Fuel Economy Monitoring?

[Art]

Using a boat 200 hours engine run time per year at 7 knots cruising speed = 1400 nm annually traveled.

If the boat's drive line accomplishes 3 nmpg = 467 gallons fuel per year.

467 gallons fuel X 3.00 per gallon = $1,400 annual fuel expense

$1,400 -: 52 weeks = $27.00 per week

Pretty freaking inexpensive for owing and enjoying a boat - if you ask me...
yrmv!

 

[BandB]

Historically fuel has fluctuated greatly in price. Currently it's off lows from a couple of years ago. On my trip this year, I've seen prices from $2 to almost $4 a gallon. With price information available on the Internet, one may be able to reduce speed by a knot to almost double range (in displacement mode ), and bypass areas of substantially higher fuel costs. Should fuel costs reach previous highs (> $5 per gallon), having the knowledge of actual fuel consumption at different speeds, may be the difference between cruiser and dock queen.

Ted

Someone mentioned low fuel prices above. We're lucky. When we decided to get into coastal boating and budget ownership costs, we expected to spend $4 a gallon and budgeted $4.50. Now, with prices low, I hope no one is depending on them staying low. They won't. They never stay low, they never stay high. They go up and down. I remember those who said it's the end of the boat business if prices ever hit $3. Others then said the same at $4. Then prices went to $2. I will never speculate on fuel prices but people must consider all possibilities. When you talk about doubling fuel costs, it's significant. I would assume most here compare prices at different places. They choose to save $0.30 per gallon. Not big money in the scheme of things, but it's important. We saved $0.30 on 1500 gallons yesterday vs where we're headed today.

For most boaters, fuel is not a big issue, but for most boaters it is at least somewhat important as a cost.

It does lead to dock queens. If money is tight at the moment, the marina raised prices this year, I had some major maintenance, my car had to be replaced, now I'd like to go cruising and four days will cost me $200 in fuel, that is totally discretionary spending and it's the first thing to be cut. The marina cost is much more than fuel, but I can't get by without paying it.

 

[Robvald]

well said!

 

[Robvald]

For a displacement cruiser fuel burn optimization is mental masturbation.

So you burn 2.8 GPH and work out a way to be 10% more efficient.

The savings over a month wont buy a case of beer.

well said!!

 

[BandB]

Using a boat 200 hours engine run time per year at 7 knots cruising speed = 1400 nm annually traveled.

If the boat's drive line accomplishes 3 nmpg = 467 gallons fuel per year.

467 gallons fuel X 3.00 per gallon = $1,400 annual fuel expense

$1,400 -: 52 weeks = $27.00 per week

Pretty freaking inexpensive for owing and enjoying a boat - if you ask me...
yrmv!

Well, not using it at all would be cheaper. Now, would you say the same if you used the boat for 800 hours a year and covered 10,000 nm and averaged 1 nmpg for $10,000 or 192.31 per week?

Or what if it was 1000 hours a year and covered 18,000 nm and averaged about 0.33 nmpg for $162,000 or $3,115 per week?

It's relevance is based on boat and usage and the individual. What may be relevant to one person isn't to another. Even $1,400 a year is relevant to a lot of people, to the vast majority of all people in the world. However, for all of us, it's a discretionary cost and the easiest single cost to change.

 

[dhays]

This thread caused me to look.
I've spend a bit under $1,450 in fuel in the first year of ownership. In that time I put a bit over 250 hours on the boat.

I just filled up the tanks again however with another $480 of fuel.

 

[Art]

This thread caused me to look.
I've spend a bit under $1,450 in fuel in the first year of ownership. In that time I put a bit over 250 hours on the boat.

I just filled up the tanks again however with another $480 of fuel.

I was close with general $1400 annual fuel cost in post #31

 

[dhays]

I was close with general $1400 annual fuel cost in post #31

Yup, that is what prompted me to look.

I just hope that I spend more money this year in fuel! Maybe I can hit $2,000?

 

[Art]

Yup, that is what prompted me to look.

I just hope that I spend more money this year in fuel! Maybe I can hit $2,000?

With new engine [you lucky dog!!] bet you will spend more time cruising!!

 

[Simi 60]

The simplest way to have no depreciation cost is to purchase an older boat..

Pretty much - we couldn't give a jot about depreciation.
Previous owner took the 90% haircut over 10 years for us.
Financially we are way in front vs land based living.

 

[Simi 60]

Fuel usage about $6000/ year here @ $5.29/gallon - $1:40/l average.
But zero/mth in mooring/marina fees

 

[FF]

"I hope no one is depending on them staying low. They won't."

