Easy Aluminum Fittings For a Sailing Canoe
by Charles E. Campbell
The sailing rig for my canoe is a conventional design that needs the usual set of fittings--control horns for the cable connection between the rudder and inboard tiller, and a pair of cheeks to attach a swing-up rudder blade. I wasn't sure how to go about building these. I wanted something trim with, hopefully, just enough design so they look as if they belong on the canoe. Wood is OK but seemed too bulky. Carbon fiber is sometimes used for this sort of thing but I have too little experience with it. Cutting the pieces out of aluminum plate would have been my first choice but I had neither the saw nor convenient access to the aluminum stock that it needed. The rudder on my old Sportspal sailing rig is attached with a wraparound piece of aluminum sheet; something like that seemed a possibility. Aluminum sheet is available at the local hardware in several convenient sizes and I already had the metal snips for cutting it. But for this job it would need to be a lot sturdier than the Sportspal rig.
With a little finger testing in the store, I could see that three plys would be stiff enough for the size of my pieces. As a user of WEST System epoxy, I have a copy of The Gougeon Brothers on Boat Construction. In it there's a chapter on using WEST System for hardware bonding. Perhaps if I epoxied the aluminum plys, the finished pieces would have a little more integrerity and strength than if they were simply fastened. It seemed worth a try so I reread that chapter and went ahead. What I ended up with is some very nice, trim fittings. They're light, strong and rigid. The technique is simple, convenient and requires no metalworking experience or expensive tools. It opened the door for me to get the custom fittings for my sailing canoe that I wouldn't have been able to get otherwise.
For anyone familiar with epoxy, the technique is straightforward and a detailed description makes it seem more involved than it really is. On the other hand, it's a bit messy at times and the aluminum sheet gets bent and looks as if it isn't going to work out all that well. Perhaps for that reason a walkthrough of how I went about it might be helpful for someone who hasn't done this and would like to give it a try.
The tools and materials for this are a short list. Here's a rundown:
TOOLS:
- Metal cutting shears.
Aircraft style snips work well and are cheap. The jaw size allows for going around small curves. If you're not familiar with these, they come in three types: right hand cut (green handles), left hand cut (red handles) and straight cut (yellow). I'm right-handed and find the right hand cut to work best for me. I proceed around the working piece counterclockwise so the shears cut away from it rather than into it. Someone who's left-handed will probably find the opposite to be the case. But these things are cheap enough that it's reasonable to buy the set of three and decide by trial which works best for this job. - A file or two.
A medium file to draw along the edges, and possibly a coarser file for removing epoxy that's spilled over on the outside. - Sandpaper for roughing the surfaces to be bonded.
I use 80 grit. - Some clamps.
The number and size depends on the size of the pieces but it wouldn't hurt to have a dozen or so for this. I needed 10 or 11 small ones on a control horn of approximately 3 x 8 inches. I find spring clamps work well at applying enough pressure to flatten slight bends without having so much they cause epoxy starvation in the joint. In lieu of clamps weights might work OK. - A marking pen for tracing the patterns. A wide tip works well for this.
MATERIALS:
- Aluminum alloy sheet.
The aluminum sheet available in the hardware store is .025 in. thick in various sizes. This is a good thickness for cutting with snips. With a little research on the part of the store clerks, I found out the alloy is 6061. If there's a choice, this is probably the best for this job but others may be OK, too--these aren't heavily loaded pieces and whatever seems strong enough probably is. - Epoxy.
I used WEST System with a slow hardener (#206). The recommended filler is high density filler (#404) because of its high compression strength. If you don't use WEST System (or don't routinely build with epoxy), some alternatives are mentioned later.
A QUICK OUTLINE:
- Trace and cut the patterns in aluminum sheet.
- Trim the edges and sand the mating surfaces.
- Epoxy the plys together.
- After curing, trim off excess epoxy and sand the outer surfaces for overcoating.
- When cured, sand and paint the pieces.
- Et voila!
The first thing I needed, of course, is a design. I did this on paper and pasted it to light cardboard for tracing onto the aluminum sheet. A nice wide indelible marking pen is convenient for this--it doesn't rub off. Because the cutting goes easier the less metal that has to be removed, I trim off what excess I can around the piece before cutting to the line. Being right-handed, I find it easiest to use right hand snips and work my way around the piece counterclockwise. That way the tendency of the snips is to cut away from the piece rather than into it. The stiffness of the aluminum makes it impossible to make the cuts without some bending of the working piece. It loses its pristine flatness this way but that's OK. I just try to avoid sharp creases in these bends. I found that cutting inside curves goes easier by snipping piecemeal at it to make room to get the snips aligned without having to bend the working piece too severely. I didn't get all my cuts exactly on the traced line but this isn't a problem--small differences wash out later when the plys are bonded and overcoated.
When the ply is cut out, it's a bit bent up and the edges are pretty ragged. I draw a file around it to dull the edges (and save the fingers). This only takes a few moments. Because it makes me feel better at this point, I flatten it back out a little so it doesn't look quite so bent out of shape. Some light finger bending is usually sufficient for this.
When all the plys for this piece are cut, I stack them up to see how they go together. Because of the inevitable variations in cutting and bending, some combinations fit a little better than others so I take a couple of minutes to play around with it, adjusting the flattening in the process. I test it with the clamps, too, making sure I have their pressure at the best spots for flattening down any bends. This is the clamping pattern I'll use when it's epoxied.
