| B2 | ||
|---|---|---|
| 1 | Single hull | The hull bottom and sides have only one layer of watertight hull surface. |
| 2 | Double bottom | The hull sides have a single layer of water tight hull surface while the hull bottom has two layers. |
| 3 | Double hull | The bottom and sides of the hull have two complete layers of watertight hull surface; an outer and inner hull. |