Complex sentence: The Lake Tanker was a small vessel in comparison with the larger ocean going oil tankers; they had a very shallow draft with a flat bottom, which allowed the ship to maneuver over the ever shifting sand bars that blocked the channel going into Lake Maracaibo.
Split into simpler sentences: The Lake Tanker was a small vessel in comparison with the larger ocean going oil tankers; they have a very shallow draft with a flat bottom. This allowed this small ship to maneuver over the ever shifting sand bars that blocked the channel going into Lake Maracaibo.