As long as there is not a revolution , or government seizure , and the fracking industry is allowed to function , unless there is a world wide disaster oil at $-50 a BBL looks solid.

 

[what_barnacles]

"I hope no one is depending on them staying low. They won't."

As long as there is not a revolution , or government seizure , and the fracking industry is allowed to function , unless there is a world wide disaster oil at $-50 a BBL looks solid.

You can add global warmists kept out of power to that list.

 

[ranger58sb]

I like having more precise and we have compared all curves we have developed to those from our boat builder and/or tests that were conducted by them or others. Whether I have a true need to know or not, I like knowing. Then there are those occasions I do have a need and I have that information readily available.

Not saying this is critical for anyone else, but for me it's an absolute desire to know.

I'd like to know more precisely too... but due to the cost of knowing, it's not an obsession for me. Close enough is close enough.



-Chris

 

[O C Diver]

"I hope no one is depending on them staying low. They won't."

As long as there is not a revolution , or government seizure , and the fracking industry is allowed to function , unless there is a world wide disaster oil at $-50 a BBL looks solid.

In case you missed it, there was a significant pull back in fracking. In many areas, fracking was profitable at $75 a barrel. When oil prices nose dived a couple of years ago, a number of fracking companies failed leaving investors and banks to fight over the crumbs. Banks are not as excited about investing in that industry at $50 a barrel.

Ted

 

[BandB]

"I hope no one is depending on them staying low. They won't."

As long as there is not a revolution , or government seizure , and the fracking industry is allowed to function , unless there is a world wide disaster oil at $-50 a BBL looks solid.

History says it will at some point go up. Then sometime after that back down some. I can't tell you when or what the cause will be, but oil prices have always been cyclical. There are any number of things that can cause that. It can be war, revolution, artificial. I'll repeat. Don't base your entire boat ownership on fuel prices remaining where they are today. Diesel was $3.97 five years ago, $3.83 three years ago.

Cycle over last 20 years has been, drop for 2, rise for 10, drop drastically in one year then rise for 5, then drop for 2. Historically, the time has varied, but it has always reached it's previous high again.

 

[Bigsfish]

My first off-shore boat was gas fed, I paid 30 cents per gallon back then. [emoji16]

 

[rwidman]

One could spend thousands on fuel monitoring equipment and save a few dollars per moth on fuel.

On the other hand, one could calculate the theoretical hull speed of his boat and run at or below that for good economy and use the thousands of dollars saved in monitoring equipment to buy more fuel.

I have a spreadsheet that shows hours and fuel purchased since I bought the boat in 2008. It show about 1.9 GPH. That's an average over nine years at 7 knots.

There's a recent post from a guy who bought a new boat with the same hull as mine but had a special low RPM, low HP engine installed in it. He posted his fuel calculations and at 7 knots (just slightly above the theoretical hull speed), his fuel burn was the same as mine.


BTW: My estimated depreciation over nine years is greater than my dockage cost or fuel cost. And I bought the boat used. If you want to save money, don't buy a boat.

 

[Ski in NC]

I have not been impressed with the accuracy of flowscans et al on low consumption engines. Measures fuel in, measures fuel out. Each measurement has some inaccuracy. Subtract two numbers that are close to each other and the inaccuracy can become very large.

Burning 50gph, the combined inaccuracy is relatively small. Burning 3gph, it can be huge.

Not worth it to instrument such a boat in my opinion.

 

[BandB]

I have not been impressed with the accuracy of flowscans et al on low consumption engines. Measures fuel in, measures fuel out. Each measurement has some inaccuracy. Subtract two numbers that are close to each other and the inaccuracy can become very large.

Burning 50gph, the combined inaccuracy is relatively small. Burning 3gph, it can be huge.

Not worth it to instrument such a boat in my opinion.

The engine manufacturer's systems seem far superior to Floscan and I think the real beneficial applications are as you say, boats using more fuel, typically planing or at least semi-displacement.

If you're talking about engines burning 8 gph at the low end and 148 gph at WOT then it's of great value. Also on planing boats you might be surprised at how different the curves are from boat to boat. We have one boat that nmpg does not change between 1250 RPM/15 knots and 2000 RPM/36 knots. However, another boat we've tested gets twice the nmpg at 1200 RPM/12 knots as it does at 2000 RPM/28 knots. Pretty much same engines in the two boats but very different hulls. Center console with triple Yamahas we have curves on gets 28% more nmpg at 26 knots than it does at 11 knots, range goes from 392 nm at 11 knots to 503 nm at 26 knots. Counter-intuitive to most people.

