Holding tank venting

[Errell]

Finally installing tank purchased from you over a year ago. Built wooden cradle epoxied to hull as far forward as possible under vee birth. Am installing two one inch vents. Problem is: If vent lines go straight out (rising only 1-2 inches),port and starboard, the thru-hull is only 11 inches above the water line. I can run the hoses further forward (about 10 inches) and up 90 degrees approximately 12 inches and the thru-hull fitting will be 23 inches above the water line. In your piece about "VENT fittings..." you stated that very little water would be taken into the tank even with a direct hit from a breaking wave due to back pressure from the tank. Will I be safe in placing the thru-hulls in the lower position or should I install them in the more circuitous route?

 

[Peggie Hall/Head Mistress]

Best to go higher.

But without the 90 degree bend. I wouldn't put the thru-hull much lower than about 18" below the toe rail. So take the vent hoses as far forward as it takes to give you the straightest run possible with a maxium rise of 45 degrees. A single 1" vent that's up to 3' long can easily work...2 of 'em should work just fine up to 5-6'. If you have two vents (it's been a while and I don't remember exactly what we did), criss cros the lines too...that will prevent spillage when you heel. And I'm SO glad you asked what to do before you did it!