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vette-ski

For those that have built their own fat sac system

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vette-ski

Doing searches it doesn't seem like many people are messing with plumbing in a vent line for ballast sacs. What's the consensus? I know what the vent line is supposed to do, but is anybody having any real issues with the sack not filling full due to trapped air? I'd like to keep the holes and thru-hull fittings on the side of the boat to a minimum. I've thought about putting a "Y" fitting for the drain line and vent line to go to a single thru-hull, and just routing the vent line in a way that will keep drain water from filling back into the bag via the vent. I don't see any issue vice versa with vent discharge going into the drain line. Thoughts?

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Chia
Doing searches it doesn't seem like many people are messing with plumbing in a vent line for ballast sacs. What's the consensus? I know what the vent line is supposed to do, but is anybody having any real issues with the sack not filling full due to trapped air? I'd like to keep the holes and thru-hull fittings on the side of the boat to a minimum. I've thought about putting a "Y" fitting for the drain line and vent line to go to a single thru-hull, and just routing the vent line in a way that will keep drain water from filling back into the bag via the vent. I don't see any issue vice versa with vent discharge going into the drain line. Thoughts?

if the air is mostly sucked out of the bag before you fill with water, you should not have any problems. The space inside the bag will be displaced with water except for any cubic inches that are already displaced by air already in the bag.

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sp0tts

http://www.themalibucrew.com/forums/index....&hl=ballast

A check valve could possibly solve the problem that person had, but personally I would run more pumps as a lot of other people do. It's going to take a long time to fill if you don't, the bags may not completely drain, and there could be other issues. That being said, the add on fly high add on system for the Xstar used to be gravity fed, not sure if it still is, but I believe it is. So it is possible. I'd try to maybe do another search or search on wakeworld if you can't find anything more.

Here's another good thread:

http://www.themalibucrew.com/forums/index....&hl=ballast

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vette-ski

I don't currently have any stock ballast tanks. I'm adding a 3 sac system, two in rear, one up front. I'll have 3 fill pumps, and 3 drain pumps. The 3 drain pumps will have 3 exit thru-hulls. My question is will I need 3 additional exit thru-hulls for vent lines.

Sounds like Cervelo is on the right track if I make sure they are sucked empty before you start. Of course I could just try it with no vents and add them later if it gets to be a problem. Wouldn't be too hard to add later. I just don't want holes all over the boat if I sell some day and don't sell the sacs with the boat.

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WakeGirl

The stock systems that I've worked with in the past had the vent plumbed into the fill side instead of the empty. This served 2 purposes - 1 obviously is to vent the bag of air, & 2 was to provide a relief for when the bag is full. It prevents the bag from popping, which truth be told is my own biggest reason for venting a bag. I use impeller pumps for filling, so it's especially important.

Making sure that they're sucked empty to start with is easier said than done, especially when working with aerators. If you're using impeller pumps, then that's easier (those pumps aren't fast, but they'll turn the bags into raisins).

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vette-ski

I'm going to use aerator pumps.

The stock systems that I've worked with in the past had the vent plumbed into the fill side instead of the empty. This served 2 purposes - 1 obviously is to vent the bag of air, & 2 was to provide a relief for when the bag is full.

Hmmm, that's interesting. I guess I'm not visualizing this. Does the vent line tap in before or after the pump? Or maybe I'm misunderstanding you. My sacs have 3 ports. I plan to fill at the top, drain at the bottom, and port #3 (also on the top) would be the vent. When I said to run the vent line to the "drain", I meant where it exited the boat at the thru hull, not tap into the line at the bottom of the sac. I know what you mean about pressure relief too. It would be nice to just hit the switch and when you hear water splashing over out the thru-hull you know you are full. Otherwise you'll need to keep an eye on them. But again, if the vent feeds the fill line, won't it just go back out the bottom of the boat? I guess I can see that working.

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whitlecj

I have not plumbed one of these systems in myself, but based off manually filling these bags, I would definitely figure out a way to plumb in the vent lines. I think it would make using bags much a less a hassle if you want them 100% full.

