How to steam bend and hang the Fiddlehead Canoe garboard planks
Feb 14, 2022Do you want to build a wooden boat?
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This video is a free excerpt from my online course on Building the Fiddlehead Canoe.
In this video, I will show you my method of hanging the garboard planks for the Fiddlehead canoe.
Like on most other boats, the garboard plank is the the most challenging one to hang, because there is a lot of twist in it.
It goes from being almost horizontal at the midships section to being vertical at the stems.
To help my larch planking take this twist without splitting, I'm steam bending the ends first.
The joint between the plank bottom and the garboard plank is fastened with screws and rivets and set in a bead of slow-setting polyurethane caulk.
Lesson transcript:
I've cut the garboard plank to the correct shape, but there are still a few things that need to be done before it can be installed on the boat.
First of all, there's just one plank and it's much too thick. It needs to be split in the middle on the bandsaw so I'll get a plank pair - one for each side of the boat.
The plank is 18 mm, or a little less than three quarter inches. I want to end up with two planks finished planks that are thicknessed to 6,5 mm or a little over a quarter of an inch.
If your planks have already been cut and planed to their final thickness, this step is of course not necessary. Instead, to get a perfectly identical pair of planks, you can tack two boards together with a couple of nails or screws and then cut them out and plane them as if they were one plank. That's what I did with the first Fiddlehead canoe I built. This method is easy and works very well.
OK, so now the plank pair has been cut and thickness planed. The garboard plank is by far the trickiest one to install, because there is so much twist in it. The plank orientation changes from being not all that far from horizontal at the mid-frame to being vertical at the stems. When the plank is twisted into place, the bond between the wood fibers is stressed, which can cause the wood to split - at least if the necessary precautions aren't taken.
When I built my first Fiddlehead canoe, I didn't take the necessary precautions, which made the installation of the garboard plank quite a stressful experience.
In his booklet, Harry Bryan writes that "If you are using northern white cedar, the planks will probably not need softening in order to take the twist at their ends. For any other species, you should wrap the plank in a large towel, saturate this with boiling water, then wrap the toweling with plastic sheeting to prevent cooling by evaporation."
I had done a dry fit of my garboard plank with a couple of clamps, so I thought I could just hang it without softening it first. But that didn't go well. As I started to attach the screws at the bow, the plank began to split. I managed to glue the split with a whole bunch of clamps, both on the plank edges and on top of the split. And everything - fortunately - turned out just fine. But it was quite stressful, and I promised myself that for the next boat, I would make sure to pre-bend the garboard plank before hanging it on the boat.
To make wood bend better, it needs to be softened. This can be done in may different ways. Usually, boiling water or steam is involved. But what is essential is really just that the wood is heated up. Heat causes a substance in the wood called lignin to soften. Lignin can be seen as the glue that bonds the fibers in the wood together. If the lignin is softened, the wood fibers can move freely next to one another until the lignin cools down and hardens again. So hot wood can be bent much more than cold wood. But if wood is hot when it is bent, it also - to some extent - stays in the same shape after it cools down.
Usually, steam bending is done in a steam box. In this case it's a plywood box with some dowels through. The dowels suspend the plank to ensure good circulation of the steam around it. The box has a hole in the bottom, where the steam goes in. One end is closed, the other end has a hinged door.
I'm using an electric wallpaper steamer to generate the steam, but an old kettle with a rubber hose attached to the spout works fine, too.
The steam box is not airtight. In fact, I want some steam to be able to get out. This will create circulation around the wood, which will help it heat up evenly.
So I've drilled a few holes along the top of the box to allow the steam to escape. But I don't want the steam to be escaping too easily from one spot, so I've stuffed some rags around the plank at the hatch end to tighten it just a bit.
The rule of thumb for steam bending is that you need to steam your wood one hour per inch to get it nice and limber. So going by this rule, a quarter inch plank should be steamed around 15 minutes. But for thin pieces of wood, less is OK, so I'm steaming my planks for around 10 minutes.
As you can see, one end of this plank has already been bent and now I'm steaming the other end. Once the plank is hot enough, I remove it from the steam box and clamp it on to the. boat. The plank cools very quickly, so I'm working as fast as I can. Then, I'm leaving it to set to its new shape, at least for a few hours. To make clamping it easier, I've screwed some cleats to the inside of each bulkhead.
Because the planks are still a bit too long, I can't clamp both planks at the same end of the boat at the same time. So for the other plank, I'm steaming the opposite end. The process is exactly the same. I'm working as fast as I can to get the plank bent into shape, and then I give it plenty of time to set to its new shape.
