Fuel tank venting though/question

[Roy & Dixie]

My 1998 CD 22' has 2 fuel tanks, each with it's own fill and vent connections. Neither tank is transparent. Like has been discussed by several others recently, both of my vents have a tendency to spit fuel overboard just as the tank fills. I have noted fuel spitting out a vent as I drive away from a service station with boat being trailered. I have not tried the whistle-in-vent suggested by some. I have thought a simple solution would be to remove the 2 vent hoses from the overboard ports, tie the 2 tanks vents together directly, "T" a single line into that line, and run the single vent line to a small see-thru catch container mounted in the transom area. I could view the catch container as I fuel and see if fuel is vented out prior to the fuel hose being shut off as the tank fills. After recapping both fuel fill ports, any fuel in the catch container would be dawn back into the tank supplying fuel to the engine as the tank vents. (much like a coolant container on an automobile functions) Why would this not solve my venting problem?

 

[thataway]

First you don't want to vent fuel back into the cockpit--so are you considering a container in the splash well? The tanks still have to vent--and I don't see how the fuel would be sucked back into the supply lines if this plastic tank were allowed to vent to the open. Then there is the possibility of water getting into an open container?

 

[AstoriaDave]

C-way,

Next time you fuel up, place a carpenter's level midships on the side deck to see if you are fueling with a nose up or nose down condition. Ideally, the level would be placed on the top of the tank surface, if it is flat and not rounded, but access probably impractical.

After a fresh fill, not unusual for a small glug of fuel trapped in the vent line to pop out as the trailer passes onto a roadway from the fueling depot. OTOH, if you are getting more than just a short splash, could be you are over filling the tanks. Mine signals near full by a change in tone, so I slow the fill to a trickle, sometimes catching any overfill in a small plastic cup. That goes in the fill hole after the tank has quit sloshing.

 

[Bill K]

This is what I use.

http://www.tgmmarine.com/nospills/pages/products.html

Bill Kelleher

 

[Roy & Dixie]

First you don't want to vent fuel back into the cockpit--so are you considering a container in the splash well? The tanks still have to vent--and I don't see how the fuel would be sucked back into the supply lines if this plastic tank were allowed to vent to the open. Then there is the possibility of water getting into an open container?

Yes, I am considering placing the vent in the splash well, not the cockpit. I plan to run each vent line slightly "up hill" to the "T", then connect the final single vent line to the "T" and run that thru the large grommet thru which pass the engine control cables, still running "up hill". I would then run the vent line to a point as high as the fill hose and bend it to end up pointing back down 180 degrees into the catch container. That way any fuel in the vent lines below the top of the 180 degree loop would flow by gravity back into one or the other fuel tanks. Any fuel that might reach over the top of the loop would be collected in the catch container. I agree that due to vent line length that the small amount of fuel that might end up in the catch container would never be sucked back to the fuel tanks. It could be poured from the container into a tank if the container was not permanently mounted. The fact that the end of the vent hose will be pointing down would prevent any water from reaching the fuel tanks at least as well as where the 2 vents are now located.

 

[Roy & Dixie]

Here is what I did concerning my fuel tank vent problem this afternoon:

I installed a new vent line (5/8") from the stb tank to the port tank vent connections. I then cut this line where it passed beneath an opening into the bottom of the battery compartment (stb side) and installed a "T", pointing the open port in the "T" up. I then installed one of my thru hull fuel tank vents as high as possible in the battery compartment, existing into the splash well. A vent line was then run from the "T" to the vent. The tank to tank line slopes toward each tank from the "T", thus allowing any fuel that over flows from a tank during fueling to flow back into one or the other tank. The vent is now higher than the 2 fill ports, so the fuel fill nozzle should automatically cut off as the tank is being filled before any fuel would reach the vent. If any fuel would ever reach the vent, the fuel would spill into the splash area where the mate can now easily hold a catch container during fueling. I should also be able to more easily hear the tank reaching full from the sound coming from the vent. Now all I need to do is obtain a fitting to fill the hole from which I removed the tank vent fitting.

 

[Sunbeam]

I then installed one of my thru hull fuel tank vents as high as possible in the battery compartment, existing into the splash well....The vent is now higher than the 2 fill ports, so the fuel fill nozzle should automatically cut off as the tank is being filled before any fuel would reach the vent.

I'm probably reading or visualizing something incorrectly, but one thing has me stumped: Since the fuel fill fittings are on top of the gunwales (at least on the 22's I have seen), how can a vent exiting through the side of the splash well be any higher than the fill fitting? On my boat it seems like the uppermost splashwell "side" of the starboard lazarette would still be slightly lower than the top of the gunwale where the fuel fill is.

 

[Roy & Dixie]

I then installed one of my thru hull fuel tank vents as high as possible in the battery compartment, existing into the splash well....The vent is now higher than the 2 fill ports, so the fuel fill nozzle should automatically cut off as the tank is being filled before any fuel would reach the vent.