 

[Ski in NC]

Modern electronic diesels, be it common rail or electronic unit injector, use an algorithm to determine fuel flow. It is not actually measured. In the dyno lab they determined that at a given rpm, % load, injector open time, fuel pressure, charge air pressure, etc, etc, the engine was burning X gph. All over the performance database at any given spot they assigned to it the actual gph they measured. Those numbers have proven to be quite accurate, unlike the flowmeter based systems.

There are a lot of reasons to not like computer engines (bugs, flaky sensors, lightning, etc) but having real time data available for all the important engine parameters is very nice.

 

[FF]

"Burning 50gph, the combined inaccuracy is relatively small. Burning 3gph, it can be huge.

Not worth it to instrument such a boat in my opinion."

Bought my Flow Scans at the Danis flea market , new in the box for $300.

With a long trip like the loop or an ICW run they can be brought very close .

Sez the boat used 74 gal and 72 goes into the tank, its close enough for me.

The fun is cracking the throttle , running the 6-71 at a lazy 1800 (our Flank) and watching the fuel flow reading!

GASP!

 

[O C Diver]

Modern electronic diesels, be it common rail or electronic unit injector, use an algorithm to determine fuel flow. It is not actually measured. In the dyno lab they determined that at a given rpm, % load, injector open time, fuel pressure, charge air pressure, etc, etc, the engine was burning X gph. All over the performance database at any given spot they assigned to it the actual gph they measured. Those numbers have proven to be quite accurate, unlike the flowmeter based systems.

There are a lot of reasons to not like computer engines (bugs, flaky sensors, lightning, etc) but having real time data available for all the important engine parameters is very nice.

My Tier 2 (mechanically injected, electronically controlled) John Deere 4045 has that system of fuel consumption monitoring. Has proved to be quite accurate.

Ted

 

[Humancell]

Scott, I came into this world a couple of years ago with broadly similar background and curiosity. Modern CRD motors use a different more accurate method and the data is available in pretty much every standard install, but with a mechanical motor measuring fuel flow is trickier than it first appears because it requires two sensors, on for feed and one for return. And the return is likely to be at a higher temperature. So it's easy to get an approximation but difficult to get a really accurate net real time consumption. I'd suggest a +/- 5% tolerance would probably be a realistic goal for common installations. Vendors may claim better, but I remain dubious of claims of perfect accuracy across the entire range of operation.

Given that, it seems to me to be of low value on the sorts of boats typically chosen for looping, other than to establish a static curve showing speed vs fuel burn. If you have a common design like I do this information can be obtained from established sources and to a certain degree be refined through empirical observation. Safe to say that the slower the speed the better the MPG on any non-planing boat, it's just a question of what the curve looks like. The universal way to improve economy is to slow down.

Optimizing for current and/or varying wind/wave/load conditions is maybe interesting, but I'm not sure it's truly useful for most of us. I decided it wasn't of enough value to me to pursue. If I were regularly operating in strong current I might reconsider, but the majority of the loop is in relatively still waters, so the static graph can be used to guide operation. Bottom line: fun to have but pretty far down the list. There are no shortage of things to tinker with and spend $$ on as you can see elsewhere in the forum.

Hope this makes sense and helps. It's worth digging into the drivers of fuel consumption in advance to inform your boat buying decision and itinerary if fuel economy is important to you, but once underway I think it sort of fades away for most operators.

I appreciate all of the various replies on this thread, and will comment on a few. Your reply summed up what I believed, and confirmed it.

My questions are related to my investigation of a first "looper" boat, and trying to understand how to create the "static curve" that you mention. As I am planning my trip, exploring the Mississippi and its tributaries, and eventually the East Coast run to get to the great lakes, I'm not in a rush, but want to get a handle on speed - which relates to fuel consumption - and time - which determines how far I get and when.

I completely understand the "go slower and you burn less fuel", but I do want to understand that static curve to better understand my trade-offs.

As for the costs - and I'll comment on one or two of the other posts - I'm not worried about depreciation (as I'll be buying used) as much as fuel, operating, and marina costs. And per marinas I'll be planning to anchor out as much as possible.

I do understand many people are using their boats leisurely, however I do have a lot of ground I want to cover over several years. If I was cruising each weekend through the year for 52 weeks, that's 832 hours a year. I'm almost more worried about an engine rebuild after a year or two!

