Diesel tank vent line question

[Sheepdog012]

Howdy Folks, Getting the Island Girl ready for spring and noticed that the tank vent line has a sag in it between the vent on the stern and the fitting on the top of the tank. I was changing the fitting on top of the tank (it failed and was weeping) and I noticed that the sag means the line fills with diesel (ask me how I know) when filling the tank and it tops out. Since diesel takes a long time to "evaporate" that means the line is typically full of diesel and so is not really doing its job of venting, especially when filling the tank. I am thinking about shortening the line so it is close to taught to remove the sag, then any diesel that makes it's way into the vent line will drain back into the tank. I am wondering if anyone has any thoughts on if this is ok to do, or if the "slack" in the vent line is needed to allow for flexing of the hull/tank or something? Any insights are appreciated, be well!

-Sheepdog

 

[Newf]

Take the sag out of it so the fuel drains back to the tank. If you don't and you get her rocking and rolling a bit you will be spitting fuel out of the vent. After shortening mine I cut a long tapered shim from a piece of rigid foam and put under and secured to the vent hose. Spitting problem solved.

 

[Sheepdog012]

Thanks Newf! Does your's still have the inline surge protector? I have removed mine because it failed and it was leaking.

 

[Newf]

Nothing on mine that I can see. I used to get lots of seepage out of the vent when I was in rough water. After I shortened the hose and propped it up with a nice gradual slope, as was recommended by others on the forum, I've had no spillage issues.

 

[rpmerrill]

I had a number of burping issues when filling my tank and always had to keep the absorber pads on hand while fueling. I ended up building my own in-line trap out of PVC hardware store fittings. Since that install I have been able to fill the tank at full speed without a problem. (Photo in my album.)

The run from the tank to the vent is pretty long and as pointed out, it is pretty difficult to not have some sags in the line. Fuel in the vent is always gonna happen. Think of the boat cruising with the bow high and bouncing around.

Someone out there must know the answer to my question: Does the vent need to be near (or below) the fuel fill fitting? The ideal location (on the old R-27) would be to run the vent line up through the head, behind the sink and mirror to the roof of the cabin. Would that be safe and legal?

 

[knotflying]

The vent line should have a loop in it that goes up and then down to the vent you see outside the boat. The loop should go as high as possible to be at the height of the fill. The loop will prevent water from the outside going into the tank and drain out if a little gets in. The loop height will prevent fuel from flowing out if any should get into the vent line because of overfill. The vent line should be on an incline from the tank without sags. If sages exist and fuel gets into the line from overfill then the vent will become inadequate. However, if a suction is caused because of lack of venting it is likely that the fuel will clesr from the line because of the suction caused. In any event secure the line to prevent the sag. On my R-27 I pulled the line up as soon as it left the tank fitting and secured it with a zip tie. And then secured it on an incline every 12 inches or so working my way back to the exterior vent.

 

[Sheepdog012]

Thanks Knotflying!

Unfortunately, putting an anti-siphon loop on the vent line on an R-21EC is impossible as there is about 1/2 inch of space above the vent where it exits the hull. I am considering a p-trap vent, but they don't match the look of the boat and they will only protect against small amounts of water, like washdown spray. A full on wave over the stern would overwhelm it and that is what i would be most concerned about. Anyone have any other thoughts on how best to protect the R21 from water getting into the tank through the vent?