the ends so that atmospheric pressure can push down on the exposed surfaces. It can be done with a simple length of clear plastic tubing, or it can be an ordinary garden hose with a length of clear plastic tube attached at each end so that you can see the level of the water.You will need about 500mm (20") of empty tube above the water level, to prevent water from running out one end when moving the tube from one bulkhead to the next.

To get two equal-level points on any structure, place the tube against the structure both at your reference mark and where you want to place the new mark. Raise or lower the tube at your reference mark until the water surface inside the tube is exactly at the level of the reference point. At the other end of the tube, draw a mark on the structure exactly in line with the surface of the water inside the tube. Ideally it needs two people working together, with one at each end of the tube to make fine adjustments to get the reference level correct but it can be done by one person if the tube ends are secured against the structure.

You can use this when setting up a bulkhead so that it is level across the boat. First, the bulkhead must have the waterline drawn accurately on the face, which should be done on the workshop floor when drawing the bulkhead for cutting. Position the bulkhead on its legs with clamps, with the centre of the bulkhead at the centrepoint of the building stocks. Position your water level so that the water is at the level of the waterline at one end. Raise or lower the other end of the bulkhead until the marked waterline is exactly at the level of the water in the tube. Check the transverse alignment of the bulkhead on the stocks with a plumb line attached to the centreline string above your building stocks, as described in my previous post about building stocks for wooden boats. Similarly, use the water level to set up other bulkheads at the same level as the first one.

Simple isn't it? But, it has potentials for error that you must take into account, or your new mark will not be accurately placed.

1. Don't use a tube that is smaller than about 12mm (1/2") diameter. The smaller the diameter the slower it will be to react to adjustments in level, due to friction of the water against the wall of the tube. The larger the tube, the more easily the water will flow and the faster it will react. The large tube also has more water surface exposed to atmospheric pressure, helping to speed the reaction. A tube of 16-20mm (5/8-3/4") diameter is ideal.
2. Don't use a tube that is excessively long. Ideally it will be long enough to reach the most distant point to be marked, with a bit extra to allow the tube to lie on the ground. Any additional length increases the friction in the tube due to increased surface area. It also allows the tube to lie in loops that will slow the movement of the water and possibly trap air to form airlocks. An airlock can stop movement of the water almost completely.
3. Purge all air bubbles out of the tube before you start. Air bubbles will affect the accuracy of your readings and will slow the movement of the water inside the tube. The smaller the tube, the more that it will be adversely affected by air bubbles.
4. Try to do your work in fairly stable conditions, so that the tube and water are not heating up and affecting the readings. Warm water will flow more easily than cold water and a warm tube will expand in diameter, holding more water. You don't want the tube to be moving between sunshine and shade because the expansion/contraction of the tube and water are likely to affect accuracy. This is particularly important if you are using a dark-coloured garden hose with clear plastic ends because the hose and water will expand considerably in sunlight.
5. Don't be in a rush to mark your new reference line. It takes a few moments for the water to find its level before you can make your mark. It will first surge up and down a few times before it stops. This is when you will see the importance of a tube that is not too small because it is possible for the friction inside a small tube to overcome the atmospheric pressure and give inaccuracy of 20mm (3/4") or more for awhile before it very slowly equalises.
6. Flick the tube with your fingernails before assuming that it has found its final level. The shock waves running through the water will help it to stabilise at the correct level.
7. Don't do this work in windy conditions. Wind blowing over either or both of the open tube ends will exert a venturi effect and change the readings. The air flowing across the mouth of the tube forms a vacuum inside the tube. That sucks the water up the tube, so the level will be higher at that end than the other. Even if the wind is blowing over both ends, it must be exactly the same speed over both ends at all times to have no effect, a very unlikely situation. If you must work in the wind, make sure that both ends of the tube are well sheltered from the wind. If the wind is strong then just don't do it because wind blowing over a bulkhead will cause high pressure on one side and low pressure on the other, so you will be unsure of the accuracy of your readings.
8. Tie a length of string to each end of your tube. Between readings, tie the strings to something at about the same level as your reference line. This will prevent the tube from dropping down and emptying some of the water unexpectedly.
9. When you have one bulkhead that is accurately set up and secured so that it cannot move in any direction, use that first bulkhead as your point of reference for the waterline when setting up all of the other bulkheads. Don't move the reference point to any other bulkhead because you could end up with a cumulative error, which is minimised by always working with the same origin as reference.
10. Buy or make some tight-fitting  bungs to plug the ends of the tube. It does not matter whether they are rubber, plastic or wood, but they should be non-porous. Use them to keep the water inside the tube when not in use.

