Location of fuel tank vent

[Peter Jenny]

I have been re-laying the teak deck on my Cheoy Lee and in the process am trying to illiminate as many holes that penetrat into the sub-deck as possible. The original fuel tank (gasoline) vent was located through the side deck directly above the fuel tank. Although the vent fitting has a screened 90 degree openning, the location seams like it would have the potential for letting water into the tank. Question: Since I have converted fron gasoline to deisel, why cant I simply vent the tank below deck through an adjacent cockpit locker baulkhead?

[Figment]

well... because it vents. Wherever you put it, it's going to emit diesel fumes. Diesel fumes in the cockpit would be unpleasant at best, and venting into a locker will just make everything in that locker smell.

Is the transom an option?

[Peter Jenny]

Yes the transom is probably where I willrun the vent line. I just wasn't shure how big a deal diesil fumes were.

[Tim]

The reason you need a vent is because fuel will expand when it gets warmer; a full fuel tank can actually vent solid fuel out through the line, if overfilled. Without the vent, the fuel (and vapors) would have nowhere to go.

The vent is also critical to allow proper suction of fuel from the fuel tank; think about how it is to pour any liquid out of a jug with no vent, and how much better it is when you open the small vent (such as in a jerry jug or fuel can). You may not even get proper fuel supply to the engine in an unvented system.

The transom is generally a good location because the fuel fumes disappear unnoticed downwind, it stays out of the water during normal sailing (thereby avoiding, under normal use, the possibility of getting water in through the vent), and generally prevents staining on the hull, too. Right or wrong, fuel and other vents have been directed overboard for years. In practice, raw fuel doesn't come out that frequently, unless the tank is overfilled.

Whatever the fuel, it's a bad idea to vent onto the decks or into an interior space.

[Noah]

My fuel vent (diesel) is vented on the decks behind the cockpit and I have never once even smelled a hint of diesel fumes. I know it shouldn't be done, but it seems to be a non-issue on my boat.