Our actual fuel burn (Lehman 120s)

rwidman said:

Why not remark them to represent gallons, not inches?

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They're already marked in inches.

I had to do the calculations initially without draining the tanks. Knowing the shape and dimensions I could know what an inch drop in fuel level meant.

SS, would you care to share the spreadsheet so we can have a template to work from?

manyboats said:

.............. measuring fuel consumption w a dip stick or sight tubes is best done by starting w empty tanks and filling 5 or 10 gallons at a time marking or measuring the fuel on the stick/tube. ....................

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If we're going to get down to the nitty and the gritty, we should also realize that on many boats, the last few gallons of capacity cannot be used because the fuel pickup not at the very bottom of the tank. So, you might put 100 gallons in n empty tank but run out of fuel after using just (for example) 95 gallons.

Rwidman,
Well you can't see the unusable amount in the sight tubes and you can't determine where it is without running out of fuel. But all this measuring very carefully and computing the last drop of fuel won't gain anything for 97% of us so perhaps out efforts would be better served talking about smaller boats that burn less fuel. Full disp will work but there's hardly enough to go around. But measuring fuel in the tank to determine burn rate won't require using the very bottom of the tank anyway and anyone running that close to the bottom of the tank shouldn't be in that situation. But running on the last 2" of fuel in the tanks thinking about the height of the sump tubes could be a sobering thought.

My gauges show empty (0 inches) even when there is some fuel remaining and available.

Our Cheoy Lee 46 has twin FL120s, and probably weighs in around 60K lbs (the original CL manual states a dry displacement of 50K lbs). After spending the summer cruising and working and measuring the tank before and after fills and usage, we averaged 2.5 gph at an average of 1400 rpms and about 7 kts.

One our last crossing of the Strait of Juan de Fuca we were trying to get across a little quicker due to a small craft advisory. So I kicked it up to 1650 rpms for 5 of the 8 hours, and that increased the gph for that trip up to 3.9.

Still very happy with our boats fuel economy. Now to paint the bottom and get a little better mileage next summer...

rwidman said:

Why not remark them to represent gallons, not inches?

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The previous owner of our boat who had the entire fuel system replaced-- tanks, hoses, valves--- had the sight tube on each of the four new saddle tanks calibrated in gallons. Very handy to keep track of fuel usage during a trip.

A nice feature of our tanks is that they gravity feed from the bottom so we can, in fact, use every drop that's in each tank. The tank we don't want to run dry is the center day tank as that's the tank the engines and generator normally feed from. But it has an electric sender with a fuel gauge on the helm console so we know how much fuel is in that tanks at any given time. Even though that tank, too, feeds from the very lowest point in the tank we don't let it get much less than a quarter full before transferring new fuel in from the saddle tanks.

For me, fuel burn is only a consideration regarding range. I'm not interested in bragging about my mpg, just want to know if i can get there and back. Measuring fuel 'depth' in inches, liters, meters or gallons is fine I guess, but I sprung for a Floscan that measures gallons used, and I don't have to go poking about in the bilge to see what is left...it's accurate within tenths of a gallon for fuel sent to the the engine.

Haven't fine-tuned my Floscans yet. They read about 30-to-40 percent high. I'm lazy.

jeffnick said:

For me, fuel burn is only a consideration regarding range. I'm not interested in bragging about my mpg, just want to know if i can get there and back. Measuring fuel 'depth' in inches, liters, meters or gallons is fine I guess, but I sprung for a Floscan that measures gallons used, and I don't have to go poking about in the bilge to see what is left...it's accurate within tenths of a gallon for fuel sent to the the engine.

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Range is my consideration as well although fine tuning RPM for economy could be nice.

Because I have only electrical fuel gauges to measure level, I am not comfortable trying to extend my range and I may take on fuel when I don't really need to. I think the most I've ever used was 2/3 of my capacity before filling up.

I looked into a fuel use monitoring system, but for my diesel. it would cost in the neighborhood of $1K and I figured it wasn't worth the investment for me.

manyboats said:

Rwidman,
Well you can't see the unusable amount in the sight tubes and you can't determine where it is without running out of fuel. But all this measuring very carefully and computing the last drop of fuel won't gain anything for 97% of us so perhaps out efforts would be better served talking about smaller boats that burn less fuel. Full disp will work but there's hardly enough to go around. But measuring fuel in the tank to determine burn rate won't require using the very bottom of the tank anyway and anyone running that close to the bottom of the tank shouldn't be in that situation. But running on the last 2" of fuel in the tanks thinking about the height of the sump tubes could be a sobering thought.

