Ask SAIL: Generating Energy While Underway

I just read Nigel Calder’s article on the costs of generating energy (“The Cost of Energy,” Dec. 2012) and found it fascinating. I understand there is a high cost for generating energy at anchor by running an engine, but is there an additional cost to generating energy while underway? If my engine is running the alternator to recharge the batteries, as well as moving the boat, surely it must add to the load and increase my fuel consumption. Is the increase significant, miniscule or somewhere in between?
Author:
Updated:
Original:

Jay Adamsson of Kingston, Ontario asks:

I just read Nigel Calder’s article on the costs of generating energy (“The Cost of Energy,” Dec. 2012) and found it fascinating. I understand there is a high cost for generating energy at anchor by running an engine, but is there an additional cost to generating energy while underway? If my engine is running the alternator to recharge the batteries, as well as moving the boat, surely it must add to the load and increase my fuel consumption. Is the increase significant, miniscule or somewhere in between?

Nigel Calder replies: 

In almost all cases, due to the manner in which a propeller loads an engine, engines are never operating at peak efficiency underway. However, as a general rule, the higher the ancillary loads from things like alternators, refrigerators, etc., the more efficient they become. Fuel consumption rises, because the engine is doing more work, but it rises proportionately less than the increase in work.

To put it in terms of a power bill, instead of paying around $0.20 per kilowatt-hour (kWh) of energy used, you will pay $0.15 per kWh. If usage goes from 10 kWh to 20 kWh, the bill may rise from $2.00 to $3.00, but the unit cost will decline. Running an alternator underway, we are not only getting housepower at a much cheaper rate than when charging at anchor, we also get our propulsion power at a cheaper, more fuel-efficient rate, because the engine is operating more efficiently. The bottom line is that any time you are running your engine for propulsion purposes at less than, say, two-thirds of its full speed, there is a significant benefit to loading it up with other jobs.

Got a question for our experts? Send it to sailmail@sailmagazine.com

Related

02-'17-Trans-Atlantic_Downwind-Schralpin

At The Helm: Man Overboard!

Imagine this simple scenario: the boat’s powered up, sailing close-hauled in a building breeze under full sail. I come on deck as the skipper during the watch change to make sure the new crew is comfortable and the boat is properly set up for both the current conditions and ...read more

Promo-01-LEAD-MGR00321

Contrasting X-Yachts & Moody Cruisers

One of the most fascinating things about sailboats is the different ways that sailors, naval architects and builders will approach a single design problem. The result has been a bewildering array of rigs and hull forms over the years, and in the case of the two boats we’ll be ...read more

04-Yacht-anchored-in-front-of-one-of-Lastovo's-gunboat-tunnels-(3)

Cruising Charter to Croatia

As is the case with so much of the Mediterranean, to sail in Croatia is to take a journey through time. Centuries before the birth of Christ, Greeks traded amphoras of oil, wine and grain across these waters. During the first millennium, the Romans built lavish palaces and ...read more

m123728_13_01_171012_PMA_02901_9999

Alicante Announced as an Ocean Race Europe Stop

The Ocean Race Europe, a new event in offshore sailing, will include Alicante as one of four stopover cities. This European offshoot of the former Volvo Ocean Race will include the biggest change to the racing rules under the new title—fully crewed IMOCA 60s will join the ...read more

01-LEAD-doublehanded2

Preparing for a Doublehanded Race

A few months ago we took a look at the development and attraction of doublehanded racing (Two to Tango, June/July 2020). Hopefully, that served to whet your appetite. If so, the question becomes: “How do I get started? The good news, as we explained in Part 1, is that if you are ...read more

01-LEAD-Day-three---dolphins.-300-dpi

A Key Approach to Passagemaking

How you approach offshore sailing is key to the success of each passage. In addition, some of the most valuable, even crucial attitudes and skills may not be either learned or valued in everyday life on shore and may even fly in the face of talents that are greatly admired and ...read more

OceanVoyagesInstitute-2048

Point of SAIL: Mary Crowley of the Ocean Voyages Institute

In this episode of Point of SAIL, Principal Editor Adam Cort talks with Mary Crowley, founder and executive director of the Ocean Voyages Institute, a not-for-profit based in California that has been both educating sailors and working to preserve the health of the world’s ocean ...read more

01-Ocean-Voyages-Institute_PHOTO-READY_1_pg

Tracking and Catching Plastic Waste

Plastic waste—in the form of everything from plastic soda bottles to abandoned fishing nets—constitutes a major threat to the health of the world’s oceans. Giving the immense size of an ocean, though, actually finding all the plastic floating around out there in a time-efficient ...read more