Fuel Tank Capacity vs. Useable Fuel Capacity

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Author Topic:   Fuel Tank Capacity vs. Useable Fuel Capacity

Tom W Clark posted 06-20-2005 01:58 PM ET (US)
In another thread about a classic 25 foot Whaler, Larry Goltz stated that he always understood the fuel tank capacity of this model to be the USEABLE fuel capacity, not necessarily the same as the actual volume of the tank.
This is not how I have always understood the fuel tanks to be rated by Whaler. The fuel tank for the classic 25s made after 1985 is 140 gallons (earlier models had a pair of 70 gallon tanks).
I recently had the opportunity to run the tank in my 1988 Revenge 25 Walk Through empty and then refill the tank at a gas station on Saturday. I put 139.5 gallons into that tank which topped it off to the point where gas squirted out the vent.
This morning while cleaning the boat I pulled all the deck plates to allow air to more easily circulate below the fuel tank cover. I wiped the grime off the original placard on the tank, made by Florida Marine Tanks. The placard clearly states the fuel tank capacity is 142 gallons.
It would seem that Larry is correct, but the difference between the two figures is very small, 2 gallons. This observation assumes the fuel pump is calibrated accurately, which they not always are but I have no reason to assume it isn't.
I also know that in my 1983 Outrage 18 the fuel tank capacity according to Whaler is 63 gallons. The capacity on that Florida Marine Tanks aluminum tank was stated as 63 gallons. No difference.
Is the 25 unique in this tank capacity vs. useable capacity difference?

Bulldog posted 06-20-2005 02:14 PM ET (US)
Tom it might matter how the boat is sitting on the trailer, was the part of the tank at the fill and vent ports the highest part of tank. My 77 gallon Revenge tank has the fill and vent outlets about a foot or so back from the front of tank. My Revenge sits with the bow up slightly on the trailer, meaning that the vent outlet would see gas before the front would fill all the way. It's my theory and I'm sticking to it!......Jack
Jerry Townsend posted 06-20-2005 03:38 PM ET (US)
Tom - I believe that the specified tank capacity is just that - and that Larry is a bit askew (now don't tell Larry I said that).
Frankly, the tank manufacturer cannot know the attitude of your boat - or how the boat manufacturer installed that tank - or .... and therefore cannot determine the 'usable' capacity of your tank.
And your experienced difference of 2 gallons (in a 142 gallon tank) - about 1.5% - is small as you point out. A 1.5% error on a tank is pretty good. In your case, your tank may not have been "bone" dry, may have not been level, may not ..... - in other words - the 139.5 gallons may not have filled a dry, level tank. ---- Jerry/Idaho
phatwhaler posted 06-20-2005 03:42 PM ET (US)
My 1996 19 Outrage brochure says I have a 91 gallon tank. The decal on my Florida Marine tank says I have a 87 gallon tank. Interestingly, the 1997 and 1998 20 Outrage, which is the same boat as mine, lists the fuel tank capacity as 87 gallons. I have never emptied the tank and refilled it.
phatwhaler out.
LHG posted 06-20-2005 06:40 PM ET (US)
But then, Jerry, if Tom ran his tank was "dry" (ie engines died), and it only took 139.5 gallons, then the "Useable 140" is correct, and he couldn't use the last 2.5 gallons that it holds?
Actually, I got my information from someone at the factory, who said, at least for my 25, they install tanks slightly larger than stated, as on a boat it generally is impossible to suck every last drop of fuel out of the tank. He was the person who told me the 140 gallons was "useable". Think about all of the adverse conditions you could be in that would affect fuel withdrawl.
As a matter of fact, I have always thought (and could be wrong), that a tank manufacturer is usually the one who states the "useable" capacity as the tank's capacity. So I would think that if the 25 tank is stated as 142 gallons, it may actually hold 145? I just don't know.
But one think I have discovered, is that with the red above deck Tempo/Moeller plastic tanks, they tend to hold less than stated.