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You are the one who brought it up.

I don't think this has been mentioned but measuring fuel consumption w a dip stick or sight tubes is best done by starting w empty tanks and filling 5 or 10 gallons at a time ..................

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Alaskan Sea-Duction said:

SS, would you care to share the spreadsheet so we can have a template to work from?

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Sure. It's on my work computer. Send me an email and I'll send to whoever is interested. I was bored and wrote a small model that has sliders for adjusting tank dimensions (I didn't have exact measurements as I was writing it), so it's useful for any size rectangular tank calculation. I used it on my water tanks as well.

somesailor@gmail.com

Knowing your precise fuel burn and exact range or whatever isn't usually necessary ...just nice to know.

However there are times, if you CAN precisely determine usage... it may help in troubleshooting engine/fuel issues or it may be necessary to run down to the last few drops and it's nice to know you can.

As far as moving to smaller more efficient boats...great topic ... but NOTHING AT ALL to do with this conversation about the actual burn on your Lehman engine and how it was determined as some of us like OUR boats just fine....

Marin,
Except for having too many tanks it sounds like you've got at least close to the ideal fuel system. When I got new tanks I asked for 35 gallon tanks instead of 50 and the fuel pickup off the bottom of the tank and at the low end. I got none of the above. Was furious. Needed to remove the new engine just installed to remove the tanks to make things right so I just let it go. I'm still mad.

rwidman,
Assumably "it" is the anount of fuel remaining under the pickup tube and clearly you started that topic on post #33. It's fly stuff and dosn't warrant further discussion but I like your post #24 about short trips. Very true but even on long trips there is usually (probably 90 percent of the time for most all of us) a very significant amount of engine time (hour meter measured) that is below cruising load and thus consuming much less fuel so that claiming "X" amount of fuel burned per hour gallons to hour meter is only great if one wants to convince himself he's burning considerably less fuel than he or she really is.
Ron you said "Range is my consideration"...
Range? I would think your living in such a populated area there would be places to get fuel almost everywhere.

psneeld,
Had no intention of starting a discussion on smaller boats. It seems I'm surrounded by guys that are VERY worried about fuel consumption and any fool can see that smaller boats is a good solution to that problem. But the fuel consumption issue is (as you say) just "nice to know".

manyboats said:

..............Ron you said "Range is my consideration"...
Range? I would think your living in such a populated area there would be places to get fuel almost everywhere.

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On the AICW, south of Savannah, GA, there is a stretch of nearly one hundred miles with no fuel source without going several miles off the ICW. Knowing in advance that there is enough fuel on board is important here.

The other thing is just planning trips and stops.

Ron,
I obviously have a warped view of what it's like on the east coast. I just thought it was like a city all up and down the coast except some parts of Maine and Florida. Intend to come and visit but still haven't done it. Perhaps someone will make a thread somewhat like my "Long Way Home II" thread. Would really love to see that. Some still think folks in Alaska live in igloos and it seems to some extent the reverse is true.
For a semi-planing hull your Camano Troll is a very efficient boat. Going slow enough you should have little chance of running out of fuel. Turbo Volvo an I right?

Going slow enough makes a semi-planing boat essentially a displacement hull. It may have a less than an ideal displacement shape that's not AS efficient as a hull designed for slow speeds only....but it will be surprisingly efficient nonetheless.

Small boats are just one solution for improving fuel economy....the least desirable solution for most of us that want boating comfortable (any fool can see that )...not just camping on the water which I'll bet some of us did that for years and prefer more room and conveniences.

My solution was one engine and going slow...bringing my fuel budget to the point where I can have both... the bigger boat and enough fun money to enjoy the slow ride. That solution isn't for everyone as we have heard many times...

These shots are the Flowscan pics of a Lehman 120

That's a single isn't it?

manyboats said:

Marin,
Except for having too many tanks it sounds like you've got at least close to the ideal fuel system.

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The previous owner replaced the boat's original three large tanks with five smaller ones that could be installed without having to remove engines or anything else except possibly the transmissions. Originals were cut up in place and the pieces removed, new tanks went in though the floor hatches and past the engines. It's a very common practice when retanking a boat like this.

In operation the engines and generator all feed from the 60 gallon day tank in the bilge. This is filled as needed by gravity from the four saddle tanks, two on each side. If necessary the engines can be valved to feed from any of the saddle tanks. Fuel returns can be valved to go to any tank-- we leave them set to return to the day tank. It's a terrific system and allows us great flexibility to ensure that fuel does not sit very long on the boat.

