Streaming Video!

Why Are We Doing This?
Speed
After 25,000 Miles
360-Degree Views
A Different Perspective

Heavy Wx Issues
Directional Control
Stability,Comfort, Capsize Resistance
Hull Shape & Pitching
Hull & Deck Structure
Hull Maintenance
Glazing
Comfort

On Deck
Interior
Storage
Hull Shape
Forepeak
Engine Room
Systems
Tankage
Range
Structure
Factors of Safety
The Team
FAQs
Update-Spring '08
The Next Step

Flying Bridge
Tropical Considerations
Working on Deck
Jury Rig
Roll Control
Swim Step

Interior Layout
Galley
Saloon
Staterooms
Nav Station/Bridge
Ship's Office
Laundry Facilities

Drive Line
Electrical Systems
Refrigeration
Heating/Hot Water
Motion Control
Air Conditioning
Domestic Water

Operating Costs
Windshield Wipers?
Storage Mode
First Anniversary
Fuel Update Apr 08

Recent Press

Range Under Power

There are all sorts of ways of calculating fuel burn and range under power. You can use just the power requirements of the boat, add in (or not) requirements for electrical and hydraulic, consider adverse weather (or assume smooth water), and allow for the boat getting lighter as it burns its fuel load (or keep it heavy as a fudge factor).

The data which follows is from our preliminary drag and prop analysis. We've had two outsiders come up with their own figures, and we are all in the same ballpark. The assumptions are that the bottom and prop are clean, the boat is at nominal half load (75,000 pounds/34,000 kg) and we are operating in smooth water. There is no allowance for hydraulics or electrical, nor rough water drag. The data is based on a usable fuel load of 3400 US gallons (12,800 L).

The columns above indicate (from left to right) horsepower, speed, fuel burn, the number of hours, and range in nautical miles. The two key columns are speed and NM (range) highlighted in light blue and yellow. The data above is the "industry norm" for presenting this range information. On this basis we show a 9400 mile range at nine knots and 6300 mile range at ten knots. However, this is not the real world and the numbers are not very helpful for passage planning.

Now let's plug in some added power loss for hydraulics and electrical.

In the spreadsheet above we've added 0.7 gallons/hr (2.6 L/hr) to the fuel burn. This is what we think we've averaged with Wind Horse over the last couple of years (it is hard to differentiate exactly what fuel is being used for propulsion vs. what fuel is going to auxiliary requirements). Hydraulic loads are light with the load sensing hydraulic pump being used, and the fact that it does not normally take much energy to keep the boat upright in waves. Electrical fuel consumption depends primarily on air conditioning usage. However, when AC power is being used this is efficient in terms of fuel consumed as the big alternators on the engine provide AC through inverters (which is much more fuel efficient than using a genset at the same time the engine is running).

You can see that at 8.5 knots we've got a range of 8500NM (right hand column) and at ten knots range is just over 5500NM.

OK - here's how we look at range with an eye towards crossing oceans. We've reduced the theoretical range by 15% to accommodate extra drag from wind, rough water wave drag, or maybe a dirty bottom. We think this last set of numbers are better as they make an allowance for weather and maintenance issues.

Even in this worst case scenario we've still got over 7000 nautical miles of range at a 200-mile-a-day clip (8.5 knots), and almost 5000 NM at 240 miles a day (10 knots).

A final word on range. It is worth restating that this data will vary with conditions. If you are running with following wind and waves, you can maintain speed, drop engine load and RPM, and substantially reduce fuel burn, sometimes by 10-to 20-percent. Going uphill we've seen fuel burn increase from 15% to as much as 30% (the latter maintaining 11 knots into 30 knots of breeze and big waves). The data here is based on smooth water.

As already mentioned, bottom and prop condition have a lot to do with efficiency and fuel burn. A thin crust of scale on the prop will reduce efficiency by 10- to 20-percent. A dirty bottom likewise will have a big effect on your fuel burn. You have plenty of power to maintain cruising speed, but the dirty bottom/prop will cost you fuel.

In figuring how far to go between pit stops you also have to consider fuel burn at anchor for the genset and diesel heater. On Wind Horse, for heating, we averaged about 4.5 US gallons per day during early summer in Alaska, with night time temperatures in the mid-30 degree F (0 to 2C) range and mid 40s F (7C) during the day. We typically average three quarters of a gallon per day for the genset when at anchor.

You can, of course, substantially improve range by reducing or eliminating air conditioning usage under way, and allowing the boat to move a bit in the waves (by de-tuning the gain settings on the stabilizer control). The biggest variable is boat speed. Backing off from 10 knots to 8.5 results in a 50% improvement in mileage.