I'm planning on adding a second vent line when I pull this spring. I borrowed Fred's picture because I forgot to take one last weekend. The actual space in the MKI is different, but the space above the tank appears to be about the same, which causes problems. Peggy has said on numerous occasions that more vent is good, so I intend to keep the original stanchion vent in use. I see these as my options.
1. replace the current "L" with a "T" and vent both lines using the existing vent hole.
2. Move the current vent line to the end of the tank (A). It will be easiest to add the vent to the back wall because of vertical clearance. But worried about it plugging when the tank gets full.
3. Add the second vent somewhere on the top, perform surgery on either the removable cover or fiberglass to allow clearance.
If option 2 or 3 is chosen, what is the best method for putting the fitting into the tank?
very interested in what you come up with, I am also at the point you are. Been thinking about point A for me, I just don't see the room for method 3 if you are going to install the one inch that Peggy recommends.
Curious what Peggy has to say about method 1, the tee instead of the L.
I have already installed a clear see through removable 3" beckson port in the top of my tank so I can get my hand in there to tighten locknuts or what ever. Also I find it invaluable to really, really, clean the tank before winter layup.
Thinking about it somemore. I think I need to modify choice 2.
2. Add new vent line to near the top of the back tank wall near A. If the vent gets plugged when the tank is full, it will be easy to clean out with a hose because of the easily accessed thru hull.
Ken, with #1 would would be restricting the opening to the original diameter, like a bottleneck, so I doubt the new vent line wold be effective.
1. replace the current "L" with a "T" and vent both lines using the existing vent hole.
Definitely NOT an option...nor is any other idea that would connect two vent lines a viable option...'cuz the air will just travel across the top of the tee instead of going through the tank.
I like #3: Add the second vent somewhere on the top...you'd need about 3" clearance above the tank.
IMO a Uniseal http://www.aussieglobe.com/uniseal1.htm is the easiest way to put a new fitting into a plastic tank--which is what your tank SHOULD be if it's a Catalina OEM tank...no locknuts or anything else that would require acess to the inside of the tank needed.
We may need to have a phone chat to sort out the best way to do this. 30 minutes on the phone will accomplish more than 50 more posts here. Send me an email if you'd like to take me up on that offer.
I thought that #1 was a non starter, but wanted confirmation.
Also not real keen on either version of #2, unless I can get the vent on top. But the area around the back of the tank is getting crowded. One more line will complicate replacing the macerator or new cable runs to the electrical panel.
So #3 it is. The Uniseal is a neat product!!! Thanks, that will save a tremendous amount of work. It will be a couple weeks before I'm back to the boat to measure and sort out the best way to accomplish this.
My question is that bringing both to the same vent would equal only have one vent line anyway as they are exiting the same size, single opening.
My thought is with 1 vent line the tank would only vent. In..Out no sizable exchange of air. With 2 vents, an exchange of air(oxygen). Is this a good theory?
Jim
Quote from: Jim Hardesty on March 29, 2012, 08:18:19 AM
My thought is with 1 vent line the tank would only vent. In..Out no sizable exchange of air. With 2 vents, an exchange of air(oxygen). Is this a good theory? Jim
That depends on how long the vent line is, size of the diameter, whether it's straight or has bends in it, and how steep the rise is.
A 1" vent line that's absolutely straight, no more than 5' long, doesn't rise more steeply than 45 degrees, AND has nice open bulkhead thru-hull with no cover or screen in it will exchange air with the gasses in the tank just fine. The longer and/or steeper the line, the harder time it has exchanging air...bends in the line make it impossible. When none or most of the above is possible, a second vent may be needed...sometimes aeration is the only solution.
In a perfect world, all toilets would be right behind the v-berth...the tank would be under the v-berth...and the vent line would run forward off the top of the bow end of the tank to exit the hull about 2' aft of the stem, about a foot below the toe rail. 'Cuz that guarantees that air will be continuously forced into the vent any time the boat is underway or on a mooring or anchor. Unfortunately, boat builders often have a different idea what makes a perfect world, so we have to work with what the give us.
Ken, I have 1988 and I see no viable way of using option 3 with a 1" fitting on my tank, there simply isn't any room on top of the tank under the hardboard cover for a fitting and hose, I am curious on what you come up with there and where you vent it to the outside, please keep us informed thanks Bob
...I have 1988 and I see no viable way of using option 3 with a 1" fitting on my tank, there simply isn't any room on top of the tank under the hardboard cover for a fitting and hose...,
Where on the tank is the existing vent fitting--on the top, or AT the top of a vertical surface? In either case, is it closer to the hull or closer to the centerline of the boat?
