Mini-Brig Project: Hull Construction - Step 3

Stitching and gluing the bottom:

Now that all the "frames" are in place, we stitched the bottom of the hull into place. You attach the sides and bottom with thickened epoxy glue. If you want to use epoxy it is available at:  or at very reasonable prices.

However, instead of using epoxy to glue the panels in place we used Lepage's Bulldog Grip ® PL Premium Polyurethane adhesive.

This adhesive is water resistant, weatherproof and is sandable and paintable. At only $4/CDN per tube it is considerable less expensive than epoxy but not quite as strong. Make sure that you "fillet" all your joints with either epoxy or caulking before you tape.

A fillet is a continuous bead of thickened epoxy mixture or caulking glue applied to the angle created between two parts. It increases the surface area of the bond and serves as a structural adhesive and brace.

You can make a very very strong glue by adding a filler powder like wood flour or silica to epoxy.

Gluing plywood structures with epoxy fillets has become extremely popular because it allows extremely thin plywood panels to be bent into compound curves and temporarily stitched together at varying angles with plastic wire ties or copper wire that are then permanently joined together with epoxy fillet. 

In order to make the epoxy thick enough for a fillet you will need to add a thickening agent like wood flour or anti-sag silica. When mixing in the thickener into the epoxy, you’re aiming for a mix the consistency of peanut butter, or slightly thicker if you haven’t been able to let the priming resin go tacky.

Filleting creates an effective glue joint that requires no fasteners of any kind and can result in a joint that is as strong as the parts being joined together.

If wood components have not previously been sealed in epoxy, it is good practice to apply a thin coat of epoxy to saturate the surface prior to applying the thickened epoxy fillet so the edges of the fillet don’t soak into the dry wood and cause a dry edge.

You can let the initial coat of epoxy cure, then sand it in preparation for applying the fillet; or you can allow the initial coat of epoxy to tack up a bit before applying the thick epoxy fillet; or you can wipe off uncured epoxy remaining on the surface with paper towel so the uncured epoxy does not cause the thickened epoxy to slide or slump. In this last scenario, by wiping off the remaining liquid uncured epoxy from the surface you can now apply the thickened epoxy fillet without it sliding off of the wet and uncured liquid epoxy.

A basic fillet

For more information on epoxy fillets take  look here:

To attach the hull bottoms we flipped the boat up onto a pair of sawhorses and stitched the bottom in place using wires or zip ties. Once we wired the bottom in place and had the sides faired up, we filleted the inside and outside of the boat.

If you are planning on using the caulking to "glue" the hull and fillet. It should be mentioned that while the caulking should be liberally applied, it does expand. This caulking is particularly strong, and it could take alot of sanding to fair up - tedious dusty sanding!! It will save time if you have a trowel, or plastic applicators like you would use for putty/autobody work, to help smooth the caulking and remove excess material before it hardens, as you would an epoxy fillet.

Also, if this stuff if it gets on your hands is likely to stain them for days, and even weeks. In working with this particular caulking it is adviseable to use nitrile gloves. It will make cleanup alot easier. This caulking can only be removed by mineral spirits, so use clothes that you are willing to sacrifice. Once it dries on anything, it won't come off.. this is some tough adhesive!! 

 Bottom being stitched in place prior to gluing



Attaching the Brig Sides

Once you have allowed the caulking to drive overnight, the next step is to flip the boat back over and attach the "brig" sides. We did this by attaching them to a 3" x 3" plywood panel placed on the inside of the hull. These panels also serve as reinforced"mounts" for the braces and sheet cleats. Once we screwed the "brig panels" into the "mounts" we reinforced the sides by caulking the seam. We later reinforce this with fibreglass tape, on the outside of the seam.

 mini brig stern
 Once the caulking dries (24 hours),
attach the "brig" modified stern side by screwing it into the stern plate
and the 3" x 3" plywood "mounting" panels

Brig Stern
This shows the inside of the brig sten sides attached

Once both stern sides are in place, then it is time to attch the "false" stern backing. This will help hide and propulsion devices and give the brig its character shape.

The brig with both sides and false stern attached.

We used a piece of 2" x 2" in each corner where the "false" stern meets the brig sides to help reinforce the joint. This can be cut the full length of the brig side and stern (approx 4" long), or cut down to allow "through" mounting of an eyebolt. These 2"x2" also serve as mounting points for rigging eyes...

   2"x 2" Corner Reinforcement (Note this is full length)

Top-Down view on corner reinforcement (this is a 1/4 size length for through mounting)

Side-view showing eye-bolt

Another view of reinforcement

The final step is to attach the bow sides in the same fashion as the stern sides.

The stern attached and the bow brig sides.

Everything is in place. Ready for the next step!