DN Iceboat hull construction part2

In this part I will discuss resawing the glued up side panels and a form to give the hull shape, cutting the top deck profile and adding the stem and stern blocks.

So now we have two 13 foot 8 1/2 inch wide boards made by gluing up strips of Sitka Spruce. Since the first 9 feet of a DN are straight the plans suggest resawing the last 3 feet and filling the sawed out wood with 1/16 inch (1.6 mm) plywood. The stern is bent into shape and the layers glued back together to give it the curve. Les and I resawed the entire length of our boards, planed the surfaces and then glued the layers over a form.

DN Iceboat hull construction part1

This series will cover the construction of a DN iceboat hull from raw materials to finished product as built by Les Druiven and Mike Druiven in Milton during 2021. This is the way we constructed a DN. It is not the only method and, sure, parts could be improved. This is our third build. The first 2 boats have competed in regattas including the NA championship. 

For the most part we used small "garage" type wood working equipment in a 10.5 foot by 20 foot garage/shop. You will need, or need to have access to

• thickness planer
• drill press
• small bandsaw
• large bandsaw to resaw boards 8 1/2 to 9 inches wide
• stationary sander 
• handheld belt sander (shaping, scarfing)
• handheld palm sander (finishing)
• table saw
• for crosscutting I use a skill saw
• plenty of clutch style bar clamps
• plenty of C clamps

Glue up procedure

This procedure was used wherever wood is joined to wood. Make sure all the surfaces to be glued together are clean and smooth.

• On hot humid days your epoxy will harden very fast.
• Cover any surface that is not to be glued with wax paper.  For instance gluing up the side panel blanks is done on a 14 foot flat workbench covered in wax paper. Aluminum angle used to spread clamping forces also have wax paper between the workpiece and the aluminum.
• Mix enough epoxy to apply a first coat to all the surfaces being joined.
• Next mix another batch of epoxy with 403 and 404 added until you get a paste and apply to all surfaces.
• Apply pressure forcing all surfaces to be glued together with sufficient force to provide good adhesion without cracking or buckling your work. In most cases that means tighten that clamp down hard!
• If no epoxy squeezes out you did not use enough. If some squeezes out you did good. If a pile of epoxy squeezes out you used too much!
• Drips need to be caught or they will ruin a concrete floor or whatever else it lands on.

Part 1 materials

• Sitka spruce rough sawn 5/4 lumber
• Epoxy glue
• West 105 epoxy
• West 207 Hardener
• West 403 filler
• West 404 high density filler
• Disposable nitrile gloves
• Disposable 1" or 2" brushes (cut the bristles short)
• Wax paper (30 lb kraft paper waxed to 43 lb, industrial if you can. You are going to use lots)

We planed the rough sitka to find checks and splits taking it down to 1 1/8 thickness. Next the lumber was cut into 1 3/8 inch wide strips. The strips were planed down to 1 1/4 inch. We wanted 13 foot blanks so strips that were not long enough were scarfed together to make them 13 feet long. The 1 1/8 thickness gives us room to plane down the resawed blanks to 1/4 or 1/8 thickness. The finished sides are 5/8 thick (1/4 + 1/8 + 1/4).

Here are some pics of the scarf jig on the table saw. Our scarfs are 20 inches long.

We put enough wood to make a side panel together dry, mixing up scarf locations so they aren't all in one area and numbered everything. We followed the glue up procedure. After the coat of thickened epoxy is added to the scarfs we used a couple of staples (which get pulled later before planing) to hold the scarfs in position. The angle aluminum is used as a force spreader. Between each length squeezing the boards together with 2 clamps there is an angle and a clamp holding all the boards flat to the table. We need at least 28 bar clamps and 28 x 16 inch lengths of angle aluminum (or force spreading material) for this procedure.

In part 2 I will discuss resawing the glued up side panels and a form to give the hull shape, cutting the top deck profile and adding the bow and stern blocks.

Iceboat Runner Sharpener

 

The video shows our prototype runner sharpener made using mdf, plywood and sitka stringers. The mdf "ribs" were cut out using a CNC router and the stringers machined to fit snuggly so once assembled the frame is very true.

We added a 1/4 inch steel backer plate and a plywood deck. We had an old 1HP 1725 rpm reversible motor and our friends at Hamilton Metal Stamping helped us mount a rubber drum on the motor shaft. A plywood front holds an on/off switch and a reverse switch (covered to prevent accidental operation when the motor is energized). 

The belt idler down at the other end is made from a couple of large bearing wheels. The idler supports "float" on springs and are trapped by steel plates. Additional L shaped brackets are added with 1/4 24 bolts threaded through to adjust the "tilt" and centre the belt. in order to put a belt on, the adjusters are backed off and the idler pushed inwards by hand, compressing the springs and allowing the belt to slip on.

Insert runners part 2

Now that our runner bodies are finished we wanted to add a carbon fibre skin for added strength and looks. My cousin Les and I have never used carbon fibre before so this was going to be a learning experience (which sometimes looked like a circus). We've started 4 runners to date and each time the process of getting the cloth to adhere everywhere is getting better and better.

For our first few tries we decided to use Mighty Stor Extra Large Vacuum bags. These bags are commercially available and used to compress clothing and bedding for storage or travel. We coated the inside of the bag with furniture wax to release the plastic. The runner is given a thick coat of epoxy. We wrapped the cloth all the way around and used wood slats covered in wax paper to push the cloth up under the bottom edge. More epoxy is brushed on to thoroughly soak the cloth. We slid everything into the bag, sealed it up and used the central vac. to pull as much air out as possible. Since the runners are not perfectly rectilinear the cloth, soaking in epoxy, did not get pushed onto all the surfaces cleanly.

When we upgraded to a proper vacuum pump the results were much better. We could fire up the pump every hour or so to make up for leakage. Since a runner is not a rectangle it was still difficult to deal with the slack cloth created by the trapezoidal shape. Getting the cloth to fully wrap around the bottom edge up to the steel also proved to be a headache.

We decided that this could work better if we ignore the bottom edge and just glass the sides and top. The small lips at the bottom could be epoxied later with some carbon added to make the epoxy black.

In this photo you can just make out that the pivot hole is over-bored and then remade using an epoxy graphite mixture. The hole is reformed around a heavily waxed 3/8 bolt mounted in a custom made jig to hold the bolt in the correct position relative to the top edge of the runner.

The runners still need finer sandpaper and finish work. This one was used once and seemed to run just fine. While using another set the front of the boat went through the ice and hit bottom in 3 feet of water at full throttle! The boat was fine! The steering push rod and steering runner chock were both bent out of shape. The runner itself did not come apart or even bend but suffered a deep gouge on one side, probably where the steering push rod ran into it.

We formed a little dam around the pivot hole and overfilled it. Instead of being left with a concavity after the epoxy sets and shrinks it will be proud and can be sanded level.