I have to cruise about 6,000 miles cruising to Rio de Janeiro-Brazil. I have 2xCat 3208. My question, can I cruise little more than an Idle? I can make about 7 MPH and very low consumption to my Hi Star 55.

Sergio "Alemao" Sztancsa, Sent from my iPhone using Trawler

manyboats said:

Ron,
I obviously have a warped view of what it's like on the east coast. I just thought it was like a city all up and down the coast except some parts of Maine and Florida. ......

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Here's a link to a trip I made:

http://www.widman.biz/indigo/Adventures_of_HIGH_COTTON.pdf

An Internet search will turn up hours and hours of reading from other people's ICW trips.

If you don't mind spending a few $, there's a great two hour DVD available here:
Snowbirders Home Page

And of course, there are several books and cruising guides that make good reading.

"I have to cruise about 6,000 miles cruising to Rio de Janeiro-Brazil. I have 2xCat 3208. My question, can I cruise little more than an Idle? I can make about 7 MPH and very low consumption to my Hi Star 55."



Its not the total distance , Its the distance between fuel sources that counts.

No matter your tankage will probably need a bunch of 55g drums lashed in the cockpit .

Since this is a life and death matter it would be worth the time to make a speed/fuel burn graph.


This would easiest be done with borrowing a pair of 12 gal outboard fuel tanks , and using one to fuel each engine.

Then a GPs could let you adjust your speed for say 6K (naut miles not land miles as that is what your chart will show) .

After an hour stop, refill the tank from a measuring can and do it again at 7K.

Could also be done by RPM, 1100,1200,1300, till on the pin.

A graph of this sort will allow you to create a "how goes it" a log of distance covered vs fuel burn.

Quick inspection will let you compare your current DR or fix to the distance remaining , and the speed you can go.

At least 30% reserve for heavy weather should be on board , as boats use loads more energy climbing 10fters than in a flat sea.

FF.

Fred,
How's that going to work in tidal waters? It's the speed through the water that counts for your fuel burn analysis. As that will determine how much fuel you burn. You would need fuel consumption per hour running at a given rpm. Armed w those numbers along the way one can find speed over ground at any given moment by observing the SOG at a given rpm and compare that to what you know the boat will do w no current at that rpm. If your bucking a 1 knot current and your speed through the water w no current is 7 knots at 1600rpm then you know at 1600rpm when your GPS says 6 knots your'e actually going 6 knots OG. Put another way if w the same boat as above when your GPS says 8 knots at 1600rpm your'e going with the current at a rate of of 8 knots but will still be making 7 knots through the water. So the method you presented will work great but only w no current, tidal or otherwise. Your "A graph of this sort will allow you to create a "how goes it" a log of distance covered vs fuel burn." Your log will indicate the distance through the water and not the distance over ground. And there's almost no place without current in seawater. I'm usually not that good at such things so maybe I missed something and am making a fool of myself but I don't see it.

On a typical day's outing, I'm going either 5.5 knots or 8 knots with the engine at the same RPM.

It's not rocket science anymore. Hook your 9000 Series FloScan to your GPS and get real time mpg.
Floscan Instrument Co. Inc.

My boat being a gasser, the unit paid for itself the first year...substantially by reminding me of the consequences of even a little too much throttle, not to mention consumption at 30 mph!

BTW, if you are doing a new installation, you don't need two toggle switches (mpg-or-gph & reset). Get a single bilge pump style switch with a momentary side for reset, and off and on for mpg-or-gph.

jeffnick said:

My boat being a gasser, the unit paid for itself the first year...substantially by reminding me of the consequences of even a little too much throttle, not to mention consumption at 30 mph!

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Since our old gal is powered by a pair of Lehmans... it wouldn't pay for itself over a lifetime.

... and 30 MPH isn't a problem anymore.

I installed a Floscan on my Camano, 220 HP Volvo, It is not something really important to have but very interesting and easy to measure flow rates MPH etc. The installation is not difficult, I wouldn't mind having one on the Monk but I'm not sure if I want to add more wiring to what is already in place.
Steve W

markpierce said:

On a typical day's outing, I'm going either 5.5 knots or 8 knots with the engine at the same RPM.

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If you're on the AICW, that will change with each inlet so you can go from 5.5 to 8 several times per day.

rwidman said:

If you're on the AICW, that will change with each inlet so you can go from 5.5 to 8 several times per day.

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Feels like we're brothers.