What is the estimated cruising range for the 40hp & 57hp Yanmar engines on one tank of diesel?

The below data is following the initial commissioning sea trials of the twin Yanmar 57hp inboard diesel motors installed on 1370 Hull 1 during her maiden sea trail at the factory.

These figures are boat speed river trials without sails in flat water conditions only, conducted over a series of approx. quarter mile tests.

Using the Yanmar fuel burn data, we can then calculate  theoretical range estimates: 

Note: Rounded fuel burn rates are the "loaded" Yanmar figures ("at the prop") and used for range calculations.

Obviously sea state, wind, water currents, will have some affect on these figures which could either increase or decrease depending on any of those factors at that time.

From the test team, it appears the best rpm range is around 2200, which is where the engines are at about 98% maximum torque and 83% maximum hp. When you start to increase the rpm, the fuel burn rate increases exponentially but you don’t gain much more hp and you lose some torque, and with that additional fuel burn, you lose a lot of those range miles. If you decrease the rpm you get a much greater distance but at a much slower boat speed.

The blue area highlighted showed a reasonable position for extended range, running on one motor. With different conditions, it may be better to run both motors however.

At this stage, there is no further data for the 40hp base boat engine so we can only revert back to the original post response to this question ifrom 2022, which was 100% based on theoretical numbers: