A Shipwright in Training

Let’s just make this clear from the get-go, the teeth gnashing is coming from people other than me this week. But we’ll get to that later.

Monday was the deadline for getting shutter planks in, and almost everyone made it. Normally Jen makes cookies for us when we make a deadline, but her daughter was sick that day so she didn’t come in. However, on Tuesday, we got a big plate of star-shaped rice crispy treats. That was pretty great, especially when I hadn’t made time for breakfast that morning. There was a great chewing with teeth, but no gnashing. That came later.

There was minor frustration when I had to make a repair at the aft end of a plank that got chipped out.

No big deal. A little epoxy, a little fitting, it’s all fine. You can see the string inside the transom / plank joint. I’ll mention that later.

So, once you have all your planks on your boat, and the hull is faired, the next thing on your list is to caulk the joints. This is one of those things that boatbuilders do that no other woodworkers do, and so it’s extra cool to learn.

In the old days, and perhaps still in some places, boats were caulked with oakum. You could go run off to Wikipidia or my glossary to figure out what that is, but I’ll save you the trouble. From Wikipedia:

Oakum is a preparation of tarred fiber used in shipbuilding,
for caulking or packing the joints of timbers in wooden vessels and the
deck planking of iron and steel ships, as well as cast iron plumbing
applications. Oakum was at one time made from old tarry ropes and
cordage of vessels, and its picking and preparation has been a common
penal occupation in prisons and workhouses. In modern times it is made from virgin hemp fibers. White oakum is made from untarred materials. The fibrous material used in oakum is most commonly a hemp or jute fiber impregnated with tar or a tarlike substance.

It should be understood that this “tar” is not the tar used on streets and roofs, but rather pine tar, also called Stockholm tar, an amber-colored pitch made from the sap of certain pine trees.

We don’t use oakum. But now you know about something cool and old and you can impress people with your grasp of arcane boat building facts. We use cotton.  We take a length and pull off a thickness that seems about right for our seam. It looks like this:

Yep, that’s a pizza roller. We use it initially press our loose cotton into the caulking bevel. Like this:

That gets it in the bevel, the next task is to pound it into the bevel, but no so much that it bursts through the wood-wood joint where the planks touch. To do this, we use a tool called a caulking iron. They make tons of different types of irons, but this is a the most common shape.

Caulking irons come in different blade thicknesses to accommodate the different size caulking bevels a ship builder might encounter. You want one that’s just thick enough to drive the cotton into the bevel without being so wide that you tear up the wood in the seam, but also without being so thin that you just poke at and through the cotton. A No. 0 or 00 works well for our boat.

Now this photo is not showing proper caulking iron holding technique. If I were to miss my iron with my mallet, I could easily cream my thumb against the hull. Here’s better technique:

If I miss the iron, the mallet is more likely to glance off my thumb or fingers this way. Also, you often will caulk a boat right side up, and this hand position is natural for caulking a hull that’s overhead. And yes, that’s duct tape and a band aid, mom. The duct tape holds the band aid on better. It’s ok, just a little nick with a plane. Yes, I put antibiotic on it.

So, you start from one end of the boat and caulk along to the other. Here’s the aft end where I started:

I like this picture because it shows almost all the lines of defense that a boat employs against water infiltration. You’re looking at the planks that end at the transom here. Between the transom and the planks you can see bedding compound. If you’ll recall the string in the bedding compound in the earlier photo of the repair, that string acts like caulking. it will swell up and form a gastket if it gets wet. Looking at the plank seam, you can see that the bottom edges of the plank butt up against each other. As the wood swells that seam will close up even more and become watertight. Above that seam is the cotton caulking. It too will swell when it gets wet, forming a gasket in the caulking bevel. At the top of the caulking bevel, on top of the caulking will be seam compound that will further seal the joint.

Anyway, I was telling you about caulking.

You run the caulking in with your pizza roller, pound it carefully into your caulking bevel, and continue on this way until you get to the stem. Now you’ve got an interesting little situation: the seam makes a T intersection.

So, at this point, you take your caulking, split it in two, and have half go up into the rabbet, and half go down.

Tap it in just like you’ve been doing so far, and voila!

All sealed up. It doesn’t matter if the cotton from the planks below gets pounded on top of these fibers rather than twisted in like a rope. All we care about is that there’s cotton in the seam, above the wood-wood joint and below the seam compound. Once it swells, it doesn’t matter if the layers are twisted together.

So, you go on and do this for the whole boat.

When you’re done, you have lots of little rabbet tails hanging out of the end.

Next, it’s time to add a little extra waterproofing by putting primer paint on top of the caulking. This is different than the seam compound, and it just adds a little layer of protection when things get wet. We used a plastic syringe to get the paint right into the seam.

Red oxide for below the water line, white for above. This is because we’ll be painting the boat with red bottom paint below the water line and a light color above. This way we don’t have to worry about colors bleeding through the paint. You can see where I’ve rough sketched in the water line to guide where I make the color change.

All faired, caulked, and seam primed (at least my side… Kev’s coming along).

Still no gnashing of teeth. That started today.

Remember how I said the other day that you want to be careful when planing your hull so that you don’t take too much material off? Unfortunately, some folks accidentally planed their hulls too much. Instead of ending up with a 1/2″ thick plank, they brought their plank thicknesses down to 1/4″ or less. That’s just too thin. So, those nice, beautifully fitted planks have to come off and be replaced. It’s one thing to do that when you’re in planking mode and just humming along. But after you’ve Finished your planking, eaten the rice crispy treat, and finished with your Fairing… to realize then that you have to start over with 3 or 4 new planks including your shutter… Well there was a butt load of teeth gnashing and general angry gloom.

I feel terrible for them, because they now have a LOT of work ahead to just catch up. It’s like hitting a chute when you’re ahead in Chutes and Ladders, but there aren’t any ladders in this game.

Next: scribing the water line.

This entry was posted on Wednesday, March 7th, 2007 at 10:05 pm and is filed under Classes. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.