Of Strips and Stripping
Rev. August, 2003.
The wood strip is the basic building block of canoe and kayak construction. We all know that. Slice a bunch of strips off a flat board, glue them together over a form, and voila! We have a boat. What could be simpler? The simplicity of the method can be its downfall, however. What wood? How wide are the strips? Exactly how thick? How long? Beaded and coved edges or rolling bevel? What glue? Stapled to the forms, or stapless? Buy ready made or cut and mill your own? Do you still think it is that simple? In this chapter we will find out….
Answers to most of the above questions are often casually answered or even ignored during the initial planning stages of building the boat. But the correct answers become important during the later stages, and may even affect the fiber glassing and finishing steps and ultimately the quality of the finished boat. Lets look at them one at a time.
Almost any flat-sawn straight-grained knot free wood plank can be cut and milled to produce strips for boat building. The most popular is western red cedar. It is harvested from old growth tree stands, producing tight-grained clear lengths up to around 20 feet. Close behind is northern white cedar and redwood. The length of clear white cedar boards is limited to around 10 or 12 feet due to the growth characteristics of the tree. It is the lightest of the common boat building woods, and bends readily without cracking. It is generally used along with red cedar or redwood to produce pleasant contrasting effects. Redwood is available in long lengths, is free of knots, but must be bent carefully due to its tendency to crack under strain.
Other woods less commonly used for hull building are clear pine, basswood, mahogany, cypress, and Spanish cedar. The pine is light in color with little grain, available in long clear lengths, sands and glues nicely, but is slightly heavier than the cedars. It can have pitch pockets in it, though. Basswood, the favorite of wood carvers, is usually reserved for accent stripes and artistic trim. It is very light colored with hardly any perceptible grain. Mahogany is hard, tough, and heavy, but when properly milled and assembled, produces one of the most beautiful boats one can build. Honduras mahogany is preferred, followed by African. Philippine mahogany (lauan) is considered too weak for strips alone, but is used in plywood used to make stitch and glue boats. Cypress is similar to pine in its working characteristics, and has a more pronounced grain pattern; much like southern yellow pine but softer. I don’t know anything about Spanish cedar other than it makes great cigar humidors. A few suppliers offer it for sale as boat building strips.
Exactly What Size?
High quality precut and milled cedar and redwood strips are readily available from several suppliers, both in the U.S. and Canada. Strips of other wood species are available, sometimes by special order. The “standard” size is 3/4" wide and 1/4" thick, with interlocking bead and cove edges. As with species, some suppliers will mill special sizes.
Since strips are cut from a flat plank, the thickness of the plank determines the width of the strip. Without going into the nomenclature used by the lumber industry for sizing board thickness, the common plank sizes range from an actual 3/4" to around 11/2". The red cedar I use is 7/8" thick as it comes from the lumberyard, rough on one side. Construction lumber, e.g. spruce, is 11/2" thick, and so-called "five quarters" is about 11/8" thick. Common pine can be 3/4", 11/8", or 11/2".
If you are going to make your own strips, what thickness lumber do you buy? Since the common strip width is 3/4", a plank at least that thickness is required. With my 7/8" cedar, I thickness plane the boards to 3/4" before cutting strips. I could just as easily cut strips at the 7/8" plank thickness, and they could be used to build a boat. They would work fine along the sides where the hull is essentially straight sided. When you get to the turn of the bilge and beyond, however, the bending required is not so much across the thin part of the strip, but across the width. Tightly fitting the strips in this area is difficult enough without having to contend with wide strips. Here, the curvature of the hull is generally a lot tighter than elsewhere, and the relatively wide flat strips will not closely conform to the curve. A lot of wood has to be planed off to shape a smooth curve, both inside and out. The more wood that has to be removed, the thinner the hull gets. Conversely, if narrow strips, say 5/8" or even 1/2" wide are used to plank this area, the amount removed in fairing is a lot less and hull thickness is not unduly compromised. To plank the entire hull in narrow strips requires more strips, however. This translates to requiring an extra plank or two.