So this is my process of steam bending the garboard planks. But if you don't have access to a steam box, I would encourage you to try out Harry Bryan's towel steam bending suggestion:
I must admit that I haven't tried this method myself, but here's how I would suggest you do it:
First wrap your plank in a big towel and put some plastic sheeting underneath it. Then pour a big kettle of boiling water over the towel and quickly wrap it in the plastic sheeting. Wear gloves to avoid scalding. Install it on the boat right away with a clamp at the mid-frame. Slowly and gradually twist the plank ends into place at the stems and fasten them with a clamp. Add a few more clamps at the bulkheads and then leave the plank to cool down - with towels and everything - at least for a few hours.
While this method may not be quite as efficient as traditional steam bending, it should still provide sufficient softness to your garboard planks to make them take the twist they require.
OK, now, all my four garboard plank ends have been steam bent and cooled down and I'm figuring out their precise alignment. To do this, I'm matching the pencil marks at the plank ends with the end of the stem. Once that's done, I'm making a mark at the plank edge right at the mid-frame. This will be my reference line when I'm installing the plank on the boat.
Then, I'm marking the lap line on the plank. This is the line that marks the overlap between the garboard and the middle plank. This overlap is five eights or 15 mm. Once that's done, I'm tracing the shape of the stems. This will allow me to make a cut that's so close to the line that there will be room for both planks at the stems the same time.
Next up are the gains. Gains are a lapstrake speciality: They are ramp-shaped rabbets that allow two planks to meet in a watertight fit at the stem or the transom of the boat. The gains can be cut once the plank is installed on the boat, but I like to do most of the work on the bench.
Here's how I cut the gains: First, I'm making a mark at around 25 centimeters or 10 inches from the end of the plank. This is where I want my gain to end. Then, I'm attaching a strip of wood that will work as a fence for my rabbet plane. I'm making a mark halfway down the thickness at the end of the plank. This is how deep I want the cut to be. I'm also checking that the edge of the plane blade is flush with the side of the plane - if it's not, the cut will tend to wander off.
I'm starting out with a short cut all the way towards the end of the plank. Then, I'm making a slightly longer cut. Then a slightly longer cut again. I keep on going like this until I reach the 25 centimeter line, and then I start over. I'll need to do a few of these cycles until I reach my mark at half the plank thickness.
Now, the gain is done, and I can remove the fence. I need to cut gains at both ends of both planks.
Now, the plank is ready to be installed on the boat. I'm running a bead of slow-curing polyurethane caulk along the entire joint from stem to stem. I'm using 3M 5200, which is very slow curing. This gives me plenty of time to get the plank into place, even if something unexpected should happen. The 5200 is both a sealant and a glue. So it helps keep the boat watertight, but it also strengthens the joint between the bottom and the garboard.
So there are a lot of good things to say about this stuff. But one bad thing about it is the fact that it is extremely messy. It gets everywhere in no time if you're not careful. And even if you're careful, it'll still get everywhere. When it's uncured, it can be removed reasonably well with acetone, and when it's cured, it needs to be removed mechanically with chisels, planes, sandpaper and such.
So now that I'm hanging my plank, I'm wearing rubber gloves, and I'm trying to get the alignment as precise as possible before the plank comes into contact with the caulk. If you can get a helper or two go assist you with the alignment, it's definitely a plus.
OK, so now the plank is aligned at the mid-frame mark, and I'm using a clamp to hold it in place. Then I'm clamping the plank to the stems so it matches up with the lines there. I'm also adding clamps to the bulkheads and the remaining two frames.
Now I want to fasten the planks to the stems. I will be using four 3/4 inch or 20mm screws for this. But first, I need to mark the locations of these screws. I want the screws to go into the stem right at the edge of the stem bevel. This will give the best strength, because the screws will be backed away from the end of the plank as much as possible.
It can be a bit tricky to get the location of these screws precise. I am eyeballing the location of the screw that is closest to the gain, and then I'm using my double square to draw a line for the remaining screws. This is perhaps not the most accurate method. Measuring the placement of each screw with a ruler would probably be better, but it would also involve getting quite a bit of caulk on your measuring tools.
Now the plank has been attached at both stems. Next up is fastening it to the bottom. The plank is not perfectly tight against the bottom between the frames and the bulkheads, and it's not possible to use clamps there. So to get it pulled tight, I'm using some thin, steel screws. These screws are temporary and will be removed once the caulk has cured.
