I was usually stopping at marinas while coastal cruising because it would take 2.5 to 3 hours of 1800 RPM to get the batteries up.  Conventional wisdom has the limit at 70A upgrade due to limitations of the power that can be transmitted via the V-belt.  Going 50A OEM to 70A seems hardly worth the effort.  Then I found a kit that also switched all the pulleys and belt to multi-v serpentine style belt, allowing lots more power to be transmitted.

The new alternator is 140A rated and is controlled by a Balmar 614.  At a fast idle when the battery is 50% down I get 100A delivered.  Now I anchor out whenever I have the opportunity, no need to recharge on AC at a dock.  This summer I never had to sit and listen to the engine at anchor.  With the much higher charge rate I find that the 30 minutes poking about harbor under power while looking for a good anchor spot is enough to get the battery up to 98%.  By the time I back down on the anchor the battery is good.
 
Other things of note: 

• An AGM or Optima style battery is needed for this sort of charge acceptance rate.  Regular batteries can overheat at high charge rates.
• It's a good time to add terminal fuses and a direct wire from alternator to batteries.  Wiring suggestions are found on this site and over on the C34 site.
• MaineSail (aka: Compass Marine)  is a most excellent advisor on this sort of thing.You can hit his web site or look up his messages, He often hangs out at the C34 forums.
• I've found that this alternator upgrade has eliminated any thoughts I was having about getting a Honda generator.  100A at 12V is 1200 watts.  That's more than 1.5 hp of electrical power.  I cannot run air conditioning on it, but I can get very liberal on all other uses of electrical power.
• Anybody want my old 50A OEM alternator?