Tech Tip Tuesday

Class has been ticking along with the students getting their frames near completion.  The canoe plans came from S. Jeff Horton's book on skin-on-frame building that's available on Amazon - he's even got a second book available.  

Before you take issue with what I write here and think that I'm throwing Jeff "under the bus" as it were, I'm not.  I think he does some interesting things and offers some good designs, but I think he lacks some experience with other canoe building traditions.  Even he states that he's not really a "canoe guy" and I think that hampers him in designing a skin-on-frame canoe.  I do think that for our application, we've made some improvements to the design in terms of functionality and aesthetics.

He's got what looks to be a great shape for the canoe, but I take issue with a few of his construction details.  First, in his design, he notches the bottom of the frames where a plank boat would have garboards to put in floors.  First, the notching weakens the frames significantly.  While Jeff shows a slightly raised seat in his design, we really want the paddler to sit as low as possible in the canoe. This would have the paddler's butt in any water that might be on the floor if they were sitting that low.  Last but not least, the fabric rides right on the floors, which doesn't allow the fabric to flex over obstacles that you might encounter in the water, resulting in potential damage to the skin. 

To avoid these issues, we didn't notch the frames and will lash a floor to the top of the frames which I think will be a practical and more attractive solution.  It should look very much like "duckboards" used to in a traditional canoe.

The other thing that I've been thinking about for quite some time is how to make the gunwales more traditional in their appearance.  When building a wood and canvas canoe, the ends of the inwale and outwale often have a graceful taper to them and the stem is mortised to allow the gunwale to pass by and give a nice triangular area for the deck to sit within. 

On Jeff's canoe, he has the deck as a "cap deck" which lets him hide the fact that the inwales aren't well fitted.  He claims that this type of woodwork is beyond most, but I think that's a little simplistic.  To be honest, I've been thinking about this for a while and last weekend, we made a test cut on the first boat.

We started by placing the inwale in place and clamping it to the end of the stem.  We made a horizontal mark at the bottom of the inwale.  We also marked the centerline of the stem face.  Using a bevel gage, we took the angle that the inwale met the stem and marked from the centerline to outside faces.  A vertical line completes the marking.

 Using a handsaw, we roughed away the material and finished with a chisel.  Here is the result:

 

The next step was to take the inwale and taper it from a 1/8" thickness at the end of the stem to full thickness at the first form.  We repeated this for the outwale and made a tapered spacer that went between the inwale and outwale.  The length of the spacer was such that the thickness of the outwale was 7/16" where the spacer ended.  There is an important reason for this - we'll be using 3/8" long staples to attach the fabric to the outwales and don't want the staples poking though into the scupper openings.

 

I think that the tapered ends look very nice.  We still have a bit to go on this idea yet - Jeff's scupper blocks were irregularly spaced, so we're going to deal with that.  To do that we'll cut down the frames by about half an inch or so in order to hide them with pieces of the Western Red Cedar used for the gunwales allowing us to make more uniformly spaced scuppers.  Also, the stem ends will be cut down and the breasthooks tips will be notched underneath to allow only the deck to be seen, not the end of the stem frame.

More to come!

Details, details...

When we finally get the bottom of the canoe glued together, it is now time to pay attention to the stems. The picture above shows what we normally end up with after stripping. If we had taken pains to finish the stripping very carefully at the bow and stern, we could proceed to fairing and fiberglassing the hull. I like to have my students do one more step and to laminate an outer stem made from hardwood. I think it is a better-looking and more professional detail. I prefer hardwood here because this area - particularly the bow - bears the brunt of any impacts the boat might have. While the fiberglass and epoxy coating on the outside of the canoe is very flexible, and generally will spring back from an impact, the soft cedar of the hull (or stem material) will crush and not come back to it's original shape. This causes a delamination of the fiberglass and epoxy from the wood and generally requires a bit of repair. Hardwood stems tend not to crush as easily and provide for a more durable buffer.


The first thing I like to do is to find out where the end of the inner stems are located along the keel. You can either mark this position before you bond the football in place (note the pencil mark in the picture above - top right...) or you can come out from the line of staple holes at the station nearest the stem and mark a distance of about 1-1/2" towards the end of the canoe. The reason is that you are about to make a cut into the hull to accept the stem and you want to make sure you will be having the inner stem behind your cut. The inner stem hides this cut when you come through the hull, so it will not be seen from the interior. I like to cut down into the hull at an angle as shown above. (The reason is solely cosmetic. You could just cut straight down, but I think you'll like the detail shown in the last picture. ) I then stop cutting when I reach the inner stem. This cut is usually made with a chisel.


Another view - note the lighter colored wood of the stem.


