Hello, Is it common to run a single engine when making long (slow) crossings? I've read of people doing this to reduce hours (alternate engines) and get better fuel economy. They say it's better to run one engine at a higer RPM than two at low RPM. Thanks, Jason

This is a much discussed question - with no simple answer... Certainly, shutting down one engine reduces engine hours. But whether it actually saves fuel, is open to question. In general, it works most effectively on vessels equipped with variable pitch/featherable props. With fixed-pitched propellors, the drag associated with the "dead" prop, plus the yaw drag (due to offset thrust), can easily offset the potential gain from shutting down one engine. Bottom line: each situation must be analyzed individually. On Sno' Dog, our PDQ 34 powercat, our best guess is that some fuel can be saved by running on a single engine, but only at speeds below 6 knots. Above this speed, we're better off running both engines. (I've posted some comments on this subject on SnoDogLog, see: www.snodoglog.com/Performance.html.) There are other considerations as well. Some mariners hesitate to shut down an engine at sea. (Restarting has a lower reliability than a running engine). Also, not all boats are set up to allow proper lubrication to the freewheeling shaft seal. (This appears not to be problem on our PDQ.) For someone trying to extract maximum range from their boat, this practice probably does offer some benefit. In practice, however, few of us ever push our boats to the limits. If you do plan to do this, approach it as intelligently as possible. Don't assume that you'll cut your fuel burn dramatically by cutting one engine - unless you have actual data to back up your assumptions. Henry aboard Sno' Dog - still in beautiful downtown Ft. Lauderdale (New River) www.snodoglog.com On Feb 4, 2010, at 4:09 PM, R. Jason Adams wrote: > Is it common to run a single engine when making long (slow) crossings? > I've read of people doing this to reduce hours (alternate engines) and > get better fuel economy. They say it's better to run one engine at a > higer RPM than two at low RPM. > > Thanks, > Jason

                             Bert Harrott

For the price of a variable pitch--feathering prop one can buy a reliable fourstroke outboard motor with a fixed prop that is pitched precisely to the vessel's characteristics. This outboard may then be raised clear of the water removing all drag, increasing fuel milage . The resulting efficiency will further sway the cost factor debate onto the side of outboard powered cats. Bert Harrott ----- Original Message ----- From: "Henry Clews" <hclews@aol.com> To: "Power Catamaran List" <power-catamaran@lists.samurai.com> Sent: Thursday, February 04, 2010 2:15 PM Subject: Re: [PCW] Single engine for long crossings > This is a much discussed question - with no simple answer... > > Certainly, shutting down one engine reduces engine hours. But whether it > actually saves fuel, is open to question. In general, it works most > effectively on vessels equipped with variable pitch/featherable props. > With fixed-pitched propellors, the drag associated with the "dead" prop, > plus the yaw drag (due to offset thrust), can easily offset the potential > gain from shutting down one engine. Bottom line: each situation must be > analyzed individually. > > On Sno' Dog, our PDQ 34 powercat, our best guess is that some fuel can be > saved by running on a single engine, but only at speeds below 6 knots. > Above this speed, we're better off running both engines. (I've posted > some comments on this subject on SnoDogLog, see: > www.snodoglog.com/Performance.html.) > > There are other considerations as well. Some mariners hesitate to shut > down an engine at sea. (Restarting has a lower reliability than a > running engine). Also, not all boats are set up to allow proper > lubrication to the freewheeling shaft seal. (This appears not to be > problem on our PDQ.) > > For someone trying to extract maximum range from their boat, this > practice probably does offer some benefit. In practice, however, few of > us ever push our boats to the limits. If you do plan to do this, > approach it as intelligently as possible. Don't assume that you'll cut > your fuel burn dramatically by cutting one engine - unless you have > actual data to back up your assumptions. > > Henry > aboard Sno' Dog - still in beautiful downtown Ft. Lauderdale (New River) > www.snodoglog.com > > On Feb 4, 2010, at 4:09 PM, R. Jason Adams wrote: > >> Is it common to run a single engine when making long (slow) crossings? >> I've read of people doing this to reduce hours (alternate engines) and >> get better fuel economy. They say it's better to run one engine at a >> higer RPM than two at low RPM. >> >> Thanks, >> Jason > _______________________________________________ > Power-Catamaran Mailing List

                             Bert Harrott

>From a net result stand point, managing your fuel load and buying more fuel when you find a good price, might be a more affective method of fuel savings. No up front investment, no maintenance, no repairs, just cost savings. If I were buying a new or used Cat with a long voyage in my direct future, then other fuel savings investment might be worth while. But your voyage would have to be long enough to amortize the investment of thousands of dollars. My planned usage is 3-4 months a year, under this usage, I think I can manage fuel purchases for a better net result. Jim Meader Broker/Owner RE/MAX Today DRE# 00493029 Jim@rmtmail.com -----Original Message----- From: power-catamaran-bounces@lists.samurai.com on behalf of Noelle Harrott Sent: Thu 2/4/2010 4:43 PM To: Power Catamaran List Subject: Re: [PCW] Single engine for long crossings For the price of a variable pitch--feathering prop one can buy a reliable fourstroke outboard motor with a fixed prop that is pitched precisely to the vessel's characteristics. This outboard may then be raised clear of the water removing all drag, increasing fuel milage . The resulting efficiency will further sway the cost factor debate onto the side of outboard powered cats. Bert Harrott ----- Original Message ----- From: "Henry Clews" <hclews@aol.com> To: "Power Catamaran List" <power-catamaran@lists.samurai.com> Sent: Thursday, February 04, 2010 2:15 PM Subject: Re: [PCW] Single engine for long crossings > This is a much discussed question - with no simple answer... > > Certainly, shutting down one engine reduces engine hours. But whether it > actually saves fuel, is open to question. In general, it works most > effectively on vessels equipped with variable pitch/featherable props. > With fixed-pitched propellors, the drag associated with the "dead" prop, > plus the yaw drag (due to offset thrust), can easily offset the potential > gain from shutting down one engine. Bottom line: each situation must be > analyzed individually. > > On Sno' Dog, our PDQ 34 powercat, our best guess is that some fuel can be > saved by running on a single engine, but only at speeds below 6 knots. > Above this speed, we're better off running both engines. (I've posted > some comments on this subject on SnoDogLog, see: > www.snodoglog.com/Performance.html.) > > There are other considerations as well. Some mariners hesitate to shut > down an engine at sea. (Restarting has a lower reliability than a > running engine). Also, not all boats are set up to allow proper > lubrication to the freewheeling shaft seal. (This appears not to be > problem on our PDQ.) > > For someone trying to extract maximum range from their boat, this > practice probably does offer some benefit. In practice, however, few of > us ever push our boats to the limits. If you do plan to do this, > approach it as intelligently as possible. Don't assume that you'll cut > your fuel burn dramatically by cutting one engine - unless you have > actual data to back up your assumptions. > > Henry > aboard Sno' Dog - still in beautiful downtown Ft. Lauderdale (New River) > www.snodoglog.com > > On Feb 4, 2010, at 4:09 PM, R. Jason Adams wrote: > >> Is it common to run a single engine when making long (slow) crossings? >> I've read of people doing this to reduce hours (alternate engines) and >> get better fuel economy. They say it's better to run one engine at a >> higer RPM than two at low RPM. >> >> Thanks, >> Jason > _______________________________________________ > Power-Catamaran Mailing List _______________________________________________ Power-Catamaran Mailing List -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.