I do the same thing, except I use card stock that measures 0.008"
thick. The thickness of the shim used is very important when
comparing crown between different sailors, and I would guess that
0.008" is the most common. It helps to have a light behind the runner
so you can see the contact spot. The light also helps to identify
flat spots, or worse, hollows.
I hold the runner down at the pivot bolt hole, and slide a piece of
card stock in from the front until the runner contacts the
straight-edge under the pivot bolt hole. Then slide another piece of
card stock in from the back until it just touches. Distance between
the two is the "crown".
Ron Sherry adjusts his crown so that it is biased towards the front.
His recommendation for 36" insert runners is 18" crown (measured with
0.008" shims), with 10" in front and 8" behind the pivot bolt. Maybe
it's the toe-in under load that makes Ron so fast...
Paul Goodwin - DN US46
--- In IceBoating@yahoogroups.com, "Jeff Brown" <iceratz@m...> wrote:
> As we are talking about crown lengths for a runner, which is also
> called the contact length by other terms, I would like to mention how
> I measure them, right or wrong.
> I hold my runner on a level, press down over the axel hole then wedge
> a slice of newspaper under each rockered end, entry and exit, until
> the paper stops.
> That is my crown length which is never actually flat.
> Hopefully it is centered under the axle hole, but I have heard of
> theories to have this crown length slightly back from the axel hole
> so the runner "self aligns" or feathers while sailing. Truth or myth?
> Certainly, to have crown forward of the axel hole will cause the
> runner to toe-in under sailing load. Bad.
> I am sure there are many other methods and special gauges, light
> boxes ect. to perform this same basic measurement.
> Lets hear'em.
> Jeff Brown
> US 5232