Monday, July 29, 2013

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.

Monday, May 6, 2013

Joining Plywood - Jigsaw or Puzzle Joints

I apologise for my long gap between posts, life has been very full for awhile.

Jigsaw joints have become a popular method for joining 8ft plywood lengths into the long panels needed for building most boats. It is an easy process for those who are building from a kit but it is impractical for most people building from scratch. If building from plans or from patterns then you will have to make every cut by hand using a jigsaw and the accuracy necessary for a close-fitting jigsaw joint is just not possible to achieve.

For those who have not seen a jigsaw joint, the form is exactly the same as the interlocking curves of a jigsaw puzzle, except that the interlocking curves are laid out in a straight line rather than in a grid pattern. This forms a very accurate and secure junction between the two parts, unable to slide apart and needing no clamps, while the glue sets.

Jigsaw joint configuration.
The two parts have glue applied to the bonding surfaces, then they are laid on waxed paper or plastic to prevent adhesion to the surface below, aligned properly then a rubber mallet is used to force the fingers of the upper part down into those of the lower part. Care must, of course, be taken to ensure that the surfaces of the assembled joint are perfectly flush or there will be a permanent deflection at that point. The photos below, courtesy of Chesapeake Light Craft, show the joint before and after joining.

Applying glue to the bonding surfaces

Cleaning up the completed jigsaw joint
Tight joints as described above assume that you will assemble them on a large table or a workshop floor before moving the panel to the boat. This is OK for dinghies or for professional builders who have enough space and the staff to manhandle large panels from the shop to the boat and to position and clamp them accurately, all after applying glue to the framing of the hull and to the panel, trying to get it into exactly the right position first go so that it doesn't slide on that slippery glue and spread it everywhere except in the joint where it is needed, then clamp it accurately so that it can finally be fastened. You get the picture, of enormous potential for disaster.

For amateurs building bigger boats it is just not practical to assemble the panels before installation. Panels 8ft long are very convenient for one person to handle, without having to call on the wife, kids and neighbours to help with the task. I built the structures and interior of my Didi 38 "Black Cat" entirely single-handed. There was not a single piece of timber in that boat that I was not able to carry and set up without any assistance. But I made scarph joints by hand and I glued them in position.

Building with jigsaw joints and gluing the joints in position requires a slightly different approach. It is not practical to hammer a tight joint into place with a rubber mallet. The stringers and other supporting timbers are springy and will bounce away when hit, making it difficult to get the fingers properly flush. Another factor is that of longitudinal alignment accuracy. If the first piece is slightly out of longitudinal alignment on the framing then the accuracy of the jigsaw joint will force the other pieces to continue that misalignment. An error of 1mm on the first of 4 panels will grow to an error of 4mm by the end of the 4th piece.

The way to get around this is to machine in some tolerance into the joint. When the jigsaw joint curves are added to the CAD drawing of the panel, the curves are used to break the panels into the pieces that will fit onto 8ft sheets of plywood. Then the jigsaw curves must be offset into each panel by 50% of the tolerance that is decided upon. This means that each piece is minutely shorter than the designed length and the fingers of the joints are minutely slimmer. The result is a joint that can be easily pushed into place without hammering and which also has a small amount of wiggle room to allow for correction of minor installation misalignments.

This more loose joint may need a temporary doubler on the back between stringers so that small screws can be used to pull the fingers flush if the panel is curved at that point. Don't forget to use a waxed paper or plastic bond-breaker to prevent adhesion of the doubler to the panel.

After the glue has set you can use a belt sander to clean up the surface for a nice finish and a joint that will disappear in the painted boat.

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Sunday, March 24, 2013

Joining Plywood - Sawtooth Stepped Joints

Like the stepped joint that I discussed in my previous post, the sawtooth stepped joint is not something that the amateur builder will make from scratch. It may be that this joining method will be a feature of a kit that the amateur builder buys from a kit supplier, so he may do the final assembly of this joint without cutting the shape into the plywood.

