I swapped a couple of emails this morning with another Nordhavn owner talking about fuel efficiency.
Overall, I’m very satisfied with the fuel consumption of my boat. That said, given current fuel prices, anything that can be done to increase fuel efficiency is a good thing.
Following is a table I put together based on fuel consumption observed on my boat:
3000 gallons of fuel
300 gallon reserve (10%)
2700 Usable fuel
RPM Speed GPH GPH GPH Range Miles/
Port Starboard Total Gallon
1000 6.7 3.8 3.5 7.3 2,478 0.92
1100 7.3 4.5 4.3 8.8 2,240 0.83
1200 7.8 5.9 5.5 11.4 1,847 0.68
1300 8.6 7.4 6.8 14.2 1,635 0.61
1400 9.3 9.5 8.7 18.2 1,380 0.51
1500 9.9 12.0 11.5 23.5 1,137 0.42
1600 10.6 14.1 13.6 27.7 1,033 0.38
1700 10.6 16.6 13.6 30.2 948 0.35
Single Engine (Running with one prop in neutral)
1100 5.2 0.0 4.9 4.9 2,865 1.06
1200 6.7 0.0 6.0 6.0 3,015 1.12
1400 7.5 0.0 10.5 10.5 1,929 0.71
These number should not be considered as accurate. It is virtually impossible to get reliable data. Sea conditions, currents, how clean the bottom is, the amount of fuel and water on board, and many other factors can change these numbers materially. However, these numbers do give a broad sense of what the consumption is, and how it varies by speed.
Generally, I average around 9 knots, and average around 5,000 miles a year. Looking at the table above, this implies that I can go about .56 miles for each gallon consumed. In other words, I should budget to buy around 9,000 gallons of fuel a year. At $5 a gallon, that’s $45,000 per year! A 5% savings would be $2,250 in my pocket annually. Of course, I could save significantly more, simply by taking my time whenever I cruise, but what fun would that be?…
Also importantly, I have several long distance passages planned. I usually think in terms of the crossing to Hawaii, which is 2,100 miles. Or, a more critical distance for me is from the Aleutian Islands to Japan, a crossing we may be making next summer. Our plan is to stop in Siberia, but it is far from certain that we’ll be able to do this. If we can’t stop I need to be prepared to run 2,000 miles non-stop, and want to do so as quickly as I can. It will be typhoon season, and “hanging out” is not advised. Looking at the chart above you can see that I need to run at 7 knots to make the crossing safely. Yuck.
I do believe that these numbers were captured unscientifically, and are low. On a major passage I absolutely believe I could outperform these numbers. But, I don’t know by how much, and would hate to be wrong.
Our focus, in the discussion this morning, was on whether or not swapping the prop to one optimized for long range cruising might give the extra efficiency needed to extend range. Most boats, mine included, have fixed pitched props. Many airplanes, and some boats, have variable pitch props, which allow you to tune the pitch of the prop (the angle of attack) to maximize fuel efficiency under different conditions. My thought this morning was that it might be better to optimize the prop around the cruising that is done 99% of the time, rather than the 1% of the time when making a major passage.
I did consider putting in variable pitch props when the boat is built, but decided to go with the simpler solution. Anything I put onto the boat I need to get repaired in third world countries. A “simple” prop seemed the smarter move.
The bottom line: None .. no decision was made. It was just fun discussion…