What she weighs
Her hull's displacement, plus one per upgrade level on any track, plus one for every 100◆ in the hold.
Ram recoil
Recoil per tier is parity 3 × (their weight ÷ your weight) ^ 1.5, capped at 12 per tier, and tier counts no higher than 3. Ram something your own size and it is a knock. Ram something much bigger and it climbs steeply toward that cap. The Ram button shows you the number before you commit.
Ram levels buy damage, not safety. A level adds one to your own displacement, which nudges the gap in your favour, but that is a rounding effect and not the mechanic. A sloop should probably stop ramming things in deep water. A galleon can keep doing it. That difference is the point.
The parting blow
Getting away still costs a parting blow, and it reads the same ratio: 0.5 × their base blow × (their weight ÷ your weight). Running from something much bigger than you costs more than running from something small. It is not clamped away from lethality, and it can still sink you. A Sloop takes ×0.5 of it.
For scale
Sloop 10, Brigantine 20, Galleon 30: displacement units, bare and empty. Reef Shark 8, Young Serpent 7, The Bailiff 20, Diving Serpent 14, Shellback 16, Siren Spitter 12, The Actuary 40, Kraken 30, Leviathan 36, The Maw 60.