Hello,
If you want to use COORDONNEES SPHERIQUES = OUI (SPHERICAL COORDINATES = YES), you have to use either Mercator projection (not UTM!) or latitude/longitude for the coordinates of your GEOMETRY FILE. Then, when modelling tide with TELEMAC and TPXO-like solutions, you have to fill in the keyword GEOGRAPHIC SYSTEM with 1 or 5 (see the reference or manual, or the dictionary) otherwise the converter does not know with which geographic system the geometry file was built.
Hope this helps,
Chi-Tuan