Float-Free Enclosure - mcmurdo 406 EPIRB User Manual

3.2. Float-free enclosure

If you purchased the automatically activated version (´a´ suffix), also known as the „float-
free" version, then your EPIRB is supplied in a plastic enclosure (see section 8). This is much
more than just a protective housing, it contains a sprung loaded lever which automatically
pushes the enclosure lid off and releases the EPIRB if your vessel sinks. This automatic
ejection is controlled by a device called a Hydrostatic Release Unit (HRU). If the enclosure is
submerged then before it reaches 4 metres (13 feet) deep the HRU cuts a plastic rod that holds
back the spring and the lid is ejected, releasing the EPIRB which floats to the surface and
switches on automatically.
The diagram below illustrates the automatic release sequence:
1. As the vessel sinks, the enclosure fills with water. The HRU contains a blade which is
released due to water pressure acting on a diaphragm. Before it reaches a depth of 4
metres, the HRU will operate and cut the plastic rod, releasing the coil spring.
2. The spring pushes the EPIRB and the enclosure lid outwards. As the lid pivots off it
disengages from the screw head that helped hold it in place. The lid is weigted so it rolls
over and falls away.
3. As the EPIRB floats away from the lid, it moves out of range of the magnet. Once away
from the magnet its sea switch becomes armed.
4. The sea switch activates. The EPIRB then floats on the surface with is strobe light
flashing. After 50 seconds it makes its first distress transmission.
If you need to activate your EPIRB manually, it can be freed from the enclosure after pulling
out he R-shaped retaining pin and removing the lid.
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