Quote: ELT is the emergency Locator Transmitter, which should start its work on impact, and works above the water surface (ref its specific ELT higher frequencies). The ULB should start its work when it contacts (sea)water, and works under the water surface (ref its specific ULB lower frequencies)
Shadoko's comment:
One more time: ULBs work with SONIC waves and ELTs with RADIO waves. Two different worlds...
Yes I know. I tried to cover that with the word "specific". I should have written that explicitely as "specific to the use and medium". Your statement is clear and welcome.