It's not the weight of toilet paper that makes it suitable for use in most marine toilets or not ..."premium" TPs have added fibers for strength and creams for softness that prevent it from dissolving quickly and make it harder for macerator blades in most electric toilets to "chew up," resulting in clogs.I've been retired for 14 years now but back in the day.... 2-ply was 2X 9.2 lb. ream weight and 1-ply was 14.7 lb. ream weight .Not a lot of difference and the 2-ply feels nicer.
To find out whether a TP is suitable for use aboard, tear off a couple of sheets and put 'em in a mason jar or a glass of water. Come back in a hour and shake the jar or stir the water in the glass. If the water is milky and all you see is "snow," it's ok for use in any marine toilet...but if the sheets are still intact or mostly intact, try another brand.
Use any TP a lot more sparingly than you would at home, cause an "overload" of even quick-dissolve TP can cause a clog. But if it is quick-dissolve TP, it'll dissolve on its own fairly quickly...so don't panic, just wait 30 minutes and flush again.
--Peggie