This is a modification of the stepped scarph joint. The only difference is that instead of  the straight-line plan shape of the joint, it has a sawtooth plan shape as can be seen in the photo below. The form  in the photo is a true sawtooth shape, with straight lines between the changes in direction of the cutting tool. A variation is for the steps to have a wavy form composed of a series of curves instead of the sawtooth form.
This bulkhead in the photo is from a kit for the Dix 470 catamaran, cut by Exocetus Catamarans in UK.

These joints were developed primarily to get around the alignment problems of the straight variety of stepped scarph. The components that are being joined can easily slide relative to each other, parallel to the steps. The toothed or wavy form of the joint allows the two components to interlock accurately. As long as there is pressure to push the joint together when is is clamped then it will engage accurately.

There is a side benefit to this type of joint that is particularly beneficial to larger boats, with large loads in the structure. The form of the joint does a better job of distributing the loads between the two boards that are being joined. There is a much reduced chance of the joint initiating a crack along the line of one of the surface joints. Nevertheless, joints should be positioned away from the corners of openings and other stress-raisers in the bulkhead or whatever component is being made.

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Tuesday, March 5, 2013

Joining Plywood - Stepped Scarph Joints

A stepped scarph joint is the mechanically produced equivalent to a hand-planed sloping scarph joint. It is normally cut on a CNC router that has only three axes of movement, namely forward/backward, side-to-side and up-and-down. The sloping face of the hand-planed scarph is replaced by a series of small steps, each comprising a small vertical face and a broad horizontal face that coincide with mating faces on the other piece to which it will be bonded.

The main problem with stepped scarphs is similar to that with sloping scarphs. That is attaining proper alignment when gluing the joint and keeping it aligned until the glue has set. A sloping scarph can and will slide in almost any direction as soon as the slippery glued surfaces are brought together, so it has to be very carefully clamped. A stepped scarph cannot slide forward because the steps prevent it but it can slide back or sideways. Again, it needs careful alignment and clamping.

Various methods have been developed by different companies to overcome this problem. These methods are not patented, so can be used by others.

Mechtronics in Cape Town, South Africa, use a dowel peg system to lock the joints. The holes for the pegs are drilled by the CNC machine and hold the joint so securely that the panel can be moved right after the joint is made, without having to wait for the glue to set. After the glue has set the joint is sanded smooth with a belt sander, which also trims the dowels flush.

Mechtronics panel as it comes off the CNC machine
Mechtronics stepped scarph joint completed.
Ertug in Istanbul, Turkey, achieve a similar locking effect by programming the CNC machine to form islands in the one half of the stepped scarph that lock into holes that are cut into the other half. This is also a very neat solution.
Ertug stepped joint details.
Stepped scarph joints are good for any size of boat but care needs to be taken in high load situations or where there may be flexing of the panel. The weakness of this joint is in potential cracking along the surface joint lines, either from stress in the panel or from bending. Joints should, where possible, be kept away from edges of openings that might align loads along the joint to promote cracking. Edges of openings must be reinforced with wood perimeter frames or with glass or carbon tapes to spread the loads away from the corners and into the panel surfaces. The weak areas of the joint can also be reinforced with glass tape laid across the surface joints. Joinery shelves or locker tops that span across the joint also help by stiffening the panel, preventing flexing that might initiate surface cracking.

The CNC operator must take extreme care when cutting scarph joints to ensure that the plywood is hard against the sacrificial backing board during cutting, or the accuracy of the stepped surfaces deteriorates. There must be a vacuum on the table to suck the sheet against the table, as a basic requirement. If this is insufficient then plastic nails should be used to mechanically fasten the sheet to the table. All waste material must be efficiently removed as it comes off the router bit so that there is no chance of it getting between the sheet and table. This is best done with vacuum right at the cutting tool. Finally, the cutting paths need to be programmed so that any puncturing of the full depth of the sheet happens as the last stage of the cutting process. If it happens earlier it will increase the chances of waste material getting under the sheet and it will weaken the vacuum that is sucking the sheet against the table.