I'm probably reading or visualizing something incorrectly, but one thing has me stumped: Since the fuel fill fittings are on top of the gunwales (at least on the 22's I have seen), how can a vent exiting through the side of the splash well be any higher than the fill fitting? On my boat it seems like the uppermost splashwell "side" of the starboard lazarette would still be slightly lower than the top of the gunwale where the fuel fill is.

I goofed in my write-up. You are correct. But that vent is now a few inches higher than where the two vents were originally.

 

[Sunbeam]

But that vent is now a few inches higher than where the two vents were originally.

Okay, I see what you are saying now. I went and looked in your album and I see that your original fuel vents were in the sheer stripe (so just below the rub rail). Mine are right up near the top of the gunwale (i.e. above the rubrail, on the vertical portion of the deck molding just before it curves over onto the horizontal deck surface).

That's not to say the higher location was all good - I read a few reports of water (spray) getting into the fuel system via the vents. They were simply metal "ells" leading down at 90º and were too high to allow any sort of upward loop in the hose. (I ended up installing the "P-trap" type of vent for that reason.)

Will be interesting to hear how you like your new setup.

Sunbeam

PS: Sending you a PM to ask about the results of raising your engine.

 

[Roy & Dixie]

That's not to say the higher location was all good - I read a few reports of water (spray) getting into the fuel system via the vents. They were simply metal "ells" leading down at 90º and were too high to allow any sort of upward loop in the hose. (I ended up installing the "P-trap" type of vent for that reason.)

My original vent lines also not only had the vents mounted lower than yours, as you noted, but the lines routed straight down to the tank vent connection with no upper loop. I don't know of water ever entering the fuel tanks through the vents, but there certainly was nothing to stop it from doing so except the few mm from the vent's screened opening up to the 90 degree down pointing vent tube. I have no way to now create a loop since the vent it installed as high as possible exiting into the splash well.

When I stated incorrectly that the vent is now higher than the fill port, I should have said that the vent is now higher than the point the fill nozzle reaches in the tank fill hose. Before, fuel would reach the vent at the same time it reached the vent, so would spurt overboard as the fill nozzle tripped off. Now my hope is that the fill nozzle will sense the fuel before the fuel reaches the vent. And the mate can stand by the vent inside the boat to easily catch any vented fuel, whether at the dock or at a service station while on the trailer. At a dock, the vent was usually below the dock level and almost impossible to access easily. In addition, any spilled fuel will be into the splash well. It would take several ounces before any fuel would exit overboard to sea. I'll post how this all works out after my next outing. I'm planning a south bound ICW trip from Daytona to the Keys, possibly to include the Kissimmee River from Lake Okeechobee. I hate to think what that fuel bill will be.

 

[Sunbeam]

My original vent lines also not only had the vents mounted lower than yours, as you noted, but the lines routed straight down to the tank vent connection with no upper loop.

Ah... I see. When I first saw that some boats had lower vents, I was a bit envious thinking they had nice high loops (whereas mine didn't have room for them).

I have no way to now create a loop since the vent it installed as high as possible exiting into the splash well.

If you have an inch (or maybe it's 1.5", I forget now) to spare (from center of hole to underside of deck), then, if it did prove to be an issue on down the line you could install the P-trap vents. My original vents were so close to the underside of the deck that I didn't even have that much room, but I found that they make a flush version, and by making the larger (required) hole "off center" of the original one (but including the original one in it) I was able to fit the P-trap vents to the original holes.

When I stated incorrectly that the vent is now higher than the fill port, I should have said that the vent is now higher than the point the fill nozzle reaches in the tank fill hose.

I see what you mean. I also discovered that it helps to put the fuel nozzle in such that the curve is bending aft (sort of backwards to how you would normally think to do it) and mimicking the bend of the fill hose. I can pump slightly faster that way. (I did get some fuel out the vent the first time I filled, when I was merrily pumping away like it was a car; not sure, but I think maybe it had to do with the turbulence generated where the incoming fuel hits the top of the fuel in the tank. Now I go slower and watch that turbulence and have not had it happen again, but I do fill fairly slowly and now face the nozzle aft.)

And the mate can stand by the vent inside the boat to easily catch any vented fuel, whether at the dock or at a service station while on the trailer.... In addition, any spilled fuel will be into the splash well. It would take several ounces before any fuel would exit overboard to sea.

That does sound good as compared to having it run straight overboard.

I'll post how this all works out after my next outing. I'm planning a south bound ICW trip from Daytona to the Keys, possibly to include the Kissimmee River from Lake Okeechobee. I hate to think what that fuel bill will be.

Sounds fun though! Will be interested to hear how you like the vent improvement (and of course any trip updates).