The tank has a recessed area on the top for the original vent. Looks like easter will get in the way of boat work, so be at least 2 weekends before I can take a look at how to do it.
The physical location of an added second vent seems very similar to having as a test, a modified pump out cap with a vent hole in it.
I wonder if this would be a fair test to see if it's worth the trouble to punch new holes in tank and hull and then find out it's not really working.
I can't seem to find a way to add another vent either.
I'm trying to have the "phone call with Peggy" about this very topic also, I just can't find the time during the day to call, maybe I won't have to if you get yours in and it solves the problem.
Hi Ken, I changed my vent line last year from the stanchion to a thru hull. The problem we had was that the vent in the stanchion seemed to plug easily. Used a small hand pump to clean it out. I took the stanchion off and noted that the small diameter in the base of the stanchion. I filled all the holes and ordered new stanchions so that I could move the gate more to mid ship position. We have always used odorless in our boat and motor home. Never had problems with odors.
The physical location of an added second vent seems very similar to having as a test, a modified pump out cap with a vent hole in it.
Won't work...'cuz the pumpout line comes from the bottom of the tank...it can't provide a source of air above the surface. At best it could prevent a tank implosion from the suction of an excessively strong pumpout.
I'm trying to have the "phone call with Peggy" about this very topic also, I just can't find the time during the day to call.
So what's stopping you from letting me know what WILL work for you?
Quote from: Paulus on April 02, 2012, 04:55:30 AM
Hi Ken, I changed my vent line last year from the stanchion to a thru hull.
So where did you place the thru hull?
Thanks,
Rick
Yep,,, not a very long thought out reply. In Kens pic, it just looks like the hose is near the top of the tank. Chalk it up to a Senior moment, I haven't seen my tank since November. I stand corrected!
Secondly, I'm trying to respect Peggy's time like I would respect my own... when I get a chance to set up an appointment to call roughly between 8-5 M-F, I will. I may be a sailboat owner but I'm far from RETIRED!
I added a second vent to my holding tank this weekend. I gave Peggy a call earlier this year and got some good advice before starting the job. One thing that is recommended is to keep the vent hose rising at less than 45 degrees. I'm not sure that this is possible or practical on our C34s. Boats with the holding tank under the V-Berth could likely do this easily but our tanks under the port settee make this virtually impossible without a very long length of hose.
I picked the location for the new vent just below the rub rail and aft of the bulkhead. It's easy to get to, is hidden by speakers under normal use and "looks right" on the outside just below the rubrail. I got the fitting on ebay. It has a stainless cover and a marelon-like body. About $8.50 or so. The hull is about 1 1/2" thick at this point including the ceiling battens. I bedded the through-hull fitting with Butyl Tape.
- 1st Picture – inside view
- 2nd Picture – Stainless cover on the outside
I used 3/4" Trident XHD sanitation hose for the job. I could have made 1" hose fit but I figured the fewer and smaller holes I had to drill, the better.
I routed the hose down into the cubby behind the settee back and then through the forward locker into the holding tank locker. Drilling into the cubby took some patience and some careful probing with small test drill bits to avoid the structural elements (steel?) supporting the rigging loads through the chainplates.
- 3rd Picture
I connected the new vent hose to the old vent fitting on the holding tank.
- 4th Picture
With the speaker in place, and the cabinet closed, the hose is invisible and there is a very minimal reduction in usable space in the cabinet and cubby.
- 5th Picture
I'm at my picture limit for one post. Adding a new vent hole to the holding tank and renewing the original hose for the vented stanchion in the next post.
In addition to adding a second vent, I replaced the freshwater grade vent hose to the vented stanchion with proper sanitation hose.
- 1st Picture – old and new hose
I also had to add a new fitting to the tank. Peggy recommended Uniseal for a new vent hole in the tank, but I had a couple of extra through-hull fittings lying around and I had already installed an inspection port in the holding tank so the through-hull was very easy to install. I drilled a hole near the aft inboard corner of the tank because that is where I had the most clearance between the tank and the settee seat board. The top of the tank is 3/8" thick.
- 2nd Picture – new hole and through hull into the holding tank
The finished job is shown in the 3rd picture. I'll let you know how it works throughout the summer. Next unpleasant job – replace the 1 1/2" hose from the head to the tank and from the tank to the pumpout deckplate.
