Fuel tank vents

K

Ken O

New member
Has anyone ever had concerns about water finding its way into the fuel tanks from waves hitting the vents? The vent lines from my vents slope directly down to the tanks without high loops. I have a water separator fuel filter, but I'd rather avoid getting water in the tanks in the first place. The boat is a 1990 C-22 cruiser and it will be used in SE Alaska, which can get pretty rough. Thanks for your thoughts.
 
I had a water-in-the-gas issue that I suspected was the result of rain water coming off of my cockpit camper cover and splashing in the vent. It happened about 3 times and always after a downpour. I made a little clamshell style hood for it by carefully cross cutting a 2” diameter by about a 1 inch length of pvc pipe at an angle and using 3M 5200 to glue it at a downward and rearward angle (to avoid any wake splash of course). Never had a problem after that and it stayed on just fine. I recommend you do this by hand for safety’s sake. Using power saws to cut pvc pipe (especially small lengths) is dangerous.
 
I would think that the amount of water you could get into the fuel tanks via splashing the vents would be quite small. Unless the vents are actually submerged for awhile not much water is going to get in. My vents have a pretty small hole in the bottom with screen.
 
You should definitely have a "high loop", where the top of the loop is higher than the vent outlet itself. Water has a hard time flowing uphill, unless it has the help of water or air pressure.
Most of the installations I has seen are very poor, even with low loops that hold liquid so there is NO vent action happening.
Provide as much protection as you can.
 
Ken O,
My 22 had water in the tank after very heavy rain events. The culprit was lack of a high loop. I investigated and found that there was no physical room to actually have a loop above the vent.
 
is the vent to prevent positive pressure mishaps, in which case a bit of water in the loop would not matter, or for another reason?
 
Thanks for the thoughts. It is sounding like a loop is a good idea. The hoses are probably original, so they are worth replacing anyway. The hose I am looking at will bend to a 4.5" radius, which I think I can fit. I might have to do a 360 degree loop, but that should be OK. I'll update if it fits. Thanks.
 
You definitely want an upward loop in the line between the tank and the vent. Most c-dorys have the vent installed too high. Mine has this problem also. Attwood makes a fitting for this called a p trap fuel vent and I am going to be installing them on my boat before I go out again. I had to rebuild the engine on my last boat because of this exact problem after I got a gallon of saltwater in the tank during some rough seas. A fuel water separator is not enough protection for me. I was lucky that I had put in a separate tank for my kicker motor or we would have been making a distress call.
You do not want to make a 360 in the line as that could make a low point for fuel or water to collect and block the vent which could cause fuel starvation to the engine.
 
I feel like a broken record lately. This is yet another topic Sunbeam has hit on for a modification.
http://www.c-brats.com/viewtopic.php?t= ... c&start=45
I think the whole thread should be required reading for all us Brats! Shoot, I may re-read the whole thing tomorrow. Redoing lazzerett hatchs? Covered. Rub rail? Covered. Anchor locker? Covered. Honestly, even if you don't currently have a project going on your boat, take the time to read this whole thread and you may find yourself with a list by then and.

Merry Christmas all!

R/
John
Scallywag
 
On my first 25 we had the problem with water in the fuel form the vent. Part was solved by turning the vent--and then we put a SS clam shell vent over the vent fitting. We had to slightly modify the curve on the clam shell,
 
The fuel vents on Midnight Flyer and C-Traveler point down. I think to get water in them the boats would have to take a pretty big vertical wave right up the side of the boat, or sink. I also think both boat's hoses off those vents went straight down to the tanks. I could be wrong... Knock on wood, so far no problems with water in the fuel. But then I use auto gas (10% ethanol) too... :mrgreen: Colby
 
No 360 degree circle loops, once you have filled the lower half with water or fuel the air in the tank will NOT vent. Same for laying the vent line on top of the tank then sloping back up to the vent fitting on the top of the tank.
 
Scuppers":2dp7d2o9 said:
is the vent to prevent positive pressure mishaps, in which case a bit of water in the loop would not matter, or for another reason?
Click to expand...

The "loop" is not a 360* loop, but just taking the tubing up higher than the vent. NO you do not want water in the "loop" and it would not form if the loop is correctly configured. If there was water, it would prevent the venting of gas fumes. The vent also allows air in as you consume fuel, so it is both a positive and negative pressure "Safety".

Some boats have the loop external to the deck, where it comes up thru the deck, does a 180* turn downward, and the opening is a few inches above the deck--this loop of copper tubing is often secured to the side of the cabin house. This was how it was handled in many older boats. Not a vent in the side of the hull. Even with this type of system, when crossing The Atlantic in a major storm, the side of the pilot house, was under water enough, and the engine was running to keep a flow of water past the rudder as we ran off in 40 to 45' seas, sea water contaminated one of my 500 gallon diesel tanks. We switched to the windward tank, and transferred the diesel into that tank thru Racor filters. Eventually we opened the man hole on the tank and got inside to manually pump out any remaining salt water and clean the tank with paper towels.
 
Not sure how hard it would be to reconfigure the tanks on a Cdory to the VOPR type. I believe this system is less prone to water intrusion as it eliminates the open vent. Basically it allows air in when there is a vacuum and air out when there is pressure. I have a pic of this type of fill neck and cap in my album.

Regards,

Rob
 
Fig%201428.jpg

I have this EPA compliant gas cap on the Caracal. No problems in 12 years. Perko has several cap/fill assemblies which should work on the C Dory.
 
I like the idea of eliminating the outside/topsides vent that could allow water in. I see that West Marine sells several of these. I understand the concept of a gas vent is that it allows air in as fuel is used, and allows air (and fumes) out when filling the tank or when the tank warms up. Where does this type of filler vent gas fumes? Could the fumes be vented into the cockpit? Gasoline fumes are heavier than air.
 
Ken, the venting is through the gas cap itself. To comply with CARB & EPA USCG standards July 2011 the tank isn't actually "vented". VOPR stands for vacuum over pressure - basically when running engine the cap allows air in as a vacuum is created using fuel. On a hot day when fuel is expanding and boat not running - the cap allows the resulting pressure to escape. When pressure inside the tank is equal to the pressure outside then essentially the tank is sealed. The vent hose from the top of the tank terminates inside the fill neck at the top - close to cap.

If you study the 2 pics in my album close you can see hole in fill neck where vent is attached and interior of cap. Here is a link to one pic - once you clic on it should be able to follow arrows to second pic. If you clic on the pic a second time it will enlarge.

http://www.c-brats.com/modules.php?full ... _photo.php

Regards,

Rob

PS - here is the link to second pic

http://www.c-brats.com/modules.php?full ... _photo.php
 
Ken, they were original equipment on my boat(not a Cdory :cry ).

Thataway says Perko makes several that would work for you. You can check at whatever marine supply stores are in your area. Also could be purchased on line.

Rob
 
I bought vent assemblies that had a built-in loop in the hardware. A heavily loaded c-dory with oem vents pointing downward will allow water intrusion in rough seas. I also put an upward loop in the bilge line so it would stop inflow under similar conditions. It keeps the floor dry unless it is raining, and then a bit will come back thru the pump when pumping stops. It was made by Atwood
https://image.sportsmansguide.com/adimg ... 291_ts.jpg
 
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