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Monday, February 18, 2013

Joining Plywood - Butt Joints

The butt joint is the most basic method for joining two pieces of plywood end-to-end or side-to-side to make a sheet large enough to suit a large bulkhead, make a hull side panel or anything else larger than the material that is available. Within the label of "butt joint" there are various ways to do the job. Click on the diagrams to enlarge them.

A butt-strapped joint is a simple end-to-end joint, with the meeting edges glued together and with a piece of plywood on the inside to reinforce the joint.

A basic butt-strapped joint

With traditional adhesives you would have had to clench-nail through the panels and butt-straps to be sure that they would stay in place but modern adhesives are stronger than the wood, so the fasteners become redundant after the glue has cured. I would use short temporary steel screws that I would later remove and re-use for the next joint, then fill the holes with epoxy.

The strap width will vary depending on the thickness of the plywood being joined. About 15x the plywood thickness is good, so:-

135mm wide for 9mm plywood
180mm Wide for 12mm plywood
5 5/8" for 3/8" plywood
7 1/2" for 1/2" plywood

Be sure to chamfer or radius the edges of the strap before fitting it, which neatens the appearance of it on the inside of the boat and removes sharp edges that don't hold paint well. If you are fitting butt-straps between stringers in the bottom of the hull, stop the strap about 10-12mm (3/8" to 1/2") short of the stringers to leave a channel for bilge water, or you will create small traps where water can lie.

This joint is very easy to make but it does have drawbacks. It adds unnecessary weight and it spoils the neat interior surface of a boat that will have the inside of the hull exposed. It also adds a hard spot that affects the smooth curve of the hull surface, particularly if the joint is made on a flat surface before the panel is installed rather than being made in place with the panel already curved. There is a chance of the outer surface of the joint showing a hair-crack over time, so it is worthwhile to glass-tape the outside of the joint, as described below.

This joint is good for bulkheads, where a nice piece of hardwood trim can be used in place of plywood to cover and reinforce the joint on both sides. In that case the hardwood trim could be about double the thickness and half the width of the plywood butt-strap.

Taped joints are the simplest way to join plywood in small boats, with sheet thicknesses of 4-6mm. Easiest is to butt the two pieces end-to-end then laminate a length of 50mm (2") wide glass tape onto the outside. When it has cured, turn the panel over (being careful to support it properly so that the unreinforced side doesn't crack) then laminate a similar strip of glass onto the other side. Sand the edges of the tape to feather them into the plywood surface.

Taped and Flush-Taped Butt Joints
The main problem with this taped joint is that there will be a slight mound at the joint, which can be difficult to fair out so it will show, particularly with a gloss finish. The way to get around this is to recess the glass tape flush into the plywood surface. To do this, slightly bevel the both surfaces of each piece of plywood with a hand plane or a sanding machine, forming a slight slope about 1-1.5mm deep at the edge. See Step 1 in the diagram above.

When you bring the meeting edges together they will form a shallow V into which you can lay your glass tape. build up the glass tape so that it completely fills the V. When both sides have been glassed and have cured, sand the tape down flush with the plywood surface, producing a very neat and almost invisible joint.

For all of these jointing methods you will need to lay waxed paper or a sheet of smooth plastic under the joint before you start gluing or glassing, so that it doesn't bond onto the floor or work surface.

Monday, February 4, 2013

Joining Plywood - Scarph Joints

This is the first of a series of posts about the methods of joining plywood. It is not a course to teach how to do this work but a basic explanation of how it is made and the benefits and drawbacks. Refer to that excellent book "The Gougeon Brothers on Boat Construction" to see various methods for making joints on plywood and solid timber.

I am starting with my preferred method first, only because this has been the subject of discussion between me and a couple of other people recently. This is the scarph (or scarf) joint, more technically known as a feathered scarph because the slope tapers off to a "feathered" edge.

