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Understanding the seagoing capabilities of a vessel

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What is the issue?
It is difficult to interpret the seagoing capabilities of a vessel from its appearance. However, if you overestimate a vessel's capabilities and use it into conditions that it was not designed for, it could be overwhelmed.

Why address this?
A misunderstood vessel that is taken into conditions that it is not capable of dealing with could lead to loss of life.

How to address this?
Boats built in the EU since 1998 will have documentation that they complied with the Recreational Craft Directive (RCD) when first offered for sale, and the same is true of most boats imported through authorised dealer networks.

The RCD sets out minimum safety and environmental requirements for recreational craft between 2.5 metres and 24 metres and personal watercraft. The only exceptions to the RCD are vessels propelled by human power and surfboards designed to be propelled by the wind.

The design categories are referred to as A, B, C or D. The elements to be taken into account by the manufacturer and the end user remain the meteorological conditions, i.e. the wind force expressed using the Beaufort scale Experience and the significant wave height expressed in metres.

The first release of the RCD included design category names of 'Ocean', 'Offshore', 'Inshore' or 'Sheltered Waters' outlined below but in a subsequent 2013 revision, this naming classification was abandoned as it was felt that indicating an operating area and/or type of navigation was leading to confusion. The focus of the RCD is strictly environmental conditions, wind force and the sea state as indicated by wave heights.


  • Category A: Designed for extended voyages where conditions may exceed wind force 8 (Beaufort scale) and significant wave heights of 4 metres and above but excluding abnormal conditions, and vessels are largely self-sufficient.

  • Category B: Designed for offshore voyages where conditions up to, and including, wind force 8 and significant wave heights up to, and including, 4 metres may be experienced.

  • Category C: Designed for voyages in coastal waters, large bays, estuaries, lakes and rivers where conditions up to, and including, wind force 6 and significant wave heights up to, and including, 2 metres may be experienced.

  • Category D: Designed for voyages on sheltered coastal waters, small bays, small lakes, rivers and canals where conditions up to, and including, wind force 4 and significant wave heights up to, and including, 0.3 metres may be experienced, with occasional waves of 0.5 metres maximum height, for example from passing vessels.

Craft in each design category must be designed and constructed to withstand these parameters in respect of stability, buoyancy, and other relevant essential requirements listed, and to have good handling characteristics.

It is important to note that the wind force expressed by the Beaufort scale is not a real force but an average of wind speeds. Wind gust speed will commonly be 40% or 50% stronger and the forces do not increase in a linear fashion - see
understanding the Beaufort scale Experience. The significant wave height also refers to mean wave height (trough to crest) of the highest third of the waves that occur in a given period. Here again it is an average number, which means that in reality individual waves can be much higher.


Watercraft builder’s plate
Image: CC0
Each watercraft (boat and personal watercraft) must carry a permanently affixed builder’s plate, which is mounted separately to the watercraft identification number. The builder’s plate is usually found inside the boat, for instance in the cockpit area. The builder’s plate should contain the following information:

  • • Manufacturer’s name, registered trade name or registered trademark, contact address

  • • CE marking

  • • Watercraft design category

  • • Manufacturer’s maximum recommended load (fuel, water, provisions, miscellaneous equipment and people), excluding the weight of the contents of the fixed tanks when full, this should appear in kilograms.

  • • Number of persons recommended by the manufacturer for which the watercraft was designed to carry when underway.


Under the new 2013 revision, any boat falling within its scope, whether new or second-hand, that is placed on the EU market for the first time, must comply with the essential requirements and will have to individually undergo a post-construction assessment (PCA) with a notified body. Its CE marking must be then affixed containing the words 'postconstruction assessment' and the contact details of the notified body which has carried out the conformity assessment procedure will be mentioned instead of the manufacturer’s details.

Modified products that, as new, are subject to this Directive and which have been modified in a way that could affect the safety or the compliance of the product with the EU legislation.

With thanks to:
Michael Harpur
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