George - what specific boats (or charter companies) are you seeing with this significantly reduced water capacity? 60 gallons is ridiculously small. 185~210 gal is pretty standard for the 45-52' cats (at leaat FP, Lagoon, R&C, Voyage).

If you have freshwater flush (no smell) toilets and 8 persons onboard, you'll use 40+ gallons every 2 days just for the heads.

To practically cruise the SVI for more than a couple days with 8 on a cat and maintain the high level of comfort charter guests have become used to, you need a watermaker (regardless of tankage).