First, how did you determine that the bolts were loose? If it's just because of the crack, then the bolts are most likely tight. The torque should be checked either way.
Many years working on cars has taught me to start looking hard at any bolt that loses torque. If a bolt loses torque, something has changed. The question is, what? On a set of keel bolts, there are only a few logical reasons.
Bolt stretch. Did the bolts stretch, and if so why? On a bolt that size, the only way they could stretch is if they are corroded most of the way through.
Bolts pulling out of the keel. Again, Why? This is a very unlikely event, but one to consider if no other cause is found.
Keel stub problems. If the keel stub is delaminating, or has voids in it due to osmosis or poor layup, the bolts may be loose due to compression of the stub at the bolts. The picture below is due to keel stub problems, although I'm not good enough with fiberglass layup problem diagnosis to say exactly what the problem was.