Judging from Trafalgar (the only major battle in the game period that occurred between game powers), I would say the enemy would have to have more than twice the British strength (and maybe even thrice). However, extrapolating from a zero is always tricky (GB lost zero ships at Trafalgar, even though outnumbered by ~25%). She also "killed" ~1/2 of her enemy. In game turns, she rolled a result that resulted in 80+% of her own strength in enemy casualties (captured and destroyed together).ORIGINAL: eske
For illustration it might be interesting to calculate what it takes to get 50-50 odds versus a GB fleet of 10HS and 10LS in open sea battle.
There were other battles earlier than the game period, some of which GB even lost. But, an argument can be made that those don't count, because of the improvements between 1800 and 1805. Some have estimated that GB's navy was twice as good in 1805 as it was in the late 1700s.
Unfortunately, such numbers do not make for a playable game (who wants to play navally when it's a dead certainty that you can't win?). So, the percentages have been dropped to something that makes for a more playable game. Instead of allowing an 80% result, the table is capped at 25%.