I have no images of water levels of my own but Roy McBride of CKD Boats kindly supplied the images below, with permission to use them. His company is my agent in South Africa and supplier of plywood kits for many of our designs.

Two water level tubes. The one at left is discoloured by age but still usable. A simple plastic tube and water.

Both ends plugged with bungs to keep the water in.

This illustrates the principle. The tops of the lower two pieces of tape are level with the top of the water at opposite ends of the tube, so they are level with each other. Here they are close together but they could be 10m apart without any loss of accuracy.

Close-up of the tube and water surface.

 Thank you Roy and  CKD Boats for allowing the use of your photos.
 
To see our range of boat designs, for both amateur and professional builders, please go to http://dixdesign.com/.

Building Stocks for Wooden Boats

There are a few ways to construct building stocks for building a wooden boat but most are variations on the basic method that I will show here. These photos have been sent to me by Fred Grimminck, who has previously built our Didi Mini and is now building the bigger sister, the Didi 950. This is a boat that is designed to fit into the Classe 950 Rule. It is a radius chine plywood boat with hard chine in the topsides.

Fred's building stocks, or beds, are on short posts that are fastened to the concrete slab in his workshop. If he were building off earth then the posts would be extended down into the ground about 300-400mm and set in concrete to make them stable. Other than that, the rest of the configuration would be the same.

Click on photos to enlarge, to see detail.

Didi 950 building stocks looking aft.

Didi 950 building stocks looking forward.

Rails and transverse braces are bolted to the posts. It is good to set the rails accurately so that they can be used as an accurate reference at any stage during construction. That means setting them so that the tops of rails and transverse braces are level, with the centrepoints of the transverse braces on centreline and the rails identically positioned each side of centreline. If any bulkheads will be attached to transverse braces then those transverses need to be set up at 90 degrees to the centreline, which will happen automatically if the two sides of the beds are identical. The centreline string on the beds can be seen in the photos above, providing a good reference for checking accuracy.

Transom doubler being set up on beds.

The photo above is of the transom doubler being set up on legs that are bolted to the aft transverse brace. If the transom will not have doublers on the inside then the transom itself would be in this position. This attachment is done in the same way as a bulkhead except that the bulkhead legs are generally bolted to the rails instead of a transverse brace. If you zoom in on the photo you can see the small piece of steel angle that Fred has used to fasten the post at bottom right to the concrete slab. The angle is bolted to the leg and to the slab. This must be done for all of the posts.

A secure and accurate set of building stocks is the foundation for an accurate build. Another essential to get this right is for the waterline and centreline to be accurately drawn onto every bulkhead. These lines will be used in setting up the bulkheads themselves and also many times during construction to set up joinery, engine alignment etc.

Didi 950 bulkheads being set up on beds.

 Fred is working forward from the transom in setting up the bulkheads but you can work from either end. I normally set up the forward bulkhead first, then work aft. This is because the forward bulkhead may extend below the top of the stocks and need to be either clear of the front transverse brace or attached directly to that transverse.

In Fred's photo above, the bulkhead closest to the camera is at the front of the cockpit, so forms the aft end of the cabin and serves as a good example. Each bulkhead must be set up accurately in all directions for the hull to be built to the shape intended by the designer. It must be at the correct location fore/aft, laterally and vertically. It must also be square to the centreline and it must be vertical both fore/aft and laterally.

Correct position fore/aft is done by measurement from the first bulkhead that is set up. Check it also against the distance to the previous bulkhead because this will highlight previous errors that may have been missed.