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Juice75

I put a 3-bag system in my Sunsetter, and I didn't mess with vent lines. Since I'm using aerator pumps, when the bags get full, the excess water pushes past the drain pump and out the drain hole in the side of my boat. That's how I know they're full. I'm also using Fly High fat sacs, so the aerator pumps don't generate enough pressure to make them pop.

There are probably pro's and con's for each way, but I decided to keep it simple-ish.

Kraig

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WakeGirl
I'm going to use aerator pumps.
The stock systems that I've worked with in the past had the vent plumbed into the fill side instead of the empty. This served 2 purposes - 1 obviously is to vent the bag of air, & 2 was to provide a relief for when the bag is full.

Hmmm, that's interesting. I guess I'm not visualizing this. Does the vent line tap in before or after the pump? Or maybe I'm misunderstanding you. My sacs have 3 ports. I plan to fill at the top, drain at the bottom, and port #3 (also on the top) would be the vent. When I said to run the vent line to the "drain", I meant where it exited the boat at the thru hull, not tap into the line at the bottom of the sac. I know what you mean about pressure relief too. It would be nice to just hit the switch and when you hear water splashing over out the thru-hull you know you are full. Otherwise you'll need to keep an eye on them. But again, if the vent feeds the fill line, won't it just go back out the bottom of the boat? I guess I can see that working.

On the older systems that used a bag for the center MLS, the bag only had 2 ports on it. So they had to have some way of pressure relief. The vent was introduced after the pump (since the pump was in the floor), up high in the loop that they made to prevent auto-filling. The y was inverted, so that the vent line came back against the flow of the water. It worked pretty well. With the orientation of the vent, you didn't have too much water leaving until pressure forced it. And when the pump wasn't running it couldn't drain through that spot because it was up high enough to prevent that. Maybe there's part of this idea that would work for you.

I think that I see what you're saying. It sounds like you want to put a y on the empty line right at the thru hull, is that correct?

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vette-ski
I put a 3-bag system in my Sunsetter, and I didn't mess with vent lines. Since I'm using aerator pumps, when the bags get full, the excess water pushes past the drain pump and out the drain hole in the side of my boat. That's how I know they're full. I'm also using Fly High fat sacs, so the aerator pumps don't generate enough pressure to make them pop.

There are probably pro's and con's for each way, but I decided to keep it simple-ish.

Kraig

I saw your past post and all of the pics were great. That helped me get to the point I'm at now. From your pics, it looks like you are filling into the top and draining from the bottom. I can see how when the bag is full it will push past the drain pump and out the thru-hull, but won't the air bubble in the bag stay at the top of the bag. I don't see how the air will push out since it will always rise to the top. That's what I'm trying to keep from happening....having a sac that is 1/4 full of air. Obviously a vent is the answer, I just didn't know if it was really an issue worth messing with. But since these sacs aren't see-thru, it's hard to know how much is air and how much is water when it is fully blown up.

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vette-ski
I think that I see what you're saying. It sounds like you want to put a y on the empty line right at the thru hull, is that correct?

Correct. A tee fitting might actually be easier to find in that size. Picture a tee with the "straight through" part being the drain line to the thru-hull. The short leg of the tee would be pointed upward, with the vent hose connected to it. So air in the sac could burp out the thru-hull, but when you are draining it should shoot out the thru hull with very little if any going back up the vent line. All this thinking out loud I think that's what I want to do. Will only cost a couple fittings and hose to give it a try.

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WakeGirl
I think that I see what you're saying. It sounds like you want to put a y on the empty line right at the thru hull, is that correct?

Correct. A tee fitting might actually be easier to find in that size. Picture a tee with the "straight through" part being the drain line to the thru-hull. The short leg of the tee would be pointed upward, with the vent hose connected to it. So air in the sac could burp out the thru-hull, but when you are draining it should shoot out the thru hull with very little if any going back up the vent line. All this thinking out loud I think that's what I want to do. Will only cost a couple fittings and hose to give it a try.

