Ghosty, the pods are more efficient and flexible than conventional shafting and props, hence why they're used greatly in the oil industry for drilling platforms, also the machinery takes up less space inside the hull and is quieter with less vibration along with better steering response and ability to hold vessel position at a fixed point, also maintenance is a cost issue too. Seems that someone at Rolls Royce did not do the math when it came to bearing loadings in this particular application or was it the accountants pennypinching, just my opinion.