Seeping G Ballast

[vision]

Sorry really dumb question: are the pumps under the waterline? If so wouldn't bringing them above the waterline alleviate the pressure on/water getting past the impeller?

That is what we use to do and it worked fine with bidirectional Jabsco pumps.

[Tallredrider]

Changing the mounting location would probably fix the problem, but the question would be where to put them. Even a loop high enough to stop the seep would allow you to keep the pumps in the same location.

[Adam Greer]

As I said in a previous response. The pumps are not below the water line. Changing the pump location or running the hoses higher will not fix the problem. The siphon is started as the result of a vacuum pulled in the system. A traditional siphon break cannot be used because of the use of reversible pumps which lead to the current solution. The system was cycle tested through several thousand cycles with no issues so it has proven to be very reliable If for some reason the system did fail, the ball valves can be manually operated simply by disconnecting the ball joint that the push pull cable is attached to handle with. There is nothing that would prevent you from being able to fill or drain your ballast.

[Tallredrider]

As I said in a previous response. The pumps are not below the water line. Changing the pump location or running the hoses higher will not fix the problem. The siphon is started as the result of a vacuum pulled in the system. A traditional siphon break cannot be used because of the use of reversible pumps which lead to the current solution. The system was cycle tested through several thousand cycles with no issues so it has proven to be very reliable If for some reason the system did fail, the ball valves can be manually operated simply by disconnecting the ball joint that the push pull cable is attached to handle with. There is nothing that would prevent you from being able to fill or drain your ballast.

I've trolled these boards a lot, and never seen anyone have troubles with siphoning through a reversible pump. Not to mention installed several ballast systems and never had a siphoning problem with them. Why does this happen then? Vacuums are not created in any MC I ever heard of which uses the same pumps. I am not trying to be argumentative, just wondering what the science is behind the creation of the vacuum that is different than with other boats that NEVER have this problem.

[Adam Greer]

It is a by product of our system design. We use soft bags with a check valve so that we can pull all of the water out of the bag regardless of the boat attitude or causing the pump to run dry excessively. Mastercraft uses primarily hard tanks which you can't use a check valve with, but is typically not required to drain a hard tank. The check valve in our system allows us to do a great job pulling water out, but the pumps work so well that they will also pull all the air out of the bag. If the pump runs long enough, water might still be removed from the bag, but you are also pulling a substantial vacuum into the bag to get that water out. Once the pump is turned off, the vacuum wants to "relax" and because the system is still open to the lake the vacuum pulls water back up into the system and starts a siphon (and you wouldn't believe how high the vacuum in the system can lift the water). Removing the check valves wasn't an option and many other alternatives were tried, but none of them fixed the problem 100% of the time unless you closed the system or we added another set of pumps to drain the bags (which would add significant cost).

[Dandy21]

Adam - somewhat a side note. I for one do like having separate drain & fill pumps. If the boats had a dedicated drain pump that was thru-hull, it would drain faster as it is not pumping against the "head pressure" created by the lake. In addition to this, we had separate drain pumps in our previous boat and it was nice to have the visual with the t-hull drain that the ballast was actually empty. This is one thing that I actually do not like about our G is not knowing for sure that the ballast is drained completely as we do trailer. I have thought about adding a drain pump but am not familiar enough with the factory ballast/wiring to accomplish this and keep it with the LINC system. If there happens to be any "random" drawings of how to accomplish this, please share as I would seriously give it consideration and provide feedback. I would guess the overall cost of pumps, plumbing, relays(?) and t-hull fittings would be +/- $1000.

Your explanation of how the vacuum is being created thought the bags "relaxing" is excellent. Thanks for the insight.

[Tallredrider]

It is a by product of our system design. We use soft bags with a check valve so that we can pull all of the water out of the bag regardless of the boat attitude or causing the pump to run dry excessively. Mastercraft uses primarily hard tanks which you can't use a check valve with, but is typically not required to drain a hard tank. The check valve in our system allows us to do a great job pulling water out, but the pumps work so well that they will also pull all the air out of the bag. If the pump runs long enough, water might still be removed from the bag, but you are also pulling a substantial vacuum into the bag to get that water out. Once the pump is turned off, the vacuum wants to "relax" and because the system is still open to the lake the vacuum pulls water back up into the system and starts a siphon (and you wouldn't believe how high the vacuum in the system can lift the water). Removing the check valves wasn't an option and many other alternatives were tried, but none of them fixed the problem 100% of the time unless you closed the system or we added another set of pumps to drain the bags (which would add significant cost).

Excellent. Thank you for the explanation.

