Catalyzes the conversion of (2E,6E)-farnesyl diphosphate (FPP) into drimenol, a precursor of the sesquiterpenoid polygodial (PubMed:28258968). Polygodial has been shown to be an antifeedant for a number of herbivorous insects (Probable). (2E,6E)-farnesyl diphosphate + H2O = (5S,9S,10S)-drim-7-en-11-ol + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.