Building a stripper dinghy

There's really no question in my mind between inflatable and hard dinghies. One is a boat and one isn't.
That's not to say an inflatable can't be utilized as a tender and be a convenient accessory. It's just a more temporary displacement device. Climbing aboard a rubber bubble in a chop never quite works for me. Rowing against a breeze will challenge either type, but I'll get there sooner in a solid craft with a hull shape that works in the flow of water.

The second major consideration in dink choice is power. Blowing the budget on the Mother ship precludes shelling out for an outboard motor for several seasons at least. That and the avoidance of gasoline fuel storage and transport issues is a big plus for me. I also actually like to row, for a while yet, anyway.

All that rationalization and a pile of surplus basswood, along with a mahogany plank end just perfect for a one piece transom lead me to build a dinghy over the winter of 2013. Juniata was 200 miles away under her dirty shrink wrap and snow. I had room in the shop. What the heck?

Starting with the transom shape, I drew a midship station and several forward sections and set them up with thin splines to visualize the shape.

The hull was to be formed with basswood strips. From a run of a picture frame molding I had 1"x3" off cuts. These were dressed, ripped and thickness sanded to 3/8"x 7/8"x 11' long. The total ended up being 45 pieces per side. Over 1000 feet when you include a few breaks and defective pieces.

The adhesive is West System Epoxy with microfiber filler. The strips were buttered up and pinned to the forms with 6d finish nails. The practical limit of stable assembly worked out to about 6 pieces per batch. Clamping at the stem was the biggest problem. After a few rows of fumbling with clamps and goo, an alernative had to be developed. The stem form block emerged from the scrap pile shortly and worked like a charm as the angle of the strips against the stem rabbet held them against the previous row as soon as they were pinned to a form. Clear packing tape protected the form block and the station forms from the adhesive.

First strips

Circus of clamps

The stem block solution 

Dealing with the twist required of the strips as they turn the forward sections was the next issue to develop.

If there were no limits on clamping and I wanted to steam the strips I could have continued to apply the same section pieces. However, in the interest of stability and the easy route, I opted for a cutting a taper on the forward ends. These were pulled through the table saw in an entirely 19th century freehand fashion not to be recommended and smoothed with a hand plane to 'epoxy tolerance'. That is to say a medium gap that leaves plenty of room for thickened epoxy, which ensures a good bond and adds some rigidity to the final product.

The resistance to twist results in a stairstepping of the strips. The worst of these received another mini strip to fill the corner before the adhesive set. After the taper program was adapted the rows worked in much more smoothly. So much so that I recut the starboard side bow area to regain the more gentle bending loads. Needless to say, an opaque painted finish was planned from the beginning, as epoxy needs protection from UV radiation. 

Port side, tapered strips

Twisting issues on the starboard side

Recut starboard bows and proceeding with tapers

Closing in.

The keel strip was 1/2"x 1-1/2" mahogany, bonded to the tramsom and the stem before any strips went on. Turning the garboard I used thicker, narrower strips to be carved in later. After the hull was flipped over I layed in a wider beveled kelson board for strength and to fair the interior.

And now the sanding begins. Nails were pulled and high spots knocked down with a hand plane, the basswood's mild nature made sanding fair a relatively easy task on the exterior. On the outside the glue got scraped close as a matter of course before it hardened. The interior was inaccessable and subsequently a mess of hard epoxy dribbles. Using 4-1/2" angle grinder with 40# cut it well enough, but the compound curves made a tricky job of it. After the grind, interior surfaces required several curved blocks and lots of grunt work to knock back to fair. Some strip built boats use a cove & round edge profile to register the strips and leave a more fair surface. If and when I do this again, I will jig up for edge matching and the taper.

Sanding begun

Medium density filler applied

For the first fairing coat I used west's 407 low density filler. I wanted the strength for filling any open joints and remaining step corners. After glass, I applied a final fairing coat using the microlight 410 filler and a plastic longboard sanding tool.

Two layers of 6 oz. fiberglass cloth are on the outside, one layer on the inside. All wetted with West's 105/205 resin.

The skeg went on between glass layers and received two more layers of its own.

Weighing in at 68 lbs. before seats, rails & paint.

Right side up for the first time.

I had to patch a little bit of barrier coat on Juniata, so the balance of the quart Interlux kit went to a first coat on the dinghy. This sanded out very nicely and I applied two coats of Petit Easypoxy for the final roll & tip finish. 

In the tradition of advanced mathematics and empirical design I pitched the new boat in the back of the truck and dropped her in a friend's pool to plot the waterline and seat locations perched on a milk crate. 

Blue, but not the Caribbean, yet...

She rode nice and high. So much so that I cut a deeper sheer in before laminating on the mahogany rub rails.

For the painter I wanted a simple grommet around the stem. To avoid exposing the basswood core to water, I drilled for some 1/2" water hose and potted in short pieces at the bow.

Grommet for the painter

Quick and easy graphics from BoatUS website

After her first season, still looking good.

She has performed admirably during her first season. Two of us and a week's worth of provisions and Stuff can still handle a choppy row out to the mooring and remain dry. And in smooth water she is just dream to glide along in. Decent oars just a bit longer will be the icing on the cake.

Enjoy.