Most amateurs have a fear of making scarph joints that fits anywhere between mild trepidation and total panic. In reality a scarph on plywood is relatively simple work to do. If you can handle a hand plane with reasonable accuracy then you can scarph plywood. A scarph joint is no more than a sloping butt joint between the ends of two sheets or lengths of timber, generally sloped at between 6:1 and 10:1. The 1 is in the thickness of the timber and the other number is in the length of the timber. For scarphing plywood I would generally use about 8:1 slope. So, in 6mm plywood it would be 48mm and 12mm plywood would be 96mm. These numbers are not finite rules, so they can be rounded off to 50mm and 100mm respectively for simplicity as long as both halves are planed to the same angle. In imperial measurements an 8:1 scarph on 1/4 plywood will be 2" wide and 4" on 1/2" plywood.

The Anatomy of an 8:1 Scarph Joint on 12mm Plywood

It needs only a tape measure, straight edge and pencil to mark the scarph, in addition to the plane. Once you have the plywood panel cut to required shape to fit the boat, you will measure in from the edge that will be scarphed by the width of the scarph. Do this at three or more places along the edge, which will show up any errors in your measurement if the straight edge does not touch all points. Draw a pencil line with the straight edge to define the edge of the slope.

If you have a hand power plane, this will make short work of removing the excess material but don't try to get up close to the line or you will risk messing up. Stop at least 3mm above your line then use a sharp jack plane to take it down to the finished surface. The closer you get to the finished surface the finer the plane must be set. Remember that you are working to create a feathered edge right at the edge of the board, so you don't want to remove any material that will destroy that edge. Clamping your board to another sheet of plywood or a firm table, with the edges aligned, will support the feathered edge so that it doesn't move away from the plane when you work.

I can't emphasise "sharp" strongly enough for the plane blade. It must be as sharp as you can get it and you should hone the plane blade again before each scarph is planed. You will be planing across the end grain of alternate layers, which will rip instead of being sliced if the plane is blunt, ruining the accuracy.

Use the edge of your plane or a straight edge to check that your slopes are straight. If you can see light under the straight edge then the surface is not straight. If the surface is concave then the middle of the joint will be hollow. If convex then the feathered edge will not lie against the other sheet so you will have gaps .

If you don't have a hand plane but have a skill saw, you can buy a "SCARFFER" attachment that bolts to the base plate to set the slope. You can see this attachment in use in the Gougeon book mentioned above. I did the same by cutting a block of wood to the required angle and bolting that to the base of my skill saw.

If you have neither a power plane nor a skill saw then you can still do it all by hand. Start with the plane set coarse until you are nearing the line, then sharpen the plane and set it more fine for the final finishing.

Be careful not to make the most common error, which I have done a few times. That is to plane both slopes onto the same side of the plywood instead of onto opposite sides. You don't realise your error until you bring the two pieces together and they don't match.

Is it a problem if your scarphs are not entirely true? That depends on how big the error as well as what glue you are using. Epoxy has better gap-filling properties than resorcinol and also gives a stronger joint if there is a film of epoxy between the two surfaces that are being glued. Resorcinol gives maximum joint strength when there is wood-to-wood contact, so epoxy is more tolerant of bad joints than resorcinol. Still, don't use the fact that you are using epoxy adhesives as an excuse to accept shoddy workmanship from your own hands.

When gluing the joint, remember that end grain is thirsty and will suck glue out of the joint, so don't skimp on the glue. Let the glue lie on the surface for a few minutes so that it can soak in, then apply some more if needed.

Scarph joints on plywood are a lot stronger than the wood that is being glued, so there is a natural safety factor. Also, you will generally be attaching the panels to a wood structure that has stringers and other longitudinal timbers crossing the joint and reinforcing it. You are very unlikely to ever break that scarph once the panels are glued onto the boat.

Making scarph joints is satisfying work once you get the hang of it. It produces a nice smooth surface both inside and outside, much nicer if your boat will not have hull liners covering up all of your handiwork. Scarph joints are neat, strong and can be made by hand. I can't think of any disadvantages to this joint, aside from the unnecessary fear of making them.

Saturday, January 26, 2013

Plywood Matters

This post has taken longer to complete than I intended. I started on it more than a week ago, then a flood of plan orders came in and delayed my writing. Customers come first, so the post had to wait.

