DN Iceboat Hull Construction part 5

 We like to pitch the nose of the steering runner up 5 degrees by boring the steering post hole at an angle. The extra blocking keeps the runner and keel parallel so that the chock spring sits properly on the keel. A big drill press and some patience getting the hull set at the right angle is helpful. It is very difficult, otherwise, to keep a hand drill going at the right angle for such a long hole. 

We over-bored the hole. The post is 11/16 diameter. The hole is drilled using a 7/8 drill and then "filled in" using epoxy and graphite to form a smooth bearing. Here are the steps we used. (Note the black patch, epoxy and graphite, around the hole as seen above.)

1. Drill 2 holes, 3/32 diameter, into the side of the hull, midway along the steering post hole, one on either side. These are used to inject epoxy/graphite mixture into the steering post hole.
2. Put a coat of furniture wax on the steel steering post and the top of the deck around the steering post hole.
3. Set the post and hull into position clamping both so that the steering post is in the middle of the over-bored hole. Use wax paper and tape around the bottom of the hole to keep the epoxy from flowing out.
4. Mix epoxy and graphite so the the mix is thick but still flows slowly. Use a syringe to inject the mixture into the steering post hole from the 3/32 side holes to just below the level of the 3/32 holes. Inject the rest of the epoxy from the top taking care to avoid air bubbles. 
5. Stop up the 3/32 holes and add epoxy/graphite mix until the steering post hole is full. If you can, build a dam around the hole and overfill slightly. The epoxy will shrink and instead of being left with a concavity you will have a slight mound which can be sanded down.
6. When the epoxy has set (I like to give it 2 days) the steering chock will come out with a couple of mallet taps. 

This gives us a steering post bearing with a very tight tolerance, a smooth rotation and a low seizure risk. We use the same method for our runner pivot holes. See Insert Runners part 2.

This sheet block was formed by wrapping several layers of carbon fibre and epoxy around a styrofoam mold.

The layers were done one at a time using a vacuum bag and fixture seen here. Imperfections were cleaned up between each layering.

The styrofoam is dug out and an aluminum tube has been glued into the top edge. The block attachment points are cut into the top edge using a router table and 1/2" core bit as shown here. The lines on the green tape guide each pass for even spacing.

The blocks are held with a long steel pin through the block shackles and aluminum tube. The "pin" is restrained using ring and shackle. (Picture coming).

Here is the finished hull, runner plank and a couple of home-made insert runners. The head rest is made in much the same manner as the sheet block - several layers of epoxy and carbon fibre over a wood and tin can mold.

The 3 fiberglass over styrofoam knees are an experiment that turned into a lot of sanding. Next time we will make the knees from wood outside the hull and then glue them in once they look nice. 

Test everything before you attach fittings and as it comes together to insure the boat is set up the way you want it.

DN Iceboat Hull Construction part 4

 The next step is to make the fore and aft bulkheads. The stringers are 1/4 inch plywood and the bulkheads are similar to I beams made with solid sitka spruce sides supporting an 1/8 inch plywood wall. The mast support is a sitka spruce I beam made from pieces left from cutting the hull profile. The steering post support is also 2 hull profile cutoff pieces supported by 1/8 inch plywood stringers on either side, top and bottom.

The aft bulkhead supports the seat and blocks. 

The block support is 1/2 inch Baltic Birch plywood shaped to fit the aft profile. 1/2 inch Baltic Birch runner plank supports and 1/2 inch high cockpit deck support strips are glued into the corners.

Additional 1/2 inch high strips are cut to support the cockpit deck and 1/2 inch thick foam pieces cut to fill the spaces between the supports. Note the position of the bob stay anchor and add a larger piece of 1/2 inch plywood.

Clamping the 1/8 plywood deck top over all of this would be difficult so we decided to use several hundred pounds of weights.

DN Iceboat Hull Construction part 3

Getting the stern block glued into position took some engineering and jigs. We glued the bow and stern blocks in first making sure we had the correct width (depends on sailor size and preference) at the seat position.

Next we glued in the stern structure to support the seat and tackle.

With the bow and stern blocks glued in we had our over-all shape so we cut sheets of 1/8 baltic birch marine plywood roughly to shape and glued on the bottom - lots of clamps and extra wood and aluminum force spreaders. The sheets come in 60 x 60 inch squares so the bottom is made of 3 pieces. Rather than butting the pieces together we used a 6 inch long scarfed overlap. 

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.