Construction - part three

Mike Griffiths (guest blogger) gets a little side tracked during his canoe construction.

The challenge of cutting out the five half planks of a lapstrake canoe from a sandwich of four sheets of marine ply looked daunting without a good working surface to support the job. The only existing work surfaces available for carpentry (my wife is not inclined to let me use the kitchen table) are an odd collection. They consist of a badly repaired Chinese copy of a “workmate”, a couple of adjustable trestles and a broken occasional table. The one unifying feature being that none of them are exactly the same height. I needed something to support the sheet material properly, set at a level suitable for sawing.

The initial plan was to use a couple of sheets of kitchen/bathroom grade chipboard (the green coloured variety) as the work-surface and to construct some arrangement of timber to support it. The serendipitous find of some cast iron legs holding a rotting plank in the damp corner of one of the barns changed the plan – I now had a base from which to construct a proper work bench. With a breakfast mug of tea in hand, I went through the timber stack to see if any combination of pieces gave me inspiration. A number of scenarios presented themselves while I drank my tea but in the end I settled for simplicity (and a slice of toast). Three timbers of similar thickness bolted to the iron legs with a narrow length of chipboard between two of them. I am not entirely sure what this valley arrangement is for but I definitely recall that the work-benches we used in woodwork class at school had them so they must be important. See! I did pick up something during those years of ‘durance vile’ at grammar school.

The result, as you can see from the pic, is unlikely to meet the approval of a master joiner and certainly not my old woodwork teacher but might, just, pass for an amateur canoe builder. At least it is robust – so robust in fact that it is just about impossible to move. I plan to rebate a channel between the two butted timbers and fill that with a slice of the same wood (to avoid losing small things down the gap) plus the wood needs belt sanding – oh and I will add a vice. Hmn – this is building into a project of it’s own. I have already spent the time I might otherwise have used to cut the canoe planks building this monster – so perhaps back to plan A – lay the chipboard on top of my new platform to get a smooth surface and get on with the cutting out.
So I came up with a simple, indirect way to screw the sheets to the (putative) workbench and “voila” I now have a strong, rigid and demountable table ready to saw my planks. (The back edge looks a bit curved in the picture but in fact it is nice and straight.)

In other exciting news – Paul rang up to say that he was posting me a container of wood dust. My wife Tracy was under-whelmed when she heard about this gift – thinks we have altogether too much dust as it is. The wood dust will be used to thicken the epoxy resin when it is used to form a fillet or when used as stopping in areas that will later be varnished. Mixed with this wood dust the result will be a closer colour match to the mahogany (okoume) faces of the marine plywood. In other areas colloidal silica can be used as a thickener for the epoxy resin.

Next time I will be back on track and doing some actual canoe building.

Construction - part two

Mike Griffiths (guest blogger) continues his chronicle of a canoe construction.

Lofting the lines

What a grandiose term for the process of transferring some 90 odd measurements from a book to a sheet of marine ply. It evokes the days of craftsmanship, wooden sailing ships and the shipwrights that built them. Back to reality, I am building a lapstrake canoe and using some pretty modern materials to do it.

Essential tools for lofting proved to be a good quality ruler, a sharp pencil and a large set square – oh and an eraser. My set square is metric but that does not matter – size is the key here with my 40 centimetre model proving only just big enough. Using a cheap “mechanical” pencil proved to be the best way of always having a sharp point – and you can buy them by the packet for very little.

“Measure twice and cut once” goes the refrain but in reality measuring more than twice looks like a good policy. I crosschecked the offsets by calculating and then measuring the plank widths at each station. I am not sure just how paranoid one should be about accuracy. The fact that you only have a set number of fixed points along the curve of a given plank (one for each ‘station’ set at twelve inch intervals) makes me think that minor inaccuracies can be resolved when drawing a fair curve between them. I also assume that any errors in the published table or (more likely) in my reading of that table should become reasonably obvious when drawing the curves. I would not expect to see anything other than a smooth line along the whole length. Humps or hollows would imply an error somewhere.

In truth, once into the swing of things, marking out the offsets does not take much more than an hour. Now the interesting bit – drawing in the curves.

Good news on clamps - you may remember that, in my first post, I wrote that I need at least sixteen clamps for this project. Paul suggested I look at 'F' clamps and I have found that the local “pile it high and sell it not quite as expensive as the others” builder's merchant has pairs of 'F' clamps at €1.30 the pair. They also had large spring clamps at around a Euro a piece.

Curve Drawing

My trusty guide and inspiration, Chris Kulczycki’s “The Canoe Shop” suggests that the best way to draw the curves that form the upper and lower edges of each plank is to hammer a panel pin into the lofted marks at each ‘station’ and to push a flexible wooden or metal lath against the pins – drawing a fair line against the curved lath. Our blog host Paul has posted pictures of the non-slip weights that he uses to hold a lath against the waypoints on a curve – these are the business as you need something to hold the lath in position – unless you are blessed with more than the usual complement or arms.

I ended up using a combination of pins, weights, spare hand and my knees to get my lines drawn in. Again, this is not a lengthy process. I took the opportunity to re-check every measurement but otherwise found that each plank took shape fairly quickly. I did have to check that my lath was square as it had a tendency to twist slightly so I needed to check that before running my pencil down it’s edge.

I am slightly embarrassed to have to admit that I have got to my current (great?) age without realising ‘till now what the wedge shaped back end of a cross-peen hammer was for. I now understand that it is to start panel pins held between finger and thumb – how brilliant! I have been using a French cross-peen hammer – a style that I have always regarded as looking somewhat crude. This one at least, is nicely balanced and a delight to use. Anyone with a twelve year old son will know why I had to buy a new one – my rather more stylish wooden handled one is “out there somewhere” along with quite a few other tools silently “borrowed”, never to be seen again.