I have found that the best compromise for my boats is to make all strips from 3/4" planks. Those 7/8" cedar planks are planed to 3/4" by alternately removing a little from each side until the desired thickness is obtained. Planing both sides cleans up any dings in the board, and exposes surfaces with equal moisture content and the same color. It also discourages cupping due to uneven moisture content. Trying to cut strips from a cupped board will likely produce strips with a lot of saw marks, and can be downright dangerous if the board binds while being ripped.
The 3/4" width works well for the straight sides, while still bending without too much difficulty across the width in the lower sections of the hull. When the planking is correctly done with good tight joints, hull thickness does not suffer significantly when the strips are faired.
We now have the planks all planed or purchased to 3/4" thick. Before ripping them up into strips, we have to know how thick to make them. The classic thickness is 1/4", although for a hull built from a heavy hardwood like mahogany, 3/16" should be considered as a weight reduction measure. There are builders that use 3/16" cedar for hulls, and even 1/8". Additional fiberglass is usually required in these cases, however.
Let’s say at this point that cedar strips 3/4" wide and finished to 1/4" thick are the target. Getting the width was easy. Getting the finished thickness takes a little more effort if you want perfect strips. Briefly, the strips are cut about 9/32" wide (thick) off the plank. They are then run through a planer to remove about 1/64" from one side, followed by taking the other side down to .250 ± a frog’s hair. This may seem like a lot of work, and professional builders would scoff at the extra time required since time is money. Then there is the "too much waste" argument. The amount of extra waste is a mere pittance when the quality of the strips is considered. Sure, you can build a boat with strips cut right off the table saw. I have done it. The secret is a well-tuned saw, a sharp thin kerf blade, long and rigid infeed and outfeed tables, and the capability to feed the plank tight against the fence for the entire length of the cut with no wavering. Not impossible, but not likely, either.
Many builders prefer to use a band saw to cut strips, the reasoning being that since the strips are sanded extensively when on the hull, the wavy and/or rough surfaces on band-sawn strips will be sanded off any way. True enough. But the reason for making nice smooth uniform thickness strips lies in milling accurately centered bead and cove edges.
The router bits, sometimes called “canoe bits” by suppliers, widely available for milling the bead and cove edges are virtually all made with 1/8" radii, or 1/4" diameters. If you cut a perfectly centered bead on the edge of a precise 1/4" thick strip, that edge will fit snugly and precisely into a cove cut with the 1/4" cove bit. This accurate fit ensures a good glue joint with no gaps. No gaps mean fewer fills. Fewer fills mean less work filling, scraping, and sanding.
Now suppose you rip a plank into nominal 1/4" strips (not .250±) and immediately rout the edges. You get edges that will fit together quite nicely, but where that cumbersome extra long full length super sized beauty wavered as it was run through the saw the strip quite possibly is a bit thin. Where is the bead or cove? Not centered, of course. On the hull, this shows up as a plank that is lower or higher than its mates. During fairing, more wood has to be taken off both sides to get everything fair. The shavings and sanding dust on the floor used to be hull thickness, which would still be hull thickness if you started with precision cut strips before milling the edges.
The typical canoe ranges between about 12 and 18 feet long. Obviously we need strips at least that long, right? Yes and no. Due to the curvature of the sides of the hull, the strips need to be around a foot longer than the length of the finished hull. While red cedar and redwood can be obtained in lengths up to 20 feet, milling a 20-foot plank is more excitement than I would like to have on any afternoon. Getting planks that long home is also challenging. My personal best is a 16-foot pine plank used for the bottom board in an Adirondack guideboat. I lashed half of an aluminum extension ladder to the roof rack on the car, and then securely tied the plank on top of the ladder. I had a few feet hanging off each end, but it didn’t cause any problem.
Assuming you get the perfect plank into the shop, you still have to plane it, cut it, rout it, and store it. That means extended infeed and outfeed tables for the saw and router, and shop space at least twice as long as the board, at least temporarily. The back door to my shop opens into a family room, which serves as an auxiliary shop for the purpose of holding the infeed table. I have heard of other such shop extensions, including a laundry room window. What ever it takes….
