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Thread: Fuel Tank Vent Hose

  1. #1

    Default Fuel Tank Vent Hose

    I have a pair of these 20 gallon tanks that came with the 22' Harvey I'm working on. The vent hoses were routed through holes cut in the transom. I'm not sure if that is kosher...Is there some terminal tackle that should be attached to the hose ends? Should the vents exit through the hull sides or is through the transom ok? Finally got the floor and new transom built and installed but neither has been glassed. Weather as of late has not been my friend.

  2. #2

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    Quote Originally Posted by Garyak View Post
    I have a pair of these 20 gallon tanks that came with the 22' Harvey I'm working on. The vent hoses were routed through holes cut in the transom. I'm not sure if that is kosher...Is there some terminal tackle that should be attached to the hose ends? Should the vents exit through the hull sides or is through the transom ok? Finally got the floor and new transom built and installed but neither has been glassed. Weather as of late has not been my friend.
    Thru the transom is fine but you want a thru hull vent fitting with a water trap so spray doesn't get water in your tank. Glen

  3. #3
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    get them up as high as possible, put a clamshell cover over the outside and have a loop in the line to catch water from running down the vent and into the tank.

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  4. #4

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    Thanks for the help, guys. The way it was rigged before, if water was to get in the end of the hose it would have drained downhill right into the tank...not good.

  5. #5

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    This is what I had in mind. This is a scan out of the Fisheries Supply (Seattle) catalog. Glen


  6. #6

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    Looks like the image is gone now...but I did see it earlier. That should solve my problem. Thanks, Glen.

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    Here are some gas vent problems I have seen.
    When the boat is just getting to plane know when the bow wave hits the boat.
    I have seen gas vents installed right where water hit the hull.
    Be sure the clam shell is positioned to keep water out. I have seen them in the wrong position.
    Be sure there is a loop in the fuel line and do not make the loop to short and pinch the fuel line.
    If practial mount the vent high on the rear transom.
    If the vent hose touches any part of the hull. Secure a second piece of hose around the vent hose.

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    I don't know any of the details about you're boat or the fuel tanks, so this may not be relevant. A lot of aluminum fuel tanks in boats are not install properly to prevent fuel tank corrosion. Just one more thing to check out.

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    Quote Originally Posted by Tiderunner View Post
    Here are some gas vent problems I have seen.
    When the boat is just getting to plane know when the bow wave hits the boat.
    I have seen gas vents installed right where water hit the hull.
    Be sure the clam shell is positioned to keep water out. I have seen them in the wrong position.
    Be sure there is a loop in the fuel line and do not make the loop to short and pinch the fuel line.
    If practial mount the vent high on the rear transom.
    If the vent hose touches any part of the hull. Secure a second piece of hose around the vent hose.
    Hope you meant the vent line and not the fuel line with the loop in it ??

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    Here's where the vents for my tanks are located
    20130728_215338.jpg
    I have 2 80gal.fiberglass fuel tanks bedded in foam.
    20130909_151434[1].jpg

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    I like Potbuilders interior vents. Mine is interior as well. If fuel does splash through it, it is inside the boat so I can wipe it up instead of putting it in the water. I like Potbuilders even better in that they are up high, seems like this would never spill fuel.
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    Quote Originally Posted by jrogers View Post
    I like Potbuilders interior vents. Mine is interior as well. If fuel does splash through it, it is inside the boat so I can wipe it up instead of putting it in the water. I like Potbuilders even better in that they are up high, seems like this would never spill fuel.
    I can hear them gurrgleing when i'm getting close to full !! My fuel fills are in the top of the gunnel 4ft away.

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  13. #13

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    I like the idea of interior vents. I raised mine higher this spring and had no problems this summer, but yesterday I started thinking about even higher and interior. Good idea

  14. #14

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    I also like potbuilder's set up. I'm glad I asked about this as there is more to it than I thought. My vent line pictured in post #1 is 3/8" id. I was looking in the current West Marine catalog at the different vents/devices and see that they all are 5/8" id but they didn't have a single listing for a 5/8 id hose barb. I guess I'll need to change mine out.