Just before bonding the piece, I sand each of the faces to be epoxied including the edge, giving special attention to the area near the edge. 80 grit works well for this. I sand thoroughly and haven't needed anything else to prepare the surface other than to wipe it with a clean rag to dust off the sanding residue. I mix the epoxy with the filler (#404) leaving it moderately thick--not quite so thick it will hold a peak. With the bottom ply laid flat, I apply the epoxy thick enough to be sure it will fill any variations from flatness in the ply that's going on top of it. I put that ply on and epoxy it in turn. After the last ply is placed, I line up the stack and apply finger pressure to squeeze out some of the excess epoxy before clamping. This is where it gets messy. Filled epoxy responds slowly to clamping pressure and squeeze out continues for 15 - 20 minutes or so. I try to wipe off what I can as it comes out. When I've had enough of this mess and the stack is aligned OK, I leave it to cure. (I make sure none of the clamps is going to get accidentally epoxied to the piece.) There may be additional squeeze out after this and usually some unwanted epoxy scattered around the outside. All that gets cleaned up after it's cured. At the moment it looks anything but trim.
When it's sufficiently cured (I usually wait 20 - 24 hours with this epoxy-hardner combination), I trim the edges with the file. Then I file or scrape off whatever's on the outside faces. This is where a coarser file is handy. It tends not to fill up with epoxy. Getting the stuff off the outside usually scratches the face, too. That's OK. It's going to be sanded for an overcoating of epoxy anyway. By now the piece has recovered its flatness--or at least close enough. The edges all around should look more uniform, too. At this point, before overcoating, I usually drill any holes whose position I know (other holes will wait until I find out where they're going). Because I lay the piece flat for the overcoating, I can only do one side at a time. I sand the side, as before, and apply epoxy. For the overcoat, I use the same filler, although any filler (except graphite) would probably serve the purpose, but I mix it thinner--thin enough so it will self level fairly well when laid flat. (Also, I use WEST 207 hardner here but only because it has a wider range of paints it's compatible with than 206.) When that side has cured, I do the other. The overcoating is also an opportunity to make sure any voids in the edges are filled with epoxy. Wiping away the squeeze out earlier may have removed some epoxy from inside the edge.
Now about all that's left is to paint it. I think it's a good idea to wait a few days (at summertime temps.) to let the epoxy continue to cure before painting. I sand it down to whatever smoothness seems appropriate for the paint, perhaps about 220 grit. Pictures of the finished fittings are below. In this case, the paint is from an inexpensive spray can I had around (a color that didn't seem to be at odds with other colors on the boat). These pieces are all flat but this technique could be used for curved fittings as well, for example, a piece that needs to fit around a spar.
The rudder cheeks installed.
The rudder control horn. (The fairleads are for the uphaul lanyard.)
A gooseneck.
It's not necessary to use WEST System to make fittings this way. Here are a couple of alternatives:
System Three has an epoxy product called MetlWeld specifically formulated for bonding metal, including aluminum, and a variety of other materials. I have a review of using it for this job elsewhere here on Nessmuking. I didn't like it as well as WEST System for this but it will certainly do the job. It's quite thick and that may make it difficult to get a neat overcoat with it, though. If you don't have a supply of epoxy hanging around, MetlWeld is a good choice. Application is simple because it doesn't need any filler and System Three makes it available in kits as small as half pint (which is easily enough for the pieces shown above).
Another approach is to try some small tests with whatever epoxy you currently use, substituting colloidal silica for the WEST System #404. I made a test piece using colloidal silica with some of the trimmings that were left over and it looked to me as though it would be just fine for this application--it certainly wasn't going to come apart under any loads I would be subjecting it to. Epoxies are bound to vary in their suitability for metal bonding (some may advise against it) so a little testing is always a good idea. The fittings here aren't subject to extreme loads and if what you get seems strong enough, it probably is.
There are a few additional things that ought to be noted:
The marine epoxies we use for canoe building, as well as other epoxies for home use, are not high temperature epoxies. This method isn't suitable for fittings that might be used near a heat source, say, an engine exhaust (an unlikely scenario for a sailing canoe but I thought it should be mentioned).
A constraint with aluminum is the use of graphite. Because of the electrical potential between carbon and aluminum, it's a good idea to avoid using graphite filler or fiber with it. While there's little reason for doing that, the two can come into close contact in other ways. The finish coat on my rudder is graphite filled. I have plastic washers (from coffee can lids) between the rudder and the cheek plates. Besides being a silky smooth bearing surface they're an additional layer of separation between the two.
The Gougeon Bros. instructions for using WEST System with aluminum calls for prepping the surface with an etching kit. The etching kit is a two step process. The first uses an acid to etch the surface. The second uses another material to stabilize the oxidation; oxidation being the enemy of a good bond. I didn't do this. All of my fittings, by virtue of being attached to something, are through fastened so even a complete delamination wouldn't result in a catastrophic failure. Nevertheless, curiosity got the best of me and I called Gougeon Bros. technical support to see if I could expect problems from having omitted this step. What I found was that they had had good success with aluminum bonds made without using the etching kit. From their testing, they found that there's no difference in ultimate strength between bonds made with the etching kit and those without it. The difference shows up in consistency. Bonds made without the etching kit weren't as consistent in strength as the etched bonds. After this conversation, I felt I needn't worry about my fittings. The advantage of omitting the etching step, besides saving some time and money, is avoiding the hazards of working with acid. (System Three makes no mention of etching aluminum in their instructions for MetlWeld, by the way.)
In the end it would have been quicker to bandsaw the pieces from stock that's the right thickness to begin with. It takes a little longer to snip several plys out of sheet--and there's the waiting time for epoxy to cure. But I was willing to take the tradeoff for the convenience of being able to make the pieces with inexpensive tools at hand and material I can easily pick up down the street. It's easy to do and I didn't have to compromise and cobble something together that wouldn't have been what I was looking for.