The design of the competition will be one of the subject in our next XPRIZE meetup (July 30th).
We'd be excited to see this on the agenda of other teams globally in the next month!
My first thought is that scaled demonstrators based on smaller scale model of actual marine transportation engine to which scrubbers (the innovation we're looking for) can be applied to during static testing.
But perhaps we need to go further, and allow for the design of new engine or complete ship design? Then I would think we want to focus on the bottom line, which is shipping containers around efficiently with minimal [air,water,noise] pollution... Maybe a complete scale model of a container (singular!) ship?
We'd also welcome referrals to sponsors for the competition itself (ship manufacturers, shipping industry, etc) to collect pledges towards the prize. Although it seems it would be unlikely that the shipping industry has the means to fund this sort of competition itself as it is currently experiencing industry-wide problems... OTOH... perhaps this means that they would like to optimize their current ships?