The longest boat that I have built with strips cut in my shop was 16 feet long. The longest cedar available in my area was also 16 feet long, which is a little too short when you consider the bends required. I opted for a nice assortment of 8, 10, and 12-foot planks. The strips were cut and then scarfed to 18-foot lengths before milling the edges. Some strips had one scarf joint; others had two. When mounted on the hull, the joints were then able to be staggered. The hull turned out great. The point is you don’t need long unwieldy strips to make a boat. Shorter, more manageable strips may even be preferred at times, being easier to handle, less prone to cove edges damaged by cumbersome handling, and less expensive than the extra long planks. The color and quality selection is also a lot better, there being more of the shorter planks available at the lumber yard than those big long honkers.
See the chapter on Working With Short Strips for details of making scarf joined full length strips.
Bead and cove or rolling bevel?
The redwood canoe that I mentioned in the first chapter was designed to be built from rectangular strips measuring 1/4" x 3/4". There were no routed edges. Each strip was nailed to forms, and the edges were simply glued together. Some shaping of the edges was done to change the angle of the edge for a better fit to the adjacent strip. I’m glad I never built it.
One of the first edge treatments I have seen reference to for strip boat building was a V notch cut into one edge, and the other edge double beveled to fit into the V. I don’t know when half round bead and cove milling came about, but it has been likened to one of the great inventions of all time, right up there with disposable diapers, the microwave oven, and canned beer. The ability to make around a thousand linear feet of potentially perfect edge-glued joints with thin strips as long as 18 feet, and do it simply, repeatedly, and reliably is one of woodworking’s greatest achievements.
The bead and cove joint is hailed by most builders as making high quality boat building by novices not only possible, but commonplace. There is a cadre of builders who dislike the bead and cove joint, however. Bits are too expensive, you don’t need bead and cove edges, a little work with a block plane is all that is needed, joints are just as good with straight edge gluing – these are some of the reasons given to forsake God’s gift to woodworking and set about to labor over hand beveled strips. Horse hockey.
For starters, the cost of the bits is peanuts compared to the several hundred dollars invested in plans, a good strongback, wood, fiberglass, and epoxy, not to mention the high cost of several coats of varnish. Throw in a few new tools, a bunch of clamps, and dinner out on occasion to placate the better half, and a set of bead and cove bits doesn’t amount to much.
It can be shown by simple calculation that the bead and cove joint provides about 57% more gluing surface than a flat joint in the same strip. Alignment of adjacent strips is assured when the bead and cove are accurately mated resulting in no “stair steps”, where the surface of one strip is higher or lower than that of its mate. Less wood has to be removed in fairing, resulting in a more uniform hull thickness and fairer hull shape. Glue lines are much thinner and more uniform, with no unsightly yellow streaks where glue filled gaps between strips.
Maybe there is a builder out there with a steady enough hand to plane an accurate rolling bevel consistently. There are far more builders, especially first time builders, who have chosen to eliminate several variables by using bead and cove strips.
A complete description of making high quality strips is in Making Strips.
A Word or Three About Gluing....
The purpose of gluing the strips together is to hold the strips in place until they are sandwiched between layers of fiberglass and epoxy. This composite sandwich is what provides the extraordinary strength inherent in the relatively lightweight wood strip boat. Given the complexity of operations in creating a finely crafted boat from a pile of lumber, one of the least understood seems to be the use of glue. Virtually any of the common woodworking glues will allow a joint to be made that is stronger than the wood itself - provided the joint is properly made before the glue is applied. I have seen recommendations to use polyurethane glue for gluing strips together. Another builder (a professional, at that) uses epoxy. Even hot melt has been tried, and rightfully and rapidly abandoned.