Tom, when you filled up the tank from empty, I hope you noted the number of gallons it took for each gradation on the tank gauge. Even though you were on a trailer, that will at least give you some idea of the repeatable accuracy of the gauge. On my 25 in the water at rest, when the gauge is at 1/4, I only have 20 gallons, 1/2 = 50 gallons. As the guage just hits "E", the engines die! I had to spend an entire night anchored 1/4 mile off the beach in Lake Michigan to find this out
Tom W Clark posted 06-20-2005 07:04 PM ET (US)
Well, it's splitting hairs a bit, but I now agree with Larry about the tanks in our boats having a useable capacity of 140 gallons.
It is not the tank manufacturer who calculates USEABLE capacity because, as Jerry notes, the tank can be installed different ways. The tank manufacturer simply states the volumetric capacity of the tank. It is the BOAT manufacturer who would state the USEABLE capacity.
Based on my experience, I am confident the tank will actually hold 142 U.S. gallons and that 140 of them are useable under normal operating conditions.
As to how the boat was fueled: it was parked at the gas station with a very slight bow high attitude much as it would be if it were floating, so no loss of capacity was due to the fill being lower than an air pocket in the rear of the tank.
Larry, I did not precisely note the gauge needle position as I was filling but I did look when it was half full and it had taken around 50 gallons, so I am going to use your benchmarks from now on. I suspect our tanks and gauges behave very similarly.
WSTEFFENS posted 06-23-2005 10:17 AM ET (US)
Tom:
You have stumbled onto a potential problem. The gage is not accurate due to the fact that the gage is opperated by a cork float thru a gear mechanism. The tank however is not square in cross section but has a tapered bottom sort of a "V" that makes the gage read weard. Larry is right I also have run out of fuel, before I mapped the tank. Also there should be a sticker close to the "clear" deck plate above the gas gage that says something on the line of "gage only works with boat at rest in water."
To map the tank, do what you did before, suck the system dry, (put it in cans to be used later), launch the boat with dry tank, and tow to a fuel dock. Fill the tank noting the gallons at each mark on the gage. Make a chart and laminate it and tape it to the inside of the clear deck plate and then you know what the gallonage is.
As for inaccuracy, it is a fact of life. Seems when I hit the 1/8 mark I have about 5 gallons, when It runns out, the port engine quits about 2 min before the stbd engine.
Best
LHG posted 06-23-2005 03:49 PM ET (US)
Walt - that's exactly what I have at 1/8 - 5 gallons! I'm paddling as it falls to E. What really confused me is that my 18 Outrage has 15 gallons (1/4 tank) at "E"!
These gauges do have great REPEATABLE accuracy though. One just has to know what they are telling you.
Tom W Clark posted 06-24-2005 01:45 AM ET (US)
Walt,
I haven't stumbled onto a potential problem; the behavior of the gauges on these boats is well known. Nor is it a "problem" if you know what the gauge is really telling you. All it can do is measure the fuel level at the spot where the gauge itself is; it doesn't tell you what the volume of the remaining fuel is.
We all understand how the gauge and float work, but the non-linear readings are influenced far more by the location of the gauge than by the shape of the tank.
You are right, the tank is not rectangular in cross section, but the real reason the fuel gauge takes a long time to come off of "full" and then rapidly goes to "empty" is because the gauge (and especially so on the 25s) is towards the rear of the tank.
These boats always float and run with their bows higher than their sterns and the fuel tank is not level fore and aft. Thus there is always more fuel in the rear of the tank than in the forward part.
Imagine the tank viewed from the side. Cross sectioned this way we will see that it is rectangular, but the rectangle is sloped towards the stern. The fuel level in the tank is level. As the fuel level begins to drop, the void left behind will first appear at the forward end of the tank. Only after being drained quite a ways will the level get to the point where the gauge is and the float begins to drop. Once the gauge float is half way down, most of the tank is empty; the gauge is really only reading what is in the rear of the tank.
The fact that the bottom of the tank is tapered adds to this deception, but it is minor.
The Owner's Manual for these boats explicitly caution against interpreting the fuel gauge unless the tank is level.
I agree with Larry, the gauges have good repeatable accuracy, or should I say they are precise.
And Walt, you are correct about the port motor dying first. That is exactly what happened to me and again it is because of the slope of the tank fore and aft. The fuel withdrawal tube for the port motor is ahead of the withdrawal tube for the starboard motor thus it goes dry first.
