Every boat sold in the EU between 2.5 m and 24 m long carries a design category on its builder's plate: A, B, C or D. It says what conditions the boat was designed for, and ISO 12217 is the stability and buoyancy assessment behind it.
The categories
From Sailboat Cruising and YachtBuyer:
| Category | Name | Wind | Significant wave height |
|---|---|---|---|
| A | Ocean | Above force 8 | Above 4 m |
| B | Offshore | Up to force 8 | Up to 4 m |
| C | Inshore | Up to force 6 | Up to 2 m |
| D | Sheltered waters | Up to force 4 | Up to 0.3 m |
YachtBuyer stresses the categories are about wind force and wave height, not distance from shore. And they depend on load: its example is a yacht that is Category B with 12 people aboard and Category C with 14.
How ISO 12217 sets them
ISO 12217 assesses a boat's stability and buoyancy and gives the category it qualifies for. Sailboat Cruising notes the STIX stability index used for sailing boats is defined under ISO 12217, and that a category isn't set by length or displacement alone.
What surveyors check
Read the builder's plate: the category, the maximum persons and maximum load. Check the owner's manual agrees. Then compare with the boat's intended use: a Category C boat bought for an ocean crossing is a point for the report, as is a plate missing or unreadable. Modifications that add weight high up, such as an arch, a radar mast or a heavy davit, can affect the stability the category was based on.
Citing it in a report
In the vessel particulars: "Design category B, maximum 8 persons, per builder's plate." Where use and category don't match, say so plainly in the findings, with the category's limits.