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Author Topic:   Is it okay to fill up an internal tank completely?
elaelap posted 06-09-2004 10:45 AM ET (US)   Profile for elaelap   Send Email to elaelap  
I want to accurately check fuel usage by filling up my tank completely, running the motor for ten or twenty hours or so, refilling my tank completely, and doing the simple math to determine gallons per hour. My Outrage 18 has an internal 63 gallon tank with a filler hose which extends a couple of feet above the tank to the gunwale. I'm concerned about possible leakage/spillage if I fill the tank all the way up until the fuel rising up the hose stops the gas flow from the pump (as we all do in our cars). Is there merit to my concern, and if so please suggest an alternative method for measuring fuel usage.


My gauge works fine, but registers fuel levels in very general terms and would not be much use in accurately determining gallons/hour. And sorry but I'm not going to install a fuel flow gauge.

kamie posted 06-09-2004 11:16 AM ET (US)     Profile for kamie  Send Email to kamie     
If you fill it up at the same place you can use the automatic shutoff on the gas pump. Fill her until the pump shuts off and then stop, don't try to top her off. Go out and run, keeping track of the hours. Go back to the same pump if possible and fill until the auto shutdoff kicks in. Now you have the gallons used. It wont be perfect since your hours will include idle time and times when you are simply running at the worse possible RPM's for gas milage but it gets you a good average.

I plan to do just the same thing, once I get her up and running a bit.

elaelap posted 06-09-2004 11:47 AM ET (US)     Profile for elaelap  Send Email to elaelap     
Thanks for that, Kamie, and that's just what I plan to do if I don't have to worry about spillage/leakage caused by overfilling the internal tank.


andygere posted 06-09-2004 12:01 PM ET (US)     Profile for andygere  Send Email to andygere     
As you get close to top-off, slow the fill down to prevent aerated gasoline from bubbling out the vent tube. If you really want to top off your fill, do the last gallon or so with a jerry can.

For what it's worth, I have a Standard Horizon fuel flow monitor, and it verifies (along with the numbers from the pump) that the in-floor guage is quite accurate. With that thrifty 4-stroke on the back, it may take you a long time to get the needle to move!

Buckda posted 06-09-2004 12:01 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Tony -

I filled up my 18 on Sunday (43 gallons)...the pump shut off right as the vent spewed gas. I was trying to listen to hear the level rising up the fill tube, and had slowed the flow, but it still "overflowed". Keep that in mind as you fill it up at a station. If you can find one where traffic noise is minimal, it should help you hear the difference as the gas level rises up the tube.

Just FYI.


Gep posted 06-09-2004 01:15 PM ET (US)     Profile for Gep  Send Email to Gep     
I would think that if you filled it completely and went into some rough water you would have alot of gas sloshing out the vent hole.
elaelap posted 06-09-2004 01:18 PM ET (US)     Profile for elaelap  Send Email to elaelap     
Andy, the first twenty or so hours I put on the motor hardly DID make the deck gauge move at all, and I started to worry that it wasn't working and that I might suddenly run out of gas at sea. Having that huge 63 gallon tank takes some getting used to. I got great fuel economy with my 50 4/s on my 16/17 (1.25-1.6 gallons/hour at a moderate cruising speed, about 18-20 mph), but was ready for some serious disappointment with the larger motor on the larger boat, especially during break-in and getting-to-know-her hours, but so far so good. And now I want to know my fuel usage as accurately as possible so I can determine my boat's approximate cruising range.

I don't think I clearly expressed my concern. To simplify, is it okay to have a full internal gas tank sloshing around at sea (and from your responses, Dave and Andy, I guess I already know the answer). Any differing opinions?


elaelap posted 06-09-2004 01:20 PM ET (US)     Profile for elaelap  Send Email to elaelap     
Exactly my concern, Mike. What say you, other folks?
Peter posted 06-09-2004 01:37 PM ET (US)     Profile for Peter  Send Email to Peter     
It is OK to have a full tank sloshing around at sea. I used to fill mine up at the dockside gas pump all the time.

The mechanical gauge on my 18 Outrage was always quite accurate and consistent. Each 1/4 increment on the mechanical gas gauge represents approximately 15 gallons. To spot check if your gauge is working properly, let it get to the 1/2 mark and then put 15 gallons in. It should read around the 3/4 mark if its working properly.

Even with a gas guzzling carbureted 150 2-stroke, I had to go about 60 to 70 miles to use up a 1/4 of the tank. With a 4-stroke, you'll have to go even farther.

andygere posted 06-09-2004 06:34 PM ET (US)     Profile for andygere  Send Email to andygere     
I usually fill my tank to just a few gallons short of full. I use the totalizer on my fuel flow monitor to tell me how much room I have in the tank, and watch the floor guage while filling. In those instances when I've missed the stop point and filled essentially to overflow, my thirsty 200 Merc takes the top off quickly enough that I haven't had a problem with gas spilling out the vent at sea. Even when gas bubbles out the vent at fill up, once the air burps out, the fuel level is usually quite a bit lower than the vent overflow. Being an environmentally sound kind of guy, I prefer not to let even that small amount of fuel bubble out, but it has happened a few times.