My experience also agrees with yours, the starboard motor ran for about another 2 minutes at fast idle speed before it died.
Larry, the difference between the fuel gauges in the 25 and the 18 is the location of the fuel gauge. In the 18 it is more centrally located in the tank and thus suffers less distortion.
andiamo posted 06-24-2005 08:02 AM ET (US)
Depending on where you live and the type of pump the air temperature on the day you filled could account for the 1.5% variance. Around here the law has been changed so that gas stations can now sell gas as if the air temp were 15 degrees c so that they are selling a constant quantity no matter what the air temp. Otherwise, as I understand it, you get more gas when you buy 100 gallons when it is minus 20c than when it is plus 35c and the gas in the tanks and pumps has expanded.
jimh posted 06-24-2005 08:39 AM ET (US)
Tom--Your observation about how the location of the fuel gauge along the longitudinal axis of the tank affects the interpretation of the gauge's level indication is very good. I do not recall anyone mentioning this previously. You have pointed out a very important variable among different models of classic Boston Whaler boats and their fuel tanks.
The behavior of the fuel tank gauge can vary considerably between different models depending on where in the tank the gauge is positioned. Assuming a boat would have a bow-high trim at rest, the farther forward the gauge is located in the tank, the more gas remaining in the tank at a particular gauge reading.
WSTEFFENS posted 06-24-2005 12:57 PM ET (US)
Gentlemen:
Tom, Please don't think I was crossing your intelligence. The tank issue is worked out if you know the problem. The gage is a "dum donkey" and very repeatable. No question. I just wish the dealer had told me about how it read. Your observation about the location of the gage for and aft makes good sense. Seems to me as I fuel up the head of the boat goes down about 2"' (25 WT). I never realized the sender unit was not located in the center of the tank. (remember the sicker I told you about on the deck plate). It only reads with the boat at rest, not underway!
Larry: yea I learned the hard way, a Cypress Garden Ski makes a lousey paddel. But then who tinks you can paddle a 25' boat? Wish I had a picture of a (young me) paddeling the 25 with a water ski!
Best
JOHN W MAYO posted 07-03-2005 11:36 AM ET (US)
A friend of mine who ran a gas station years ago told me when a tanker truck is filled, it may take on say 10,000 gallons, cold fuel. When it dumps its load, after heating from the sun in transit, at the station it might be 10,020 gallons, and thats the amount they would be charged for.The temperature, expanision of the the fuel acconted for the increase in fuel volumne and they charged him for it. Figure that. I cannot see how any thing like that would count on a Whaler being fuel or fuel volumne, but the fact that of the heat expansion in the hot summer time you may not want to completely fill the tanks so as to allow for that expansion of the fuel and so it won't overflow throught the vent as I have seen on some boats and airplanes. A Cost Guard man I know told me of a case where this happened on a fighing boat, the fuel expanded and left the vent into the water. Owner got a heafty fine.
SpongeBob posted 07-03-2005 10:22 PM ET (US)
Why hasn't one of the instrument companies come up with a programable digital fuel guage. Sounds like it would have a market. The dead reckoning method works if we are aware of it but how many boaters don't realise there is a difference in what is actually in the tank and what the guage reads?
Jerry Townsend posted 07-03-2005 11:12 PM ET (US)
John - the change in volume is quite small - but it exists. That is, in part, why many in the colder climates will fuel up in the cold/cool morning - rather than in the warmer afternoon. But 20 gallons in 10,000 is small - lets see, in my Outrage with a 56 gallon tank - the same expansion would amount to about a tenth of a gallon.
Your engine doesn't care about this expansion - as it is burning the necessary weight of fuel to provide the energy that you are demanding. Of course, one could convert that to volume - but the conversion would be temperature dependent.
Bob - having a perfectly accurate gauge would not help all that much - as, as I mentioned much earlier - the attitude of the boat and the installation of the tank by the manufacturer are the principal culprits to the problem.
And then, the typical gauge is not linear - nor all that accurate. For example, in my 3/4 ton pickup - when the gauge first hits the 1/2 mark, I have about a 1/3 of a tank - and the gauge will hang on the 1/2 mark for many miles. When it starts to move down-ward, I had better be looking for a gas station. What are the characteristics of your gauge?
