The most commonly used rating for deep-cycle batteries is amp-hour (AH) capacity. It is calculated by C/20, i.e., how many amp-hours the fully-charged battery can deliver over a 20-hour period with a resistive load 1.20th the capacity of the battery (C/20) before reaching 10.5 VDC, whence the battery is effectively depleted.
For a 232AH rated battery, the resistive load would be 232/20 or 11.6 amps.
In plain language: take a fully charged battery, attach a 11.6 amp resistive load, and see how long it takes before reaching 10.5 volts. A fully healthy and fully charged battery should take 20 hours.
The above poster is correct. One doesn't normally use more than 50% of the capacity (i.e., don't discharge below 50% or 12.2VDC) before recharging. In practice while cruising, only about 35% of the capacity is really available for use, because that last 15% of recharging takes a very long time....too long for mechanical means unless motoring a lot.
So, effectively, house batteries on cruising boats normally cycle somewhere in the 50-85% state-of-charge range until plugged into shore power
and given enough time to reach 100% recharge.