Ship hullstrengths are all over the place. The Spanish 122 heavy firstrate has 2000+ hull strength than its British compatriot. There are other anomalies but I can't list them for sure right now.
The Santisima Trinidad has less hull strength than the Spanish 122, the british 106 is weaker than the 98.
I dont have any other addons to the DarthMod so this submod is my primary suspect, I'm sorry if I'm wrong.