4.1.1 Hyperbaric evacuation units designed to float should be provided with
adequate stability for all conditions of operation and envisaged environmental
conditions and be self-righting. In determining the degree of stability to be
provided, consideration should be given to the adverse effects of large righting
moments on the divers. Consideration should also be given to the effect equipment
and rescue personnel required to be placed on the top of the system, to carry out a
recovery from the sea, may have on the stability of the hyperbaric evacuation
unit.
4.1.2 Buoyancy and stability on the surface should be such that the
capsule/chamber will have self-righting characteristics together with a reserve
buoyancy of not less than 10 per cent of its total buoyancy. The connections on the
capsule/chamber for towing and lifting should be well emerged above the equilibrium
water plane of the capsule/chamber and lifting must be possible from a single point
by the HRV’s own slinging arrangements without requiring special spreaders or other
gear not likely to be available in a vessel with a suitable crane. In meeting these
objectives the beneficial effect of any auxiliary buoyancy, which is provided by
buoyancy bags, or by other buoyancy which is flammable or otherwise prone to damage,
should be disregarded.
4.1.3 In cases where the buoyancy, which is afforded by the pressure hull and
the rigid watertight external appendages of the capsule/chamber, does not fulfil the
objectives of Pt 7, Ch 1, 4.2 Protection against damage 4.2.1, the necessary additional buoyancy should be provided
by additional buoyancy units securely connected to the structure of the
capsule/chamber. The additional buoyancy units should be nonflammable and of
adequate strength for the maximum depth of submerges which may occur.
4.1.4 Consideration should be given to the use of buoyancy bags, or other
suitable alternatives as a means of augmenting freeboard, trim and stability over
the standard defined by Pt 7, Ch 1, 4.2 Protection against damage 4.2.1 and thereby improving the visibility of the
capsule/chamber and the accessibility of the towing and lifting connections. All
attachments between the buoyancy bags and the capsule/chamber should be carefully
designed for the loads involved. It should be ensured that the towing and lifting
attachments remain accessible and the self-righting characteristics are maintained
under any situation where one or more of the buoyancy bags are damaged.
4.1.5 Towing attachment points should be so situated that there is no likelihood of the
hyperbaric evacuation unit being capsized as a result of the direction of the tow
line. Where towing harnesses are provided they should be lightly clipped or secured
to the unit and so far as is possible be free from snagging when pulled free.
4.1.6 Where hyperbaric evacuation units are designed to be placed on board a rescue vessel,
the unit should be designed as to permit it to remain in an upright position and
attachment points should be provided on the unit to enable it to be secured to the
deck.
4.1.7 Hyperbaric evacuation units provided on ships required to have fire protected
lifeboats should have a similar degree of fire protection.