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.

NigelCalder_4

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

Beneyteau-Excess12

Boat Review: Excess 12

Groupe Beneteau, builder of Lagoon catamarans, has introduced a new multihull line called Excess. The first of the boats to reach U.S. shores at the Annapolis boat show was the Excess 12, a 38ft 6in design based on the popular Lagoon 40. The thought process behind this new boat ...read more

Spindriftracing

Extreme Sailing: No Piece of Cake

It can be easy to take for granted the incredible performance of today’s most cutting-edge grand prix racing boats. The latest crop of full-foiling 75ft America’s Cup monohulls, for example, were all up on their foils and even successfully tacking within hours of their first ...read more

Solar-Dinghy-pump-photo

Gear: Solar Powered Dinghy Pump

Tired of forever finding your dinghy or open daysailer filled with water when you arrive to go sailing? For years, sailors and engineers have sought a solution to this seemingly eternal problem, and now it appears the folks at Sea Joule Marine may have finally found it in their ...read more

BestBoatPromo-03

Best Boats 2020

How’s this for a thought experiment: imagine setting a diminutive Tiwal 2 inflatable dinghy alongside a Catalina 545 cruiser? It would be hard to imagine two more different watercraft, and yet they are both still very much sailboats. They are also both winners in this year’s ...read more

Hanse-675

Video Tour: Hanse 675

This past fall at the Annapolis Sailboat show, we had a chance to catch up with Hanse’s  Maxim Neumann, who kindly provided us a tour of the company’s new flagship, the Hanse 675. An impressive, well-built production yacht that boldly ventures into maxi-yacht territory, the ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com Be thrifty with propane  If you like to cook on board, the propane tanks supplied as standard with many modern yachts won’t get you far. Whether we bake bread or not, the one thing we all do is boil ...read more