A proper joint to be glued must fit together smoothly and be snug, but without binding, and without the use of clamps to force the closure of the joint. For example, the mortise and tenon joint commonly used for seat frames should be able to be put together dry with normal hand pressure, not fall apart, and be easily disassembled the same way. When glued, the joint will have the proper amount of glue between the mating surfaces. Clamps are only used to maintain alignment until the glue sets. If the clamps are used to force the closure of the joint, glue may be excessively forced from the joint resulting in a starved and weak joint, ultimately leading to failure. In the case of gluing strips together, the bead and cove edges provide the perfect mating surfaces. Glue is applied, and the new strip clamped to hold the joint. It may seem an inconsistency to say that the clamping arrangement is not being used to force the joint. Not so. Often, due to the bends and twists required in the strips, the clamps force the strip to shape - they should NOT force the closure of the joint, merely render it immobile until the glue sets. More glue up information and detail can be found in the section on stripping a hull (to be written).
How Does Glue Work?
Works great! Certainly, without it we would be nailing our boats together. But what happens when we slobber some glue on a piece of wood, lay another piece on top of it, and let the whole mess cure? Glue has to penetrate or soak into the pores of the wood in order to produce that bond "stronger than the wood itself". This, regardless of the glue chosen. It is especially important when using epoxy, as discussed in the section on making stems. Between each surface of the joint there must be just the right amount of glue. Too much, and the joint is weak. Too little, and the joint is starved and likewise weak. The bottom line is, enough glue to soak in, just enough between good fitting pieces, and the best bond is made.
Myths abound in gluing a boat together. I have heard of a builder that cuts his bead edges with a flat on top, to act as a reservoir for the excess glue between it and the properly cut cove. Excess glue is a weak joint, and is also more susceptible to creep (discussed in the fiberglassing section). Another builder uses polyurethane glue for gluing strips together. Something about Titebond II showing something under the fiberglass. If the joint was properly made with the right amount of glue in the joint in the first place, there wouldn't be a problem. Ah, the perils of using staples... Then there is the professional builder who uses epoxy, allowing the epoxy to fill the gaps between strips. Even though light shows through here and there, the joint is said to be tight! Whatever happened to craftsmanship?
A well-built boat will have tight joints between strips, nearly invisible glue lines, and look and feel like the hull grew that way. Would you want to settle for anything less?
What Glue to Use?
The glue of choice is a polyvinyl acetate (PVA) formulation, also called yellow or carpenter’s glue. This glue is readily available, inexpensive, easy to use and clean up, doesn't harden in the bottle, has a reasonably long shelf life, and does the job quite nicely. Titebond, Titebond II, Elmer’s, etc. are some of the commonly available brands. They set up rather quickly, having open working times on the order of five to ten minutes, which is ample for gluing strips together. The type II PVA’s are water resistant and are recommended for outside applications above the water line. One would think that this would be the glue to use for boat building. The jury is still out on that one, though. Titebond II contains coloring dyes that can potentially be a problem, leaving a stain in soft woods like cedar. This becomes a problem when fresh squeeze out is incompletely wiped off with a wet rag. The diluted glue soaks into the wood, carrying the dye with it. If the squeeze out is allowed to stay in place, it can be scraped off easily while in the rubbery stage, or even after it has hardened. Phil Greene at Wood Song Canoes uses Titebond II, lets it harden, then sands it off during the fairing process. While Titebond II can be sanded quite easily, other PVA glues may melt and gum up the sandpaper if it is not at least scraped off first.
While working on a non-boat building project a while back, I ran out of my favorite glue. My trip to the glue department of the local big box store was disappointing in that they did not carry the glue I wanted. Rather than schlep around town looking for it, I decided to try another brand, with the “no runs or drips formula”. Back on the bench, the glue worked fine – until I had used about half of it. It wouldn’t run out of the damned bottle! In a fit of frustration, it wound up in the trash.
Epoxy is used extensively in boat building, but is not recommended for gluing strips together. It is expensive, tricky to use, messy, and not needed for gluing strips together. It does not take too well to certain woods like ash and oak. In order for the epoxy we use for fiberglassing to be effective as an adhesive for wooden boat parts, some mixed but unthickened epoxy is applied to the pieces to be joined and allowed to soak in. The remaining mixture is thickened with colloidal silica, wood flour, or other thixotropic additive and applied to the joint after wiping off the excess soak coating. If no preliminary soak is performed, there is a potential for the resin in the thickened mixture to soak into the wood, leaving a starved joint behind. Joint failure is a distinct possibility for which I have first hand experience.
