Archives for Marc's Miscellanea

The graphite bottom

applying graphite 1

 

One of the things I knew I wanted to do from the beginning was apply the black bottom. This is a mixture of graphite and silica powder in with the epoxy. It gives the bottom of the canoe a finish that is very abrasion resistant and super slick. It does hide the beauty of the wood, but it’s below the waterline so when the canoe is floating it won’t be visible.

I measured up to the projected waterline amidships and picked the strip that was closest to that and chose that as the masking point. Following a strip made the line more aesthetically pleasing than following a straight line I think.

 

applying graphite 2

Once you mix the graphite and silica into the epoxy it becomes very runny. Definitely a throw away clothes job as well. It went on pretty easy though.

You want to make sure you pull the masking tape off after the black goo has set, but before it’s fully cured. I think it was probably about 4 or 5 hours for me. Environmental conditions (and of course the epoxy you use) will make this vary. If it was fully cured I think you’d be chipping masking tape out with a chisel. And you’d be sharpening that chisel a lot.

Once it’s fully cured it’s rock hard. Really noticeably much harder than the clear epoxy on the rest of the boat.

 

graphite coated

I did two coats black goo. They are fairly thick coats, but it adds weight so I didn’t want to go overboard.

 

DSC00733

After the final coat is cured, I buffed the black finish with a scotchbrite pad (aka green scrubbie). Started by hand but then inspiration struck and I put it under the random orbital sander. That made the job go much quicker. The green scrubbie leaves a matte finish which is unbelieveably smooth to the touch. It’s not hard to see how much this will make the boat slide over rocks, weeds and logs more easily.

Glassing the inside

glass inside

Today was fibreglassing the inside of the hull.  This time it actually felt like I knew what I was doing a bit. So I’m sure my next canoe will have a better glass job all around. I had a better feel for the squeegee and was more diligent on cleaning up the runs. The wrinkles in my cloth were still there but I was able to keep going back to them as the epoxy was setting and flattening them out so they are a lot less prominent than on the outside.

It was a long job though so I didn’t get home until 2am. Wetting out the glass in the narrow areas of the stems was the most frustrating part of the build so far. It’s really difficult to do a tidy job of it. I’m really glad the decks will hide that area partially.

 

inside wet out

I’ve got a board with notches in it to keep the hull held to the proper width during the glassing process. The cradle/forms that it’s sitting in do a pretty good job of keeping the shape right, but they only go up half the hull so the beam at the shear line needed to be held open by 1/2″ or so. The spacer is waxed and notches lined with packing tape so it doesn’t get stuck to the epoxy.

 

inside wet out 2

inside all wetted out

 

Fairing the inside

off the forms

It was very satisfying to get the canoe upright. It feels floppy but it looks canoey.

I built the cradles to hold it similar to how they show in Canoecraft. However, CC calls for the height to be 26″ on the upright members. I knew that would be too low for working so I made mine 30″. It turns out that is still far too low. They should be more like 36″ – 40″ high for me to work comfortably in. I don’t know who would want the canoe down at 26″…

I ended up making some inverse forms and putting them back on the strongback for most of the inside fairing work. That got things to a much better height.

 

glue squeeze out

You can see where the epoxy has come through any small gaps in the hull. This is good to see in a way because you know that the hull is watertight and those voids are now full of epoxy. But all those drips need to be scraped off now. You can see the wood glue squeeze out as well in lines where the station molds were. It pays to be diligent in wiping up squeeze out right away but you can’t get under the forms. Next time I’ll use less glue for the strips for sure. By the end I was using a much smaller bead of glue and had barely any cleanup to do. I never had problems with strips not holding once the glue had set up.

 

fairing inside 2

The curved scraper leaves neat curly shavings much like old spills that preceded matches. Fairing the inside is labourious work though. It’s very difficult to reach the areas in the stems with anything other than sandpaper. Given my aversion to sandpaper it was a long day for me. For the next canoe I’ll get a convex sole plane to do this step. And a better interface pad for my ROS.

 

fairing inside

 

Filling the weave

partially sanded

After the fibreglass is wetted out, two more coats of epoxy are applied to fill the weave of the cloth and then finally bury the cloth. This surrounds the fibreglass completely in a blanket of epoxy. This is important so that any scratches the canoe receives don’t cut the cloth. Damage to the cloth fibres themselves will weaken the canoe.

The second and third coats of epoxy go on more quickly than the wet out coat. They also use a lot less resin. My second coat I applied with a foam roller. I found that to be pretty unsatisfactory due to the amount of bubbles it produced. After sanding out the bubbles when it had cured I applied the third coat with a decent varnish brush and that worked much better.

 

inner skid layer

To protect the stems from damage I’m adding extra fibreglass to them. They got an extra layer up to a few inches above the water line, and then another layer over that. The third layer is full length and goes off the stem into the bottom of the hull by 20cm or so.

