On our way back from the city, we hit slack tide at San Mateo Bridge. And the water is dead flat. We thought, hey, what a perfect chance to test our fuel consumption.
Methods:
We ran our main engine (Caterpillar 3306 225hp) at various RPM, to achieved fuel flow at 2, 3, 4… to 11 GPH with interval “1″ (measured with floscan fuel flow meter) . We recorded the actual speed (SOG) and RPM after the speed stabilized. And then we did the same testing in the reverse order (11, 10 … 2 GPH) to avoid the potential bais associated with sampling order. Notice we don’t have stabilizer on during the test. The whole testing took about 25 min.
We calculated the fuel consumption for our longest non-stop trip (2650 NM, from Cabo to Nuku Hiva) based on the various speed, with additional fuel used by the hydraulic cruising generator (estimating 2 hour a day @ 0.5 GPH).
Results
| GPH | Speed | RPM | Total hours | Total Days | NMPG | Total Fuel | Gen time (2hr a day) | Total Fuel with geneset |
| 2.00 | 7.20 | 1225.00 | 368.06 | 15.34 | 3.60 | 736.11 | 15.34 | 751.45 |
| 3.00 | 7.85 | 1350.00 | 337.58 | 14.07 | 2.62 | 1012.74 | 14.07 | 1026.80 |
| 3.50 | 8.10 | 1425.00 | 327.16 | 13.63 | 2.31 | 1145.06 | 13.63 | 1158.69 |
| 4.00 | 8.35 | 1475.00 | 317.37 | 13.22 | 2.09 | 1269.46 | 13.22 | 1282.68 |
| 5.00 | 8.85 | 1575.00 | 299.44 | 12.48 | 1.77 | 1497.18 | 12.48 | 1509.65 |
| 6.00 | 9.15 | 1640.00 | 289.62 | 12.07 | 1.53 | 1737.70 | 12.07 | 1749.77 |
| 7.00 | 9.55 | 1750.00 | 277.49 | 11.56 | 1.36 | 1942.41 | 11.56 | 1953.97 |
| 8.00 | 9.75 | 1800.00 | 271.79 | 11.32 | 1.22 | 2174.36 | 11.32 | 2185.68 |
| 9.00 | 9.95 | 1850.00 | 266.33 | 11.10 | 1.11 | 2396.98 | 11.10 | 2408.08 |
| 10.00 | 10.10 | 1900.00 | 262.38 | 10.93 | 1.01 | 2623.76 | 10.93 | 2634.69 |
| 11.00 | 10.20 | 1925.00 | 259.80 | 10.83 | 0.93 | 2857.84 | 10.83 | 2868.67 |
For reference, this is the theoretic estimate (tank testing for the 62) from “Voyage under power”
| GPH | Speed | |||||||
| 1.32 | 6.00 | |||||||
| 2.10 | 7.00 | |||||||
| 3.48 | 8.00 | |||||||
| 4.50 | 8.50 | |||||||
| 5.70 | 9.00 | |||||||
| 7.62 | 9.50 | |||||||
| 10.68 | 10.00 | |||||||
| 14.64 | 10.50 |
Fuel consumption vs Speed
Speed vs Fuel consumption
Cruising generator usage adds a small increment to the total fuel consumption and does not change the fuel-speed relation much.
It seems to us that a cruising speed around 8-8.5 knots is the sweet spot for N62. Any suggestion?
I just found your blog. I intend to read the entire blog, and stay current with your journey. I wish you all the best, and thank you very much for taking the time to blog/document your experiences.
First off, just found your blog and starting from the beginning, even though a year old.
This is interesting. Curious how these tests are comparing against ‘real world’ consumptions. But perhaps that is covered in a later entry!