User's Manual

7
4.2 Float-free enclosure
If you purchased the automatically activated version (406a), also known as the “float-
free” version, then your Precision 406 is supplied in a plastic enclosure (see section 9).
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 Precision 406 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 Precision 406 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 weighted so it rolls over and falls away.
3. As the Precision 406 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 its
strobe light flashing. After 3 minutes it makes its first distress
transmission.
If you need to activate your Precision 406 manually, it can be freed from the enclosure
after pulling out the R-shaped retaining pin and removing the lid.
H
R
U
1) HRU cuts rod
2) Lid ejects
4) sea switch
activates
3) EPIRB arms once
away from magnet
Magnet