Buoyancy of Small Vessels

There is a lot of hype around the issue of buoyancy and even technical debate about the word itself.

In the context of boating in South Africa it has for over 20 years been used to refer to the bottles and/or foam placed inside the boat in order to maintain flotation in a damaged or flooded state and that is the use of the word buoyancy in the regulations.

On most seagoing categories of vessels built-in buoyancy is expected to replaces the need to provide a liferaft, which it can only do if there is sufficient buoyancy provided to ensure a stable level platform upon which the crew can be secured in an emergency (fully flooded, swamped or capsized).

Category R vessels do not need to meet this high performance requirement however they still require sufficient buoyancy so as to keep the vessel afloat in an emergency.

Form of buoyancy for seagoing vessels

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.

Form of buoyancy for inland vessels

Although the same standards are recommended, the reality is that due to the variations of craft involved, strict adherence to the above mentioned standard is not required. A reasonable and appropriate effort should be made to ensure that the vessel cannot sink.

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 (Mass) of water 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 etc. (See a worked example on the SAMSA flotation certificate further down)

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 (inland waters) and the exempted vessels mentioned in regulation 27, 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. They are required to 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 impracticable", were required to comply with the buoyancy requirements as of August 2009, or fit a liferaft. (See regulation 39(3).

Documenting built-in buoyancy (Buoyancy certificates)



What is really important is that the regulations require that owners be able to demonstrate to a surveyor, safety officer or any enforcement officer (SAPS, municipal police or other designated enforcement officer) that their vessel complies with the regulations which include the buoyancy standards.

As the provision of adequate buoyancy aboard small vessels is so important, it is very likely that owners arriving at any launch site may be asked to show that their vessels comply before being allowed to launch.

The only way to do this at short notice, without a great deal of trouble, is by carrying and producing the valid buoyancy certificate required by Annex 1 of the regulations.

Buyers of vessels should be aware that they are not only ill advised to purchase vessels from sellers unable or unwilling to underwrite and certify their vessels by producing a proper buoyancy certificate, but that it is illegal for any seller, to sell a vessel that does not comply. However, a seller may sell a non-compliant vessel if they make a full declaration of the non-compliance.

The form of the Buoyancy Certificate

Wherever issued by a SAMSA officer, there is a prescribed way of certifying the buoyancy. (Attached as Annex 5).

Note that the example would have to be modified for different situations, for example where the vessel is an inflatable, or has watertight subdivision (i.e. has 'one compartment' flooding capability), or has complied with the passenger vessel buoyancy and stability requirements. But the layout and relevant sections must be kept intact.

Where SAMSA officers or Authorised Agency safety officers and inspectors are faced with alternative documentation produced by other parties, the following principles must be applied to all forms of buoyancy certificate.

  • It must be clear who the issuer is, for instance the boat builder, private surveyor, safety officer, owner etc.
  • The vessel itself must be clearly identified by photograph, serial number or similar.
  • The basic dimensions and build details of the vessel must be included to aid the reader with not only identifying the vessel but also making it possible to detect any major alterations which may affect the validity of the certificate.
  • The quantity, type and distribution of buoyancy must be described in detail.
  • The net weight (light weight) of the vessel must be noted, as this is the best method of monitoring absorbency or water retention of either foam or bottles.
  • The certificate must attest to compliance with the requirements of regulation 6 and Annex 1 or conversely state exactly what is in fact being certified.
  • Any limitations, conclusions or comments must be clearly noted, especially when bottles are used as they have a limited lifespan.


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