So what is your take on diesel fuel prices after 2020?

Those ships have at least three options. Low sulfur diesel, install scrubbers, or convert to natural gas. I agree that the additional cost to ship the fuel will increase the world prices. Refining capacity could be squeezed for some time as lower sulfur fuel is required. How much effect on price is anyone's guess. Supply side changes could mute the entire thing or could add additional pressure independent of the transport fueling issues.