Posted by: Paul Goodwin on January 07, 2006 at 13:39:59:
In Reply to: runner slide-out posted by Lowell D. Ross on January 07, 2006 at 10:08:40:
Lowell,
Reducing mast angle (eg. by shortening the forestay) can
increase the tendency for the rear runners to slide out.
Actually, you summed it up when you commented "I've also
reduced mast angle to get more thrust and weight over the
front runner". Creating more bite on the front runner can
have the opposite effect at the rear runners.
There a few things you can do to reduce the tendency for
the rear runners to slide out:
1) Move the mast step forward. This does two things: a) it
moves the CE (center of effort) of the sail plan forward on
the boat; b) it reduces the angle between the forestay and
mast, which will make the mast bend a little easier.
2) Increase the side stay length. This allows the mast to
lean to leeward and also does a couple things: A) ncreases
downward load on the leeward runner: b) reduces the angle
between the side stay and the mast, which will make the mast
bend a little easier.
3) Try a little softer plank. This will effectively
increase the sidestay length when the wind strength picks
up (side rake will increase as the plank bends).
4) Change the angle of the chocks (runnners) to increase
bite. While this can increase bite on the ice and reduce
skidding, it has a negative effect on runner drag. There has
been a lot of discussion on when you want the runners to be
vertical to the ice (a condition for least drag), but I think
everyone agrees there is some condition when you want the
runners perfectly vertical and perfectly aligned to reduce
drag as much as possible.
A softer plank and bendier mast will spread out some of the
energy from gusts, and will dynamically change the geometry
of the boat to reduce side slip (reduces loading on the
sail, and creates more downforce on the leeward runner).