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.

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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.

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