Fueling Difficulties

Discussion in 'Powerboats' started by Fly-n Fin, Mar 5, 2007.

  1. Fly-n Fin
    Joined: Mar 2007
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    Fly-n Fin New Member

    Greetings Folks, I'm new. Can anyone help me figure this out? I bought a 1996 Wellcraft center console with the fuel port on the side, not atop the gunnel. Its got a Johnson 112SP two stroke OB without an auto oil feed system. First problem is a virtually inoperative fuel guage and/or fuel quantity sending unit. So I tried filling the tank one 5 gal mix at a time. Tedious, but gets the fuel/oil mix correct. I also devised a hose and nozzle to the 5 gal tank that fits into the neck of the fuel port. Works great. However I occaissionally got a back pressure fuel belch from the fuel port and left perhaps a quart of petrol on the lawn. I lifted up the hose in the bilge area enough, to eliminate dips. I also had lowered the tongue of the trailer to the max. But I still don't know how much is in the tank, since I've only put 10 hours of operation into it. Any ideas about a venting problem? The feed to the motor is just fine. Runs great through the entire operating range. There are no fuel consumption numbers in the manual, but a 110 HP aircraft engine burns 6-7 gph at 75%. How much does this engine burn? Thanks.
     
  2. charmc
    Joined: Jan 2007
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    Location: FL, USA

    charmc Senior Member

    The backflow while filling could be caused by partial blockage in the vent line or fitting.

    Here is a good discussion of filling problems and how to avoid or minimize them, also has some tips on fuels gauge problems.

    http://www.boatus.com/foundation/cleanwater/drops/FuelSystems.asp

    I found that getting the info from the manufacturer on my fuel tanks' exact capacities and shape, then making a dipstick calibrated for fuel quantity at each inch of depth, gave me reliable info on fuel remaining in the tanks.

    Fuel consumption will depend on the boat, prop, passenger, fuel, and equipment load, as well as the engine. You might be able to get some fuel consumption curves from Wellcraft or Johnson for your boat/engine/prop combo, but they will be guidelines at best. You can make your own fuel consumption charts by recording fuel use, rpm, and load info. Over time that will be your most accurate measure. There are flow fuel measuring devices, but the good ones are pretty pricey for pleasure boating.

    Cheers,

    Charlie
     
  3. Ike
    Joined: Apr 2006
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    Ike Senior Member

    fuel tanks on boats are typically designed to be level or slightly high on the forward end when the boat is sitting on the water and resting on it's lines, that is not down at the head or at the stern. When it is on the trailer it is a pretty safe bet the tank is no longer level. If the builder did it right the vent is at the high end of the tank, so that it continues to vent until full. Also many boats have a built in Ullage, that is 5% of the tank at the top is never filled to allow for expansion when the temperature climbs. This is usualy accomplished by simply extending the vent tube down into the tank an inch or so. The point is you may not be able to fill the tank completely. But the capacity of the tank that is on the label is the amount it would hold with the vent at the top minus 5 %.

    So make sure the tank is level or slightly high on the vent end of the tank. This may not mean lowering the tongue. It may mean raising the tongue. It depends on the boat.

    The easiest way to find out how much you boat consumes is to fill thetank, take it out and run it for a known amount of time, say 30 minutes, at 3/4 throttle (which is usually about cruisng speed) and then take the boat back and fill the tank. The amount you use is the gallons divided by time. You can get a good estimate from the manufacturer, but every boat is different, because of the amount of stuff you carry on the boat. More weight, more fuel used. Also make sure it's at the optimum trim when you do this. If the trim is off then it will use more fuel.
     
  4. Fly-n Fin
    Joined: Mar 2007
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    Location: Florida

    Fly-n Fin New Member

    Peter and Charlie, Thanks for the great feedback. I was away since the 7th. Sorry I didn't get to reply. After I posted I had the fuel guage tested at a marine shop and bought a replacement sender. Works like a rheostat, I guess. Well, anyway, I couldn't believe how "Mickey Mouse" the sender is in design. It was a perfect match for the one I pulled out. The guage tested out as OK. And I took care to get the rod length on the float arm just the right length and the friction devices to position the float correctly to grip OK. Yet after all reinstalled I still see 1/4 tank on the guage when, in fact, the tank is at least 3/4. I'm thinking that if there is no better sender on the market, that I might do a dip-stick or sight guage set up. The hole at the top of the tank receives the sender mounting plate (with wire attachments to the guage and ground). It has 5 screws that are not symetrical. Perhaps I'll find a clear plastic beaker-like unit with a flange to mount into the tank at the sender hole with gasket and screws. Then I could use a dentist-type mirror and flashlight with the "beaker" marked with rough calibration. But Peter's dipstick idea sounds more reliable, provided the manufacturer can provide me with good data. I might even go to the hardware store for PVC fittings with flanges and a screw top, so that I can take off the deck plate, screw off the PVC cap and use my dip stick. That would also solve any venting problem which Charlie addressed, if the cap is taken off to monitor while fueling. Imagine that! A reliable method, done before launch, that involves no wiring. I'll post later. Thanks again. Eric.
     