But I maintain that the best (better ?) solution is an accurate and properly calibrated flow measurment system - such as the Standard Horizon or a couple of others. ---- Jerry/Idaho
SpongeBob posted 07-04-2005 12:06 AM ET (US)
Jerry what I ment was something that could be easily calibrated by the boatowner while the boat was in the water as the tank was being filled the first one or two times. They now make digital speedometers that you the owner can calibrate and adjust for different tire diameters. 35" rockcrawler wheels and tires on the weekends and 31" all terrains for the weekday. Why not gas tanks?
Jeff
JOHN W MAYO posted 07-04-2005 12:08 AM ET (US)
Jerry,
I agree with the fuel flow meter.......I have a standard and it provides excellent information.
Drisney posted 07-04-2005 02:13 PM ET (US)
Hi Tom,
Where were you when you ran out of fuel? Did you know it was happening? I did it once in my 16 out of Moss Landing and it sucked! Dave
Buckda posted 07-06-2005 11:36 AM ET (US)
This is great information...I notice the same characteristics on my 18' Outrage tank gauge - it reads "F" for an awful long time - many miles but once it hits "1/2" it will drop pretty fast.
I agree with others - taking calibrated measurements is a good idea, but the idea of using a fuel-flow meter system is probably best, if used in conjunction with a similar "run it dry first" mentality. Then you will have your TRUE usable capacity in gallons, and can program your meter to warn you when you're within a few gallons of that point. I would expect that there is a 5% "reserve" capacity that is generally unusable when underway. For me, that means that instead of 63 gallons, I have just under 60 gallons of usable fuel, or about 180 miles of operation, under normal cruising conditions.
The nice thing about that fuel flow meter is that you can see what is "really" happening. For instance, last weekend I ran about 115 miles on about 31 gallons of gas on Saturday: following seas at around 2 feet, then running through protected water against a current. On Sunday I ran probably 80-90 miles into 3-4 foot headseas, stacked, as the 25 MPH wind was going against the current. I burned about 36 gallons of gas. A fuel flow meter would help me to guage how much gas I had left much more accurately when the conditions get adverse and you need to make decisions about where to go to make it home safely.

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Author	Topic: Fuel Tank Capacity vs. Useable Fuel Capacity
Tom W Clark	posted 06-20-2005 01:58 PM ET (US) In another thread about a classic 25 foot Whaler, Larry Goltz stated that he always understood the fuel tank capacity of this model to be the USEABLE fuel capacity, not necessarily the same as the actual volume of the tank. This is not how I have always understood the fuel tanks to be rated by Whaler. The fuel tank for the classic 25s made after 1985 is 140 gallons (earlier models had a pair of 70 gallon tanks). I recently had the opportunity to run the tank in my 1988 Revenge 25 Walk Through empty and then refill the tank at a gas station on Saturday. I put 139.5 gallons into that tank which topped it off to the point where gas squirted out the vent. This morning while cleaning the boat I pulled all the deck plates to allow air to more easily circulate below the fuel tank cover. I wiped the grime off the original placard on the tank, made by Florida Marine Tanks. The placard clearly states the fuel tank capacity is 142 gallons. It would seem that Larry is correct, but the difference between the two figures is very small, 2 gallons. This observation assumes the fuel pump is calibrated accurately, which they not always are but I have no reason to assume it isn't. I also know that in my 1983 Outrage 18 the fuel tank capacity according to Whaler is 63 gallons. The capacity on that Florida Marine Tanks aluminum tank was stated as 63 gallons. No difference. Is the 25 unique in this tank capacity vs. useable capacity difference?