Why 2 vents? As Peggy has noted that we need a good vent that works. A 2 vent system is a good idea but has not addressed the problem, the original vent is not working as it should. The problem as I see it:
1. the old vent has 4 90 degree angles
2. the opening in the stanchion is small and prone to filling with water and dirt
3. the 2nd 90 degree angle after leaving the tank forces the hose to dip down below the top of the holding tank and acts as a trap
To correct the problem, I did the following:
1. took out the 2 corner panels that hide the pump out, vent line( 4 screws in each set)
2. removed the old vent line
3. checked out the space and how I could get a new thru hull next to the pump out hose behind these panels.( about 1' from the deck) marked this spot.
4. took off the old pump out hose and put my new thru hull fitting in place
5. at this time I also drilled a new 1" hole in the storage bin at a 45 degree angle for the new vent hose. This was to keep the vent line from dipping down.
6. replaced all the hoses with new, tested the vent system to be sure that it drained back into the tank. Replaced all parts. Worked great last season.
PS: My previous boat was an Irwin 34 with a vent system that travel about 14 ft with numerous low spots. Constant blockage.
Paul
very nicely done Dave, pictures are great, Paulus, I think I understand what you did, but, do you have pictures as well, were you able to increase vent size to one inch as peggy suggests? Is your new thru hull just below the rub rail?
Bob, I stayed with the existing size. The thru hull is about 8'' to 12" below the rub rail, as high as I could get it before the pump out hose no longer would flex to allow for a thru hull. I did not want the hose showing in the cabin. The vent is only used to let gas out. The only time that air travels down this vent is during pump out.
Paul
I have read several post about members repositioning the holding tank vent to just below the rubrail either just forward or just aft of the port bulkhead and it is my intent to do the same this week. My only question is has anyone found this location to allow seawater to enter the vent when sailing deep angles on a starboard tack. It is rare for us to sail for any length of time with the rail under water it does happen on occasion and I don't want to fill my holding tank with lake water. The addition of a clamshell comver should negate this concern, but I do't like the look of them so I would prefer to not install one.
Thanks in advance
Dave Spencer has two identical vents for all intents and purposes. He doesn't really say, but it would seem he kept the stantion vent intact. According to the experts he now has two vents that won't work due to not being at less than 45degrees slope. With any luck you may get a breeze through your tank if air pressure hits the opening on one vent, maybe. Is that a fair assumption?
Paulus has only eliminated the stantion vent and shortened the run to the opening about a foot.
I'm thinking that if folks are making this modification putting the thru-hull below the rub rail, that the odor is somehow being, more often that not, directed away from the cockpit... unlike the stantion vent which dumps the smelly gas right at nose level when the head is pumped. Nobody has really pointed out that the tank odor smells all the time or just when the head is pumped. In my case, I only get assaulted by tank smell when the head is pumped. My stantion does not have a slit. It is 7/8ID until it exits the stantion vent hole which is the same diameter as a 1/4 pipe thread. In fact, I threaded my stantion hole with a 1/4 pipe tap and put a 1/4x3/8 hose barb in the hole, for which I slip on a piece of 3/8 clear tubing to hang over the side when we are onboard. This puts smelly gas exiting the tank at the waterline.
After talking with Peggie about conquering the aerobic/anaerobic tank environment I was fairly sure no vent mod in my c34 will accomplish what is needed to achieve this. So the next best thing is to direct the smell away from the deck. There are tank aerators that run off 12 volts pumping fresh air into the tank all day... but, I don't know about that solution...
A brief addition. I also changed the water tank vent. Filled all holes with epoxy and then moved the opening gate forward so that it was more at mid ship. Note the rectangular foot print on the support stanchion. This was changed to cover the vent hole.
I had the vent line off on a recent trip... because I was using the elbow access to view inside tank to determine level... and had a thunderstorm. When the rain really started to fall, and the scuppers stopped being able to keep up, I was shocked to get water flowing back down my vent line. Has anyone else seen this?
Interesting thread, but a second vent line for the holding tank, what's the point?
What is the problem all this is trying solve?
Why would there be backflow their the vent??
Perhaps an answer in search of a problem.
Lots posted over the years, here and elsewhere, about what a second vent does, and why it is often needed.
Mike
I'm intertested -- which vent and where is it located that you were getting the back flow?
-k
I have experienced the same issue, and having researched it on this (incredible) web site, plan to place the second vent this winter. In my case, a water lock occurred in the vent line, leaving no where for the gas fumes to go, expanding the tank and pushing water back toward the bowl. My vent had been relocated to the deck, next to the pump out fitting, using a standard vent mushroom like we have for the fresh water tank.
Interestingly, my neighbor's Sea Ray powerboat suffered the same consequence caused by the high velocity flow of water down the side when under way.