Vent size

[Ghaegele]

I have worked out most of the issues regarding the installation of a new tank in my C&C35 (much thanks to those who offered opinions) but still have a question regarding the vent. There seems to be conflicting advice. I plan to run the vent from the center of the tank which will be in the bottom of the v-berth, up to the bow near the deck. It's about a 6' run with a curve from the bow end of the v-berth up through the chain locker. The tank is 13 gallons. Is one 3/4" vent line enough? Is one 1" advisable? Do I need two vents on opposite sides of the hull or is that only where the tank is further away? Also, clamshell over the the vent opening or no?

 

[Steve Dion]

Why not just vent it into the chain locker. The only problem is if you overfill your tank. I would like that a 3/4" line is fine if it only 6' long.

I do not like clamshell vents for waste, it is much easier to backflush a straight thru fitting.

 

[Ghaegele]

Chain locker opens to the cabin. Yuck. I think there are removable clamshells. My boat's 36 years old and rides a bit low. On a heavy tack in moderate sea waves wash up the forward hull and could enter the vent. Probably not gallons, so I could go either way. Guess I could always add a clamshell if it becomes a problem.

 

[Steve Dion]

Yes, that would be a problem if it opens into the cabin.

The only problem with the clamshell is that it does not allow you to rinse the vent hose, but if they make them with a removeable shell that will be fine if it does not fall off.

 

[Peggie Hall HeadMistress]

Bad advice!

Why not just vent it into the chain locker. The only problem is if you overfill your tank. I would like that a 3/4" line is fine if it only 6' long. I do not like clamshell vents for waste, it is much easier to backflush a straight thru fitting.

Because methane is flammable, CG regs REQUIRE that all black and gray water tanks be vented to the outside of the boat...which rules out venting any waste tank into the chain locker.

A 3/4" vent line is the absolute minimum size I recommend for a vent line that's only 2-3' long and straight as an arrow. 1" or even 1.5" is preferable for longer vent lines.

I'm not a fan of clamshells either, but the vent thru-hull location and use of the boat can sometimes make it the only viable option. But you didn't seem to think it necessary to ask enough questions to find out whether it is or not.