Fuel Economy

A few folks have asked about fuel cost. This is something I have taken lots of interest in. The money certainly matters to me, but I also have a strong sense that we shouldn’t be consuming more fossil fuels than we have to. I have been driving hybrid and electric vehicles for years now, and have made a point of slowing my highway speeds to optimize fuel usage.

In fact, it was my experience with cars that influenced my boat decisions. I wasn’t sure whether I’d be happy going slow. For the most part I am.

My boat was originally delivered with a 165 hp diesel. It currently has a 250 hp diesel. I think of it as a poor person’s fast trawler. I can cruise all day at speeds up to about 15 mph if I want to. It’s a semi displacement hull form, fairly narrow by modern standards and easily driven at a wide range of speeds.

What’s the bottom line? I’m going to use US measurements here, but have a wide variety of metrics. To me the number that matters is mpg.

For my 2018 voyaging I’ve kept careful track of fuel and my consumption for the trip so far has been 4.0 mpg. My average over the last three years has been slightly better @4.15 mpg.

I should also mention that I have a generator as well that shares fuel with the main motor. I use it for cooking, hot water, air conditioning when needed, and battery charging if I’m in one place for days without a plug in. But generally speaking if I’m on the move it doesn’t use much fuel compared to the propulsion motor. Its use is included in my stats.

A lot of boating folks talk about gallons per hour (gph). I guess that’s interesting, but for voyaging the mpg figure makes more sense to me. Here’s some easy math. For a basic great loop voyage of 6,000 miles I’ll use about 1,500 gallons @4 mpg. At $4.00 per gallon that’s $6,000.

I should also say that I have tankage for about 220 gallons. So my range on average is about 800 miles.

So that’s the basics, and it’s not a bad story. Keep in mind that looping 6,000 miles will take a year, so that’s $500/mo for fuel.

Digging deeper into this, my average moving speed to get these numbers has been about 7.3 mph. This is key. Fuel consumption is related to speed. The faster you go the lower the mpg.

Drawing from this year’s experience, the first 400 miles of my trip was through the Trent Severn waterway and inside passage up to Parry Sound. I went at my slow cruising speed of 6.5 – 7.5 mph and got 5.1 mpg. Heading out into rougher open waters of the northern section of Georgian Bay and North Channel I traveled for a day at 11-12 mph and then more moderate speeds of 7-10 up the St Mary’s river, and got about 2.5 mpg on that segment.

My plan for the rivers is to go slow when in slack water or with a favourable current, and I expect to get > 5 mpg under those conditions. At the same time I have the ability to speed up to make deadlines or fight adverse current, which I will do selectively. As long as I maintain this discipline my fuel consumption will remain reasonable.

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