Fuel tank vents

Ken O · Posted: Fri Dec 25, 2020 4:54 pm Post subject: Fuel tank vents

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.

Fairbro · Posted: Fri Dec 25, 2020 5:41 pm Post subject:

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.

ssobol · Posted: Fri Dec 25, 2020 5:54 pm Post subject:

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.

san juanderer · Posted: Fri Dec 25, 2020 6:48 pm Post subject:

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.

srbaum · Posted: Fri Dec 25, 2020 6:53 pm Post subject:

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.

Scuppers · Posted: Fri Dec 25, 2020 8:06 pm Post subject:

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?

Ken O · Posted: Fri Dec 25, 2020 8:57 pm Post subject:

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.

clayhubler · Posted: Fri Dec 25, 2020 11:10 pm Post subject:

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.

Brewkid · Posted: Sat Dec 26, 2020 1:08 am Post subject:

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=19284&postdays=0&postorder=asc&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

thataway · Posted: Sat Dec 26, 2020 11:50 am Post subject:

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,

colbysmith · Posted: Sat Dec 26, 2020 12:05 pm Post subject:

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... Mr. Green

Colby

san juanderer · Posted: Sat Dec 26, 2020 2:21 pm Post subject:

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.

thataway · Posted: Sat Dec 26, 2020 11:26 pm Post subject:

Robert H. Wilkinson · Posted: Sat Dec 26, 2020 11:50 pm Post subject:

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

thataway · Posted: Sun Dec 27, 2020 9:49 am Post subject:

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.