Over the years many people have asked me for advice about plywood for their boatbuilding projects. One of the problems is that plywood types vary tremendously from one country to another and between suppliers in the same country. Sometimes the same supplier offers a few different grades and finishes, causing much confusion for the guy who is doing the buying. Maybe this post will help with making the choice.

If you are in North America, Europe or even South Africa, you are lucky enough to have a wide selection from which to choose, generally of high quality. Builders of my boats in many other countries simply don't have the luxury of choice, with only one grade available. When that is the case the only available grade generally also has some disadvantages when compared with the optimum that may be available elsewhere. For that reason, I am writing from the point of view of making the most of the plywood that you can get rather than insisting that you must build with plywood fabricated from any particular species of wood or that you must build with certified marine plywood.

The most important thing to ensure is that your plywood was glued with a suitable waterproof glue. Marine plywood is only manufactured with resorcinol  or melamine glues, no epoxy or other glue qualifies for certification in marine plywood. This is for good reason; resorcinol glue does not let go of the wood that it is bonding, whether that wood is wet or dry. The wetter the wood, the stronger the bond. Epoxy, in contrast, likes the wood to be fairly dry and can come loose if the wood is saturated with water. I have seen epoxy simply peel away from very wet wood.

Resorcinol is dark brown to dark purple in colour, most other glues are clear or light in colour. Look at the edges of the plywood sheets before you buy. You should see thin dark lines at the joints between the various layers. If you don't see dark glue lines then don't consider using it in a boat because it is not likely to stand up to exposure to the elements.

Exterior grade plywood is generally also glued with resorcinol. Many boats are built with exterior grade plywood and they can give give long service. Exterior grade plywood is considerably cheaper than marine grade but everything comes at a price, of course. Exterior grade is heavier, made to a lower and less stringent standard and could have any of a variety of timber species in the construction. Marine plywood is generally manufactured to British Standard BS1088 or BS6566, which have very tight requirements that cover the thicknesses and standards of the veneers, veneer jointing and patching within the boards and the surface finishes. Exterior grade is likely to have a lot more patching on the surface, splits and knots in the surface veneers and voids showing in the edges of the sheets.

If you choose to build with exterior plywood, the edge voids are possibly what you should pay most attention to repairing. Those voids provide channels for water to travel into the centre of the board, from where it can penetrate to the very core of the hull skin and start rot problems. You can epoxy-coat the surfaces of the board to protect it but any exposed edge void has the potential to destroy your boat from inside the timber. The best thing to do is to mix some epoxy or resorcinol with some sawdust or other filler to make a sloppy paste that you can inject or squeeze into the open joints. Don't just push a little in to seal the opening at each end, force it as far into the joint as you can. If you can totally fill the void, so much the better. Filling the voids is worthwhile for the hull and deck skins. For the bulkheads and interior joinery filling to a distance of about 50mm (2") is OK.

To get back to marine plywood it can be manufactured from a variety of wood species, including okoume, mahogany or meranti. It can also be finished with decorative surface veneers of other species like teak, oak or cherry.

Weight and strength vary depending on specie of timber. If the designer has designed for okoume plywood and only mahogany or other heavier type is available, the designer may allow you to use thinner boards. The increased strength adds weight and might be compensated by reducing thickness. I originally calculated the Didi 26 for okoume plywood and detailed the hull and deck skin for 9mm thickness. I was asked by a builder in Russia to recalculate for beech plywood because that was all that he could get. The beech plywood was much heavier than okoume but also much stronger. My recalculation allowed the skin thickness to be reduced to 6mm and resulted in a weight gain of only about 15% in the plywood components and very little overall weight increase.

The extra stiffness of the heavier plywoods brings some benefits and some drawbacks. The extra stiffness imparts increased impact resistance but the plywood becomes more difficult to bend or twist. Our radius chine designs have a laminated curved portion of hull that is more easily done with okoume plywood than a stiffer type. The same applies to the Cape Cutter 19 and Cape Henry 21, which need okoume plywood for the bottom panels forward of the mast because stiffer sheets are too difficult to twist.

