Remora or sucker fish usually attach themselves to the bodies of larger, seagoing creatures in tropical waters. They have also been known to cling to small boats.
Today’s invention involves massively scaling-up this behaviour.
Given that the fish are highly streamlined, the approach is to arrange that they attach themselves, in large numbers, to the hull of a ship travelling in warm seas. This would result in a potentially large improvement in the thrust-to-drag ratio for very large seagoing vessels (since the extra form drag caused by adding a layer of such fish to a big vessel is tiny and yet they do each provide some extra propulsion).
This source of extra drive could be powered simply by providing a stream of waste food particles via hoses hanging from the prow. It also has the advantage of reducing the many causes of marine fouling which coat the undersides of ships.
If necessary, the fish could be contained within wire cages attached to the hull, in order to stop them jumping ship and to protect them from predators.