Final answer:
The precise tonnage requirement for additional safety regulation of ships cannot be determined with the provided options. These options likely fall below the typical thresholds for large ocean-going vessels. Concerning safety limits for a water taxi, exceeding the set threshold of weight would indeed pose a safety concern.
Step-by-step explanation:
To make navigation safer, regulations for the operation of ships are usually set according to international and national maritime organizations. These regulations often include specifications on the minimum tonnage for equipment requirements, training, and operational protocols aimed to enhance safety. The multiple choice options provided in the question suggest we're looking for a specific threshold that would trigger additional regulations for ship operators.
Based on the reference information, it is evident that the threshold for enhanced safety regulations is likely to be higher than the options provided, considering that container ships operate with loads much greater than 200 tons. Hence, without specific regulatory details, it is not possible to ascertain the correct answer from the given options of a. 10 tons, b. 50 tons, c. 100 tons, d. 200 tons.
However, to address the separate inquiry based on part b of the reference, involving 20 men on a water taxi with a sum weight greater than 3,500 pounds, this scenario indicates a safety concern if it exceeds the safety limits set for such a vessel. This observation is consistent with the principle that vessels have a maximum load capacity, which when exceeded, can negatively impact the stability and buoyancy of the vessel, potentially leading to dangerous situations.