Hello togehter,
some years ago they was another discussion about these marks on the hull:
http://models.rokket.biz/index.php?topic=221.0From my point of view these marks are not related to the torpedo system.
These "bumps" have a very simple work to do: They helps to get out the huge amount of water inside the free flooded structure.
This water at this position was a big problem out at sea. Water at this position results to a hard working boat.
This problem occurs first at Type I. Later also on Type VII A. They try to fix it by many different changes of the first flooding holes. At some pictures of U35 you can see that they have also opend additional flood holes just at the position of the "bums" of later Types. This helps to get out the water. But also the water could fast get in.
At development of type VII B they ad these "bumps". This are just open flood holes. But at speed foreward the water could easy get out but nothing or only slow get in.
If someone owns a smal boat he maybe used a very similar thing to get out the water. In german it calls "Selbstlenzer".
Regards,
Uboatfan