Depth soundings are handled somewhat specially in the S-57 format to efficiently represent the many available data points. In S-57, one sounding feature can have many sounding points.
The FME S-57 reader splits each sounding point into its own feature type, SOUNDG feature, with an s57_type of s57_point3d.
All soundings from a single feature record have the same AGEN, FIDN, FIDS, and LNAM values.