My 13' sailboat has a mahogany daggerboard. There is a crack in it, running
about 1/3rd of the length, about 1" from the trailing edge.
It does not affect anything, but I am concerned it will crack further and
break off; so I am hoping to stabilize it to prevent that.

I showed it to a cabinet maker. He suggested routing some slots in it,
perpendicular to the crack, and filling the slots with fiberglass/epoxy.
The slots would have to be pretty small, because there simply isn't much
material to work with so close to the edge. I would then put a layer of
cloth over it to hold it together. (there ought to be enough clearance for
a layer of cloth.)

I have some leftover glass cloth and epoxy from another project, but wonder
about the technique. Would I take some cloth apart and soak the yarn in
epoxy, and then stuff it in the slots?

Any advice would be appreciated.