Use tag bridge=boardwalk for mapping duckboard.
|Definition:||Duckboards along a trail|
|Rendered as:||Like a bridge|
Duckboards are platform of wooden slats built over muddy ground to form a dry passageway. Hikers and other pedestrians currently use duckboards to safely pass moist areas of ground, such as a swamp or shores of a lake. They are often built from one or two parallel, wide split logs. Specially wide duckboards are often used to provide wheelchair access.
Ability to add a "duckboards=yes" tag to footways (highway=footway). Additional tag that can be used is width, that is especially useful information for wheelchair access.
Currently closest way of tagging is using "surface=wood" and using width to indicate if a wheelchair can fit.
Rendering something similiar as a bridge (bridge=yes).