Pictures of some beautiful cross-peen hammers made by Lie-Nielsen Toolworks (they make tools a work of art) and then my more workaday French equivalent from the builder’s merchant.

The hardest curve to draw is the first twenty odd centimetres of the garboard plank (the one that forms the bottom of the canoe). This curve is quite tight and detailed offsets are not available to those of us too mean to purchase the full sized plans. This curve must smoothly run into the slightly convex flow of the next 90 centimetres or so of what will become the line of the keel. A ‘flexible curve’ – basically a length of lead between two steel ribbons with a moulded plastic outer - proved helpful in getting this to look right. This simple device retains it’s shape allowing you to make minor adjustments until the overall curve is fair.

Construction - it's contagious

I had been warned by Paul at Fyne Boats that building kayaks and canoes is addictive, but I had not realised that it is also contagious. Brother Mike has started a build, and his experiences so far appear below as a guest entry.

Whatever you choose to build, you are likely to need to create 'fair' curves and I favour the following method for holding a batten in place.

The 'pots' are filled with lead and weight about 1.7Kg. The base of each pot has 4 screws that protrude a small distance from within the pot. These provide a stable base on a wooden work surface while being resistant to sideways pressure.

Anyway, enough excitement from me - some thoughts from Mike.

Guest Blogger

Mike Griffiths (guest blogger) starts a chronicle of his canoe construction.

The project is to build a canoe for paddling on the great rivers of France – which is where I live. The chosen design comes from a book titled “The Canoe Shop” by Chris Kulczycki and the 16ft Sassafras lapstrake (clinker) canoe is constructed from 6mm marine ply and epoxy resin.

I am going to skip lightly over the trials of locating reasonably priced marine ply in France in general and in the rural ‘department ‘of the Dordogne in particular. Suitable timber merchants and boat chandlers are in very short supply this far from the sea. However, West epoxy resin and five sheets of marine ply eventually turned up so the project could move from the conceptual phase to the practical – or to put it another way, it was time to stop faffing about and actually get some boat building work done.

I was aware that the canoe plans (and in particular the table of offsets) were a product of the USA but once my pencil was sharpened ready to start marking out the boat planks on a sheet of ply it was still a bit of a shock to realise that I was expected to do this in inches – to the nearest 16th * (see below). Fortunately, my toolbox came up with a slightly rusted metal rule calibrated to that great old British measure. Just to be sure (I had been caught out with quarts once) I checked that US inches were the same. I found out that, while they were not quite the same, the tiny difference could safely be ignored. I was also most entertained to discover that in July 1959 the US inch had been redefined to be exactly 2.54 centimetres long. Now you would have though that it might have occurred to our US cousins that re-calibrating one of their fundamental units of measurement to a size defined by an international standard might be a good basis from which to go the whole hog but – well clearly that did not happen.

The canoe is constructed from five pairs of identical planks (or more properly strakes, see below **). The bow and stern sections of each plank are identical so ‘lofting’ the lines of the canoe requires you to lay out one half of each of the five different planks on a single sheet of 2.4 metre by 1.2 metre ply. The idea is that you will then cut the design out from four sheets of ply clamped together thus ending up with 20 half planks ready to be scarfed together into ten full planks, each about 16ft (4.8 metres) long. Hefting the first sheet of ply down onto my office floor to mark out the design convinced me that handling and cutting four thicknesses together was going to require a little more support than the general ramshackle collection of collapsible benches and props I have used for woodworking in the past. So the first proper construction task is going to be knocking up a suitable bench from some spare timbers and a couple of part sheets of flooring grade chipboard that are, fortuitously, to be found in the barn.

Tools are another issue as well. It is clear from my copy of “The Canoe Shop” that a reasonable number of woodworking tools was going to be required to complete the cutting and shaping of the marine ply. This is one of those temptation moments – on the strength of a single project you suddenly get giddy and start to plan the purchase of one of everything. Fortunately common sense prevailed and a sensible evaluation of the tools already available suggested a much reduced shopping list. This was a chance to learn to use that router that has been sitting on a shelf waiting for it’s opportunity but it was clear that I was going to need a new fine toothed saw plus a low angled block plane for cutting the scarfs. Clamps were another issue – it looks like fitting the inwales and outwales was going to be one of those jobs where you just can’t have too many clamps. The book suggests that between 16 and 32 clamps would be adequate but that you would need twice as many if you wanted to glue on both gunwales at once. I found I had four good G clamps which left me with something of a deficit. Unfortunately the season for “les vides grainier” (the equivalent of car boot sales here in France – garage sales I think they are in the US) is just about over; so filling in that gap might prove more difficult and costly than one would hope.

Anyway – it is time to start putting pencil marks on a piece of plywood – the first step of many towards conjuring a canoe from the sheets of board leaning against my office bookcase. Enough of procrastination! Now where did I put that pencil I sharpened?

* I must admit that to a software developer like myself halves, quarters, eights and sixteenths have a certain binary appeal but when you get down to it millimetres rule. I did think of converting the offsets to the metric system but with some 90 points to plot one is almost certain to introduce an error. In any case, building a lapstrake canoe has a certain anachronistic appeal – so why not go the whole hog.

** While the 5 planks forming one side of this canoe should properly be called strakes the individual timbers are named (from the bottom) the garboard plank, the first broad plank, the second broad plank, the third broad plank and the sheer plank. Which clears the naming up nicely I think – strakes they are then.