@jparadis Hopefully this isn’t an overly simplistic or offtopic answer to your question. For a number of reasons, the maritime industry is risk averse and notoriously slow to innovate. Nevertheless, ships have gradually become cleaner and more efficient over the last few decades, mostly driven by regulatory requirements. The rapid growth in ship size and increases in propulsion efficiency have enabled ships to achieve significant reductions in energy consumption per unit cargo carried. However ships typically burn residual fuel, a very dirty fuel that is essentially a refinery waste product and therefore much less expensive than cleaner fuels. All that is changing right now as one of the biggest environmental changes to shipping takes effect on Jan 1, 2020 when new fuel restrictions go into effect that either require a vessel to burn much cleaner low Sulphur diesel or to install expensive scrubbers. The much higher cost of clean diesel has changed the economics so that alternative fuels like LNG and biodiesel are competitive and in some cases less expensive.
In California and some other locations outside the US, “coldironing” (the ship plugs in to the electrical grid and secures its own diesel generators) has been phased in to reduce emissions in port. Other changes have taken effect over the last decade to reduce NOx and SOx, invasive species, toxic hull coatings, and sewage discharges. Ships are gradually getting greener but have a long way to go. Large companies like Maersk(Danish) and CMA CGM (French) will likely be the drivers for innovation and adoption, as most of the fleets (Greek, Chinese, etc.) will do the minimum to comply with regulatory requirements as they would not be competitive otherwise. The US is a minor player in the industry and doesn’t have a large impact on innovating vessel technologies, but the US does have a significant role in dictating regulatory requirements for foreign flag vessels calling US ports.
As for slow steaming, I believe the statistics being quoted are somewhat misleading. Without doing aa deep dive on this, this concept primarily applies to long haul container ships (vs. tankers, bulkers, etc.) Major container operators run their ships on “liner” service which means that they might offer a weekly service to a port (every Tuesday at 0800 one of their ships will call Los Angeles for example). When ships slow steam, they either have to reduce the number of ports they serve or they have to add a vessel to the rotation. So if previously they had five ships on a five week run operating a weekly service, they would change this to a six week service and add a sixth vessel to the string. They still have to move the same number of containers each week (or they’d start piling up) so while for a given vessel it can be more efficient to slow down, it may not reduce overall emissions. Slow steaming originated during the financial crisis when many vessels were being laid up. Slow steaming was a solution that took advantage of idle vessels to save fuel costs. Since then the equation has changed, and most ships built in the last five to ten years have been optimized for slower cruising speeds rather than the fastest attainable speed that was historically the norm. Reducing speed even further on these vessels by slow steaming would not achieve the savings that it once did. Please note that I haven’t analyzed any specific data to back my opinions up, just offering this from my experience.