Just to add when the engine is running with no load (no electrical consumers switched on) you should be charging the batts even at idle speed, once your engine is running at cruising speed your alternator will generally not supply more than 14.6v, when you apply a load to the engine such as putting it into gear from neutral at tickover the charge rate will drop but so long as it is over 12.5volts its charging, when you switch on an electrical load such as lights, pumps etc the charge level may drop slightly, the alternator will deal with the load with a slight drop in engine speed, however as soon as you take the engine speed back up to over tickover speed the alternator will be charging at anything between 13 to 14.6v again the only problem you will have is, if you demand more from your batteries than the alternator can deal with in a short period or exceed its rated output, ie if your alternator has an out put of 85amps dont expect it to charge the batts and supply 85amps it will just wear out quicker.
I think some of your replies were relating to running the engine in gear at higher revs, (you dont need to do this for optimum charging) the manufacturers recommend doing this to clear the combustion chamber of soot due to the constant low running speeds, it has nothing to do with charging! In the old days people use to rev there car engines up before switching off so as to clear the cylinder of unburnt fuel and clean the plugs a bit, however modern engines have moved on but they do benefit from the occasional high speeds under load, better to do this in a marina, well tied up for at least 10 to 15 mins so long as the noise doesn't cause a nuisance to your neighbours.