MN 13 of 2011 Page 26 of 130
9 Buoyancy and construction of Small Vessels
On all categories of vessels, other than category A & R, built-in buoyancy only replaces the liferaft
when it is sufficient to provide a stable level platform upon which the crew can be secured in an
emergency (fully flooded, swamped or capsized).
Category R vessels are not required to carry liferafts however they still require sufficient buoyancy so
as to keep the vessel afloat in an emergency.
Buoyancy must consist of either foam or approved plastic bottles, or a combination of both. Buoyant
material may not be affected by oil or oil products. Foam should be of a suitable closed cell type
(usually a polyurethane type) and until such time as ―approved‖ bottles are identified the only plastic
bottles used should be ―H.D.P.E.(High Density Polyethylene) Grade 2‖ plastic bottles with secure
watertight caps, or sealed six-sided ―boat floats‖ manufactured of H.D.P.E, designed specifically for
the purpose of providing buoyancy in small vessels. Sufficient hatches are to be provided for
inspection of the bottles.
9.1 Amount of buoyancy to be provided
It should be obvious that a simple standard amount of buoyancy will not be appropriate as vessels are
constructed of various materials such as steel, aluminium, or from lightweight and buoyant materials
such as foam sandwich construction. An individual calculation has to be made in every case to ensure
that the vessel achieves the desired platform. An industry norm has been developed where 60% built-
in buoyancy has been shown to be sufficient on wood and GRP constructions. SAMSA accepts this
standard on categories B, C, D and E vessels so constructed.
The 60% means the following:
The volume displaced by the buoyancy (i.e. the foam or bottles) provided inside the vessel must
represent a figure of 60% of the gross weight of the vessel. Gross weight means; the weight of the
vessel, engines, stores, fuel, persons, fish etc. (See Annex 5 for a worked example on the SAMSA
flotation certificate.)
It is important to note however that this is only a tried and tested formula on the type of vessels for
which it is intended, namely the mass of wood and GRP ski-boats which make up the majority of the
vessels at sea.
Regarding category R vessels and the exempted vessels mentioned in regulation 37, SAMSA, in
conjunction with the Boat Building Industry Association of South Africa (BIASA), has determined
that sufficient buoyancy is provided to meet the requirements of the regulations when 30% of the
vessel‘s weight (weight of boat, engine, fuel, stores, equipment but not persons) is fitted as buoyancy.
Once again, this refers to the common wood and GRP constructed vessels.
A different buoyancy requirement applies to inflatable vessels and the regulations require these
vessels to have at least 3 compartments, the smallest of which must be able to keep the vessel afloat.
Note, a rigid hull is not included in this calculation, and also that extreme uses of inflatable vessels for
commercial use such as cargo carrying or the like may require additional buoyancy to the satisfaction
of SAMSA, by way of foam filled hulls or additional compartments, as this was never the intention of
this exception.
Vessels such as category C, D & E pleasure sailing vessels (yachts) are still exempted from buoyancy
or carrying a life raft, provided that they carry life rings (1 per two persons) and operate no more than
30 miles from a safe haven during daylight hours (sunrise to sunset).
The ―chukkies‖ or vessels described as ―commercial small vessels, being fishing boats of more than 7
metres in overall length and of such heavy construction that the fitting of built-in buoyancy was