Charging Problem?

[cruiser_pete]

Since I launched this year (about a month ago) I have noticed that it takes longer than last year to charge my batteries via the alternator. While the boat was on the hard, I charged the batteries via shore power monthly, and it never took more than 10 minutes to top up my 2 4D cells. I would assume that this means that the batteries are still holding a good charge.

I am assuming that either my consumption has gone up, or there is a problem with my charging system. The charging is done by the alternator on my Yanmar 3YM30 and a Xantrax charger. With the charger (and motor) on and the batteries topped up, i see a voltage of 13.5 volts.

My first thought was that the alternator belt might not be tight enough as I loosen it for the winter, but the tension on the belt seems ok. I then thought that maybe i have a leak that is causing the bilge pump to run more frequently and draining my batteries, but i see no evidence of this.

Any ideas of what I can do to get a better understanding of what is happening here?

Thanks,
Pete