Bulldog	posted 06-20-2005 02:14 PM ET (US) Tom it might matter how the boat is sitting on the trailer, was the part of the tank at the fill and vent ports the highest part of tank. My 77 gallon Revenge tank has the fill and vent outlets about a foot or so back from the front of tank. My Revenge sits with the bow up slightly on the trailer, meaning that the vent outlet would see gas before the front would fill all the way. It's my theory and I'm sticking to it!......Jack
Jerry Townsend	posted 06-20-2005 03:38 PM ET (US) Tom - I believe that the specified tank capacity is just that - and that Larry is a bit askew (now don't tell Larry I said that). Frankly, the tank manufacturer cannot know the attitude of your boat - or how the boat manufacturer installed that tank - or .... and therefore cannot determine the 'usable' capacity of your tank. And your experienced difference of 2 gallons (in a 142 gallon tank) - about 1.5% - is small as you point out. A 1.5% error on a tank is pretty good. In your case, your tank may not have been "bone" dry, may have not been level, may not ..... - in other words - the 139.5 gallons may not have filled a dry, level tank. ---- Jerry/Idaho
phatwhaler	posted 06-20-2005 03:42 PM ET (US) My 1996 19 Outrage brochure says I have a 91 gallon tank. The decal on my Florida Marine tank says I have a 87 gallon tank. Interestingly, the 1997 and 1998 20 Outrage, which is the same boat as mine, lists the fuel tank capacity as 87 gallons. I have never emptied the tank and refilled it. phatwhaler out.
LHG	posted 06-20-2005 06:40 PM ET (US) But then, Jerry, if Tom ran his tank was "dry" (ie engines died), and it only took 139.5 gallons, then the "Useable 140" is correct, and he couldn't use the last 2.5 gallons that it holds? Actually, I got my information from someone at the factory, who said, at least for my 25, they install tanks slightly larger than stated, as on a boat it generally is impossible to suck every last drop of fuel out of the tank. He was the person who told me the 140 gallons was "useable". Think about all of the adverse conditions you could be in that would affect fuel withdrawl. As a matter of fact, I have always thought (and could be wrong), that a tank manufacturer is usually the one who states the "useable" capacity as the tank's capacity. So I would think that if the 25 tank is stated as 142 gallons, it may actually hold 145? I just don't know. But one think I have discovered, is that with the red above deck Tempo/Moeller plastic tanks, they tend to hold less than stated. Tom, when you filled up the tank from empty, I hope you noted the number of gallons it took for each gradation on the tank gauge. Even though you were on a trailer, that will at least give you some idea of the repeatable accuracy of the gauge. On my 25 in the water at rest, when the gauge is at 1/4, I only have 20 gallons, 1/2 = 50 gallons. As the guage just hits "E", the engines die! I had to spend an entire night anchored 1/4 mile off the beach in Lake Michigan to find this out
Tom W Clark	posted 06-20-2005 07:04 PM ET (US) Well, it's splitting hairs a bit, but I now agree with Larry about the tanks in our boats having a useable capacity of 140 gallons. It is not the tank manufacturer who calculates USEABLE capacity because, as Jerry notes, the tank can be installed different ways. The tank manufacturer simply states the volumetric capacity of the tank. It is the BOAT manufacturer who would state the USEABLE capacity. Based on my experience, I am confident the tank will actually hold 142 U.S. gallons and that 140 of them are useable under normal operating conditions. As to how the boat was fueled: it was parked at the gas station with a very slight bow high attitude much as it would be if it were floating, so no loss of capacity was due to the fill being lower than an air pocket in the rear of the tank. Larry, I did not precisely note the gauge needle position as I was filling but I did look when it was half full and it had taken around 50 gallons, so I am going to use your benchmarks from now on. I suspect our tanks and gauges behave very similarly.
WSTEFFENS	posted 06-23-2005 10:17 AM ET (US) Tom: You have stumbled onto a potential problem. The gage is not accurate due to the fact that the gage is opperated by a cork float thru a gear mechanism. The tank however is not square in cross section but has a tapered bottom sort of a "V" that makes the gage read weard. Larry is right I also have run out of fuel, before I mapped the tank. Also there should be a sticker close to the "clear" deck plate above the gas gage that says something on the line of "gage only works with boat at rest in water." To map the tank, do what you did before, suck the system dry, (put it in cans to be used later), launch the boat with dry tank, and tow to a fuel dock. Fill the tank noting the gallons at each mark on the gage. Make a chart and laminate it and tape it to the inside of the clear deck plate and then you know what the gallonage is. As for inaccuracy, it is a fact of life. Seems when I hit the 1/8 mark I have about 5 gallons, when It runns out, the port engine quits about 2 min before the stbd engine. Best
LHG	posted 06-23-2005 03:49 PM ET (US) Walt - that's exactly what I have at 1/8 - 5 gallons! I'm paddling as it falls to E. What really confused me is that my 18 Outrage has 15 gallons (1/4 tank) at "E"! These gauges do have great REPEATABLE accuracy though. One just has to know what they are telling you.
