Dec
7
Written by:
Tom
12/7/2011 8:14 PM
Now that the Watch Hill 15 has been framed, it's time to fine tune. The crew uses battens laid along the frames to check for fairness.
As the batten rides along the frames and floors, the crew looks for areas where the batten seems to ride up on a rise, or span over a low spot. Sometimes the frame may be canted just a little bit, and one edge is higher than the other. They use this information to selectively spokeshave off little bits here and there. The goal is for the batten to come down and touch each frame with no high or low spots. Since the batten will bend in a fair manner, it's the perfect way to check that a curve is fair and pleasing. Our eyes are very good at detecting straight lines, but nothing beats a batten for assessing tiny deviations from a given curve.
Jen, the lead instructor, has been helping out the WH15 team from time to time. It's a nice break from the normal demands of the office side of things and the regularity of working on Beetle cats.
The centerboard trunk is just about done now. The trunk will be painted from the level of the waterline down, and finished bright above that. The mahogany and oak should look very nice when varnished.
The lobster yacht team is now finishing up the transom frame. The students are using bit braces to drive their screws. The brace is a nice tool for driving big fasteners with a great deal of control.
Each section of the frame is fastened together using bronze screws with 5200 in the joint. In case you don't know, 5200 is an adhesive polyurethane sealant. It's sticky as sin and remains flexible once it sets. It's a wonderful product to use in places where you want a permanent, adhesive, waterproof seal. It's not a good choice for places where you expect to remove the parts sometime in the future. Toe rails on small boats, for instance, are subject to a good deal of wear, and one can expect to repair or replace them somewhat regularly. Using 5200 to bed these parts would result in needless headaches as you attempt to wrest your toe rails from the deck fabric against the pull of this tenacious stuff.
If the transom frame needs to come apart in the future, dealing with the 5200 is probably the least of your worries.
Over on the sailing dinghy, planking is proceeding nicely.
The students have some of the nicest cedar you've ever seen to work with. Even so, it's not always easy to find a piece that's wide enough, long enough, and perfectly clear.
The mahogany rudder has been glued up and cut to shape.
This rudder has a series of bronze drifts that run through it. These drifts strengthen the rudder and help to hold the glued boards together.
You can see the lines here that were used to guide drilling the holes for the drifts.
Let's take a second here to recognize just how tricky it is to drill a perfectly straight, level hole through a flat width of board. Drill bits can easily wander if they encounter a knot, a grain direction change, or a defect in the wood. If the drilling angle is off by even a small amount, the drill bit can come out through the side of the board rather than nicely centered in the opposite edge. Usually you want to have at least one other person sighting your drill with you as you work.
Let's also take a moment to remember that school is the place to make mistakes.
Oops. Right out through the side. If this weren't going to be bright finished, the hole could be filled and re-drilled. The paint would cover up the repair and all would be well. Unfortunately, the rudder Will be bright finished, so the surface has to be perfect. That means, "do over." Just think, though. If you are a prospective employer for someone on this team, you know that they've already done this particular mistake and they learned how to deal with it on someone else's dime. Score.
Upstairs, the centerboard trunk has been finished and is getting varnished.
That space ship looking thing in the background is one of the misters in the shop that help to keep the humidity up. The radiant floor heating system tends to dry everything out so we need to counterbalance those effects.
Upstairs, the lobster yacht stem and keel have been assembled, and it's all hands on deck to finish the rabbet.
The bottoms of the frames seat into sockets that are carved into the keel just above the rabbet.
You can see here how the stem is quite narrow along its leading edge, but the keel is very wide.
Forming the transition area between the thin and full width sections requires removing a lot of wood. You really don't want to spend hours planing something like this. Instead, it's far easier and more efficient to make a series of saw cuts that define the changing bevel.
These cuts then act as guides for stock removal. This is a great time to hone your skills with an adze. Here's a little video of one in use.
There are 2 general types of adzes that you may come upon in your travels. The one on the left is often used in timber frame construction or for general wood shaping.
The one on the right is the one you'll most likely find if you go to a boat shop. The edges are curved up, or lipped, for cutting across the grain. There is often a spike at the non-bladed side of the head. The spike is there to set metal fasteners below the cutting level (in case you're working on a part that's been fastened in place already).
However, most of the folks working on the stem aren't doing a lot of shaping, they're working on the rabbet.
The cut out in the aft section (where the prop will go) is just the right size for someone to sit in it to work on the rabbet there.
This student is using a fid (remember, it's a stick the thickness of the plank) to check the angle of the rabbet.
The first year students are patterning out their planks now. In boatbuilding, this process is called "spiling." Rhymes with "filing."
The students put down a length of thin wood strips (1/8" luan plywood is perfect) in the area where the plank will go. Usually they cobble together a number of pieces. This not only uses wood efficiently, but it allows one to create a curved pattern. Usually the individual pieces are hot glued together.
The edges of the plank that the student will be making have been marked out on the frames beforehand, and the spiling goes inside that line. You can also see that this student has marked the frame locations on the spiling. These will be used to orient the plank during fitting on the boat.
The students use a compass to transfer the location of each plank line to the spiling.
After it's marked, the spiling is laid on a potential plank to see if it might make a good plank candidate.
We'll have more on this later...
You might be asking yourself, "how did those plank lines come to be marked on the frames?" Well, the students made sure to mark the previous plank locations on their frames before they removed them. That's not enough, though. The students use flexible battens to line off the plank locations to make sure that they're fair.
There's a boat at the shop that had been worked on previously, but the planking wasn't quite up to snuff. Here, teaching assistant Joel Sanger helps a student remove a ribband in preparation for re-lining off some of the new planks.
There's a little something that has to be done before getting to lining off your planks. You need to deal with the fact that the frames on the Beetle cat don't butt into the rabbet. Instead, they ride up and over the keel. This makes for quicker framing (critical in a production boat) but leaves the planks unsupported as they get to the rabbet. Take a look.
The red arrow on the left points to the rabbet where the plank has to land. The red arrow on the right shows the approximate location where the plank will have to leave the frame to get there. If nothing was done, the plank would be unsupported over this space. Eventually, it would flex and a seam would open up. Water pours in, customer calls the boat shop in a dripping fury. Bad all around.
The simple solution is to attach a small wedge to the frame to support the plank (green arrow). The wedge is set back just a bit from the keel to leave a small gap. This gap is called a "limber" (if it was drilled in a floor or other part it would be called a "limber hole"). The limbers allow water in the bilge to flow to the lowest point in the boat where it may be more easily scooped or pumped out.
It's not enough to simply slap on a wedge. You need to slope the wedge so that the plank will ride up it and land exactly on the rabbet. Here's a student checking her wedge fit using the ubiquitous plank fid.
You can see that the fid is just a little above the rabbet. This means that the wedge needs to be shaved down just a bit. That's why she has the spokeshave and other planes close at hand. (side note: the fid is on a string around her neck so that she doesn't lose it. Clever solution to a common problem: "where's my fid, I left it right here!")
If you have time, you can work on your half-hull.
The students use the data from their original lofting and create a half-hull model of their boat.
They start by cutting out a series of waterline sections called "lifts" and glue them up into a stack.
You can see this student using metal angle brackets to align his lifts. In the foreground are some lifts that are glued and clamped up.
Not all of the models around the shop are half-hulls. This student is making up a full model boat, just for fun.
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