Correct position laterally is done by means of a plumb bob hung from a line above the stocks that is exactly over the centreline of the stocks. In a building this line can be attached to the ends of the building. If outside it will need posts to be set up beyond the ends of the hull and the line strung between them. The plumb bob is visible in the photos above.

With the plumb bob hanging from this line you have three checks that can be made on each bulkhead. They are lateral position of the bulkhead, vertical alignment of the bulkhead face against the plumb bob string and vertical alignment of the centreline drawn on the face of the bulkhead. This last one is a basic check that one end of the bulkhead is not lower than the other end but is a check only, not the place to set it up accurately.

Correct position vertically can be done with a waterlevel, which is a whole subject of its own and best dealt with in a separate post. An alternative and quicker method is to use a land surveyor's theodolite or a laser level that can be set up beyond one end and to one side of the beds, with a clear view of the whole length of the beds. Use this to horizontally align the waterline marked on each bulkhead so that both ends are at the same level and all bulkheads are aligned to that same level.

When each bulkhead has been correctly set up, bolt it to the support legs and brace the legs to prevent movement. Once all bulkheads are aligned and secured, you will be ready to start adding longitudinal structure.

A few things about this process should be noted.

1. Wood is a living material, it changes dimensions with variations in humidity and temperature. If you set up a bulkhead on a dry day and a week later you set up the next bulkhead on a humid day, you will find that the dimensions may have changed by a millimetre or two. Work as accurately as you can but don't sweat over these minor changes. If you do, you will chase yourself around correcting and recorrecting whenever the weather changes. Just accept the changes and move on. Constructing the stocks from steel will stabilise them from changes due to humidity but not temperature. If you are like me, you like to work with wood and really don't like working with steel, so you will stick with wood for the stocks as well.
2. Don't attach the legs to the stocks or to the bulkheads with wood screws, through-bolt them or use lag screws. Each bulkhead will not weigh a lot when you set it up but by the time that you have added backbone, stringers, sheer clamps, hull skin and possibly even built much of the interior, your wood screws may be bending or even sheering off under the load.
3. A solid foundation to build your hull is the principle to aim for. Use diagonal bracing to keep everything at correct relative positions and angles.
4. You need to be able to get through between the structures of the building stocks and the hull as it takes shape. You need access at many positions along the hull, not just aft under the transom. That needs the longitudinal rails of the stocks to either be hard against the slab or lifted enough to slide under. I recommend lifting them enough to slide under, which is easy by grabbing the rail with both hands and swinging your body through. If the rails are on the ground you need to hang onto the sheer clamp or some other structure to swing through and you will likely suffer numerous bruises to your back from impact with the rail during the course of the hull construction.

To see more about our designs and buildign methods, please visit http://dixdesign.com/.

DIY Non-skid Surfaces for Plywood Boats

"Slippery when wet." How often don't we see that on notices and signs along footpaths, in shopping malls and in other places where a surface is too smooth to allow a good grip and could become dangerous?

Boats are also such places, with the additional factors of regularly being wet right where you need to be and also jumping around in reaction to wind and waves. Despite that, it is a common problem that a boat has inadequate texture on the deck or other walking surface to allow a good grip for deck shoes or bare feet.

Of course, maximum grip will come from maximum texture, or the roughest surface. However, people also sit on these surfaces and the roughest surfaces are the toughest on clothing and also on bare skin. The trick is to come up with a surface that allows secure footing on a wet and heaving deck but will not wear through the seat of your pants or skin your elbows and knees. Add to that the need for it to be applied by an amateur builder, not break the budget and to be attractive in appearance (or at least to not detract from the aesthetics of the boat) and you have a fairly difficult set of requirements to satisfy.

I have had mixed results from the various methods that I have used over the past 40 years of building my own boats. I will run through them and give the successes and failures of each of them.

In the 70s and 80s I used a rather nice non-skid deck paint that was made by a UK (I think) paint company under the trade name "Helmsman". It had a fine grit that was soft on clothing and skin yet gave reasonable grip. Problem was that the colour faded badly and it did wear down, so it needed to be redone very year or two. It was a really good product that seems to no longer be available.

