Cargo Container Ships
On a solar ship - how many solar panels of 20% efficiency can fit on it- using the surface area of the largest container ship . A container ship of 500 TEU  capacity costs $10M, and a used one goes for $4M. . Largest container ship is 400x60 meters, or 24,000 square meters. 
Small container ships weigh 50k tons. Large ones weigh 200k tons. 
Each square meter produces .2kW at best. That makes it 4800kW.
$400/kw. $2M for the panels.
Cargo ship uses 16 tons of fuel per hour. Fuel cost is $300/ton. $38M/year in fuel.
About 8000 hours per year. 16x300x8000=$38M. It is about $100M for a 12k TEU container ship . This means solar payback time is under 1 month. PV costs less than the engine itself. 1 container ship creates as much pollution as 50M cars.
A large container ship uses 80MW of power. . This makes the surface area of a solar ship 1/17 the power. Cost of engine? Hard to tell. If 2300 tons, then $5M if cost of engine is a dollar per pound. It's likely much more than that. A 2MW diesel locomotive is up to $2M for comparison. So the cost of replacing with PV is equivalent, probably much cheaper if we discount the electric motor cost on the cargo ship. However, electric motors are highly modular, so probably not a bad deal to go with electric for lifetime and simplicity.
Diesel locomitives are 2.2MW .
With telescoping panels, solar come to 1/6 the power of a diesel drive train. This may be a case for solar trailers, which just carry extensible solar panels behind the ship. Anyway, the effort to save burning 16 tons of fuel per hour are worth investigating.
Night time power - could be addressed via solar hydrogen production, but that is questionable.
While the solar large-scale vessel can match industry standards to within 1/3 of the speed by using a single power trailer - at significantly lower cost - A small cargo ship can be solar and match industry standards of speed and cost by employing a power trailer. Without using a power trailer, a smaller solar cargo ship can meet industry standards of performance - at much lower cost and environmental footprint.
Specifically - analize a 100 TEU ship operating within the Economy of Affection, which costs 10x less to build, and has an environmental footprint (energy use) at least 100x lower than conventional diesel oil options.