Graphite on the centerboard?

[PAR]

The use of graphite on boards and bottoms is a bit over rated. Unless you're in a class racer, where every ounce of energy may be necessary to be competitive, it's often not worth the bother. This said, it does tend to "harden" the areas it's applied, though there are better materials that are easier to apply, that can employed too.

One good and cheap way to harden up the board's surface, if not also reinforce the leading edge from impacts is decomposed granite dust. This is cheap, easily available and will dramatically harden epoxy. On a board's leading edge, I'll make a shallow groove and pile heavily thickened goo into it, shaping this non-sag mix roughly into a leading edge (if I don't use a mold). Get to it while still green, as this stuff is a bear to shape once cured. I sometimes wrap Mylar around the leading edge to help with the molding process. The same thing applies to a lesser degree if just coating the board sides. The hardened surface rubs against the case, which has HDPE or other (Teflon) applied and since it's harder than the case sides, it works well.

The HDPE disk idea on boards is one I use frequently and it works well. HDPE is the stuff cutting boards are made form and it's naturally "self lubricating" with most substrates, including itself. I also use Teflon sheets for this, often bonded directly to the inside of the case and the outside of the board. Both Teflon and HDPE don't like to stick to epoxy (or anything else) very well, but if you heat the surface with a torch (caramelize the surface), it sticks much better then without this treatment. I make the disks as big as the area of the board that will rub against it, rather than just some big washers sort of deal. You can have too much, but sure can have not enough.

Lastly about gaps, I try for a 1/8" (3 mm) total space in the case, but this is often difficult to achieve, but less than a 1/4" (6 mm) is a good goal. Much more and it'll hum, much less and it'll probably jam, depending on how silty your sailing area is.