Er, "Ask the customer?"
They WANT "lowest total cost".
They NEED safety and reliability to get their money back, and to continue operations on the waterways without fines and bankruptcy.
Lowest cost REQUIRES the fewest hours possible to make up pipes and rig pipes to the ship, and to spend as few days/hours/minutes as possible loading and unloaded the tanker, right? SO, they NEED lightweight, cheap, very large pipes. Ain't possible.
Larger pipes are more expensive to buy, build, inspect, hang and support on the cranes and rigging, harder to make portable to swing out the ship, harder to make safe during tide changes, waves, storms, and hurricanes. Require more pier space and more crane expense and rigging gear. Larger pipes require larger valves, fittings, pumps, and seals.
So, larger pipes are a larger fixed price to get a cheaper long-term operating price. Go back to the CLIENT'S engineering economics decisions about the future price pf money, the current loans and environmental costs, and the cost of delays while loading. YOU don't decide on the size of pipes - the CLIENT decides how much more he can must spend now to save money later.
