Saturday, February 25, 2012

Summer Trip Planning - Fuel Cost

World events and conditions are causing fuel prices to go up, up, up.  There's speculation that gasoline prices will hit $5.00 a gallon by the Memorial Day Holiday.  And, generally diesel prices are higher than gasoline prices.  Recently I was in Canada, and considering the dollar exchange and the cost per liter fuel prices were shocking, at $4.62 per gallon (US) of gasoline and diesel at the pump was $4.69 (US).  As a result, I've heard from plenty of boating pals that they are planning to do the "Staycation" and cruise locally versus going any far distance such as Desolation Sound or the Broughtons.  Several said instead of going north, they'd go south and spend time in the South Sound.

The MV Independence has a six cylinder, naturally aspirated Ford Lehman diesel.  Over the past 20 years of cruising I've found this motor to be not only reliable but economical too.  I monitor every trip by noting the RPMs, nautical miles, the average speed, and distance traveled and enter these numbers into my log book.  Then when I get fuel I can make a good estimation of miles per gallon per RPM.  Last year I made a conscious effort to reduce my cruising RPM by 100 from 1750 to 1650 RPMs.  Sure this slowed me down, but I made sure to plan my trip to take advantage of the current.  As a result I was able to cruise almost 600 nautical miles with an average speed of 5.92 knots and a 1.38 GPH.  If I would have stayed at 1750 RPM like I have in previous years a similar cruise had an average speed of 5.98 knots at 1.63 GPH.  Hmm?  100 RPMs lower, saving me 0.25 gallons per hour, but only an average speed difference 0.06 knots?  I'd say that cruising at a higher RPM is not worth the cost in fuel.  I went back through years and years of trips up the coast comparing the miles traveled, average speed, fuel consumed, and the results were the same year after year - lower RPMs = cost savings, without sacrificing much speed.

However "dock talk" spurred a curious assumption, "Sure you're traveling slower and saving fuel, but in the end you'll burn more fuel because it takes you longer to get there."  Could that be true?  Was I just fooling myself?  So once again I delved into the MV Independence log book, looked over 20+ years of nautical miles, speed, RPMs, and fuel fill ups and came up with the following table which proved to me that there was a "sweet spot" where RPMs, and fuel cost are optimized.  I thoroughly explained the table to my "dock talk doubters" and one-by-one they all agreed, you can save cost by traveling slower.  You just need to determine what is best for your boat.
Click on chart to get a better view

I then looked at the miles a typical trip to Desolation Sound (like last year's) would cost based on the calculations in my table.  Again, I said "Hmm?"  The cost varied from less than $600 to over a $1,000 based on an estimated fuel cost of $4.76 per gallon, and depending on RPM and currents.  So, will we stay close to home, or will we travel up the coast for our 23rd year?  We will keep an eye on fuel costs, and plan the tides and currents to and from our destination.  If the current is not right, we'll make plans to stay until it is, or plan a shorter cruising day.  I'd recommend that you too evaluate your RPM, speed, and fuel rate so you too can find your "sweet spot" and then plan the tides each day for each cruising leg so you can have a great economical summer cruise.  We will also mentally adjust to recognize that it is about the journey not the destination.  For me, the worst day cruising still beats the best day at work.

Oh, and one more thing... make sure your boat's bottom is clean and free of any growth.  Any growth such as mussels or barnacles growing off a transducer, propeller, or on your rudder will affect your speed. Now I always check my boat bottom prior to any summer cruise to ensure it is growth free.  Here's an excerpt from my log book describing what growth can do to speed.

July 24, 2000  4322.6
Saturday.  Day 1 of our trip north.  The whole thing started out a little stressed.  Skies were gray and the clouds low.  We got a wee bit of a late start, but it was okay.  As we headed up Budd Inlet we weren’t making the speed as I thought we should.  We were only doing 6 kts and the engine temp was a bit high.  So we pulled into Boston Harbor where I proceeded to scuba dive the boat.  My wife drove up from town to help and brought me a nice hot cup of coffee.  The prop was covered with barnacles, it took me 20 min. and 1,000lbs of air to scrape those bastards off.  Also the engine intake had a “beach ball” sized clump of mussels growing off of it.  That’s why the engine was running a bit hot.  We left Boston Hbr. about 0910 and immediately noticed an increase in speed of over 1kt. and the engine temp. was much cooler.  Besides it was better to see Mom again; the kids were much happier than leaving her at the dock this morning.  The morning clouds are burning off and it looks to be a nice day.  No wind.  So onward north again.

For more information on Tides and Current planning see my previous blog posts at:
Happy Cruising!

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