Shimming Runners for Epoxied-On Chocks
basmoss:
I am attempting to learn how to shim insert runners and have read Bob Gray's article from 2004 several times. As I see it basically Bob is suggesting using one of the runners as a "reference" to set the position of a vertical cross hair of a rifle scope of the runner mounted in a "test" chock. Shim tape can then be used to twist the other runner of the set in the same chock until it aligns with the reference position. This ensures that the bodies of the pair of runners are parallel to each other and then with a set of triangle plates the actual chocks on the plank can be made parallel to each other and the shimmed runner bodies.
Well, with epoxied-on chocks it seems like there is another complication. If the body of the runner used to make the "reference" position for the scope cross-hair is not aligned with the chock then this procedure would only make the other runner body parallel to the first but not necessarily pointing exactly forward. In essence, any offset angle between the first runner body and the chock would then be reproduced in the other runner body by the shims. Since epoxied-on chocks can't be aligned w/o re-epoxying them- it seems that if could be possible to shim the runners so that the boat crabs when aimed forward.
How can one set the first runner used in the process so that it's body is exactly parallel to the chock?
One "extreme solution that came to mind would be to use a piece of precision-ground 1" bar stock (from McMaster-Carr for example) sharpened to 90 degrees on one edge as the "reference" runner to align all others too. Sounds like alot of work to sharpen such a thick piece of steel to a "V" edge while ensuring the edge is exactly in the middle. Other ideas appreciated!
Thanks. Ben Shaevitz DN US 5395
Ken Smith:
Ben:
There was a big ongoing discussion in the Collective Wisdom on alignment. There are many methods out there. Mine is below:
Tools: dial indicator, extension so it reaches 8' runner to runner, bench, large clamps, pair of bars for pivots- referred to here as rollers--bob stay struts work fine, pair of matched runners, checked like you described with laser level or rifle scope in a test chock. bench or 2x8 x10 ft on horses to clamp the plank to later.
note: All my runners are parallel and straight relative to each other in the same chock. A long project done once and verified from time to time...
Glue down one chock to the plank using a big triangle or jig. I think there is a description in the idniyra articles archive. The goal is to have the chock level in two planes when the plank is on the boat, deflected for light air sailing, with the runners in the chocks. If the chock is pitched up or down on your boat, mark you runners for this exercise so you can put them in the chocks at this angle later (as if on the ice). Drill holes for the other chock so it can be adjusted. Loosely attach the other chock.
Know your plank deflection target. Deflected under my weight plus 30 pounds is what I use.
place small blocks on your 2x8 to support the plank at plates that mate to the boat, place the plank on the support blocks chocks up.
place a reference board on top of the chocks. You will determine plank deflection by measuring to this board.
place one of the rollers on the plank parallel to the long direction, by the glued chock. Place a plate or bit of hard wood on top of the roller. Same deal at the other end of the plank. You will clamp to these plates.
using big clamps, two at each end, clamp the plank to the 2x8 by the plates. Deflect the plank to your target deflection with the clamps. This is how your boat is plank is loaded in light air on the ice, your target alignment. The rollers and plates make the plank free to twist, if it has a mind to, and prevents you from accidentally twisting the plank as you deflect it.
Shim the 2x8 level in the fore-aft direction of the boat, or use a digital level (or app on i-phone), and set the top edge of the glued chock to the reference level.
Put runners in the chocks (as if on the ice).
Put epoxy under the unglued chock. Before it sets, use the dial indicator and make the edge of the runner in this chock parallel to the edge of the runner in the other chock, with the chock bolts a little snug. Let the epoxy set.
Now your parallel-edged runners are in parallel chocks.
Ken Smith:
Alternative:
Set the boat up with one chock glued, the other in uncured epoxy, with a set runners you know have parallel edges when checked in a reference chock and laser or rifle scope. Set the boat on triangles or other jig with your equivalent weight plus a little in the cockpit centered where your bellybutton is in sailing position. Align the chocks. Let the epoxy cure.
Loeneke does this on a bench with glass and waxed paper under the runners and on a jig so he can use a dial indicator to measure distance between runner edges to make them parallel.
Bob Rast DN1313:
If you have a set of triangle alignment plates with the string at 90 degrees to runner edge you can get close. also to check your alignment jig you reverse the plates so they now face backwards,this will get one runner true. If using the scope and string method, with a string directly over edge and one at 90 degrees to edge measure 4ft forward,3 feet at 90 degrees , hypotenuse should be 5 ft or 8 ,6,10
For final alignment I use a dial indicator that reads the edge of the runners. I have a dial indicator with a bushing that rides on the edge.. I set up the plank upside down on a 4x4 saw horse 8 ft wide. I then clamp down the plank until the chocks are level fore and aft and plumb vertical after installing runners I check level again check fore and aft and put a level on side of runner steel to chec vertcle .I am assuming this is the right deflection for my weight in light to medium air when alignment means the most. With this set up I can get readings of less than .003. If you find readings larger or smaller at the center of the runner you are reading the crown and chocks, runners are not level and plumb.Also smaller or larger at front or rear can show runners are bent. Once out on the ice I check my chocks with a small bubble level to make sure they are paralel to ice surface. this is done with boat loaded as if sailing , as you sail and load the hull the plank deflects and and rotates up or down in relation to ice surface. I use double studs on the plank and can shim anytime with rubber washers to get the plank where I want it. with the single stud you need to shim the stud plates or put a shim on the hull.
Good luck
Bob R DN1313
cmgordon:
I'm not an expert at this like some here but here is what and how I did it. Mine seem to work well.
I figure that the chock being at right angles to the plank is more important than anything else except the chocks being parallel. So, I do it the Plumber's way. A right triangle has equal sides. The long side being 45' angle. Therefore, the short side of any triangle, multiplied by 1.414 is the long side if a triandle, measured to equal sides. Like, a 6' by 8' triangle has a 10' long side. Or, 6' (72") X 1.414 + 8.48' (101.81"). I run a string along the plank and another one along and through the chock. I can run the string, parralel to the plank front as along as I want but the point I pick will be the multiplier of 1.414. With equal measures along the string from the axle hole, I use my tape to get an exact long side of the triangle. When I have the chock, exactally parallel to the plank front, I glue it. I do the other side with mirrors with a hole scratched in them. I clamp the mirrors to the chocks and shim and clamp them perfectly level. Whn I get the other one correct, I take it off and then glue that one and re-check it before the epoxy sets up.
I run a string, down the exact middle of the boat hull and out as far as I can in my cellar. Everything is tightly held down. I take two 100' tapes over each axle hole and run them out to a convergent point. When both tapes are equal on the centerline, the plank,and chocks should be square with the hull.
I don't have a telescope and I don't think you can get much more reasonably accurate.
CMG
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