Tom W Clark	posted 06-24-2005 01:45 AM ET (US) Walt, I haven't stumbled onto a potential problem; the behavior of the gauges on these boats is well known. Nor is it a "problem" if you know what the gauge is really telling you. All it can do is measure the fuel level at the spot where the gauge itself is; it doesn't tell you what the volume of the remaining fuel is. We all understand how the gauge and float work, but the non-linear readings are influenced far more by the location of the gauge than by the shape of the tank. You are right, the tank is not rectangular in cross section, but the real reason the fuel gauge takes a long time to come off of "full" and then rapidly goes to "empty" is because the gauge (and especially so on the 25s) is towards the rear of the tank. These boats always float and run with their bows higher than their sterns and the fuel tank is not level fore and aft. Thus there is always more fuel in the rear of the tank than in the forward part. Imagine the tank viewed from the side. Cross sectioned this way we will see that it is rectangular, but the rectangle is sloped towards the stern. The fuel level in the tank is level. As the fuel level begins to drop, the void left behind will first appear at the forward end of the tank. Only after being drained quite a ways will the level get to the point where the gauge is and the float begins to drop. Once the gauge float is half way down, most of the tank is empty; the gauge is really only reading what is in the rear of the tank. The fact that the bottom of the tank is tapered adds to this deception, but it is minor. The Owner's Manual for these boats explicitly caution against interpreting the fuel gauge unless the tank is level. I agree with Larry, the gauges have good repeatable accuracy, or should I say they are precise. And Walt, you are correct about the port motor dying first. That is exactly what happened to me and again it is because of the slope of the tank fore and aft. The fuel withdrawal tube for the port motor is ahead of the withdrawal tube for the starboard motor thus it goes dry first. My experience also agrees with yours, the starboard motor ran for about another 2 minutes at fast idle speed before it died. Larry, the difference between the fuel gauges in the 25 and the 18 is the location of the fuel gauge. In the 18 it is more centrally located in the tank and thus suffers less distortion.
andiamo	posted 06-24-2005 08:02 AM ET (US) Depending on where you live and the type of pump the air temperature on the day you filled could account for the 1.5% variance. Around here the law has been changed so that gas stations can now sell gas as if the air temp were 15 degrees c so that they are selling a constant quantity no matter what the air temp. Otherwise, as I understand it, you get more gas when you buy 100 gallons when it is minus 20c than when it is plus 35c and the gas in the tanks and pumps has expanded.
jimh	posted 06-24-2005 08:39 AM ET (US) Tom--Your observation about how the location of the fuel gauge along the longitudinal axis of the tank affects the interpretation of the gauge's level indication is very good. I do not recall anyone mentioning this previously. You have pointed out a very important variable among different models of classic Boston Whaler boats and their fuel tanks. The behavior of the fuel tank gauge can vary considerably between different models depending on where in the tank the gauge is positioned. Assuming a boat would have a bow-high trim at rest, the farther forward the gauge is located in the tank, the more gas remaining in the tank at a particular gauge reading.
WSTEFFENS	posted 06-24-2005 12:57 PM ET (US) Gentlemen: Tom, Please don't think I was crossing your intelligence. The tank issue is worked out if you know the problem. The gage is a "dum donkey" and very repeatable. No question. I just wish the dealer had told me about how it read. Your observation about the location of the gage for and aft makes good sense. Seems to me as I fuel up the head of the boat goes down about 2"' (25 WT). I never realized the sender unit was not located in the center of the tank. (remember the sicker I told you about on the deck plate). It only reads with the boat at rest, not underway! Larry: yea I learned the hard way, a Cypress Garden Ski makes a lousey paddel. But then who tinks you can paddle a 25' boat? Wish I had a picture of a (young me) paddeling the 25 with a water ski! Best
JOHN W MAYO	posted 07-03-2005 11:36 AM ET (US) A friend of mine who ran a gas station years ago told me when a tanker truck is filled, it may take on say 10,000 gallons, cold fuel. When it dumps its load, after heating from the sun in transit, at the station it might be 10,020 gallons, and thats the amount they would be charged for.The temperature, expanision of the the fuel acconted for the increase in fuel volumne and they charged him for it. Figure that. I cannot see how any thing like that would count on a Whaler being fuel or fuel volumne, but the fact that of the heat expansion in the hot summer time you may not want to completely fill the tanks so as to allow for that expansion of the fuel and so it won't overflow throught the vent as I have seen on some boats and airplanes. A Cost Guard man I know told me of a case where this happened on a fighing boat, the fuel expanded and left the vent into the water. Owner got a heafty fine.