  5. Ike
    Joined: Apr 2006
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    Ike Senior Member

    I don't think your beaker idea is a very safe. Glass around fuel tanks is not good. That is why sight glasses aren't used. Federal regs don't allow any holes below the top of the tank so a sight guage is out.

    Have you ghecked the actual guage on the dash? It sounds to me like if everything else is working, the guage dial is not calibrated correctly.

    Too bad you already bought a new fuel tank sender. The technology for the typical arm and float type sensor that uses a rheostat is way way out of date and as you know, not very accurate. There are a lot of new sensors on the market that do it a different way.

    Wema is the major manufacturer of tanks sensors used in recreational boats. They make a new type that is called inductive because it doesn't use rheostat. It is simply a long tube with a float in it; some others have the float outside the tube. The float is just a coil. Inside the tube is a very long printed ciruit board that detects any changes in the magnet flux of the coil. As the float (coil) moves up and down the flux changes giving you the tank level. A lot more accurate and less sensitive to slosh and splashing. also absolutely safe. http://www.wemausa.com/tank_sensors/tank_level_sensors.htm

    Here's another inductive one made by centriod. http://shopping.rexmar.com/Merchant...Product_Code=CENCGF-12&Category_Code=centroid

    Then there are the capacitive type. Same basic principle as the inductive, only it uses two tubes and measures the capacitance between them. http://continuouswave.com/ubb/Forum6/HTML/000632.html

    The most acccurate and by far most expensive way to do it is use a fuel flow meter. This is installed in your fuel line and actually measures how much fuel you are using, it will even give you stuff like gallons per hour, tell you if you need a tune up, all kinds of stuff. Here is one made by floscan. http://www.floscan.com/html/blue/index.php

    And last but not least are the latest. These things actually mount on the outside of the tank and detect the fluid level inside. Neat! No holes in the tank. Just stick the sensors on the side of the tank and wire it to the guage. I have seen them at boat shows but I haven't found a web site for them yet. I also know they are used in RV's, because RV tank guages are notoriously bad. I have seen them in RV catalogs. These are supposedly pretty accurate. I'll keep looking for a link.

    Meanwhile the old stick it method always works, if you have don't have a lot of curves in your fill line. Just take a clean stick (long enough to reach the bottom of tank. Rub chalk on it. (you can get big pieces of chalk at Home Depot or Lowes) Then stick it. It will tell you how many inches of fuel are in the tank. Here is a rather tedious way of making an accurate stick. With tank empty, put in one gallon, measure. Put in another gallon, measure, and so on until the tank is full. As I said, tedious, but very accurate. There ar other ways. Here's an easy one, but you need to know how many gallons per hour you engine burns at cruising. Fill tank, stick it mark it on the stick. Go out to the lake, run the boat for an hour at cruising speed. Stop stick it again. If you burn 8 gallons per hour it should be down 8 gals. Stick it again. Repeat several times.

    I don't recommend doing it the way you propose because then you are constantly opening the tank and allowing a lot of gas fumes to enter the boat. A real recipe for disaster. One little spark and your whole day is ruined.
     
  6. Fly-n Fin
    Joined: Mar 2007
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    Fly-n Fin New Member

    Thanks, Ike. I'll stick with the sensor idea. The replacement sensor cost can be chalked up to an inexpensive lesson learned. Now its off to Wema's and Centriod's websites. The device outside the tank would be too hard for me to install, so I'll save you the time looking for their website.
     
  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I always replace the sender and gauge together. The difference in price in minimal, and in my experience when one is bad the other is usually too.
     
  8. Lancerbye
    Joined: Mar 2007
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    Lancerbye Junior Member

    You could replace it with a back pressure gauge. This requires no power. you need to know the volume of the tank at all levels and have a chart that displays this. You usually have a small hand pump that applies a pressure to the bubble pipe inside the tank and with a few strokes of the pump you get a backpressure reading to a gauge calibrated in inches or cm of the fuel. They are very accurate and basically fool proof. You can even have the pressure gauge marked with corresponding values of fuel. Its also handy for several different tanks using a selector valve.
     
  9. MommyDearest
    Joined: May 2007
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    MommyDearest Junior Member

    Newbie here, and am finding this whole Forum MOST INFORMATIVE!

    Hopefully, you've answered my own query.

    Thanks
     

  10. Lancerbye
    Joined: Mar 2007
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    Location: Canada

    Lancerbye Junior Member

    There is a product called The Tank Tender which is what I previously discribed.www.thetanktender.com/4.htm . I have one on my boat and it works great. No power needed.
     
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