In reference to Kurt Reno's post: The most important lesson there is range is potentially important. There are a lot of viariables--including wind, seas and current which you do not--and cannot factor in--and they are not self canceling. Probably the most significant difference between your 26 foot boat and the Williard 30's is the LWL--which makes a lot of difference at low speeds.. The 4-108/107 Perkins are essentially 35 hp engines, not 50 hp in marine applications. The alternator probably will not be putting out 130 amps all of the time. If it is, you probably need to rethink the charging system and power utalization. This implies that you are pumping out 780 amps for each days utalization--or have a battery capacity of 1560 amps (if you follow the conservative philosophy of never discharging your batteries more than 50 %). In fact because of ineffeciencies in charging systems you will require significantly more charging time/ or an bigger alternator. The most effecient way to run the refigeration--boat is with holding plates and an engine driven compressor. I am a bit puzzled by your statement that you want to run Air Conditioning during the day. If you are going cruising in a small boat you should design in good ventillation so that AC is not necessary. In many thousands of miles of cruising A C (much in the tropics) was never necessary. There were a few nights when it would have been nice--but not essential with proper ventillation. I only found it "necessary" when visiting marinas in Florida, after I had switched to powerboats which had poor ventiallation--even then after the boat was cooled down with ports and hatches open later in the evening. How often will you deploy paravanes on a 26 foot boat? In most near shore or ICW cruising that does not make a lot of sense unless you are in some very specific conditions--and under those conditions you will probably drop your speed down for reasons of seas and fuel economy. The point that you make is extremely important--what is your actual cruising range (and you use until dry--most calculations allow 10% residual). What runs are your making in a 26 foot boat that are going to be such that you need a range of 500 or 1000 miles? You can get to the Caribbean running only a few hundred miles between ports where fuel is avaialable.--same is true on the West Coast of North America all of the way to Panama. Other than "bragging rights" ie: my boat gets better fuel milage than...... If your boat gets 10 mpg or 1 mpg, the fuel cost and range is really not important in the over all cost of owning and running a boat for over 95% of boaters. Formulae are just estimates. The real life situation is how many miles can you safely travel on the tankage that your boat contains. If you want longer range, you slow down. Regards, Bob Austin