Epoxy is the only glue to use for gluing a wood part to a previously fiberglassed area, like gluing inwales and outwales to a fiberglassed hull. It is also quite useful for gluing outer stems on a completed hull, since the deep soak in the end grain of cedar provides for an excellent bond. I'll also use it to glue cedar blocks to the inwales to make scuppers, and it is great for the mortise and tenon joints on seat frames, nicely filling any side-to-side gaps in the joints. Preliminary wetting is required with hardwoods, of course. I will not use it to glue stems together - Titebond or Titebond II is adequate, and a lot easier to use.
One occasionally sees reference to using polyurethane glues, like Gorilla Glue. It would be useful anywhere a type II PVA is used, and it has the dubious property of expanding (foaming) to fill gaps. If you have to depend on filling gaps with foam when gluing strips together, your craftsmanship is in serious need of attention. The expanded foam that is produced when the glue sets is no substitute for a properly made joint. Polyurethane glue can also be expensive, it will harden in the bottle at times, and cleanup before curing requires solvents. Cured glue can be scraped or sanded off. Once cured on your hands, you wear it off. The shelf life can be rather short, especially once it has been opened. It is sensitive to moisture, requiring it to cure properly. Controlling shop humidity just to make the glue cure seems like an inordinate amount of detail better applied to doing the job with a less demanding alternative. I have used polyurethane glue for non-boat work, and misted the joints with a little water before applying the glue. It worked OK, but over a few weeks the glue kicked off in the bottle, rendering it useless. Safety is another concern. At least gloves are recommended for intermittent use, and significant health problems can occur when long term usage is made without protective equipment.
A few other glues used for boat building are resorcinol and urea formaldehyde, although not generally for strip boats. They are powders, some mixed with water, or with a liquid catalyzing agent. I have used the two part stuff for a non-strip boat, and in spite of the dark colored glue line, it worked well. These glues also contain formaldehyde, a known health hazard. Other unfriendly components may also be present, like furfuryl alcohol and phenol.
Hot melt glue is used in stripping for holding strips to the forms during stapless construction, mostly of kayaks. The angle between a strip and the form is usually a lot greater in a canoe than a kayak, leaving little of the form to bond with. It should never be used to hold strips together due to its poor strength, and the fact that it will be cooled and solidified before the strip has been placed. Since it is only effective while hot, it is difficult to remove smeared and soaked in glue from hull strips. Sanding only heats it, liquefying it once again and exacerbating the problem.
Staples, or stapless?
If a war were ever to break out among boat builders, it would not be between canoe and kayak builders, or bead and covers vs. flat bevellers, or even between amateurs or professionals. It would be the argument that has raged since strip boats began – to hold strips to forms with staples or not. I have done it both ways, and there are pros and cons for each.
For the uninitiated, a hand staple gun is loaded with ceiling tile staples, and a staple is driven through a strip and into each form as the glued strip is applied to the hull. The Guinness Book of World Records does not have an entry for how quickly a hull can be built using staples, but I have seen it mentioned somewhere that one professional builder can lay up a hull in a day and a half. By contrast, the casual amateur may do two or three rounds (matching strips, one on each side) of stapless strips per day.
You go to a wooden boat festival, Regatta, Rendezvous, or some other gathering of strip building addicts. Sooner or later, as sure as Murphy’s Law is Truth, someone, somewhere, will look at and admire your boat, and ask…The Question – “What are all those little holes in the boat?” That rushing sound only you can hear at that moment is the wind going out of your sails as you fumble through an explanation of how you built the boat by banging staples through each strip 12 or 15 times. The onlooker accepts your explanation, and then moves off to admire the next boat, curious why there are no holes in that one. Crash. Resolved – your next boat will be built without staples.
In trying to think about why one would consider using staples, the only thing that I could come up with besides speed of building is simplicity. It has got to be the easiest way going to hold strips on a form while the glue dries. The speed aspect comes into play because of the simplicity. For the first time builder, seeing the hull take shape has got to be one of the most rewarding moments in boat building.