I think that the theory of this is spot on, but the implementation of it will be difficult. If you think about how much room is under the gunnels (not much), by the time you get a tee on there, there may not be enough room for the hose to bend up & around. That may force you to look at adding 90 degree fittings to the equation, but that may decrease the effectiveness of the vent line. Plus it's going to make the hose stick out from the thru-hull quite a bit farther, so your bags in the trunk may interfere with that.

Not trying to poke holes in your idea, just trying to see any potential problems. I've torn my system apart at least 3 times on the current boat alone, so IME these are the kinds of things that we don't think of. :)

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Juice75
I saw your past post and all of the pics were great. That helped me get to the point I'm at now. From your pics, it looks like you are filling into the top and draining from the bottom. I can see how when the bag is full it will push past the drain pump and out the thru-hull, but won't the air bubble in the bag stay at the top of the bag. I don't see how the air will push out since it will always rise to the top. That's what I'm trying to keep from happening....having a sac that is 1/4 full of air. Obviously a vent is the answer, I just didn't know if it was really an issue worth messing with. But since these sacs aren't see-thru, it's hard to know how much is air and how much is water when it is fully blown up.

There usually is a small bit of air in the bags, but not much. I would say I probably only lose a pound or two because of the air. If the bags are empty when you start filling, then not much air gets in. And you're right, the air doesn't push past the drain pump. About once a season, I'll pull the other plug on the top of the rear bags to "burp" the air out while their filling. I usually do this about once or twice a season. It's not that big of a deal for me.

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Juice75

And D-GOOSE, glad to see my install post is still getting some good use. Thumbup.gif

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Mechmaster
On the older systems that used a bag for the center MLS, the bag only had 2 ports on it. So they had to have some way of pressure relief. The vent was introduced after the pump (since the pump was in the floor), up high in the loop that they made to prevent auto-filling. The y was inverted, so that the vent line came back against the flow of the water. It worked pretty well. With the orientation of the vent, you didn't have too much water leaving until pressure forced it. And when the pump wasn't running it couldn't drain through that spot because it was up high enough to prevent that. Maybe there's part of this idea that would work for you.

Do you have any photos of the stock vented loop assembly?

Edited by Mechmaster

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WakeGirl

Unfortunately no. It was something that I always intended to do, but I have a bad habit of getting into a project & just going right through without stopping to document any of it.

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Mechmaster
Unfortunately no. It was something that I always intended to do, but I have a bad habit of getting into a project & just going right through without stopping to document any of it.

OK, if I'm understanding your right, this is how the stock Malibu MLS system used to work with the 2-port center bag. See the attached image:

Ballast1.jpg

In the Figure, the yellow is the fill circuit and and red the drain circuit. Water is drawn from the lake by the fill pump; it passes through a loop of hose extending above the waterline and into a wye ('A' in the diagram). Wye 'A' is then connected to the fill port of the sack.

Wye 'A' accomplishes (2) things: 1) it vented the fill loop such that a spihon cannot start and drain the bag while under way, 2) When the bag fills, air can escape.

The vent line is plumbed from Wye 'A' into the empty circuit and out the thu-hull on the side of the boat.

Am I close to the configuration of the stock system? Comments are appreciated.

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WakeGirl

Pretty good approximation, the only thing with the y is that on the systems that I've seen the y was right at the top of the loop, with the vent line in the upper position. The other thing is that they used a separate thru-hull for the vent instead of tapping into the drain line. Again, the only reason that they did it this way was because the bag that they used only had 2 ports on it, so it was a clever way of overcoming that issue.

I haven't actually torn into my stock system to see how the hard tanks are set up, but the little that I have seen indicates that they've all got independent vent lines. I've got an issue with my bow tank that I need to resolve, so I can report back on that one when I get it apart.

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Mechmaster
Pretty good approximation, the only thing with the y is that on the systems that I've seen the y was right at the top of the loop, with the vent line in the upper position. The other thing is that they used a separate thru-hull for the vent instead of tapping into the drain line. Again, the only reason that they did it this way was because the bag that they used only had 2 ports on it, so it was a clever way of overcoming that issue.

