The disapearance of the wooden schooner Nina was
extensively debated over at
Cruisers Forum, by some highly experienced sailors. The mods finally locked the thread after more than 900 posts (sailors love to argue). I sampled few of the posts. More than you ever wanted to know about South Pacific weather patterns, EPIRBs, seaworthiness (or lack therof) of Nina, competence (or lack therof) of New Zealand SAR, etc etc. Some very heated exchanges, and strong opinions.
Regarding
"....EPIRB that automatically activates on submersion ....", the EPIRBs used on sailing vessels are typically dual activated. They are clamped in a mounting bracket with a hydrostatic release (activated by water pressure). Since in a big storm, waves can and do wash clear over vessels, the hydrostatic release is designed so that it only releases the unit when it is several meters under the water (in other words when the boat sinks). When the EPIRB is released from the bracket, it flips a switch that turns the unit on. The EPIRB then bobs to the surface and starts signaling. The EPIRB can also be activated manually by simply pulling the EPIRB from the bracket.
Some possible reasons no EPIRB signal was recieved:
1. It was stuck in the bracket by corrosion or similar.
2. It released but was tangled in ropes or sails as the boat sank, and carried down with it.
3. The EPIRB was defective (dead battery, or loose antenna, etc).
4. Whatever sank the boat also smashed the EPIRB.