Reasonable Payload of Annapolis Wherry Tandem

I’m considering building or purchasing an Annapolis Wherry Tandem. I’m surprised by the given payload of 650 lbs since it seems like such a large load would create an extremely short freeboard. What seems to be a reasonable payload for those of you who have rowed this? Is it feasible to load 3 adults and a child in one of these? Would it just slow it down and require very calm water? Thanks.