With Wind Horse at rest we have been able to get an accurate measure of the fuel left aboard. To do this we have moved all remaining fuel to the forward central tank, and then measured its height with our calibrated Tank Tender. The fuel data for the passage from Las Palmas in the Canary Islands to Fort Lauderdale looks like this:
- Nautical miles traveled through the water (including current, plus or minus, is required for accurate mileage) – 4244
- Hours run – 378
- Average speed 11.23 knots
- Speed length ratio – 1.247
- Fuel consumed – 2885 gallons/10,900 liters
- Fuel burn per hour – 7.63 gallons/28.9 liters
- Mileage – .68 gallons/2.56 liters per nautical mile
- Total range under these conditions based on remaining – 5060 nautical miles
The fuel burn rate is a bit higher than our experience in the past. This is due to several factors. First, we were running a quarter of a knot faster than our sweet spot, costly in terms of efficiency. Weather, a daylight finish requirement for ARC photographers on the first leg, and a narrow comfort window weather wise on the second leg made this worthwhile.
Next, air conditioning was run for much of the trip. An educated guess on the fuel burn this required is around a quarter of a gallon/one liter per hour.
The bigger issue is something we overlooked when going through the logic on our new props. They do allow us to reach cruise speed at a lower RPM, and we are quieter as a result. But we are now running out of the sweet spot for our engines in terms of power draw and RPM. This means we burn more fuel for a given horsepower load than if the engines were turning a few more revs. We can address this by derating the engines from M4 to M3 which takes the fuel curve sweet spot to a lower range of RPMs (accomplished with a change in the injection pump rack settings).
That should get us back to where we should be on fuel consumption, a touch under seven gallons/26.5 liters per hour at 11 knots.
Posted by Steve Dashew (December 15, 2010)
December 15th, 2010 at 7:59 am
Hey Steve, check your math! I think your fuel mileage should be 1.47 nmpg, not .68. Love your boats and website. What’s up with FPB 64s #3 & #4?
Mike
December 15th, 2010 at 2:29 pm
Hi Mike:
It is fuel burned PER nautical mile, which I think is correct as is the inverse in your calcs of mileage per unit of fuel. Either way, we will take the results.
February 5th, 2012 at 10:31 pm
I’m with you on this Mike, I’m getting a fuel consupmtion of 1.4710…knots traveled for every gallon consumed! I LIKE IT!
Regards,
Scott M. Barnett
December 15th, 2010 at 8:22 am
So a bit more than the cost of 2 first class tickets to cross the Atlantic with a better view, less stress, and no TSA strip search…what a deal!
December 15th, 2010 at 7:00 pm
Mike,
Steve’s worked it out as Gallons per Nm, you’ve calculated Nm per gallon 🙂
Anthony
January 1st, 2011 at 5:11 pm
Mr. Dashew: The aviation industry has a pretty good handle on fuel flow instrumentation – is that same technology not available for the marine environment? It should be easy (hah! how many bad ideas start with that?!) to get fuel flow (total out of the tank), fuel into the engine(s), less fuel returned from the engine, ditto the generator(s), all neatly summed up on a display, and a solid handle on fuel consumption.
Or what am I missing?
Thanks very much for your efforts: I enjoy reading them.
January 3rd, 2011 at 1:43 am
There are several systems on the market that do this, Rick. But none are totally accurate from what we know.
February 5th, 2012 at 10:28 pm
Rick,
At present I am sitting in the control center of a large airline as a maintenance controller and I shiver at the thought of having capacitance style densitometers embedded in the tankage of an ocean going vessel. In the aviation industry we at least have the luxury of moving vast quantities of fuel through our wings to feed the engines. This fuel is filtered on average 12 times before it hits the tank of an aircraft and then has one final fuel filter to go through prior to arriving at the fuel control/fuel pump array. Even with all of the high grade kerosene we use, you can’t imagine the amount of water which collects in the tanks of large jumbo jets. This water in turn turns to ice at high altitude and wreaks havoc with the densitometers. You also have an added issue of large quantities of diesel sitting in tanks over long periods of time, as in with a yacht, the perfect place for filliform to begin to grow. Compound that with high humidity and high water absorbability and you have the perfect recipe for a non functional fuel indication system. KISS it, and you will be happy!
Regards,
Scott M. Barnett
February 6th, 2012 at 1:48 am
Howdy Scott:
Our experience with diesel tanks is if they are vented correctly water is not a problem. On Wind Horse we might see 1/4 liter every couple of years in the engine room day tank sumps and nothing in the main tanks.
February 6th, 2012 at 9:22 pm
Steve,
Interesting, I would have thought over the long haul that bacteria, water settling, and water absorption by the fuel was the reason for many of the fuel conditioning systems we see on todays yachts.
Regards,
Scott M. Barnett
February 7th, 2012 at 12:50 am
Scott:
By clean fuel from the same high volume dealers the commercial guys use, prefilet it, never return hot fuel to the main tank, and have a good vent system, and you will not have problems.
January 3rd, 2011 at 3:42 am
There exist reliant systems used for fuel consumption testing and homologation purposes. They take care for the returning flow as well and are temperature compensated. An example:
http://www.corrsys-datron.com/fuel_flow_meters.htm
But prepare some boat units…
Hubert