So the stem under the waterline ends up with 3 layers of glass and there are 2 layers above the waterline. These extra stem plates are feathered in with each coat of epoxy so that the transition is unnoticeable. There’s still enough thickness on the stem to add a brass stem band but I believe I’ll use it without for a season and see how they hold up. Brass is heavy so if the skid plates and graphite bottom do a good job by themselves that’ll save me weight.

skid plate 2

 

 

The graphite bottom coating that I’m putting on is another layer of epoxy. So the third fill coat of epoxy I didn’t apply to the area where the graphite will go. Canoecraft recommends levelling the canoe on the floor and marking the designed waterline with a block and pencil. I wanted the graphite to be more unobtrusive than that so I picked a strip that would be below the DWL and followed that with the masking tape. This should still provide the protection where it’s needed most but not make it too obvious while the boat is in the water. I think following a strip rather than having it cut across the strips will look better when the canoe is upsidedown as well.

 

waterline 3rd coat

Fibreglassing the outside

glass draped over

By far the most nerve wracking part of the whole build this far is applying the fibreglass. I’m pretty confident in my woodworking skills. Most of the mistakes I made in planking I could repair or hide. But I’ve always been lousy at painting. Which is mostly the same skill set as fibreglassing I think.

Above you can see the layer of fibreglass draped over the hull. It’s 6oz standard weave glass. This is what Canoecraft recommends and what most people use. The book says make sure you buy it on a roll, not folded because creases are hard to deal with. Apparently you need to ensure that the roll was rolled well because mine still had some creases from being rolled too loosely on its tube. Because I paid so much for the shipping and I am on a fairly tight time schedule I couldn’t send it back. So I forged ahead and thought of it as a challenge.

 

mixing epoxy

Part of the reason that the fibreglassing is so stressful is that you need to get it right the first time. You also have a limited time to work. Once you put the first dab of epoxy on the glass the process can’t stop until it’s finished. Your epoxy has a pot life and a working time so you need to get it done, and done well before those times are up.

The trouble is that if you’ve never done it before, you’re learning as you go. The materials are so expensive that it’s not something most people can afford to practice before hand. This also affects the final look of your canoe, probably more than anything else. So yeah, that’s why it’s an intense part of the build process.

The stuff I’m using is MAS epoxy with the slow hardener. After doing some reading and consulting the vast collective experience of the internet it had a lot going for it. The viscosity is fairly low compared to a lot of other epoxies out there. This means it saturates the cloth and fills the gaps more easily. Less pressure is required when squeegeeing to ensure the weave is completely filled. It also has a long pot life and working time. So it takes some of the pressure off you if you’re working by yourself and learning as you go. Which I was.

I don’t have experience with a bunch of other epoxy systems to compare it to. That being said, I was very pleased with the MAS epoxy. It seemed very easy to work with. I feel pretty comfortable with it now, and would use it again for the next canoe.

 

wetting out

The way this works for those unfamiliar with fibreglassing, is that liquid epoxy is applied to the cloth draped over the wood substrate. The epoxy soaks through the cloth and into the wood. You then run a flexible plastic squeegee over the cloth to force out any air bubbles. The trick is using enough pressure to do that and still leave the cloth fully saturated. Too much pressure and you squeeze out the epoxy and starve the cloth.

You also want to do this with the temperature falling in the workshop. As the chemical reaction of the epoxy setting takes place, it creates heat. The warmth causes the air inside the wood to expand, and this forms tiny bubbles. If the temperature of the workshop is falling faster than the epoxy is heating up then you avoid these bubbles more. This is another plus for a slow cure epoxy. The slower the reaction the more time the heat has to dissipate and less trouble you have with bubbles.

If you were to starve the cloth, not saturate the cloth, or have bubbles form under the cloth and not catch it then once the epoxy sets you will forever see the cloth. There were a few places that I did this. The only remedy would be to sand through all the expensive epoxy and fibreglass down to bare wood and start again. If the bubbles were large or the wet out was very  poor than that would affect the strength of the canoe. Tiny bubbles and some visible weave are just aesthetic. Some of my visible weave will be covered by the graphite finish I’m going to be applying on the bottom. The rest I determined I could live with. Most of it will only be visible in bright light to the discerning eye. I hope.

 

all wetted out

All wetted out it looks like this. You can see the two creases in the cloth that I just couldn’t work out to the right of the post and halfway down the hull. It could have gone much worse, and I learned a lot from it. So I’m calling this a success. But probably only a B, or B+ at best. It’s sound structurally but far from presentation grade.

Fairing the stems and lots of sanding

stem chunky

The stems are glued in place, and now it’s time to shape them into a fair curve with the rest of the hull. This is another spokeshave job, so I really had fun doing this. I did use my #4 smoothing plane to bring the bottom of the stem (on top of the inverted boat…) down to match the hull. But it could have all been done with the spokeshave.