I'm drilling pilot holes through the waste part of the garboard plank and into the bottom. Then I'm driving in the screws, just enough to pull the joint tight. I'm being careful not to overtighten the screws, because that might cause the joint to open up on the inside of the boat.
Now I've driven in a few temporary screws, and I'm checking if the plank is tight against the bottom all the way. If it moves when I push it, I'll just add another screw. If you are unsure of the tightness of the fit, don't be afraid to use a few extra screws. The screws may poke through the bottom panel, but don't worry: It will be easy to repair these holes later.
Next up is adding the permanent fastenings to the garboard-and-bottom joint. To figure out where to place these fastenings, I'm using the jumpstick. The jumpstick will show me where the bottom of the boat will be once the garboard edge is planed flush with the bottom.
My bottom panel is around 13mm thick, and I want my fastenings to be in the middle of that. So I'm measuring halfway down from my jumpstick line - around 6 mm - to get the location of my fastening. There are already two screws at the bottom-to-stem joint, so I'm placing my first screw so that I'll avoid those. The next screws are placed around 2 inches or a little over 5 centimeters apart.
As you can perhaps see, I have already drawn some vertical arcs that mark the fastening locations. I did that while the plank was on the bench. However: It's not a good idea, because this will not take into account that you will want to drive fastenings into your frames and bulkheads. So don't do this. Later in this video, I will show you a better way, which will help you get the spacing right.
From the stem to the watertight bulkhead, the plank is fastened to the bottom with screws. This is possible because the plank is almost at 90 degrees to the bottom. Between the two watertight bulkheads, the angle gets steeper, so screws won't work very well there. Clench nails or copper rivets will be used instead.
To make sure I get my screw straight into the middle of the bottom panel, I'm holding my drill almost horizontal. Then I'm driving my screws. These are 3 by 20 mm bronze screws. If you are in the Imperial world, a three quarter inch long number six screw would be a good choice.
Then I'm marking the locations for the rest of the fastenings. I will be using copper rivets, but clench nails will work well, too.
I'm using an awl to make the marks. In this larch, the light-colored earlywood is a lot softer than the brown latewood. So a precise dimple made by a sharp awl will help my drill bit go straight in instead of it drifting off into the soft earlywood. Again, I'm making my awl marks around 6mm from the jumpstick line.
Then, I'm drilling my holes. I'm using a 2mm drill bit, which is the same size as the copper nails I will use for the rivets. I want my holes to be perpendicular to the plank surface. To help me get the angle right, I'm using a small block of wood that's cut at 90 degrees at the end.
Here, you can see the drill bit coming through on the inside of the boat. It is best if the holes are not too close to the edge of the bottom panel because this will increase the risk of the wood splitting.
Then I'm driving the nails for my rivets. I'm holding my backing iron against the bottom panel to provide some resistance to the hammer blows.
With all the nails in, I'm driving a screw into the frames and the bulkheads. I'll show you a few more details about this when I add the plank on the other side of the boat.
Now I'm almost ready to hang the other plank.But first, I'm trimming a little bit off the plank ends to make sure they won't get in the way.
Then I'm adding the caulk and aligning the plank at the mid-frame mark.
I'm making sure that the edge of the gains is at the same height as the opposite plank.
Then, I'm adding the screws at the plank ends. To avoid the risk of the screws hitting the ones from the other side, I'm drilling the holes slightly offset.
Then, I'm driving in a few temporary screws to pull the plank tight between the frames and the bulkheads.
After that, I'm drawing the jumpstick line and driving bronze screws through the plank into the frames and the bulkheads.
I want the screw to go straight into the frames and the bulkheads. To make sure that I get my aim correct, I'm sighting from below the frame. This makes it easy to see exactly where the screw hole should be.
Here, I'm stepping out the locations of the fastenings. I have set my pencil compass to two inches. I'm starting out at one of the screws I have just driven into the frames or the bulkheads. I'm going about halfway to the next screw. Then I'm going the other way. If the marks don't match up when they meet, I'm erasing a few marks and making a slight correction. The spacing here will not be exactly the same, but the difference will be so small that it won't be visible to the naked eye.
Next up is drilling holes and driving the fastenings. As with the first plank, I'm using screws from the stems to the bulkheads, and then I'm using rivets in the middle section of the boat - between the two bulkheads.
I won't be riveting the joint at this point. This will be a lot easier to do once the boat is turned over. But to make sure that there is good contact between the plank and the bottom while the caulk cures, I am finishing a few of the rivets about halfway between each frame and bulkhead.
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