Deckhead repair

[osteoderm]

Tim,

Carefully colour-matched gelcoat can be sprayed in small batches, and the feather edge wet-sanded with finesse to leave virtually no trace of a repair, but this is (i lament to say) often best left to a professional.
As Ian wisely advises, it will be best to elimanate all traces of compromised wood. If the resulting area doesn't actually extend too far from the mast step, i'd be tempted to fill the gap with a high-strength filler such as West 404 instead of using a wood patch. In any event, the surrounding wood ought to be well-sealed with a penetrating/thinned epoxy.
A lovely tapered scarf might prove problematic; instead, a step-scarf is straight-forward to achieve with several router passes. A scarf is a good idea whether filling with either epoxy or wood.
In addition to Ian's suggestions, the transition from a smooth area to a non-skid area is a good way to camoflage a repaired area.

Yuri