By Jan C Gougeon
Iceboat nuts agree: when you increase the speed of your DN Iceboat, there is a snowball effect on the amount of fun to be had during the chilly winter season. If you want a faster, more enjoyable sail out of your DN, it is very important to get the runner blades parallel to each other. Proper alignment requires a little extra work, but can mean the difference between first and second place in this season's DN iceboat races. Here's how we do it in the icy Saginaw Valley.
Mounting the Chocks
First, create a bend in the runner plank that simulates being on the starting line in light wind. With the plank upright and the ends supported by small wooden blocks, stand on your plank with 30 to 50 pounds of weight in your arms. Note the amount of deflection in the plank by measuring the height above the floor at the center and the ends of the plank. The runner chocks will be mounted on the plank so that the runners will be perpendicular to the ice in this position. Duplicate the bend by clamping the plank upside down to a 7 ft long 4" x 4" beam with "C" or bar clamps placed 6" from each end of the plank. Draw the ends of the plank down until the bend is duplicated. Sight across the ends of the plank to measure the amount of deflection and assure that the ends are parallel to each other.
There are different methods of lining up the chocks to make them parallel. We use the triangle method. A jig, made of three pieces of 1" square steel or aluminum tubing, is welded together in the shape of an equilateral triangle. The base of the triangle (about 4' long), bolts into the runner chock. (A 1" section will fit into the runner chock, just like a runner.) The two equal length sides of the triangle (a little over 8 long) should come to a sharp point at the peak and almost touch the chock on the opposite end of the plank. The point should fall on a centerline that bisects the triangle equally, and is exactly perpendicular to the base. Drill a hole through the middle of the base tube in line with the perpendicular centerline for attachment to the chock. (Lay it out on the floor to get it perfect.)
Dry-fit the chocks in position. One through-bolt holds the tang for the shroud on top of the plank, passes through the plank, and then threads into the middle outer hole of the chock. One-inch Allen head set screws are threaded into the other five holes in the chock. The through-bolt hole in the runner plank is drilled to size. The holes for the set screws are drilled slightly deeper than the screw length, and oversized to allow for adjustment and better bonding. A 7/16" hole will do. The chock should be able to pivot slightly around the through-bolt.
After the plank, jig and chocks have been prepared, wet out the holes and the surface of the plank under the area of one of the chocks with WEST SYSTEM epoxy. Follow with a generous amount of epoxy/406 Colloidal Silica mixture. Carefully place the chock on the plank end with the triangle-jig bolted firmly in place. Align the triangle point with the center of the runner bolt hole in the opposite chock. Shim the triangle point so that it rests with the center of the 1" tubing even with the center of the hole.
Epoxy should squeeze out everywhere. With the chock tightened down on the triangle, and the triangle end centered in both front and top view on the opposite runner bolt hole, the chock will be correctly positioned from both front and top views. Note that the inner edge of the chock may be slightly raised. Clean off excess epoxy, and allow the epoxy to cure thoroughly with the chock in this position.
After the epoxy cures, mount the other chock in the same manner and allow to cure thoroughly before proceeding.
NOTE: Do not turn the aluminum triangle over. Mark the surface that is up and always keep it up. This way, even if there is an error in the triangle, the chocks will still be parallel to each other.
Tuning the Runners
Now that you have the chocks on the plank, the next step is to fine-tune the runners. With the runner plank still clamped to the 4x4 with the same deflection used to mount the chocks, bolt the runners firmly in the chocks so their edges are parallel to the bottom of the chock. The runners should also be parallel to each other. Put two marks on each runner, 6" fore and aft of the runner bolt. Use a stick about 9' long and about 3/4" square to measure the runner alignment. Lay the stick across both runners on the aft mark. Press the stick against the edge of one runner to make a V-shaped indentation in the wood. With the indent resting on the runner edge, squeeze the stick against the other runner edge at the aft mark to make a second V-shaped indentation. Slide the stick to the marks on the forward end of the runners to check the difference in distance between the fore and aft edges of the runners.
NOTE: It is important not to push down on the stick, but to squeeze the stick against the runner with your hand. An inaccurate reading can result if the runner and plank are even slightly deflected when marking the stick.
According to Murphy's law, the runners probably won't be perfectly lined up. There are two ways to get them into line. The usual method is to grind the running edges to the correct alignment when you sharpen the runners. If the runner edges are sharpened so they are in the middle of the steel that makes the runner body, and there is still considerable error, the runner stiffener can be modified to correct the problem. One method is to sand the appropriate areas of the stiffener where it contacts the chock. Remove enough material to allow the stiffener to move to the desired alignment when the runner bolt is tightened.
If you have a little clearance between the runner and the chock, there is an easy way to remedy the situation. Remove the runners and coat the inside surface of the chocks with an automotive paste wax. Remove grease from the runner and sand the runner stiffener in the area that goes into the chock. Mix up a small batch of WEST SYSTEM epoxy and coat the runner stiffener on both sides where it fits into the chock. While the epoxy is wet, wet-sand it into the metal. Add some 406 Colloidal Silica to the batch of epoxy and apply the thickened mixture to the runner stiffeners in the same area. Place the runners in the chocks, with the runner bolts in place, but not tight.
Use thin wedges of wood between the side of the runner and the chock to get the correct alignment, tighten the runner bolt a little to squeeze out some excess epoxy, and then check the alignment one more time.
When the epoxy cures, trim off the excess and you'll have a well-fitted and correctly aligned surface that, when greased, will last a very long time.
Mounting the Runners
The last step is to mount the runner plank on the iceboat. You want the plank to be centered and at 90deg to the centerline. The plank should also be mounted so that (from the side view) the bottom edge of the runner chocks are parallel to the ice when the boat is in powered-up sailing trim. To simulate this powered-up sailing trim, place about 400 pounds of weight in the cockpit in the area of the runner plank. With the three runners installed (place 1/4"-thick plywood under each runner), measure the bottom edge of the chock to see if it is parallel to the floor from the side view. Shim the front edge between the hull-to-plank fitting and the runner plank as necessary to get the chock parallel. Bond the shim to the hull-to-plank fitting when you are satisfied with its position.
These steps will help you to get the most out of your runners under the widest range of sailing conditions.
Note: This article is from the Fall 1989 edition of The Boatbuilder (Number 27).
The Boatbuilder is published by Gougeon Brothers Inc.
updated August 22, 1999