Well, they may seem to be the same but with realistic turned off you’ll generally encounter ships with higher classes meaning that most of the time you’ll get outclassed, and when you find a stronger encounter they will have fewer ships in the fleet, so to summarize, realistic encounters makes things fairer because for instance if your ship is class 5 you’ll generally find enemies with class 6, 5 or 4 in most of the common encounters, large powerful fleets will still have higher classes, but with the option turned on you’ll also find that the powerful fleets will have more ships than with the option turned off.
Now if you’re in trouble with your little brigantine you might have to consider adding more ships to your fleet, try recruiting other hero captains to join you, it will be much easier, but if you don’t like commanding more ships you should stick to the merchant sloops in the world map, they will have 1 to 2 ships with no escorts and will always be class 6, or you can take on pirates that will have 1 to 3 ships class 6, but this one is trickier since the medium and small pirate fleets are both displayed as sloops in the world map so you might get outclassed if is the medium one that might have 1 to 4 ships class 6 to 5.
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