I haven't actually torn into my stock system to see how the hard tanks are set up, but the little that I have seen indicates that they've all got independent vent lines. I've got an issue with my bow tank that I need to resolve, so I can report back on that one when I get it apart.

I revised the diagram; the stock MLS is plumbed like the following figure:

Ballast2Medium.jpg

Two questions:

1. Is there any point to adding a check valve in the indicated location, or is the venting/loop assembly enough?

2. Using aftermarket bags with (3) or more ports, should I use the 2-port system or plumb in an additional vent?

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D-GOOSE
And D-GOOSE, glad to see my install post is still getting some good use. Thumbup.gif

That is a class act install and shows step by step how to add a ballast system. You put a lot of time and hard work into that project. Thumbup.gif:salute:

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WakeGirl
Pretty good approximation, the only thing with the y is that on the systems that I've seen the y was right at the top of the loop, with the vent line in the upper position. The other thing is that they used a separate thru-hull for the vent instead of tapping into the drain line. Again, the only reason that they did it this way was because the bag that they used only had 2 ports on it, so it was a clever way of overcoming that issue.

I haven't actually torn into my stock system to see how the hard tanks are set up, but the little that I have seen indicates that they've all got independent vent lines. I've got an issue with my bow tank that I need to resolve, so I can report back on that one when I get it apart.

I revised the diagram; the stock MLS is plumbed like the following figure:

Ballast2Medium.jpg

Two questions:

1. Is there any point to adding a check valve in the indicated location, or is the venting/loop assembly enough?

2. Using aftermarket bags with (3) or more ports, should I use the 2-port system or plumb in an additional vent?

On the fill side, that's it, you've nailed it. In the stock system since the bag was below the floor, no check valve was needed because the loop came up through the floor (that I may be able to provide a picture of, I'll have to check) & the top of it sat about 6-8 inches above the floor. If you're using 3 port bags, just put the vent line on the 3rd port. You don't have to bother with this setup since the vent on the 3rd port will both vent the bag & act as pressure relief when it gets full.

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Mechmaster
On the fill side, that's it, you've nailed it. In the stock system since the bag was below the floor, no check valve was needed because the loop came up through the floor (that I may be able to provide a picture of, I'll have to check) & the top of it sat about 6-8 inches above the floor. If you're using 3 port bags, just put the vent line on the 3rd port. You don't have to bother with this setup since the vent on the 3rd port will both vent the bag & act as pressure relief when it gets full.

In your experience, is the loop enough in the fill line to prevent siphoning? An advantage of the vent in the top of the loop is that it breaks the siphon.

I might lean towards a two-port setup (combo fill-vent/drain) rather than 3 ports (separate fill/drain/vent) to reduce the siphon issue.

Comments?

Edited by Mechmaster

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WakeGirl
On the fill side, that's it, you've nailed it. In the stock system since the bag was below the floor, no check valve was needed because the loop came up through the floor (that I may be able to provide a picture of, I'll have to check) & the top of it sat about 6-8 inches above the floor. If you're using 3 port bags, just put the vent line on the 3rd port. You don't have to bother with this setup since the vent on the 3rd port will both vent the bag & act as pressure relief when it gets full.

In your experience, is the loop enough in the fill line to prevent siphoning? An advantage of the vent in the top of the loop is that it breaks the siphon.

I might lean towards a two-port setup (combo fill-vent/drain) rather than 3 ports (separate fill/drain/vent) to reduce the siphon issue.

Comments?

I didn't think of that, that's a great point. In my experience, yes it's enough. But there are others that won't agree with me on that.

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vette-ski

I may consider this two port install if I decide to go to a locker bag (have been considering a bow under seat sac). Reason being is port #3 is way at the other end of the sac, and impossible to reach way up in the ski locker. It may be easier to work with the two ports at the open end of the ski locker (IE, access quick connects to pull the sac out). Thanks for this info.

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