Plywood has more stiffness in one direction than the other. It bends more easily parallel with the surface grain than across the surface grain. If you are cutting a component that must bend considerably when being built into the boat then orient the grain so that it runs parallel to the curvature.

Increasing the number of layers, without changing wood species or plywood thickness, also adds both stiffness and weight. It gains stiffness because the greater number of layers lock the cross-grain more effectively. Wood stretches more across the grain than with the grain. In plywood, each crossing at a glue joint locks the cross-grain and prevents it from stretching. The result is that many thin layers are more stable than a smaller number of thick layers. It becomes heavier because glue is more dense than wood and the amount of glue in the sheet increases in direct proportion to the increase in number of glue lines. So, if you are doing something that needs flexibility in the sheet so that it can bend, go for less layers in your plywood. If you are doing something that doesn't need to bend and strength is more important, go for more layers. More layers equals more labour to make the plywood as well as more material in veneers and glue, so more layers also means more money.

Whatever grade or species of plywood you use, make sure that you properly seal all exposed edges of the plywood. If you don't it will absorb water or even moisture from the air through the end grain of the exposed edges. That moisture will travel deep into the sheet and with time may cause rot to start. Wet wood has more volume than dry wood, so it will swell from moisture absorption, possibly cracking your coatings.

Another reason for sealing the edges is very important if you live in an area where marine woodworm is a problem, or if you intend to sail through such an area. With properly coated plywood there is nowhere for the worm to enter the timber because everything is protected by a layer of epoxy. If it can get into the surface veneer through some damage to the surface coating then it is restricted to the surface veneer, limited from travelling further into the hull by glue lines. If the sheet edges are unprotected then the worm can get into any layer and probably will, destroying the integrity all the way through the board.

Finally, if you use a plywood that is made from fir or a species of pine, it will be worthwhile to add a light layer of glass reinforcement into the epoxy coating on the outside of your boat. This is because fir and pine plywoods generally have bad surfaces and are not as stable as other species. Unreinforced epoxy is not likely to hold the surface together, so it will soon crack, look unsightly and allow water to penetrate. For the sake of extending the life of your boat you should glass the outside if skinned with these plywoods.

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Saturday, January 12, 2013

What happens if you make a mistake?

Are you scared to start a boatbuilding or other project in case you mess up, in case you make a mistake? What will people say, will your friends joke about it and embarrass you?

Nearly everyone makes mistakes. Those who say that they don't make mistakes are either lying or are not pushing the boundaries of their own ability. As long as we are trying new things, taking on new life experiences, we will make mistakes. It is an essential part of the whole learning experience. Sure, it is nice to learn from the mistakes that are made by others but we learn more lessons, we learn them faster and the message sticks better when we make those mistakes ourselves. The more painful the mistake, the stronger the lesson that we will learn.

When I designed the Paper Jet, I had a particular building procedure in mind for the boat. As it turned out, the Paper Jet could not be built the way that I had envisaged. So, I had to go back a few steps and think of a different way to assemble it. I did that and went ahead and built my boat by a different method. I had a few other smaller backtracks and eventually had my boat complete.

Did I make some mistakes? Yes I did but so what? I made those mistakes because I was doing something that I had never done before. I was doing something that nobody had done before. I needed to learn the lessons that had to come out of building this prototype so that I could write the building instructions in the best way that I could, to enable other builders to get it right without making those same mistakes.

If I was scared of making mistakes I would not be trying new things. I designed and built the first radius chine plywood boat, my own "Black Cat", and made some mistakes along the way. Every time I was able to recover the situation very quickly and move on to the next stage of building. Overall, the project was a great success. Along the way I shrugged off the comments and criticisms of others because they were of no consequence unless I allowed them to be. They were generally from people who have never built anything major themselves. It is normal that the people who will laugh when someone makes a mistake are those who don't achieve much themselves. Disregard those people.

