The portuguese can send a HC card (Carrack) to increase caravel hitpoints by 15%. I mean, this card is not worth sending. It only add 120 hitpoints to caravel. By contrast, dutch can increase fluyt hitpoints by 75% and spanish can increase galeon hitpoints and attack by 30% with a HC card.
I don’t think portuguese are OP relative to other nations in sea battle. They lack both the Naval gunners and offshore support cards. The only think they have is Navigation School, which reduces warship cost and train time. Danish also have a similar card that reduce warship wood cost and train time (Royal Naval Academy). They also have Naval gunners.
I think the Carrack HC card should be changed to +25% hitpoint, so that it is worth sending in some cases (blue water map). It fits nicely with the portuguese theme (advanced early warships) and does not make them OP.