You'd think the torp would do more damage than a bomb. I remember us (blue team) going in to this during the Italy SEOW.
The best distance any of us could do was ~3000m, soon after that the motors stop. I dont remember us being too successful with torps.
Some naval vessels have an armoured belt in the middle at the waterline, and are a softer target towards the bow or stern.
We tried the German PC1600 armour piercing bomb, quite effective if used from altitude via a Stuka or level bomber, difficult to do though.
Enforcer and Sid had some success against shipping, skipping SC500s in off Bf110s.