Take a look over the boat for clues of what it was like before it went down. Old GRP develops fine cracks from uv damage and stress and this lets moisture into the substrate matting and wood of various quality. Take a small hammer with you and start tapping the deck
, bulkheads, hull
, etc. it you hear a nice crisp solid return sound, it's good. The opposite is a dul thud which means the structure sandwiched between the GRP is wet/rotten and this is where the work starts. It's very uncomfortable and a health
risk working with fibreglass matting and resins so take precautions. Agree with most others re the wiring
, particularly if there was power in the battery
as all circuits are active as soon as they become submerged. Research
the cost of hauling the boat out, storage
while working on it etc. do it for the love!