Tom,
Yep, my setup is overkill however there are a few things to remember:
I inherited the batteries I am using for a house bank, the 3 group 31's. Originally 2 were house and 1 for start. I added the 4th group 31 for starting and just tied the original 3 together. The cost increase to do this was pretty small.
I upgraded to a 100amp alt/reg package as the boat is on a mooring and never at a dock for shore power recharging. The original 3 batteries were chronically undercharged by the stock 50amp alt and single stage regulator.
Currently (no pun intended) the electrical demand is low but that was a concious decision. Running the AB refrigeration was hard on the batteries as the system works hard due to poor icebox insulation and lack of air to the condenser due to poor installation choices. All inherited problems.
The future will bring better insulation, inprovements to the AB systems location, etc. It will also include a belowdecks autopilot. Using these systems I expect the electrical demands to triple or quadruple. The upgrades I have made should easily handle them.
I have tried to get the engine pulleys to not eat belts but they ate a Gates belts last season. I finished the season on a 3/8ths belt. Being a belt-n-suspenders type I would like the correct pulley groove sizing for the crank and waterpump pulleys. I have two possible sources for locally made custom pulleys in aluminum. I have checked pulley alignment with straitedges and metal rods. They are correctly aligned.
Here is the situation where I might need the extra battery capacity: Enroute to or from either Cuttyhunk or Block Island the weather turns from reasonable to ugly. Unforcasted and unpredictable the weather in New England does this with regularity. Increased headwinds and larger seas slow progress enough to end up running against a tide which slows us down further. Then the fog rolls in. All this means running the radar full time, nav gear, vhf and if the schedule is far enough off, nav lights. Now I could always start the engine to keep up with demand however nothing is 100% reliable. If the engine fails or the alternator dies there will likely be enough juice to get us home. I've also been pinned down for days by weather that was predicted to be 15kts and proved to be 35kts. Having the extra juice while sitting in an anchorage is nice.
While my setup may be overkill, the cost so far is nothing compared to the money I have spent on sails, running rigging, accessories, etc. To each his own, I wouldn't recommend my methods unless they work for you. Everybodys situation is different and we all should be happy and comfortable with the changes and choices we make. Given that MarkA is going to be increasing electrical demands exponentially and going out for weeks at a time makes a system-wide upgrade seem smart. Granted he could wait until the parts are installed and the need is there before proceeding.....
RT