Electric powered submarines that can remain submerged running on batteries for a couple of days have been around for a long time. Recent advances with fuel cell technology produced a German built submarine that can remain submerged and operational for three weeks. However both of these vessels are really Diesel-Electric powered, as has become normal in many applications. Electric motors are incredibly efficient and produce higher, more variable torque than any other kind of engine. The problem to make these a renewable energy proposition is to provide stored energy in enough volume to power lengthy journeys across oceans.
There are solutions such as the Azipod that deploy electric motors outside the ship’s hull, that can reduce overall fuel costs through efficiencies – but they still need the diesel engines providing the electricity.
Another commercially available technology to reduce fossil fuel consumption is the addition of a large kite to cargo ships to reduce fuel consumption on long journeys. There are a few vendors for this kind of product that appear to be operational, but this hasn’t become a mainstream solution. Development of the idea of using wind power to move ships again is diverse and large new container ships are being built now that will source the majority of their power from the wind. The natural combination of wind and solar power is being explored by the “Aquarius Marine Renewable Energy (MRE” ship design. 
As in many areas, the final solutions need to evolve over time and will likely involve many hybrid systems to meet the demand for lower cost transportation as fossil fuel prices inevitably double and triple in the next 25 years.