SpongeBob	posted 07-03-2005 10:22 PM ET (US) Why hasn't one of the instrument companies come up with a programable digital fuel guage. Sounds like it would have a market. The dead reckoning method works if we are aware of it but how many boaters don't realise there is a difference in what is actually in the tank and what the guage reads?
Jerry Townsend	posted 07-03-2005 11:12 PM ET (US) John - the change in volume is quite small - but it exists. That is, in part, why many in the colder climates will fuel up in the cold/cool morning - rather than in the warmer afternoon. But 20 gallons in 10,000 is small - lets see, in my Outrage with a 56 gallon tank - the same expansion would amount to about a tenth of a gallon. Your engine doesn't care about this expansion - as it is burning the necessary weight of fuel to provide the energy that you are demanding. Of course, one could convert that to volume - but the conversion would be temperature dependent. Bob - having a perfectly accurate gauge would not help all that much - as, as I mentioned much earlier - the attitude of the boat and the installation of the tank by the manufacturer are the principal culprits to the problem. And then, the typical gauge is not linear - nor all that accurate. For example, in my 3/4 ton pickup - when the gauge first hits the 1/2 mark, I have about a 1/3 of a tank - and the gauge will hang on the 1/2 mark for many miles. When it starts to move down-ward, I had better be looking for a gas station. What are the characteristics of your gauge? But I maintain that the best (better ?) solution is an accurate and properly calibrated flow measurment system - such as the Standard Horizon or a couple of others. ---- Jerry/Idaho
SpongeBob	posted 07-04-2005 12:06 AM ET (US) Jerry what I ment was something that could be easily calibrated by the boatowner while the boat was in the water as the tank was being filled the first one or two times. They now make digital speedometers that you the owner can calibrate and adjust for different tire diameters. 35" rockcrawler wheels and tires on the weekends and 31" all terrains for the weekday. Why not gas tanks? Jeff
JOHN W MAYO	posted 07-04-2005 12:08 AM ET (US) Jerry, I agree with the fuel flow meter.......I have a standard and it provides excellent information.
Drisney	posted 07-04-2005 02:13 PM ET (US) Hi Tom, Where were you when you ran out of fuel? Did you know it was happening? I did it once in my 16 out of Moss Landing and it sucked! Dave
Buckda	posted 07-06-2005 11:36 AM ET (US) This is great information...I notice the same characteristics on my 18' Outrage tank gauge - it reads "F" for an awful long time - many miles but once it hits "1/2" it will drop pretty fast. I agree with others - taking calibrated measurements is a good idea, but the idea of using a fuel-flow meter system is probably best, if used in conjunction with a similar "run it dry first" mentality. Then you will have your TRUE usable capacity in gallons, and can program your meter to warn you when you're within a few gallons of that point. I would expect that there is a 5% "reserve" capacity that is generally unusable when underway. For me, that means that instead of 63 gallons, I have just under 60 gallons of usable fuel, or about 180 miles of operation, under normal cruising conditions. The nice thing about that fuel flow meter is that you can see what is "really" happening. For instance, last weekend I ran about 115 miles on about 31 gallons of gas on Saturday: following seas at around 2 feet, then running through protected water against a current. On Sunday I ran probably 80-90 miles into 3-4 foot headseas, stacked, as the 25 MPH wind was going against the current. I burned about 36 gallons of gas. A fuel flow meter would help me to guage how much gas I had left much more accurately when the conditions get adverse and you need to make decisions about where to go to make it home safely.