Some hulls are specified with 3 values:
Waterline width
Maximum width
Gunnel width
Depending on hull design, the gunnel width will be less than the maximum width, and may even be less than the waterline width. Many flatwater hulls have tumblehome, where the gunnel width is less than maximum width, to make it easier to reach over with a paddle.
Some whitewater hulls have considerable flair at the gunnels, for reserve stability.