Well good afternoon Doug, nice to meet you too!
CB, good link to the boatfix page, but a small problem with their diagram for a twin engine boat with a third house batt. The good majority of builders, Aquasport included, have a selector switch (OFF/1/ALL/2) for each stating batt. That precludes putting the house batt on the same switch as either one of the start batts...
Soooo, Doug could have 1 of 2 setups, seeing as he has only 2 switches. The first may be that one start batt is wired in parallel with the house batt to create a large house/start bank, still 12V but double the amp hours. The second may be that the house batt is connected to an isolator, VSR, ACR, or the like, whereas the house batt is brought into the charging loop when the motors are running, then isolated when they are shut down.
John (Double Trouble) just re-did his cabling a couple years ago on his 275. Can't remember how he did it (think he used a Blue Seas ACR), be good for him to chime in here...