Freighters were not equipped with anti-torpedo protections, either bulges or thickened bulkheads. However, tankers would often have double hulls. This was intended to reduce the risk of leaks from accidental damage, but could also prevent a torpedo hit from causing significant damage to the ship. Where a torpedo hit had a great impact on the effect it had. A torpedo hit amidships that flooded an engine room or one of the holds would cause a ship to sink fairly rapidly. A hit to the ends, meanwhile, would cause flooding that could be easily prevented from spreading, and was unlikely to cause a sinking. Bigger ships, with greater reserve buoyancy, were more likely to survive than smaller ones. The cargo carried by a ship could also determine how likely it was to sink. A ship carrying heavy, dense cargoes, like iron ore, would often sink rapidly when torpedoed, while ammunition ships had a tendency to explode when hit; those carrying less dense cargoes like wood (especially cork), could remain afloat after sustaining a surprising amount of damage. Numbers from the First World War suggest that ~70-85% of ships struck by a torpedo would sink, depending on size. I would expect the numbers for the second to be similar.