Build a Dinghy: Part 22 Quarter Knees

As described in Part 21, these quarter knees were cut carved and shaped from a glue-up of 1" x 4" pine . That way I didnt end up with "short grain" along one of the "arms" ( You always want wood grain to follow the load paths.) Shaping was done with a low angle block plane, a spokeshave and a rasp. The rough shape was cut with a jigsaw. These will be installed 1/8" high of the sides and transom, then planed flush for a mating fit.

Build a Dinghy: Part 21

I made my quarter knees--the corner braces at the transom-from a glue-up of 1-by pine.I lapped the corners and and sed four boards for each "blank." I the cut the actual knees to shape, beveling their sides to fit the flare of the boat sides and the rake of the transom. Gluing up this way allowed me to orient the grain in the direction of the stresses. It is stronger than a solid piece of wood and easier than laminating curved pieces or steam bending. Here's a pic of the blanks in which you can see how I arranged the overlapping glue-up. I will post a picture of the final shaped knees later. Here, I have beveled the arms that rest along the transom, using a block plane. More shaping and beveling to come.

Build a Dinghy: Part 6

Here's the results of the scarf joints detailed in Part 5: 11'5" planks from 8-foot plywood. Once bent around the frame, flare and curves will be induced, transforming these straight cuts into sweet lines. ( I will probably have to round the angle aft, where the stern rocker forms, just a little more.)

The other photo shows a closeup of the joint itself. You can see I'm about 1/64 high on one side, a result of my temporary table ( 3/8 plywood) deflecting under clamp pressure. No biggie, just means a little more sanding and filling than anticipated.

Build a Dinghy: Part 5

Last time, we saw how mating bevels were cut prepatory to joining two pieces of plywood to achieve a length longer than the standard 8-feet. Here we see the glue-up. I use epoxy, as it is tough and strong. Others have had success with weldwood, resorcinol, and even contruction adhesive out of a tube. I'm comfortable with epoxy, having used it for decades. Comfortability with an adhesive's properties and working times is almost as important as what glue to use, as you can "blow" a glue up if the unexpected happens--like the glue setting up before you've aligned your pieces.

Here we see the mating bevels first slathered with straight epoxy, which is allowed to soak into the grain. This prevents a "glue-starved" joint. After a few minutes, I apply a thickened mixture, adding colloidal silica to the glue mix, and paint that on. The planks are flipped, the bevels mated and all is clamped, weighted and screwed to the work table. I applied lights for heat, to help the cure. Note that the clamping bar (the shelving) and the work table are covered with polyethylene film to prevent sticking to the work.

I'll leave this clamped up for at least a day, then stow the planks in a safe place while I glue up the bottom. This design uses a cool technique for getting an 11-foot boat bottom out of a single 8' sheet of ply.....

Build a Dinghy: Part 4

This boat, a Summerbreeze, designed by David Beede (http://www.simplicityboats.com/) uses plywood, 11'6" long for the sides. To get the length, I used a scarf joint and glued two sheets of ply together. This involves cutting mating bevels on the pieces to be joined. Here we see the begginning of the bevels; and then the nearly complete bevel. I did the cutting with a low-angle block plane and then finished with a sanding block. You could also use a power plane, a belt sander or a grinder. I like the zen aspect of hand-planing: here I put on some Pink Floyd, a pot of coffee, and just zoned-out for an hour.

A scarf joint is as strong as the original plywood and, when bent, wont show a hard spot like a butt block does. In Part 5, I'll detail the glue-up.

Build a Dinghy: Part 3

Here's a closeup of the limber hole in the frame. This allows any spray to flow aft where its easier to sponge out. I cut the limbers by butting another piece of one-by wood to the frame, then used a plug cutter in a drill motor to make the a circle. When I removed the sacrificial piece, I had a perfect half-circle. To protect the exposed grain inside the limber from water intrusion, I glued in PVC tube the OD of which matched the ID of the cutout. When the glue cures, I'll plane or sand flush with the bottom of the frame.

Build a Dinghy: Part 2

To get started building your small boat, select a plan and then collect materials. I chose to use Marine Plywood, made from Okuome, a tropical hardwood. I ripped the panels into planks using a piece of aluminum extrusion as a straight-edge set 3-3/4 from the cutting line (the distance between my saw's shoe and blade.

Interestingly, the "marine" designation doesnt mean rot-resistant. It means that it has more veneers for a given thickness, in this case, 5-veneer 1/4" (or 6mm). It also means there are no voids. I can attest to this, as when I cut the sheets into planks, there were no voids to be seen. Voidless means stronger--important in a lightweight structure. It also means it will bend "fairly" producing sweet curves.

You'll also need some dimensional lumber to make the frame and transom. Here's picture of the frame for the boat I am currently building. I used Douglas fir 1" x 2" and plywood gussets , cutting the angles and bevels per the plan using a handsaw. The frame is glued with epoxy and fastened with silicon bronze screws through the gusset. Note the "hole" I filled with thickened epoxy at the intersection of side, bottom and gusset pieces.