Another suggestion
This works for replacing a rivet in a boom with a nut and bolt.
Need 2 people, a hardwood batten from B&Q, blutack, and a thin nail.
I assume you can see light where the bolt is missing.
Stick the nut on the end of the batten with blutack.
Person in the boat manoeuvres the nut to approximately the right position.
Person in front uses the thin nail to line the nut up correctly.
Put in the bolt and hope for the best.