I assume your loss is the price of rectifying the loose keel. If this is just the cost of you tightening up a few bolts and a bit of mastic then I'd put it down to experience.
If a boatyard is involved then perhaps have a look at your boat insurance - if it includes legal cover then maybe give them a call and have a chat about it.
Check to see if your surveyor is in the YDSA - it should say on his paperwork - if not then get a mate to call on pretext of doing a survey on a different boat and ask of his credentials then. If he is in the YDSA then you can approach them and ask about liability.
Ultimately though, if significant sums are involved then it may pay you to talk to a solicitor.