I am doing long term planning for a small fleet of tugboats. A lot of the engines (propulsion, generators, hydraulics) are Detroit Diesels of various sizes (e.g., 4-71, 6-71, 12V-71). Newer engines are more efficient, but it is not clear to me how this can be quantified. I am trying to make decisions about repowering vessels and would like to see some metrics that I can use to calculate fuel consumption for a given workload. Is there a place or places where I can get information on fuel consumption for work done for individual engine models?