Oct
25
Written by:
Tom
10/25/2009 4:42 PM
Many of the first and second year students are involved in the backbones of their boats these days.
Over on the Gar Wood, the components for the forward section of the backbone have been built. Here you're looking at the fore keel,
the gripe
and the stem.
You may be wondering about the curved joints between the gripe and the fore keel and the stem. Here's what we're talking about.
If you were going to build this boat at home, you would probably make this joint using straight cuts. After all, it's much easier to make a tight joint using 2 straight cuts than to fit 2 curved pieces together. However, if you're a company making lots of these parts, the easiest way to make them is to have a master pattern and then use a bearing-guided router to run along that pattern and cut the shape of your part. These routers can't make sharp, angled inside corner cuts, they can only do rounded inside corners.
The sharp inside corner here is formed by 2 parts, so the folks at Chris Craft never had to make this corner in a single piece.
Here you can see another place where the lofting pays off.
All these pen marks come from the lofting. They show the exact locations for cutting the edges of the rabbet. This isn't something that we just make up as we go ...
Many of the frames have been removed now, with the internal bracing holding everything in place. 
Lots of frame parts are in process.
And out in the lobby, they're scarfing long sections of mahogany together to form the battens for the batten and seam construction of the hull.
Over on the Chris Craft, the stem assembly is complete and installed.
You can see that the rabbet has been cut, and if you look closely, you can also see that this stem is constructed using curved joints, just like the Gar Wood.
Upstairs, they are using the lofting to get the shapes for the new frames,
and they're using the existing frames to make sure that their construction techniques are as close to the original as possible. Here, for instance, they are copying the screw pattern layout for the gussets that connect the two frame members.
On the other end of the boat, the transom frame is being rebuilt. Original:
and new:
One of the things that these students have had to confront is the reality that these boats were production boats, not craft-built boats. While a home-builder would be wise to use tenons or lap joints to join some of these parts together for strength and longevity, the reality is that these boats were built as quickly and simply as possible. That means butt joints held together by screws in many cases… not particularly strong joints. So, the students have to balance their desire to build the boat as well as it could be with the fact that this is a restoration, and as such should be done as historically accurately as possible. In some cases, say where a frame typically has been underbuilt and was prone to breaking, they will make a part a little beefier than the original or they will relocate a bolt to make it hold more effectively. These changes are all done after many discussions with Warren, the 2nd year instructor, and should be invisible when the boat is complete.
The molds for the 12 1/2 have been set up and braced.
There are 2 photos hanging on the forms showing other mold setups. The one on the left shows the setup from last year's class, and the the one on the right is the actual mold setup used at the Herreshoff Manufacturing Company. They have this actual setup in storage at Mystic Seaport. They literally took a chain saw and cut out the entire section of factory floor with the molds still attached to it, and brought it to the museum. There are still bits of oak frame from the last 12 1/2 built on it attached to the bottoms of the molds. Very cool.
They've been bending steamed oak frames onto this setup. To speed up the manufacturing process, Herreshoff used a mold for every frame. You can see them attached with dark clamps on the side and wedged into little metal pockets at the bottom.
This makes the bending process very simple. Jam the hot frame into the pocket, wedge it tight, and bend it along the form, clamping with the metal L clamps as you go. You can move along very quickly using a setup like this.
Of course, not all frames agree to being bent like this.
Some of them might be a little dry, have grain that isn't exactly straight, or some other mysterious problem that causes them to fail.
The students suspect that bug damage may have contributed to these frames' failing. You can see a very small bug hole in the upper left here.
So, they are going over their supply of frames to sort out which may be bug damaged and which may not.
Before bending in the aft frames, the students bevel the molds to create a smooth curve for the planking as it runs fore and aft. They use a batten to check that the bevels are accurate.
Then they fine tune the bevels with spokeshaves.
The original boat has been stripped of decking and bulkheads to prepare it for when it will be placed onto the molds.
You can really see how rough it was looking. Much of the transom was rotting away, exposing the bronze drifts (the rods) that held the transom pieces together.
Some of the 12 1/2 crew are working on the boat's stem. Here, a student is cutting the pockets that will eventually become the rabbet.
And here's a neat little trick for transferring lines from the lofting to a plywood pattern. Tap down nails with sharp-edged heads with the edges of the heads right on your lines.
Then take your pattern stock, place it carefully on top of the nails, and tap it down hard.
This transfers the impressions of the nail heads onto the plywood, and voila! You now have your curved line accurately reproduced on a new piece of wood. Here's one such pattern. You can see the indentations of the nail shafts along the wood, and the curved line is exactly where the nail heads were. I've placed a nail in position to illustrate this.
Over in Beetle cat world, backbone work is everywhere.
Some are set up on the keel bending jig waiting for their centerboard trunks to be installed.
Some are finishing the centerboard trunks,
and some are just installing them.
There's a fair amount of stress on the centerboard trunk. The centerboard transfers the lateral forces working on the boat to the hull through the trunk. To keep the seam between the trunk and the keel from opening up under all this strain, we put a double layer of canvas soaked in primer right in the joint.
This creates a gasket that can absorb some of the inevitable flex that occurs in this joint. After the paint has dried they trim the canvas back so that it's essentially invisible.
Some students are setting up their attachment between the stem and keel,
while others are fairing the transition between these two parts.
This student is using a wooden batten to create a sweeping, gentle curve for this area.
It's tricky getting the transition right as there's a natural tendency for the 2 parts to form a little knuckle here.
There's been a lot of talk about the rabbet over the past months, and now we can see why getting this slot right is important. Here is a stem set up on a boat, with the old planks running into it.
Looking down from above (ok, technically we're looking up from below since the boat is upside down, but really…) you can see how the planking fits into the rabbet.
In this case, the planking has been cut short to remove the original stem, so it doesn't extend quite to the edge of the rabbet. Still, you can see how it rests on the angled inner surface of the rabbet. This is what you want. The planks will be fastened into the stem here, so you want them to land as solidly as possible on this inner face to make a strong, stable connection.
Some students have removed their boats' transoms in preparation for the new ones.
The transom is connected to the the keel with the stern post and skeg. You can see these two parts connected together here.
They just happen to be sitting on top of the glued up oak transom.
Some of the first years are finishing their drawings in the upstairs classroom.
They are drawing the Beetle cats that they had lofted earlier in the year. These drawings combine accurate views of the boats with tables of offsets and author information.
Getting those lines to curve properly can be a bit of a trick. The offsets just give you points, but you need to connect those points with smooth, fair lines. One way to get those lines is by using flexible battens held in place with lead "ducks" (sometimes called whales).
If you've got a really tight curve, you may need to pile up your ducks to resist the springing force of the batten. Here is a veritable flock of ducks ganging up on a batten.
It's always inspiring to see cooperative behavior in nature.
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