In about 1975 I saw a very attractive deck finish done by a friend of mine on a plywood Cobra catamaran that he was building. He used a simple open-weave petticoat lace and bedded it into the first coat of paint on the deck, then painted over it. It added some non-skid properties that were adequate for the particular boat, which would be sailed sitting on deck or trapezing on the gunwale. It would not have been good enough for a deck that was to be walked on when wet in big seas.

That set me thinking on how to increase the non skid properties of this method, when building my first big boat. My solution was to buy woven polypropylene tree netting. The one that was available to me in South Africa had a honeycomb-shape mesh of about 20x30mm (3/4"x1 1/4"). The strands were also woven from fine strands of polyethylene and were about 2mm thick with a woven texture. I bedded it down into the second coat of epoxy on my deck surfaces, laying it in panels that I marked off with masking tape. Once that coat of epoxy had cured I cut through the strands along the panel edges, removed the offcuts and tape then applied another two  coats of epoxy. The resulting surface was very effective for grip but rather harsh. It was tough on clothing and skin so I  sanded the rough spots off it. With the roughness removed and the deck painted with polyurethane paint, some of the grip had gone, so I painted over it with the Helmsman paint mentioned above. The final result was extremely good grip but the honeycomb pattern could be uncomfortable to lie on.

While effective, this netting method is very time-consuming because of the need to pull the netting so that it has an attractive appearance, with the cells of uniform shape and in straight lines. The netting can also lift off the epoxy in places before it hardens, so I had to return to each panel repeatedly as the epoxy started to set, running a steel roller over the netting to press it down into the epoxy until it stayed there.

Many boats have non-skid surfaces done with paint, with a grit of some sort sprinkled onto the first layer while it is wet, then finished with an extra layer or two of paint applied over the top. The grit is usually fine river sand, which has round grains to give nice grip without being sharp. Beach sand tends to have sharp corners that make it very harsh, so is not suitable.

For my Paper Jet I used a non-skid paint additive that is available from International Paints. You can adjust the texture by using more or less of the additive. The additive grains are clear, so can be added to varnish also. While suitable for dinghies, the finish is too fine for larger boats, not providing enough grip for safety on a heeled and heaving deck with waves washing over.

For my Didi 38 "Black Cat" I used a variation of the grit method. Instead of grit, I sprinkled coarse Epsom salts onto the wet paint. When it had dried, I painted another coat or two of paint over the salts. After a few days the paint was hard enough to be lightly sanded, to expose the tops of the grains. Once opened up, the salt grains are rinsed out by rain or spraying with a hose, which leaves little craters. The texture of the surface can be adjusted by light sanding to create as much grip as you want. You can also choose the desired texture with the amount of salt that is sprinkled. For good ocean-going grip the salt crystals should almost totally cover the first coat of paint.

This last method was the best of all that I have used. The texture is formed into the finishing coats of paint so slight wear on the texture doesn't wear through the colour. The grit can be Epsom salts, course table salt or even sugar. Basically anything that will dissolve in water and rinse out of the craters will work. I wouldn't recommend the sugar option because there is likely to be a sticky residue on and around the boat for awhile, attracting ants and other insects.

You can also go the route of gluing textured sheeting onto the deck. There are cork-based deck materials that give excellent grip and are available in a range of colours. They are fairly soft, so easy on bare feet but can wear quickly if constantly chafed by a rope that crosses over a cambered deck or cabin roof.  There are also imitation teak products that can be glued down either in sheets or in plank form. They do a very close impression of teak decking and require little maintenance.

For localised spots that require more grip than elsewhere, for example on the top of a bowsprit, a good solution is self-adhesive strips that are much  like very coarse sandpaper. These strips can be painted to blend into the deck. They give very secure footing but can be harsh on your skin if you choose to sit there naked. That is good reason to reserve this method for the "must have grip" dangerous spots on the boat.

Of all of these methods, my all-time favourite is the Epsom salts method. It is versatile because you can set the level of grip yourself and it has the big advantage that some wearing of the texture doesn't make the deck look tired by exposing base layers of a different colour.