O'day 39 Head question

[Panta Rei]

I have an O'day 39 . The heads are elevated so the rims of the bowls are above the waterline while docked or motoring. I usually switch pump valve to empty and lock down the plunger when sailing hard but don't worry much about it. Yet I have never had a head overflow and believe the head may never overflow unless we are dipping the rail in the water. The head is a Jabsco 29090 or similar. I do not have a vented loop between the pump and the bowl.
Am I asking for trouble?

 

[Ralph Johnstone]

Depends .........................

Am I asking for trouble?

....................... on the practicality of installing a vented loop. I've had the pleasure of working on the vented loop behind our head and can honestly say, that if it wasn't already there, the only way of installing said loop would be to cut out the interior hull liner along with a cabinet.

If yours is the same case, from what you've described as your practice in locking out the head, I'd choose the practical approach and leave it.

You could also slather decals on top of and under the lid as well as instill the fear of God into visitors re locking out the head after use .

 

[jibes138]

....................... on the practicality of installing a vented loop. I've had the pleasure of working on the vented loop behind our head and can honestly say, that if it wasn't already there, the only way of installing said loop would be to cut out the interior hull liner along with a cabinet. If yours is the same case, from what you've described as your practice in locking out the head, I'd choose the practical approach and leave it. You could also slather decals on top of and under the lid as well as instill the fear of God into visitors re locking out the head after use .

shut your through hull when under sail and put a gallon jug of water in the head for flushing. Much easier than a vented loop.

 

[Peggie Hall HeadMistress]

... The head is a Jabsco 29090 or similar. I do not have a vented loop between the pump and the bowl. Am I asking for trouble?

Yes...and it wouldn't matter what make/model your toilet is. Priming a manual toilet starts a siphon...the vented loop is an anti-siphon device that breaks that siphon when pumping stops. So without a loops, all it would take to start a flood would be for one guest or crew to leave the pump in the "wet" mode. If it happens when you're aboard, you'd like only have to spend some time manning mops and buckets...but it if it's left in the wet mode with the seacock open when no one is aboard (Don't say it can never happen...it does. People are fallible, especially at the end of a weekend aboard when they're tired), wind from the wrong direction could start pushing water up the head intake line and start the siphon needed to sink your boat in its slip. The loop is cheap insurance that saves people from themselves.

....................... on the practicality of installing a vented loop. I've had the pleasure of working on the vented loop behind our head and can honestly say, that if it wasn't already there, the only way of installing said loop would be to cut out the interior hull liner along with a cabinet..

There's no "rule" that requires the loop to be mounted directly behind the toilet... In one model year (forget what size boat), Hunter ran it all the way over into a locker forward of the vanity!

Looking at your photo, it appears that the bulkhead to the left of the toilet is a straight smooth "wall"...Why couldn't a vented loop be it be mounted on it? It has to be at least 6-8" above water line at ANY ANGLE OF HEEL, which puts it 2-3 feet above the bowl...the hoses to and from the loop would just have to be a little longer to put there. In fact I found a photo in my files that kinda illustrates putting off to one side.

 

[jibes138]

Peggy your points are valid but a siphon requires the outlet to be lower than the inlet. If the head is above the water line I don't see how you can create a siphon? What am I missing?

 

[Peggie Hall HeadMistress]

As long as the head IS completely above the waterline, no siphon will start. However there are very few sailboats under 60' on which this would be true.

But the flow started by priming a pump doesn't have to be a true siphon to continue...and that's where the anti-siphon device earns its keep...by bringing air into the line to interrupt the flow of liquid.

Very few boat owners, even those who are replacing toilets, ever bother to read the installation instructions for their toilets. If they did, they'd see that EVERY mfr recommends installing an intake vented loop when the toilet is below--or even AT--the waterline...and also include drawings showing where it belongs--between the pump and the bowl.

 

[jibes138]

As long as the head IS completely above the waterline, no siphon will start. However there are very few sailboats under 60' on which this would be true. But the flow started by priming a pump doesn't have to be a true siphon to continue...and that's where the anti-siphon device earns its keep...by bringing air into the line to interrupt the flow of liquid. Very few boat owners, even those who are replacing toilets, ever bother to read the installation instructions for their toilets. If they did, they'd see that EVERY mfr recommends installing an intake vented loop when the toilet is below--or even AT--the waterline...and also include drawings showing where it belongs--between the pump and the bowl.

great info thanks. Makes me wonder why the OEM's don't properly install them?

 

[Panta Rei]

As long as the head IS completely above the waterline, no siphon will start. However there are very few sailboats under 60' on which this would be true. But the flow started by priming a pump doesn't have to be a true siphon to continue...and that's where the anti-siphon device earns its keep...by bringing air into the line to interrupt the flow of liquid. Very few boat owners, even those who are replacing toilets, ever bother to read the installation instructions for their toilets. If they did, they'd see that EVERY mfr recommends installing an intake vented loop when the toilet is below--or even AT--the waterline...and also include drawings showing where it belongs--between the pump and the bowl.

Thanks Peggie,
A vented loop can be easily installed on both heads in an O'Day 39, plenty of room. I'll likely do it before the boat goes back In the water. It's too simple not to do it.
You and Jibes explained why O'day elevated the head. On paper, the elevated head should prevent a siphon. One paper, I've sailed around the world. There is nothing like the real world.
I'm trying to leave bread crumbs for other 39 owners who will be asking these same questions years from now. Thanks for your help.