This centre propeller on Titanic seems to got more life going for it today as was on Titanic!
There is no doubt Mark has uncovered documents that a three bladed centre propeller was said on paper to be made. However what is said on paper doesn't always follow in practice.
What does surprise me if it had be the other way around where the Olympic had started life with a three bladed centre propeller, and Titanic was to follow on with a four blade centre propeller that to me more common sense. As anything new in technology never stand still and that can be clearly seen on Lusitania and Mauretania where both ship started life with three bladed propellers and about one year later change over to four bladed propellers with improved performance. That was four years before Olympic class ship came on the seen.
Even the new big three super liners from Germany with turbines where also four bladed propellers to.
The new technology for turbines had moved on.
However since Mark has it on paper and I or anybody else cannot prove any different we have to stick with it. The only real true if the paper work is correct is still lies buried at the bottom of the Atlantic seabed. To remove the seabed debris from the propeller is a very costly and expensive operation indeed.