[Merad]

A lot of these ships carry upwards of 150000 tons of cargo. Not sure if an extra 60-70 tons (assuming a 20 day trip) of cargo would be very meaningful. A quick google suggests that would only be 2 or 3 additional shipping containers.

[mgiampapa]

You don't need to compare to the size of the ship, you need to compare to the size / mass / cost of the sails.

[jtbayly]

There’s also the cost of the fuel. Can’t be cheap.

[thih9]

I guess the question is how much space would the sails take.