My problem is that i never seem to have much more than 10 amps positive going into either battery bank when I am charging. And unless I run the engine for 3 or 4 hours I can't get the batteries up to even close to 100% charged. And that is when the indicator says that the battery is 25% depleted.
The plot of the curve that defines battery acceptance over time becomes extremely
flat for the the last few Ah charged. Bringing batteries up to a truly full charge takes an inordinate amount of engine charging because the batteries are not accepting anything like the potential of your alternator: probably as little as 1A for the final few Ah. Plug the boat in to shore power if you have an internal charger and let the charger top off the batteries.
It sounds as if you are charging 75Ah into a house capacity of 300Ah. 10A sounds low for the bulk or absorption phase. If you never discharge the bank greater than 50% (and you shouldn't) then you will likely never see the Alternator (or shore power charger for that matter) supply a very large load to such a relatively small capacity bank.