While building "Black Cat", one evening I was working with a spindle router shaping some small plywood parts. I was annoyed about an interruption unrelated to what I was doing and which had broken my concentration. In my distracted state of mind, I put my right thumb through the router bit, which was spinning at 20,000rpm. It made 11 cuts to the bone in the space of 1/2" and I was spraying blood. Within a minute or two I was passing out from pain and shock and was hauled off the the doctor. She said she had never seen such neatly done damage to human flesh and described it as sliced like deli meat. She was able to fix it with one stitch threaded through all of the slices. The worst impact from my mistake was a couple of weeks knocked out of the middle of my already tight building schedule.

OK, so we all make mistakes. Hopefully most of them will be to your boat rather than to yourself. How do you recover from your mistake? First you need to know what your mistake was, i.e. what it was that you did and what you should have done differently. That should help you to figure whether or not you can take apart the incorrect work. If you can take it apart then do so and rebuild it correctly. If you can't take it apart then you must figure the best way to modify the structure to correct it.

When you buy a set of quality boat plans you get access to a support system as part of the package. That includes being able to ask the designer for advice when needed and to steer you along the best path whenever you have a problem. You may think of a way to correct it but the designer, from past experience, may be able to offer some other alternatives and to say what will be best. It is likely that the designer or someone else has made the same mistake before.

The important things to understand are:-
  1. You will occasionally make mistakes.
  2. Some of those mistakes will be silly ones and may embarrass you. Laugh them off. Take control of the situation and correct it, don't allow the mistake to take control of you.
  3. The designer of your boat should be available to help. Contact him, explain your mistake and ask for advice.
  4. You can recover from most mistakes. It may take a bit of application on your part but you can do it.
  5. When your boat is finished you will know where your mistakes are but most other people will never see them.
When prospective builders tell me that they could not build to the standard that they see in my Paper Jet, I sometimes point out some imperfect workmanship so that they can see that my work, like theirs, is not perfect. We all make mistakes. Fix them, then get on with life.

Friday, January 4, 2013

Do you have the skills to build a boat?

This is my starting subject for this new blog because it is a question that comes often from people who are considering buying plans to build a boat for themselves. They have never built a boat and wonder if they will be wasting their time and money in even attempting a small boat.

Amateur boatbuilding is not for everyone. There are people who should not start a boatbuilding project because they have little to no chance of ever getting it done. It may be for lack of suitable skills but skill is not the only factor in building a boat for yourself.

You will probably have a reasonable feel for whether or not you are suitably skilled to do this. You don't need to be a skilled boatbuilder, you need only an innate ability to learn new skills and to take on and successfully complete projects of reasonable size and complexity.

Confidence in yourself is a good characteristic to have. Of course I can only talk from my own perspective and experience. I have confidence in my ability to tackle big and complicated projects. Friends ask me where I learned how to do something that they see me doing, whether it be building a deck or shed from scratch, or my current project of rebuilding a classic sports car. I have the confidence to know that I can do it and that I will learn the skills that I need en-route. I have not yet been wrong in that assessment of what I can do. Maybe my main recommendation should be to develop confidence in yourself, which actually comes from trying new things and proving to yourself that you really can do these new things.

What you need to know is that I failed woodwork at school. I didn't have the interest nor the drive needed to be successful making school woodworking projects. If they had asked me to build a boat I would probably have passed. Not many years after school I built a plywood 15ft catamaran that I designed first, with no knowledge of boat design. Two years later I was building a 36ft wooden offshore sailboat. The difference was that I had the interest and the desire to do it. With that came the drive and the inventiveness needed to see me through the length of the project and beyond.
My first real boatbuilding attempt
Any time that you step beyond your previous experience there will be new skills to learn and boatbuilding is no different. As long as you are not an all-thumbs person, you are probably capable of building a boat. That is not to say that you will be able to build a world cruiser with classic woodworking details as your first attempt, you should probably set your sights a bit lower and build a smaller and less complicated project first.

If you are an accomplished builder of quality timber furniture then you would undoubtedly be capable of building a boat using very complicated detailing but you will know that without asking the question of someone like me. For the rest of us, we should start with something a bit simpler.