One nice advantage of having the fuel flow monitor is that it lets me dial the boat in to an efficient cruising speed. I've noticed that few miles per hour can make a substantial difference in gph used by the big V6, which adds up over a long distance at $2.29 per gallon. Shedding just 1 gph is like getting a $2.29 per hour raise!

David Jenkins posted 06-10-2004 08:21 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
On a related subject, I just replaced the internal 40-gallon tank on a 1974 Outrage 19. The aluminum tank from Florida Marine Tanks is a perfect fit except there is a 3/4-inch space between the two aluminum bars that secure the tank and the top of the tank. I thought that the tank might move up and down that 3/4 of an inch when I am in heavy seas, so I epoxied a strip of 3/4 inch treated plywood between the aluminum bar and the tank.

Was that a mistake? Was the 3/4-inch gap there on purpose to allow the tank to expand on hot days? Do vented aluminum tanks expand?

Gep posted 06-10-2004 08:57 AM ET (US)     Profile for Gep  Send Email to Gep     
On the 18' Outrages there is supposed two shims (they looked like 1/4" masonite) and one piece of what Whaler called "Fabreeka" a type of pad, that goes in between each the aluminum straps and the gas tank.
They were the same width as the straps and taped on to the straps.
I don't know about the earlier Outrages.
davej14 posted 06-10-2004 09:05 AM ET (US)     Profile for davej14  Send Email to davej14     
Most materials expand with increasing temperature. The real question is how much the aluminum will expand vs fiberglass. I couldn't find the expansion coefficient for fiberglass but if we use glass as an approximation, which should be failly close, here are the numbers:

Aluminum = .000013
Glass = .000005

The maximum change in temperature you are ever likely to see from a room temperature of 70 deg F (where you probably did the installation) is 50 deg F. If the tank is 10 inches high, then you would have the following changes in length at + and - 50 deg F :

Aluminum = 10 x .000013 x 50 = .0065 inch
Glass = 10 x .000005 x 50 = .0025 inch

The mismatch would be just .004 inch. I doubt if this would cause you a problem. You should also consider the length of the tank where the mismatch would be greater. In general, it would be a good idea to fill gaps, with a compliant material that can compress and expand without putting pressure on the hull.

jimh posted 06-10-2004 09:07 AM ET (US)     Profile for jimh  Send Email to jimh     
A method to calibrate your fuel tank gauge:

With the tank as empty as possible, fuel the boat at a gas dock. Record the amount of fuel added as the tank gauge indicates each 1/8-th increment. You will be able to reach a level of 9/8th full, that is, over the F mark.

If you do this once and preserve the information, you will have a rather accurate chart to convert fuel gauge readings into gallons-remaining-in-tank.

(Suggested to me by LHG.)

Fueling while the boat is afloat is important because the tank gauge indication will vary with the trim on the boat. The trim while on the trailer will not be the same as when afloat.

As Boston Whaler notes, the gauge only is accurate when the boat is floating and at a stop. Any motion on the boat and the trim changes and so does the fuel distribution in the tank.

Filling to the brim will leave fuel standing in the rubber fill hose. This is probably not a good situation as it may result in a leak or in softening of the filler hose line. I think it is better to shut off the fuel when you hear the fuel begin to whistle up the filler hose. If you listen you can easily hear the pitch of the sound of the tank start to abruptly change as the fuel level nears the top of the tank.

andygere posted 06-10-2004 11:27 AM ET (US)     Profile for andygere  Send Email to andygere     
If the fuel fill hose is made to the same performance specifications as the fuel delivery hoses (from the tank outlet to the fuel filter and motor) I don't think a bit of standing gas in there will hurt it. You may ruin a good wax job by letting gas dribble down the side of the boat out of the vent, and pollute your harbor or fuel station area with the spilled gasoline. It can be pretty hard to stop based on the sound when the boat is in the water, that's why I try to estimate the amount of fuel it will take and stop just short of full. This can be done fairly well just by watching the in-floor fuel guage while you pump. If your trailer sets the boat a bit bow high, you will get a good fill and the gauge will be pretty accurate since the fill pipe and sending unit are towards the front of the tank. Not quite as accurate as a marina fill, but a lot cheaper!

All this is based on my experience with an Outrage 22, but from what I can tell it should apply to the classic 18 hull as well.

