I'm no diesel guru by a long shot, but a 315 Yanmar pushing 26 passengers? Would I be out of line to say that engine must be working pretty hard? Rather see a 300 Johnnie Deere in there... but like I said, I'm not an expert.
Net 20 tons. NOT a weight of the vessel, but a volumetric calculation of spaces within the vsl. It is for admeasurments only. The boat I run is 198 net tons for domestic tonnage. 850 tons intl net tonnage and the actual displacement (weight) is over 900 tons.