That big boat that is in your sights for the future will probably need a tender to ferry crew between boat and shore. A suitably sized dinghy would be a good starter project to teach some of the simpler skills of boatbuilding. While you are about it, make that new tender a sailing dinghy so that it can fill the added purpose of a toy to keep you and the kids occupied when anchored in your favourite places.

Stitch and tape (stitch and glue) boats are a great place to start. They use about the simplest of building details that are within the capabilities of almost anyone. Even if you have never cut a piece of wood before, you should be able to build one of these very simple boats and to do a good job of it. It won't teach you classic boatbuilding details but it will teach you how to work with curved surfaces as well as cutting, clamping, gluing, screwing and planing timber and working with resins and fibreglass. After that you will probably have caught the boatbuilding bug and be ready to expand your skills into more complicated boats and different materials.

There are also plenty of bigger boatbuilding projects that are suitable for first time projects. Make sure that you choose a design that is intended for amateur builders with basic to a reasonable level of skill. If your end goal is a 36ft boat then there is no major advantage in building a smaller boat of similar concept first, as a learning step. If the details are similar, you will learn the procedures just as easily on a 36ft boat as on a 20ft boat, so save yourself the time and cost of building the smaller boat unless you want it to play with on the water while building the big boat.

So, don't be scared of diving into a boatbuilding project. What you should know before you start is that you will learn new skills along the way. You will also develop resilience and endurance as well as improving your problem solving skills. You will shape the character of each boat that you build and each boat will strengthen your character. Boatbuilding is also a wonderful character-building activity to prepare children for the future.

To see what designs we have that might suit your needs, please visit or our mobile website at

Thursday, January 3, 2013

The Aim of this Blog

First post on a brand new blog, I guess that I should explain what I plan to do with it.

I have been an amateur boatbuilder most of my life, in one way or another. From building toy boats for myself from plywood tea boxes brought home from work by my mom, or carved from pieces of dead protea bushes scavenged on mountain walks, to canoes shaped from salvaged galvanised sheet steel, wood from peach boxes and pitch melted into the joints and nail holes. This eventually led me through designing and building my own plywood beach catamaran to building a 36ft sailboat designed by Ricus van de Stadt. This led further to me studying yacht design then designing and building a few dinghies, canoes and two more large sailboats of 34 and 38ft (The 38ft boat forms the background to this blog). Along the way I also designed many boats for other amateur or professional boatbuilders for various materials.

My first big boat project. A 36ft boat in my mid-20s.

Despite my status as a professional yacht designer, all of my boatbuilding escapades were as an amateur in the worst sense of the title. I built the big boats in my garden, working through extremes of hot, windy summers and cold, wet winters. I was always on a tight budget, skimping on the family budget to buy what was needed for the boat that was in progress at the time. My wife had to endure losing kitchen utensils that sometimes found their way to a more useful role in the workshop, finding epoxy chilling in the freezer if I needed to slow the cure or discovering welding rods drying in the oven. Even newly painted scale models were sometimes drying in the warm oven. I don't know how she put up with me but that is the much needed and loved tolerance of the wives of most amateur boatbuilders. I am lucky to have the support of my wife in these ventures and hope that you are as lucky too.

My most recent project, a 14ft high performance skiff.

All this has given me a large amount of experience and knowledge that I am always happy to share with anyone who can benefit from the info. It places me in a good position to help others to make the best decisions for whatever boatbuilding project they are considering or have in progress. I expect that most of the posts will be of my choosing but I will be open to readers sending me their boatbuilding questions or problems that are looking for answers.

I anticipate that I will post on it weekly but the frequency may change. Let's just see where it goes, I hope that you will join me in the experience.

Addendum: Due to limits on my own time available to work on this blog, I need to keep it to a basis that allows me to post about once a week. I can't allow it to turn into a forum type of blog, on a question and answer basis because that will become very demanding of my time and rapidly fail. I will endeavour to provide interesting and informative content that will be of value to you, the readers, on this basis. If you have any particular subjects that you would like me to cover, please send me an email and I will add it to my list of subjects. You can do that via the email link on my website at . Thanks for understanding.

To see my designs, please visit