I am obviously not ruling out anything at this point but why do you
jump to the conclusion that it is a cracked block? My (poor)
understanding is that a starting system is composed of many parts
(battery, starter, ignition switch, alternator, solanoids, etc.) so
wouldn't it be more likely to be something related to the above parts?
I am having a hard time to believe that the motor APPEARED to be
working perfectly for 25 minutes going to the cabin and, following a
restart, I would end up with a cracked block 3 minutes later while
going to drop a prawn trap... Just my unprofessional thought....
Andre