What's the best way rto repair a DS II Centerboard crack?

[CptnNate]

I pulled my centerboard to repair over the winter. The overall shape seems pretty good with no chunks missing.

On the leading edge however there is one large crack/gap. It looks like wood has rotted away. The pencil isn't forcing the crack open, it's just a reference for size.

There is also a smaller crack on the leading edge further up the centerboard.

Since I've pulled it out and the downhaul is looking a bit frayed, I plan on digging out the embedded knot and replacing the line.

[GreenLake]

To build up the leading edge you will need something stronger than a fairing filler. I'm partial to 3M High Strength Filler from their marine line. It is reinforced with chopped fiberglass and will support standing proud of the surrounding surface.
It cures quickly and despite its strength can be shaped readily enough by sanding. My technique would be to use a stiff plastic foil or even wax paper to press it into a rough shape before it cures. That makes the rest easier. Regular fillers can be used at the flanks , or wher the new leading edge transitions to the flat sides of the CB.

The desired shape of the leading edge is more blunt and cylindrical than the production board. Don't hesitate to bulk up the front half of the board a bit to make the widest point about a third of the way across. You won't be able to fully match a true foil section, but you can improve the approximation.

You might even find that your board is a bit narrower than allowed by class rules, which gives some room to extend the trailing edge to be more of a wedge shape. And still remain inside the limits.

I've done both when I had a similar repair.

To fix the deep split, my first thought would be to fill it to some depth with thickened or non-saggig epoxy.

Make sure there aren't any deep voids that you don't want to fill with epoxy. You just need enough to keep the two sides from separating. If needed you may apply a bit a clamping pressure, but remember, if the front is a bit wider than factory original, that's not a problem. To the contrary.