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    Default Having worked on boats for several years,

    We filll them full and treat them with stablizer ,especially customer boats that don't get used often. Probibly hard to emagine in your neck of the woods . It seems that the partially full tank obsorbs moisture with the changes in barametric pressure , the more air space the more moisture in the air is drawn in. And because water is heavier than gas it goes to the bottom of the tank. Many of our boats have gone to plastic tanks to reduce the corrosion problems . As for the vent . The pounding is like a pulse drawing air in and out like breathing it's hard to out engineer this. but during storage I would recomend putting a ball valve on the vent preventing moisture and out gassing while in port ,doesn't age quite so quickly. Emagine shaking up a soda and letting the gas off , eventually it goes flat. You'd need to open that vent everytime you went some where but you'd be reducung the losses. Some one that didn't know your boat would run out of gas on a full tank , having left the valve closed. All our boats have a water seperating fuel filter , they look like an oil filter cartrage , We dump the contence into a bucket on inspection to see the amount of water is being cought , Pour the fuel back in and reinstall. The only time it 's replaced is if we see corrosion ,then flagg that on the service chart. It's not unusual to get water in the gas from a vender , so our pumps have filters as well. NAPA carries them 1" fpt . Hope this all helps

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    Quote Originally Posted by Garyak View Post
    I have a pair of these 20 gallon tanks that came with the 22' Harvey I'm working on. The vent hoses were routed through holes cut in the transom. I'm not sure if that is kosher...Is there some terminal tackle that should be attached to the hose ends? Should the vents exit through the hull sides or is through the transom ok? Finally got the floor and new transom built and installed but neither has been glassed. Weather as of late has not been my friend.
    I would check USCG regs also. I'm pretty sure they have to be near the fill opening and below it.....close enough that you can see and hear gas coming up through the vent line.

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    Default Of all the boats I've worked on the primary concern is,

    The vent does not empty into the boat . Most I've seen are high on the gunnel ,prferibly facing to the rear. New boats don't even put a loupe in the hose but that is not one of their concerns . Water in the fuel is enevitable just getting it from the fuel dock and their suppliers. Hence the need for water seperating fuel filters. Both on the boat and the fuel dock dispencers. OMC made a product like Stabil called 2+4 and it worked very well for us . Every time a boat or truck sank we went through the routine of draining every thing and refilling and adding stablizers/fuel dryers, to the fuel to take care of any thing we might have missed . With alcohol laden fuels you will see more water in the gas .

  18. #18
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    Obviously the vent fitting must be higher than the tank. A loop at the vent fitting will make it very unlikely for water to enter at that point.
    When the vent hose exits the fuel tank ...... it must be supported in a way that prevents any low spot in the line to occur. The line must rise all the way to the vent fitting. All fuel that gets into the line must be able to drain back to the tank without settling in a low spot.

    If there is a low spot anywhere in the line .... fuel will accumulate there. When expanding fuel in the tank needs to vent ... it will force this accumulated fuel to burp out of the vent fitting. This is the most common error in vent line installation.

    A properly installed vent line will not discharge fuel at the vent fitting. Vent lines should be 5/8".

    Vent lines with valves at the vent fitting (this is not a good idea) will not keep moisture from developing the in the fuel tank. The best way to prevent that is to keep the tank full ....... to minimize condensation ...... especially for winter layup.

    If you've ever had a five gallon plastic gas can sit in the sun ....... the pressure that builds up is more than enough to distort the can. If you were to put valves at your vent fittings ....... you could end up up with enough pressure in the fuel system to force fuel out: You could distort your fuel tank, force fuel to leak at at the fuel filter, or force fuel into the carburetor to relieve pressure ....... in some cases you could fill the crank case with fuel.

  19. #19

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    I have this pair of Perko vented filler caps. The actual filler cap is vented so fuel flows back into the filler tube as well as being vented laterally into the filler tube. Looks to me like this would make a closed loop vent system. I've seen this type filler assembly on Hewescraft boats and it seems to address what andyak said in post #16. Also, Arleigh has mentioned water separating fuel filters. Is this something you would use in addition to or instead of the racor fuel/water separator that I currently use?

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    Quote Originally Posted by Garyak View Post
    I have this pair of Perko vented filler caps. The actual filler cap is vented so fuel flows back into the filler tube as well as being vented laterally into the filler tube. Looks to me like this would make a closed loop vent system. I've seen this type filler assembly on Hewescraft boats and it seems to address what andyak said in post #16. Also, Arleigh has mentioned water separating fuel filters. Is this something you would use in addition to or instead of the racor fuel/water separator that I currently use?
    I have this type mounted on the gunwales and have gotten water in when out in the ocean and constantly having water splashing up over the cap. The water was caught by the Racor, 400 hours and this is the only time I have gotten water in the tanks.

    On my GP the filler is on the transom and the vent is on the side higher than the fill. Cormit spells it out, you really don't want a loop or low spot in the vent as it will become a "trap" and no longer serve as a vent until it burps or as the fuel cools it could suck what is in the vent back into the tank. Pretty hard to keep all the water out in all conditions, good filtration is key. I think condensation accumulating in fuel tanks is minimal, especially here in AK, most likely its the result of water getting in elsewhere.
    “Nothing worth doing is easy”
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