Moe posted 06-10-2004 11:37 AM ET (US)     Profile for Moe  Send Email to Moe     
One thing to consider when fueling is fuel expansion. In the underground tanks, the fuel is pretty cool, maybe 55-65 degrees. When pumped into a tank, on a trailer, surrounded by ambient air in the 80-90 degree range, it's going to expand. When pumped into a tank, in the water, it'll be exposed to ambient air temperature on top, but water temperature on the bottom, so perhaps not as much expansion as on the trailer.

How much it expands, I don't know, but 10% is the rule of thumb with portable tanks. That's the reason for the recommendation of not topping off after the nozzle shuts off the first time.


elaelap posted 06-10-2004 01:09 PM ET (US)     Profile for elaelap  Send Email to elaelap     
Great stuff as usual, guys/gals. Now if only the wind and seas would lay down a little so I can start burning some of that $2.50/gallon California gas. I haven't caught a salmon for two weeks and a day, and they should be thick out there this time of year. In fact, I've only caught four fish since I got my OR 18 almost two months ago, what with repowering dead time and this blasted weather. What's really annoying is listening to friends, neighbors, clients, and traitorous family members talking about how 'great the weather is with this little [!!] breeze' really IS sunny, warm, clear, sparkling at night, and I suppose beautiful here in Sonoma County, for the uninitiated that is. Give me the Bodega Bay fog and flat seas, and you can keep your damned starry nights.


David Jenkins posted 06-11-2004 06:50 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Good information. Thank you.
gss036 posted 06-11-2004 02:37 PM ET (US)     Profile for gss036  Send Email to gss036     
Tony, send some of those salmon on up north here to the San Juans. We will get to start fishing on the 1st of July. Sure hope it was beeter than Feb/March. We will get 4 months and then they shut us down again for a month then open for 2 months. Then very limited. One Chinook a day until may coho show and the we can 2 coho a day. Good Luck
elaelap posted 06-11-2004 02:50 PM ET (US)     Profile for elaelap  Send Email to elaelap     
Coho = No No down here. They're endangered according to someone, but often we can't keep 'em off our barbless hooks.
gss036 posted 06-12-2004 12:34 AM ET (US)     Profile for gss036  Send Email to gss036     
Tony, we have good runs of coho here from time to time, depends on the gill netter and purse seiner season and if the Canadians fish for them on the ocean side of Vancouver Island. Just about any of the salmon we are allowed to keep have to have adoise fin clipped showing that they are hatchery raised fish. All the others are protected with endanger species and the Boldt court decision. Sure not like it used to be.
Tom W Clark posted 06-19-2004 02:42 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

Let me address the fuel tank question in the Outrage 18, as I have some personal experience with this set up.

I think the answer to your question is yes, especially for your purposes of trying to set a bench mark to measure against, but I would not recommend filling to the literal top of the fuel fill.

Instead fill the tank until the gas pump nozzle trips. When it comes time to refill and measure how much fuel it takes, be sure you are using the exact same pump at the exact same gas station and that the boat is parked in the exact same location at the same angle to the ground.

The fuel tank in the Outrage 18 can be a pain to fill cleanly. In ten years of ownership I found that the tank fill in my Outrage 18 was very fussy about how it was filled. I learned that it was important to insert the pump nozzle in the fill from the inside of the boat. By this I mean that the curve on the nozzle curved towards the centerline of the boat and I found it was easier for me to climb into the boat, sit on the RPS and then insert the nozzle.

If I failed to do this there was often a lot of "burping" which made a mess. It is also important to get the nozzle down the fill as far as possible so that when the pump triggers the shut off of fuel flow, it is not too late and gas does not come gushing back out the fill.

Another important thing to remember is to (if possible) avoid parking the boat with the bow going down hill if there is any slope at the station. You want the fill to be at the high end of the tank and if it is not you will create an air pocket in the tank which will act as a "spring" for the fuel load which compresses as the fuel is added near the top.

After the inertia of this fuel stops and the compressed air expands again it can push a fair amount of gas out either the fill or the vent on the side of the hull.

Regarding the mechanical fuel gauge in the top of the tank, I think it is useful to understand what it is really measuring. It measures the level of the fuel's surface in the tank. That's it. While the gauge is mounted in the middle of the tank which will to a certain degree minimize the effect of the the tank's level on the reading, it is still very dependent on the orientation of the tank especially when nearly full or nearly empty.

This is why there is that placard that says something to the effect of "only read gauge when boat is level." The gauge is not that useful while underway and it is best to stop and try to level the boat fore and aft if it is in the water and you want an accurate read on how much fuel in in the tank.

What the gauge IS good at is repeatable accuracy. Once you learn what a given needle position really means, you can rely on that in the future to estimate where you are at with your fuel load.

BQUICK posted 06-22-2004 04:12 PM ET (US)     Profile for BQUICK  Send Email to BQUICK     
I got gas earlier this spring and we got a 90 deg day. Fuel was day there was fuel coming out my vent as evidenced by a big gas slick. Luckily the Natural Resources Police didn't see it!


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