How much gas?
 

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Can anyone guess how much gas is in my tank with any degree of accuracy? I rarely let it get this low, but I was out doing some prop testing last night. Boat is an 01 29 with a 132 gallon tank I believe. I know the gauge is not very accurate, I was going to guess 40 gallons left. Btw, boat was at rest in the water when I took this pic.

It could be full, empty, or exact. We just learned the hard way.in our Fountain. Twin 100 gallon tanks, 2 gauges. We were at 1/3 tank on both aprox 6 nautical miles returning to launch. Ran stbd dry, limped in on port and sputtered at the dock. My suggestion, go fill up now and note how many gallons and do your math.

Not much. The tank runs down the middle of the boat and are shaped like a V on the bottom.

Your sending unit is back at the end of the tank by your engine bulkhead, lowest part of the boat at rest. So all of the gas has ran to the back where the sending unit is. The better way is look at it when you are running.

This is exactly why I'm asking. I knew the tank is shaped like a V and that the gas gauge isn't exactly accurate like in voodoos case he ran dry while the gauge read 1/3. I was always told when the needle starts bouncing below 3/4 it's time to get gas. I never run the tank this low, so I am just curious what others have experienced. I planned on getting gas before I use the boat again. I guess what I was after was how much gas was actually left in the tank, as far as weight is concerned. Good idea on filling the tank to the top and observing how many gallons it takes.

Piling onto Wildman's note, when you know you're about to fill up, snap pics of the gauge both underway and sitting, then snap a pic of the pump wham you're done. Also a pic of the gauge after filling. Do this each time you fill-up for a while and you'll have decent data to understand what's going on.

Also, if you have a GPS, snap a pic of the trip odometer before each fill-up and reset the trip odometer. Unless you do something really unusual, the mileage can be as helpful as the gauge, and certainly a good back-up.

Next fill up: gallons of gas x 6.6lbs per gallon= weight in fuel, also I usually reset my mileage on my gps, and rule of thumb think of an average of 2miles per gallon. We will see how accurate that average is.

learned hard way first time out on water w my Scarab showed 1/2.... died about 10 miles out of Galveston..... just wouldn't START..... called dealership I purchased from and was told that when they gad out for checkout it died and they put in 10 gallons........ most expensive gas I ever bought via Sea Tow

I've posted my response on another thread but in my 27, if my gauge fluctuates at all I'm empty. Shows completely full any other time. Guy before me added 2 12+ gallon tanks so good thing for those.

I believe the sender is adjustable. One screw for full and one for empty. I haven't tried to adjust mine yet, but when the boat is sitting in water slap full the gauge reads just over 3/4. Once it starts bouncing or moving 1/2 full. 1/4 tank reading I have about 6 gal left in a 60 gallon tank. It drops like a rock from 1/4 tank reading, but the empty reading is accurate, ask me how I know.

Also the tank cannot be filled completely on trailer, I can only get it to take 60 gallons while it is sitting in the water.

mine seem to be pretty aacurate when it's on the trailer.

When in the water.... When they start to bob from the full mark, it's like 10 -20 gallons left

I too recommend looking at the gas guage at speed. It takes a long time to go from full to 3/4. I suspect 3/4 is more like 3/8s. I've let my 29' (130 gallon tank) get low only once. It showed empty running and went up to about 3/8s at rest. I think your guess of 40 gallons might be close. I would say 25-35. If you are going to play "gas roulette" I would suggest packing at least 20 extra gallons onboard. I always wonder who fetched Reggie when he speed tested all of the Fountains for their performance report with "ten gallons of fuel" onboard!

Update: filled up yesterday and it took 72 gallons. I'm sure with the boat on the trailer you never actually have truely "full". And I'm sure there is an amount of gas in the very bottom of the V of the tank that the sender can't pick up. 72 x 6.6 = 475 pounds of fuel!