OK – you have your hull all stapled together in non-record but respectable time. Now for the penalty phase. First, you have to pull all of the staples out. That takes time. Then there are all the fills that have to be done where the staples didn’t quite hold a tight joint. That also takes time. Scraping the fills before final sanding…. more time. By the time you are ready to lay fiberglass, you have a hull with a lot of fills and full of holes, but you got it built quickly. Care to fill the holes? Some builders actually poke round toothpicks into the holes, trim them flush, and sand. In all fairness, there is a professional builder that mixes a water-based filler for the holes, and turns out a really respectable fill job.
Attention to detail, or rather the lack of it, can cause problems later on. There is that myth that the air in the pores of the wood can expand during fiberglassing and produce bubbles, which can be prevented by sealing the wood with a precoat of epoxy. In reality, the bubbles originate in the cracks and gaps in poorly glued joints between strips. What happens is the extremely low viscosity epoxy settles into the crack, displacing the air which subsequently gets trapped under the fiberglass. If the hull is constructed with good tight solidly glued joints, there are very few or no gaps that "outgas". This requires more clamping than just staples can provide. Precoating will prevent some bubbling, but at the cost of an extra coat of epoxy and the time to apply it and let it cure to where the glass can be laid up. I'll ramble more about precoating in the fiberglassing section.
Another way to look at the time thing goes something like this – building a boat is fun. If I build a hull full of holes in as short a time as possible, am I having as much fun as if I took more time and built a hull with no holes in it?
Having vented about stapled hulls, it is only right that I describe the alternative – the stapless hull. The job at hand is to glue the strips together along their entire length with tight joints, and do it without staples. For this, anything goes. There are no rules. Creative clamping is learned as a natural consequence of stapless building. Clamped wedges, bungee cords, rubber bands, packing tape, duct tape, web clamps, spring clamps, C clamps, all sorts of quick clamps, stationery spring clips, scraps of stripping used for pushing, scrap pieces stapled temporarily to forms to hold glued strips, hot melt glue – whatever it takes to hold the glued strip tightly in perfect alignment until the glue dries.
Buy them, or cut your own?
Ready-made strips are widely available, as previously noted. The quality is generally excellent, with consistent dimensions and precision milled bead and cove edges. The only strips I have bought ready made were for my first boat – a kit. They were nicely made, and the supplier took precautions to preserve the delicate cove edges from damage. Ready-made strips are a convenience, and the first time builder is probably ahead of the learning curve by using them.
Once you get through that first boat building experience, however, making your own strips becomes more attractive if you plan to build a second. The primary consideration is cost. Ready-made strips average around $.25 to $.35 per linear foot, plus the shipping cost. Buying your lumber locally eliminates the shipping cost, and the finished strips are a lot less expensive. I average about $.08 to $.10 per foot by making my own red cedar strips. Another way to look at it is, boat building is fun. Why pay a supplier to have some of my fun? Another plus is the variety of lumber species to pick from, as well as being able to select your colors.
But the fun of cutting your own strips has a price. The tooling for making high quality strips comparable to professionally made strips is not always in your shop. The first is a good accurately aligned table saw. Some builders use band saws, but in order to produce top quality strips initially cut with a band saw, a planer is virtually a requirement. It is not absolutely required if your table saw is capable of precision ripping, but it sure makes milling precision strips a lot easier regardless of the type of saw used. The final tool required is a table-mounted router equipped with bead and cove cutting bits. If you have or can get the use of these three tools, then by all means go for making your own fun.
Another cost of cutting your own is noise and dust - lots of each. With the dust flying, you should (must!) have respiratory protection. Respirator masks are relatively inexpensive. For about $30 or $40, you can get a good quality mask adequate for boat building. I like the replaceable cartridge type. I can put dust filter cartridges in for cutting and routing strips, then change to activated carbon filters when spraying varnish.
As for the noise, hearing protection is highly recommended, especially during the router operations. Some builders use a two router setup, cutting the bead and cove simultaneously. For this, noise protection is a must. I prefer making less noise over a longer period and do my milling with a single router, changing bits between operations.
My mahogany Wee Lassie II with grandson (the one I dunked)