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Author Topic:   Gas Gauge
Ben posted 11-12-2001 07:52 AM ET (US)   Profile for Ben   Send Email to Ben  
I would like to add a gas gauge to the center console and not rely on the one in the floor. I have a 77 Outrage with a 40 gallon tank. I did see West Marine carries a Tempo product but was wondering who has taken this task on before and what do you recommend?


jimh posted 11-12-2001 09:01 AM ET (US)     Profile for jimh  Send Email to jimh     
I would stick with the existing gauge!

Let's look at the process of indication fuel level. I will use a symbol "-->" to represent a transfer function, that is, a conversion of mechanical movement to something else, including a different mechanical movement.

Mechanical Gauge:

Actual_Fuel_Level --> Position_of_float;
Position_of_float --> Rotation_of_gauge_shaft.

Electrical Gauge:

Actual_Fuel_Level --> Position_of_float;
Position_of_float --> Movement_of_lever_arm;
Movement_of_lever_arm --> Change_in_sender_resistance;
Change_in_sender_resistance --> Change_in_current;
Change_in_current --> Movement_of_gauge_pointer;
Change_in_battery_voltage --> Change_in_current.

For the mechanical system there are only two transfer functions. For the electrical system there are six transfer functions.

Actually there is a seventh, common to both:

Movement_of_gauge_pointer --> Reading_on_dial_scale.

The more transfer functions involved the more chances for non-linear transfer.

I would think the simple mechanical gauge should be more reliable and more consistent. Once you have calibrated it, it should give good accuracy.


David Ratusnik posted 11-12-2001 09:33 PM ET (US)     Profile for David Ratusnik  Send Email to David Ratusnik     
Ben- Just one guy's experience but the floor gauge you have now is more reliable than anything you might rig for the console. The Whaler set up is simply simpler--"keep it simple" is best nautical approach. I had a 23' Chris Craft for several years with an indash fuel gauge. It was an accident waiting to happen-off by 1/4 tank regularly. Hey, when you go out with 3/4 tank, run hard for 3 hours of skiing and the fuel needle on your dash does not move--?? where's the problem. You can fix it quick with the Whaler. My .03 David
Ben posted 11-14-2001 07:53 AM ET (US)     Profile for Ben  Send Email to Ben     
Thanks for the replies. A couple problems.
One is I have purchased a 27 gallon portable tank that sits under the seat and over the gas gauge - I can't see it any more. The problem is the cover fogs up and I can't read the gauge without prying the cover out.


jimh posted 11-14-2001 08:22 AM ET (US)     Profile for jimh  Send Email to jimh     
If the clear plastic on the gauge cover plate is scratched, you can buff out the plastic and restore it. lhg demonstrated this to me one afternoon aboard my boat; the difference was amazing. He used 3M-FinessIt-II as a polish and made the cover as clear as glass.

If the gauge cover is becoming obscured with condensation, it sounds you have some moisture trapped in the hull. This is probably more common on boats left in the water. On my boat, which spends 99% of its life on a trailer indoors in a shed, I don't see much condensation, but once in a while if conditions are right it may fog just a bit.

If the gauge is chronically fogging, I would wonder where all that water vapor is coming from and try to dry out the hull.

As for the problem of the gauge being convered by the other tank, well I guess there is no way around that.

Perhaps someone will join the thread who has installed an electric gauge.

The ideal replacement would utilize the existing gauge mechanisms access holes and mounting holes so that no new holes need be drilled in the tank. In the absence of any existing product that fills this requirement, you could fabricate your own mechanism.

A home-made gauge sender could possibly be made by removing the existing dial indicator and in some workman like manner using the rotating shaft of the original gauge mechanism to turn a small rheostat. The resistance of the rheostat's element would be chosen to match the value required by the electric gauge chosen. Typical values are probably in the order to 10-100 ohms.

The element of the variable resistor is available in three forms: linear taper, logrithmic taper, reverse logrithmic taper. By using the taper of the resistor element to best advantage, you should be able to get good calibration to the electric gauge. I would run two wires to the sender, too, and eliminate the dependency on the ground return via the tank.



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