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"DN Iceboat Building" by David Fortier - Epoxyworks 57

DN Iceboat Building

By David Fortier

The first DN that I constructed was in 1988. My brother, Wayne, gave me the International DN Ice Yacht Racing Association (IDNIYRA) official plans and a gallon kit of WEST SYSTEM® Epoxy to get started. The official plans I believe were the Gougeon® “wedge” design. I was a soft water sailor, racing catamarans in the summer, but the winter of ‘87, we had discovered these FAST winter sailboats. I would say that it changed my life, this boat and the epoxy. I had used some epoxies previously, but this was my first large epoxy project using WEST SYSTEM Epoxy.

As I said the DN is a racing class. We explored to find ice to race on, and in doing so, stuff happens—pressure ridges, open water, etc. I broke my DN many times but was able to repair it good as new thanks to WEST SYSTEM Epoxy. As far as I know, it is still together, although I know not where.

Prototype Build

In 2004 it was time to build a new DN iceboat. I decided to build a prototype first, and if all went well, I would build more using the same mold. This type of build would require a two-sided mold—one side a strongback, one side a mold for the fuselage sides.

I built the mold from quality ½” plywood, and of course, WEST SYSTEM Epoxy. I covered the strongback/mold with 6 oz. fiberglass and epoxy. Once it had cured, I filled the weave with WEST SYSTEM Epoxy thickened with fairing filler. This gave me a smooth surface. I painted the epoxy with Awlgrip®, so when polished, the vacuum bagged parts would pop off easily. I followed this same process for both sides of the mold.

I was having difficulty finding good, clear spruce to use for the side panels. I decided to use 5/8″ end grain balsa with fiberglass for reinforcement. Now that I had my mold built, and my materials selected, I could begin the build process.

I tackled building the fuselage sides first. Having a two-dimensional mold to vacuum bag the end grain balsa to worked well. The 5/8″ balsa followed the contours well, and any grain that split filled with epoxy. Then I could flip the mold over and use the strong back to assemble the fuselage.

"DN Iceboat Building" by David Fortier - Epoxyworks 57
Cutting the 5/8″ balsa core for the side panels of the fuselage.

My prototype fuselage was sailed several times in substantial wind, and sometimes I even forgot to install the bobstay post. I believe, if the side panels would have been made of sitka spruce, they would not have survived this oversight. This reaffirmed the balsa wood with fiberglass reinforcement worked. This prototype fuselage is being used today as a wheel boat. After almost twenty years, it’s still going strong.

Production Hulls… x4

After two years of testing our 2004 prototype, it was time to begin production. My friend and I wanted to build four new boats. We were both avid competitors in the DN class, and wanted to compete here at home, and in Europe. The fuselage and mast are the most difficult parts to ship to Europe, so we both wanted to build two new fuselages each. This way we could keep one in Europe to avoid that hassle of shipping. Having determined that my construction method was sound, we were able to start on constructing our four semi-identical hulls.

"DN Iceboat Building" by David Fortier - Epoxyworks 57

Because of the experience I had with the prototype, I was very comfortable with the strength of this method and the materials. Our goal was to build a fuselage that would be as close to the minimum weight as possible (46 lbs.). We were building four, so we fine-tuned the layup schedules before ordering the fiberglass to be used. Our exact layup schedules have been lost, but I know that we used a few inches wide of unidirectional s-glass on the top and bottom edges of the side panels, +/-45 biaxial fiberglass on both sides of the side panels, and 6 oz. fabric on the mold side for a uniform, smooth paintable surface.

We adjusted the design layout of the fuselage/cockpit also. We retained the full length, height, and width of the cockpit for strength and racing reasons. Full height allows for a stiffer hull. The full length and width allow the skipper to remain in the cockpit for less windage.

We’re still as happy with our iceboats today, as the day we made them.

"DN Iceboat Building" by David Fortier - Epoxyworks 57
Unidirectional s-glass tape was used on the perimeter of the panels. +/-45 biaxial fiberglass was used on the inner and outer surfaces of the side panels. 6 oz. fiberglass fabric was used on the mold for a smooth, paintable surface.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
The layup of balsa, biaxial, and unidirectional fiberglass fabric was vacuumed to the mold. The blocks at the bow and stern were for exact length. 2×2 polystyrene foam on the side panel created angled fiberglass edges.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
Stem blocks were installed to allow for the assembly of bulkheads, decks, etc. at a future time.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
Stem blocks were installed to allow for the assembly of bulkheads, decks, etc. at a future time.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
One of the bulkheads bonded in place.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
Good view of the lower angled fiberglass edge.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
It was not necessary to fully assemble the fuselage on the strongback. Bonding the stem and stern blocks to the side panels while on the strongback made the fuselage dimensionally stable. This allowed the fuselage to be moved off the strongback and allowed the start of another set of panels. The stem blocks, mast step structure, and bulkheads only weighed 19.5 lbs.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
The bottom deck (1/8″ okoume plywood) was coated with epoxy and placed on the strongback. Thickened 105/206 was applied to the angled fiberglass edge of the fuselage. The fuselage was bonded to the deck, followed by 5/8″ balsa core reinforcing the cockpit area, and Baltic birch plywood in the plank attachment area. All layers were coated with thickened 105/206 on both sides using an 809 Notched Spreader.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
Okoume plywood was placed over top of the balsa core to finish off the cockpit floor. The fuselage side panels were weighed down with runner boxes, and sandbags were used to compress the cockpit floor laminate while the epoxy cured. Pipe clamps and a temporary spacer kept the sides plumb.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
These are the cockpit stiffeners. They added strength and flotation. They were built 4″x4″ out of 5/8″ balsa epoxied together. The blocks were ripped diagonally then pushed sideways through a sharp 10” table saw blade to create the curved shape. The opposite corner was ripped off for ease of placing the stiffeners. The stiffeners were epoxied in place with 105/206/403.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
The stiffeners were epoxied in place with 105/206/403.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
The seat back and bulkhead were epoxied in place.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
Epoxy thickened with 403 Microfiber was used to bond the epoxy coated okoume deck to the fuselage.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
The rails are biased toward the inside of the cockpit, supported by the angled fiberglass edge of the side panels and the balsa core epoxied underneath. This was shaped, and ultimately covered with 6 oz. fiberglass.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
Here are all four hulls together awaiting various finishing touches.
"DN Iceboat Building" by David Fortier - Epoxyworks 57
The DN at speed on Damariscotta Lake, in Jefferson, Maine.