[andy_ppp]

I think you are wrong about this, there are so many variables and sea conditions can affect things, for example older engines and maintenance at sea. AIS data is also known to be wildly inaccurate.

Source: built an engine performance model at a maritime company.

[toomuchtodo]

Require reporting engine run times and performance stats to regulatory bodies, along with fuel loading data from fuel providers.

[jsharf]

Too easy to fake. Maybe instead base it off of fuel consumption. At the end of the day, they can't fake a full tank of gas -- Require it to be documented when they buy fuel and use that to approximate what they're using for a cross-seas voyage (giving appropriate margin so that in case of storm/emergency they can still make it, but perhaps tax them if they eat into buffer)

[andy_ppp]

Actually laughing at this, you have no idea, the people onboard type in the engine data and usually they type the exact same thing as the last reading with some decimal points changed and 0 if they were stopped (even though ships use plenty of fuel even if stopped usually).

[adrianN]

Or just put a carbon tax on the fuel.