L’Arche Dinghy Under Construction

The L’Arche Dinghy is considered a foam composite structure. It has a core of 1/2″ foam and covered with layers of fiberglass cloth inside and out set in Epoxy resin. Below are renderings of the designed construction method. The boat is built one half at a time. A strongback with molds and battens are set up to form a female mold for the planking of the dinghy. Once the first half of the hull is planked, glassed, and bulkheads are in place, the hull is removed and set aside. The molds are then reversed on the strongback and the second half of the hull is built in the same manner as the first. At this point, the two halves are joined together and the hull can be removed from the molds and the outside layers of glass can be applied.


L’Arche Dinghy- Hull #1

Noah enjoying the clean garage

Putting together the full size mold templates from the plans

With tracing paper underneath, we copy the templates to the mdf mold material

Rani joining in on the fun while Noah diligently cleans up the small scraps of wood

The result of our tracing

The cutting of the molds using a jig saw

All the molds are ready for setup

Building the strongback and checking for square

The finished strongback

Using an inexpensive laser level is helpful in setting up the molds. Here it is positioned vertically to align the DWL traced onto the mold

All the molds are setup and level. They will need a little fine tuning before calling them finished.

Another option to help with the setup is using a simple string threaded through a hole drilled at the same distance along the drawn DWL on each mold.

As you can see, the string is centered perfectly in the hole in the DWL

The molds are covered with battens and we are waiting on our shipment of 1/2″ Airex foam

First foam plank is placed vertically across the battens.

Fitting and placing of the planks

Planking has been fit, edge glued, and prepped for the fiberglass cloth

The hull half is glassed and covered in peel ply. After the peel ply is removed, the underlying glass layer will need no sanding and it has created a smooth, fair surface. I admit a small love affair with peel ply!

Once the laminate had turned “green” (cured to the touch but not nearly complete), the excess glass and peel ply were trimmed with a razor knife. Unfortunately not until 11 pm…

Onto some fun stuff! Bulkhead #1 is drawn onto a foam blank.

After applying the required layers of fiberglass cloth and our lovely peel ply, the whole part is vacuum bagged using a simple and inexpensive vacuum setup.

The finished bulkhead with it’s perfect laminate. The vacuum bagging creates a very lightweight and strong part. We have seen weight savings up to .75 lbs by bagging instead of hand layup on the larger midsection bulkheads. It may sound small, but it sure adds up over the course of a project.

After vacuum bagging the midsection bulkhead and the curved transom, the three are glued into the boat.

After the bulkheads were tabbed into place, the half hull was lifted from the molds.

The hull, held in the air by ropes, is looking pretty darn fair.

Getting a pretty good look at the shape of her hull.

At 28 lbs, the half hull is very lightweight. According to my calculations, she is about a lb lighter than designed at this point. Noah could care less about calculations, he is just excited about his bateau!

After rotating the molds, I get a little help reinstalling the battens.

Planking begins on the 2nd hull half

“It’s like decorating a Baskin Robbins’ cake”

Second half hull is glassed and peel plied

The first half is placed into the second half and bulkheads are filleted and glassed. The screws are being pulled in preparation for removing it from the molds.

We invented a great game. 250 Screw Pick-up!

It looks like a boat! She has added some weight, but remains slim at 53 lbs.

Although I was itching to be the first one in, Noah got the honors.

Sitting pretty on her new cradle awaiting the remaining bulkheads before the exterior fiberglass.

The bulkheads are in, gunhale installed, and hull to deck to gunhale has been glassed.

In preparation for glassing the hull, the screw holes and small voids are filled with epoxy

The glass is cut and dry fit prior to starting

We thoroughly wet out the hull with straight epoxy

Using a squeegee, the glass is carefully applied to the hull

Rani wets out the glass

After the peelply and breather cloth are applied, clear plastic covers the hull.

Although not necessary to complete this design, we decided to vacuum bag the fiberglass to the hull to save some extra weight and get the best part possible.

21″ of Mercury! Although this is too much pressure for this operation, it is a sign of a job well done. We will scale it back to 16″ and say goodnight.

The moment of truth! Removal of the peel ply and breather cloth

Success! The hull is looking good.

I couldn’t help myself, I had to weigh it again. 88 lbs. Not bad as she is quickly approaching her final weight.

I don’t know anyone who enjoys this task, but to produce a good paint job, fairing becomes very important. With the above tools, a lot of energy, and a ton of patience, anyone can become a fairing pro.

Who needs P90x when you have a boat to fair?

Along the way, you check your handiwork with a batten.

And then you continue sanding…

When you are ready to call her done, it is time to apply some primer. In this case, we are using clear epoxy.

Onto some mast building! Shaping the mast staves with a block plane.

Voila, it’s a mast!

Onto the interior furniture.  The aft seat is glassed up.



The wood for the mid seat is being glued.

The interior and gunwale are primed. 

The foam blanks for the rudder and daggerboard are shaped into the proper NACA foil shape. 

They are then wrapped in glass and epoxy and vacuum bagged. 

The laminated tiller ready for varnish.

The bottom is painted with gloss grey.

Sewing the rubrail onto the topsides.

Testing the ergonomics of the furniture!

Installing the rigging.

On the car waiting for this week’s sea trials.

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