I left the leading edge 3/8″ thick for eventually adding a brass stem band. It comes out looking something like this.

 

stem fair

The circled patches on the hull are high spots.  I had done one pass with the random orbital sander at this point.

I really dislike sanding. When I first read Canoecraft and after having done some reading online I was pretty bummed by the amount of sanding that was described. Sanding is dusty and if you’re using a power sander it’s noisy as well. So wearing a respirator and earmuffs for hours wasn’t something I was looking forward to.

I did find that there wasn’t near as much sanding as people told me there would be. I ended up with about 3 hours of sanding for the exterior of the hull. Maybe I did more of my fairing with the spokeshave than some people ?  I was able to get away with 60 grit for almost all of it followed by one quick pass with 120 grit.

After the 60 grit I wiped the hull down with a wet rag to raise the grain. The neat part about this is that it shows you what the hull will look like after the epoxy goes on.

 

half wetted bottom

half wetted side

 

The final strips

planking finished

 

The stripping is done, and the hull is complete. Fitting the strips to the second side of the hull was a tricky bit of business. Each strip needs to be custom cut and the ends tapered to match the angle between the centre line and the last strip. I did need to add a few micro adjustment shims of wood in a few places to get things to line up.

The last 2 strips did not go as I wanted. I had trimmed the cove off the third to last plank and glued the two final strips together beforehand. They were glued up clamped to the curve of the previous strips, but when I removed them the next day they straightened out a bit. The glue held them together fine, but I guess it flexes enough to let them spring back a bit.

I don’t have time to keep trying different things to get them to stay the shape I want, so the last section will have a flatter curve. Since they are so thin and trimmed to fit anyway, I’m hoping it won’t be glaringly obvious to anyone other than me. And people who’ve read this.

Trimming the shear lines

shearline traced on

The next step is trimming the shear line. The strips have been left excessively long below the molds to ensure that there’s material where it needs to be for this step. The shear positions are transferred to the strips and the points joined with a thin batten to make a fair curve.

 

shearline half cut

Here you can see the difference between the trimmed line in the foreground and the yet-to-be trimmed side in the background. The trimming is actually done to just shy of the line. This way when the gunwhale components are added right to the line there will be some excess to be trimmed flush.

Mortising in the Stems

mortise cut out

Just a note, this is another process that is more complicated to explain that it is to actually do.

Where the strips have gone from being horizontally adjacent to the inner stems to being vertically on top of them, material needs to be removed for the outer stems to fit flush. In woodworking terms this negative space portion of a joint is called a mortise. This mortise is tapered in cross section in two dimensions. It changes from 3/8″ at the end to the full stem width at the outside. That ugly chop job above is the only picture I got during the process, but it gets a lot cleaner at the end.

It’s a fairly intricate job that you don’t want to rush through. There is essentially just a lot of paring with a narrow chisel. You periodically place your outer stem on to check the fit and score any adjustments onto the strips.

It should be mentioned that the outer stems have been tapered down to 3/8″ at the inboard end. The taper is only on the portion on the bottom of the boat, and only in one dimension to start. the bevelling the other way to match the plank angle is done after the stems are glued into these mortises.

The inboard (narrow) end of the outer stem is also cut about 1″ shorter so that the inner stem overlaps it. If you don’t do this there’s a danger of cutting the mortise back too far and having a hole through the hull with no material behind it.

 

fitting stem

Here’s checking for fit. The mortise taper isn’t quite enough to get the outer stem seated fully to mate with the curve properly.

Once the mortise is just right, the outer stem will fit tight to the inside stem, and be recessed down 1/4″ (or the width of your planking) on the bottom of the boat.

stem fit to mortise

A generous application of epoxy thickened with sanding dust is then put into the mortise and on the outside surface of your inside stems. The end grain of of the strips will soak up a lot of epoxy so be sure not to starve the joint. It’s better to just gob it on thick, press the stems into place and wipe up the copious squeeze out after the clamps are in place.

Canoecraft recommends using screws to hold the stems in while the epoxy sets, but I found that using ratchet straps and strong rubber bungees worked very well and didn’t leave me with holes to fill afterward.

 

 

Trimming the centreline

left side closed in

The planks on one side are all on. After adding enough planks to cover the centre line and dutifully marking it I got to trim it flush.

 

marked centre line

 

I had transferred the centre line up from the station molds with a small jig and joined them with a straightedge.

Most of the waste I hogged off quickly with my knife. Then I carefully pared to the line with a chisel, working from the middle to both ends. It ended up being a very fast operation.

 

centre line trimmed

Now the job of stripping becomes much more fiddly. Each strip has to be carefully fit and trimmed at both ends to match the angle it intersects the centre line at.