If you are only sailing for a few hours at a time, it really doesn't matter. Unless you're running some big loads while sailing, a deep cycle or combination battery should not be run down from sailing for a few hours.
Run the blower and start off battery 1, leave it online to charge while the engine is running to take you out. Leave #1 on line while you're sailing to run instruments, etc. Use the same battery to run the blower and start the engine to bring you back in. Battery 2 is always in reserve on the outside chance that #1 gets run down.
Next time out, run on #2, keeping #1 in reserve.
You're charging with shore power also, right?
Now, when your aspirations to cruise start taking you away over night or for weekends , it might be time to look at what SD suggested.
I put in an ACR (60A) and dual circuit plus switch like shown here: http://bluesea.com/viewresource/69
with engine charging the starting battery (1100 MCA). A (50A) shore powered charger is connected to the house bank (450 Ah).
It makes battery management much simpler, turn the switch ON when I'm on the boat, turn it OFF when I leave. The set-up connects the house bank to the starting battery when charging, isolates them when they are discharging.