All of this has been great input to assist me in looking at boats ... and thinking about the various ways to better understand GPH/MPG ... to allow me to think through my plans.

 

[Humancell]

Typical compensation is to run at a slower than planned speed for the first 1/2 or more of the trip, then as you get closer and more confident that you have extra fuel, step it up a bit. But it's really only done that way because until modern diesels, there was no easy way to calculate NMPG. With that constraint removed, you can make better time, and with greater confidence in your fuel needs.

Yep! I like this thinking ...

 

[Humancell]

And it appears not many seem very concerned about it before they have the boat. It never seems to occur to people to get a smaller boat or a FD boat that would eliminate or greatly reduce the amount of posting here about monitoring and minimizing fuel burn.

This is *EXACTLY* what I am concerned with, and want to make sure that I investigate and understand as I explore different purchasing options.

 

[Humancell]

Seems to me that in general, former sailors and those of relatively modest means, such as myself, tend to purchase boats that use less fuel and continue to consider fuel consumption carefully. I'm not unusual in creating a table of rpm/gph/speed and use it to determine cruising speed trying to optimize that mix.

This is what I am considering ... and wanting to automate if possible. But it does sound like post-purchase it becomes potentially easy to simply build the table/curve by sampling the various readings over time and getting to know the boat.

 

[Humancell]

Using a boat 200 hours engine run time per year at 7 knots cruising speed = 1400 nm annually traveled.

If the boat's drive line accomplishes 3 nmpg = 467 gallons fuel per year.

467 gallons fuel X 3.00 per gallon = $1,400 annual fuel expense

$1,400 -: 52 weeks = $27.00 per week

Pretty freaking inexpensive for owing and enjoying a boat - if you ask me...
yrmv!

But ...

Using a boat 832 hours engine run time per year at 7 knots cruising speed = 5824 nm annually traveled.

If the boat's drive line accomplishes 3 nmpg = 1941 gallons fuel per year.

1941 gallons fuel X 3.00 per gallon = $5,824 annual fuel expense

$5,824 -: 52 weeks = $112.00 per week

====

If the boat's drive line accomplishes 2 nmpg = 2912 gallons fuel per year.

2912 gallons fuel X 3.00 per gallon = $8,736 annual fuel expense

$8,736 -: 52 weeks = $168.00 per week

Still not a huge sum ... but these are the numbers I'm juggling and wanting to better understand how to stay on top of.

 

[BandB]

But ...

Using a boat 832 hours engine run time per year at 7 knots cruising speed = 5824 nm annually traveled.

If the boat's drive line accomplishes 3 nmpg = 1941 gallons fuel per year.

1941 gallons fuel X 3.00 per gallon = $5,824 annual fuel expense

$5,824 -: 52 weeks = $112.00 per week

====

If the boat's drive line accomplishes 2 nmpg = 2912 gallons fuel per year.

2912 gallons fuel X 3.00 per gallon = $8,736 annual fuel expense

$8,736 -: 52 weeks = $168.00 per week

Still not a huge sum ... but these are the numbers I'm juggling and wanting to better understand how to stay on top of.

That's all based on every weekend of the year and 16 hours per weekend. Doing weekend cruising you're definitely not going to average 8 hours a day as you'll be doing other things, not always moving. Then where are you doing 52 weeks a year?

Looking ahead think of the Loop. You can go 6000 miles or 8000. Let's go with 6000 nm. If you're getting 2 nmpg, that's 3000 gallons or 3 nmpg that's 2000 gallons. At $3 per gallon, it's $9000 or $6000.

Now, let's look at a Beneteau Swift Trawler as a representative of semi-planing. At 7 knots, you get 2.1 nmpg, at 10 knots you get 0.7 nmpg, at anything from 12 to 21.3 knots, you get 0.5 nmpg. On the performance curve for that boat you see huge differences. So you could do 6000 nm with only 2857 gallons but if you decided to spend half your time at 10 knots you'd use 4285 gallons. And, if you decided 1/3 of your time at 7 knots, 1/3 at 10 knots and 1/3 at 15 knots, now you're more like 5485 gallons. So, obviously on this boat you can impact your fuel cost by as much as $7,884. Suddenly the insignificant fuel cost may not be as insignificant.

 

[Panacea123]

Have logged about 4000 nm on current boat
Have had flow scan in the past on gas boats (current diesel no flow scan)
They are great, but can not justify the cost for twin diesel.
As others have said use a fuel burn curve from the manufacturer and log your experience.
You'll find your sweet spot