[Public-List] Holding tank vent

[Randy Whitney]

Glenn,
Isn't that what the Jocker valve is for?
MOIRAEIII #283

On Mon, Mar 4, 2013 at 11:06 PM, <brooks.glenn at comcast.net> wrote:

> John, Great question...
>
>
> I dont think one vent line can back fill. the ambient air pressure in a
> closed tank system will prevent sea water intrusion through the vent line.
> Certainly did (prevent backfill) in my fishing boat in Alaska, which had a
> fuel tank vent at the bow.
>
>
> But with two 3/4" vent lines, the back pressure in the tank is neutralized
> and it seems like water could then enter, particularly when bashing to
> windward. One of the vent lines would be in a gravity feed position above
> the tank, so conceivably could the tank be in a position then to syphon
> water back into the boat through the commode? A n asty result to say the
> least...
>
>
> Maybe its worth putting a loop or vent or one way valve in each line to
> prevent back fill? aha, another reason to buy yet more hardware, a back
> stop valve between tank and commode.
>
>
> Is this my wildly over active imagination, or has anybody with two vent
> lines ever experience this?
>
>
> G lenn
> Dolce 318
>
> ----- Original Message -----
> From: "John Riley" <jriley at dsbscience.com>
> To: "Alberg 30 Public List -- open to all" <public-list at lists.alberg30.org
> >
> Sent: Monday, March 4, 2013 7:11:20 PM
> Subject: Re: [Public-List] Holding tank vent
>
> I asked this same question before drilling holes in my bow...or a
> similar one. What about waves in rough seas.
>
> I believe it was Mike Lehman that provided the obvious (once I thought
> about it) answer that George gives below...any water intrusion into the
> vent merely would go into the tank itself.
>
> At worse, it would help clean the tank out.
>
> I should add that I have a hand operated pump to pump the tank overboard
> offshore where it is legal to do so vice a head that can be pumped
> directly overboard. Taking sea water into the holding tank, which has
> never happened to us by the way, would only mean having to pump the tank
> empty a bit earlier than I planned.
>
> Regards,
>
> JR
>
>
> On 03/04/2013 04:57 PM, George Dinwiddie wrote:
> > Randy,
> >
> > On 3/4/13 4:00 PM, Randy Katz wrote:
> >> Greetings, Glen,
> >>
> >> I ran my vent tubes (2 of them) from the holding tank (in the same
> >> location
> >> as yours) through the bulkhead and up into the dorade over the
> >> toilet. No
> >> bad smells fliter back to the cockpit. The photo in the A30
> >> collection of
> >> ideas and photos shows vents at the bow, forward-- what about water
> >> coming
> >> down them during heeling?
> >
> > I've never had any trouble with water in the vents. I used standard
> > right-angle fuel vents (one was already there from the Mansfield TDX
> > installation done by the previous owner) and have them angled down and
> > aft. The bow is pretty high, and the cockpit goes under long before
> > the bow does due to heeling. Sometimes the cockpit dips when crashing
> > through waves, but the angle of the vents doesn't seem to pick up any
> > water.
> >
> > Of course, if they did, it would likely just drain into the tank. I
> > worked hard to eliminate any low spots where water could collect.
> >
> > Putting both vents in the same place would seem to me to be
> > ineffective for setting up a flow of fresh air. I've had lots of
> > conversations with Peggie Hall (who has sailed on Calypso, BTW) and
> > she recommended the strategy of venting on each side of the hull.
> >
> > - George
> >
>
> --
> John S. Riley
> S/V Gaelic Sea
> 1972 Alberg 30 #521
>
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