A Shipwright in Training

That’s pretty much the attitude I’ve taken regarding the mast… act as if everything is fine. The fact is, I’m 90% sure we’ll decide to re-make it when I return from Spring Break next Monday. The sealer and keeping it outside appears to have halted the propagation of splits, but the bottom line is that this mast has a huge, albeit filled, split running along her top 1/3. It stands out like a sore thumb because of the color difference. Another option would be to rout out a slot where the split is and fill it with a wood shim, sometimes called a Dutchman… the Apple dictionary defines this as “a wedge or piece used to conceal a flaw in construction.” Hmm. Can’t say I like the emphasis on flaw in construction. Of course the same definition also includes the phrase: “I’m a Dutchman” Brit. used to express one’s disbelief or as a way of underlining an emphatic assertion : “if she’s seventeen, I’m a Dutchman.” I’m going to have to find a way to insert that one into conversation some time.

So, in the service of smiling and walking, I worked out the tenon at the foot of the mast to match up with the mast step. Here’s what I’m talking about. You take the round end of your mast, find the center, draw a rectangle on it, and cut that rectangle out to make a tenon. Here it is in process.

After you finish all 4 corners you make the shoulder angled to match the mast step like so:

“Mast step?” What’s the mast step, you may ask. Clearly I’ve gotten ahead of myself.

I could just do this whole report in reverse, like “Memento” but without the boat builder being shot in the head part. Nah. Let’s start from where we left off before.

When you think about it, the biggest stress point on a sailboat is usually where the mast connects to the boat. You’ve got all that wind forcing the mast over, and since most of the mast is outside of the boat, it acts like a giant lever. So, here’s this big force levering itself over onto your nice little wood boat, and if your little wooden boat isn’t built strongly then that mast will just snap whatever is trying to hold it in place like it was nothing. The lesson of course is, Overbuild The Places Where Your Mast Connects To The Boat. No, the lesson is NOT Buy A Powerboat, smart alec.

The mast has 2 places where it connects to the boat: where it passes through the deck, and where it sits in the bottom of the boat. The upper part is called the Mast Partner and the lower part is called the Mast Step. In the Beetle Cat, the mast partner is also the breast hook, so these 2 terms may be used interchangeably. Like Bush and Bonehead. Dang, did I say that out loud?

Both the mast partner and mast step are made of really beefy wood, in this case oak, and are very solidly attached to the boat. Here’s the mast partner in place.

At the forward end it screws into the sheer clamps and the stem. At the aft end it’s screwed into another piece of oak called the yoke. The yoke is fitted and screwed into the sheer clamps as well.

You’ll notice that there’s a little hole in the mast partner with a yellow string running through it. At the end of that string is a plumb bob. Just try to say plumb bob without wanting to say “plumb bob square pants.” It’s ok, I can’t either.

That hole that the plumb bob is hanging from has been drilled right in the center of the mast partner (actually, it’s the center of the boat, but it should also be the center of the mp if you installed it correctly). That small hole locates where the center of the mast hole will be eventually drilled. Since we just drilled a small hole, however, it makes it easy to drop a plumb bob square pants right down through the mp to locate where the center of the mast will land on the mast step.

That lower chunk of wood that looks kind of like a wine bottle is the mast step. It’s also a thick chunk of oak, and it’s going to be screwed and bolted right to the keel. The transverse chunk of oak that it rests on is called a floor. A floor is usually attached to the frames and the keel to provide a flat surface for the sole boards (most people would like to call them floor boards) to land on. This one will just be through-bolted to the keel.

There’s some cool, and tricky fitting to be done here. Let’s start with the mast partner and yoke. I mentioned earlier that Kev had been fitting the mp to the bow (actually I think I was referring to it as the breast hook then, but you now are In The Know and can tell what’s going on), and if you look closely, you can see where he’s planed down the sheer clamps to provide a flat, solid surface for the mp to rest on.

Since the sheer clamps are angled out to the sides as well as curving in towards the bow, it was a bit tricky to get that all flat. The next tricky bit was fitting the yoke to the sheer clamps. This was a lot more complex. Here’s what you have to make fit all at once:

• The yoke has to be exactly straight up and down
• The yoke has to fit exactly up against the back edge of the mast partner
• the yoke has to fit down flush against the sheer clamps on both sides, and the sheer clamps are curving in towards the bow and angling outwards at the same time.
• The ends of the yoke have to fit up against the inside of the sheer plank, which is also angled inwards and curving forwards.