This cut is then extended along the hull up towards the sheer line. I am trying to accomplish three things here. First, I want to have the width be fairly uniform (within about an 1/8" or so) when viewed from the end. I also want it to be a smooth, fair curve when viewed in profile. Last, but not least. I want the "flat" of the rabbet to be perpendicular to the main axis of the canoe so that the stem isn't twisted when it is laminated in place. The canoe shown in these pictures is a Wee Lassie II, designed by Mac McCarthy. I have a small problem with the way the bow and stern are designed, because the profile gives a section that is a bit wide at the bend. This leaves us with a hollow when trying to keep the width constant. This area gets filled with wood flour, epoxy and fumed silica made into a peanut butter consistancy. The stems are then laminated in place after the epoxy cures and is cleaned up. A bevel that matches the cut in the picture above is sanded into the end of a stack of thin strips. A hole is drilled for a small wire nail near the top of the curve to keep the stack of glue-slick strips from sliding. A cleat is installed under the strongback to wrap inner tubes around. With the pack of strips glued up, it is installed and the inner tubes hold the stem together while the glue cures. Note the spring clamp that was used to keep the strips from sliding side to side. Handy.


The picture below shows the end result when you're done fairing and glassing the hull - what you see is a neat little arrow-head detail that I think is pretty sharp-looking. It is particularly impressive when you have contrasting woods for the stem and the hull.

Tech Tip Tuesday

When you build a canoe, you have several decisions to make about the boat. One of the more important decisions is about the stems of your canoe. It is possible to build a several ways:

• no stems
• only an inner stem
• a combination of inner and outer stems

No Stems

Some builders try to save weight by building a canoe without any stems at all. Gil Gilpatrick follows this building method. As a Maine Guide, he uses canoes that he's built using this method for his guiding business. Considering the abuse that these boats take, this method must be strong enough.

This method depends on the fiberglass coating to provide the strength that you need in the ends of the canoe. As you are building the canoe, the strips meet at the ends and one strip is beveled and the other passes by. The strips are glued together to hold the shape of the canoe until the builder can fair and glass the hull. This method requires glassing the hull inside and out. Glassing up in the ends is difficult and messy.

Other than the glassing, I have some concerns about keeping the hull together during the building process. There just isn't a lot of area for the glue where the strips meet in the ends. Also, the fiberglass and epoxy is flexible. If you have an impact, the fiberglass and epoxy flexes and the soft cedar underneath will crush. The fiberglass and epoxy usually recovers, but the wood fibers do not, leaving a delaminated area where the 'glass and epoxy aren't in contact any more.

Oh yeah. Did I mention that it is difficult and messy to glass up inside the stem? (Yeah, I meant to repeat that...)

One Stem

It's also possible to build with only an inner stem. The inner stem provides a larger bonding surface for the glue than strips alone. It is more rugged than without, but takes a bit more time and effort. To save weight on the small canoes my students build, I recommend softwood for the inner stem - usually poplar or basswood. On small canoes, we do not glass over the stem, but cut the fiberglass about an inch away from the stem and paint the wood with epoxy to seal it. The same delamination issue from impact still remains as you don't have an outer stem.

Inner and Outer Stem

This is my preferred method. I use the same softwood inner stem mentioned above, and either a softwood or hardwood outer stem. I feel that this provides a much nicer cosmetic appearance. Also with a hardwood outer stem, the crushing issue from impact is much less of a problem. The choices of hardwood let you choose from different colors to give many different cosmetic appearances.

In addition, there are several areas along the stem where beginners can have difficulty getting good joints. The stems cover these areas and provide a bit of camoflauge for the bad joints while also giving a pleasing appearance, cosmetically.

Building Stems

If you are lucky enough to have some unique pieces of wood that have a curve matching that of your stem (crooks or knees...) You can saw the stems out of solid stock.

Most of us aren't that lucky.

Another way to deal with the issue is to steam bend the stems. This isn't a bad or difficult method, really, but steam-bending is a subject unto itself. When Jerry Stelmok bent stems for his canoes, they were symmetrical, so he bent them out of one wider piece of stock and cut them in half with a table-saw. (This was done to avoid twisting of the stems.) The one thing to keep in mind is that steam-bent stems have a tendency to relax, so it's best to keep them clamped in place until ready to use.

The way I teach my students to make stems is to laminate them from thin strips of stock. First, I cut thin strips that will bend around the forms without breaking. As I cut the strips, I keep them in the same order that they come off the board. I want to laminate them this way. There is a reason - when it comes to bevelling the strip later, keeping the grain direction constant makes the cutting easier as the grain doesn't change directions and tear out. Here is a pack of strips fanned out:



The stem patterns are covered with a layer of tape so that the stems will not be bonded to the forms.

The strips are then bonded together. We usually use wood glue as the stem will be coated with epoxy. You can use polyurethane adhesives, but epoxies would be overkill.

Starting at one end the strips are clamped to the pattern. (there are holes in the pattern to make this possible) I usually use spring-jaw clamps to keep the strips from sliding side-to-side when slippery with glue. You want to be careful to make sure that the stem isn't twisted.

As I've said before - you can never be too rich, too good looking or have too many clamps.


Once the glue has set, the stem can be removed and will hold the shape once removed from the pattern.


In a later post, we'll talk about trimming the stems and bevelling them.