If any one of these things is off by a tiny amount, nothing fits. Here’s the good news: do your layout carefully, and make your cuts accurately to your layout, and everything will fit. Like butter. Rush it, make it up as you go, make a guess… you’ll probably end up with a lousy fitting joint. This is boat building at it’s hairiest.

So, here’s what the notch will look like:

It’s angled down and inwards. There’s a bit of tear out at the lower right edge, but that part doesn’t matter since the end hangs out in open air.

here’s a fuzzy photo showing how it fit:

Not perfect, but pretty close. Oh, by the way, see that shiny bit at the top of the frame behind the yoke? Here’s a closer shot:

yes, that’s what happens when you cut through a screw. It’s one of the screws from the sheer plank going into the frame. Ouch.

Once you get the mast partner locked in place, you can then locate where the mast should land on the mast step. You want your mast to sit straight up and down, don’t you? Of course you do. So, if you have the center of the mast resting directly below the center of the hole in the mast partner all will be copacetic. That’s why we drop the plumb bob (square pants) down from the mast partner. It gives us the center point for the mortise that we’ll be cutting in the mast step. Yep, the same mortise that matches up with the tenon in the base of the mast that you saw earlier.

Here it is a little closer up:

And here it is after the mortise has been cut and the whole thing primed.

Whoops, I got a little ahead of myself with that photo. You can see the 2 bolts that fastened it down, but there was a cool trick we did before all that. Here’s the background.

The mast step only lands on 2 places here: the forward and aft edges. Otherwise, it’s suspended above the stem and keel, partially because there are 2 bolts beneath the mast step that you have to avoid hitting. Remember how we want all these parts that the mast hooks into to be extra solid? Well, we could benefit from having the mast step be supported on the keel, somewhere behind the mortise as well, right? The way to do that is to fit in a little block of wood beneath the mast step that rests on the keel and supports the mast step. Problem is, how do you measure this thing? It’s completely below the mast step. Here’s the simple solution that Lew and Jen came up with.

Play Doh. Plop a ball of the stuff where you want your little support block to go (see those interfering bolts?)…

Place your mast step down in position, and squash your Play Doh. Take the mast step off, and look! You can now measure the height of the block you need exactly with your combination square!

How cool is that? Cut your support block to the right height, fit it beneath your mast step, drill a hole from the outside of the stem, up through that little block and through your mast step and voila! You’ve got another support for your mast step. Obviously you’d want to have screwed your mast step down at the forward end FIRST, and bolted in through the floor as well, so that everything would stay locked in while you drilled that last hole. Duh.

Let’s look at that nice, installed mast step one more time.

That’s just about the time when you realize that you really should have installed the cross bolt first. Here’s the cross bolt.

That’s a through-bolt that helps protect your mast step from splitting. You’ll notice that I hadn’t installed that little puppy in the previous photo. Ok, out it all comes, install the cross bolt, put it all back. Good practice.

Speaking of good practice, did you remember to dip all your screws in primer so that the exposed end grain in all of those holes would be sealed? No? Best to disassemble everything again and do it now.

You may have noticed that the mast step sits in the boat at a slight angle. However, the mast needs to be straight up and down. Therefore, when you cut the mortise in the mast step, it has to be angled to match the mast. That’s why the shoulder of the tenon is cut an an angle as well.

When it all fits together, the mast will sit solidly on the mast step

And here’s an odd thing. I was resawing a board (cutting through it to make 2 thinner boards) and when I was done, I saw that I’d cut through metal.

Dammit! But, wait, the saw didn’t sound any different while I was cutting, and I didn’t notice any obvious screw or nail signs on the outside edge of the board. Know what I’d found?

Good going. It took me 3 guesses. Exactly, it’s a bullet. There were 2 in fact. They’d been lodged way down near the center of the tree and the entry holes had long since grown over. They didn’t bother the saw because they were soft lead.

Cool, eh? Who knows how many years they’d been there.

During the last days before Easter break we installed our deck beams.

Then we removed the cross spalls since the deck beams are holding the boat’s shape now.

It’s really looking like a boat.

This entry was posted on Monday, April 9th, 2007 at 6:47 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.