Would it be reasonable to fill about 20 pounds of ballast to relax the negative pressure created in the sack? I know that adds human error into the mix, but it would seem to fix the issue for people who have pre-2015 G series boats.

[nyryan2001]

Not sure how his explanation makes sense.

By his logic the bags under negative pressure would suck water in to the point the vacuum is relieved and then stop.... maybe 1-2% full, a couple gallons max. His explanation doesnt explan how they continue and get over 1/2 full.... it may start as a vacuum pull....but then turns into a downhill run for the water as it all below the waterline.

[Jeb1974]

Not sure how his explanation makes sense.

By his logic the bags under negative pressure would suck water in to the point the vacuum is relieved and then stop.... maybe 1-2% full, a couple gallons max. His explanation doesnt explan how they continue and get over 1/2 full.... it may start as a vacuum pull....but then turns into a downhill run for the water as it all below the waterline.

I'm guessing the negative pressure is initially what gets the water moving back into the bags but then the system acts like a regular siphon once the hoses are full of water and the pressure differential no longer matters (similar to what happens with a siphon in a gas tank.) It also doesn't matter if you're above or below the waterline at that time.
http://science.howstuffworks.com/siphon-info.htm

I'm sure that this makes total sense to an engineer who understands fluid dynamics. I'm also curious if the same thing happens if you partially fill the bags then stop at a quarter or half full.

[nyryan2001]

Ya you are likely right.

At any rate, Adam is a stand up guy for coming on here to explain.

Adam, can you give a brief explanation on the shaft snaps, the bulletin and the way ahead?

[Adam Greer]

Jeb1974's explanation describes the phenomenon very well.

Tallredrider: We tried that, but if you stop and think about it, cycling the pump to "fill" the bag and then turning it off you are just starting a siphon again. You could run the pump to drain, fill, then drain some more again but it still leaves room for error and because the vacuum you can pull varies it probably wouldn't work very well. The same thing can happen if you had the bags full and turn the pump off. There is a small amount of leak by the impeller face (leave you bags full on a trailer and you will see this) and with the design of a displacement pump there is no way around that. Even if the impeller didn't allow leak by at first it would eventually as it wore over time. Which brings us back to the only real solution is to close the valves.

[Tallredrider]

Jeb1974's explanation describes the phenomenon very well.

Tallredrider: We tried that, but if you stop and think about it, cycling the pump to "fill" the bag and then turning it off you are just starting a siphon again. You could run the pump to drain, fill, then drain some more again but it still leaves room for error and because the vacuum you can pull varies it probably wouldn't work very well. The same thing can happen if you had the bags full and turn the pump off. There is a small amount of leak by the impeller face (leave you bags full on a trailer and you will see this) and with the design of a displacement pump there is no way around that. Even if the impeller didn't allow leak by at first it would eventually as it wore over time. Which brings us back to the only real solution is to close the valves.

I would add to what Jeb said. That is great to have someone from Nautique come to explain. Some of us are going through this for the first time, and it is good to see that corporate has considered various options.

This is the kind of thing that breeds Nautique owners for life, so I hope that you come back and don't feel like we have thrown fruit at you. Nauti should be giving you a raise.

I guess you guys probably tried removing the check valves on the overflow lines too? My experience has been that these pumps will still get all of the water out even without a check valve. Then air could easily enter the sack once the pump is shut off and break the negative pressure that creates the siphon. If the sack does not empty completely, it could be emptied just by raising the bow a little to get the rest out.

[vision]

Ahh, check valves in the overflow lines. That makes sense as to why locating the pumps above the water level does not eliminate the problem. Thank you Adam for providing such detailed information. As TRR indicated, it is this kind of feedback that generates loyal customers.

[nyryan2001]

follow up on this:

So I have a theory here. If you are getting seepage into your tanks when your boat is left in the water overnight that's an indication your impellor pumps are starting to wear past their optimum use.

So my starboard pump started pumping waaaay slow this season at ~180hrs, 2 winters on originals. I remove the impellor to inspect and all ribs/fins look perfectly intact except that they are all bent like a hurricane to the DRAIN direction. unless you hit fill one last time on the lift or trailer, your boat impellors spend 99.99% of their life bent, frozen and kept in the DRAIN orientation.

these are your options:

-replace the impellor with a new one

-replace the impellor with the old hurricane bent one, but put in in backwards/upside down. I did this and immediately its back on par with the others. again, it was in perfect condition, just bent in the drain direction. I left my boat in the water all weekend, seacocks open, no seepage at all into my tanks. I hit fill for a second on all 3 pumps before I shut it down.

so if you are seeing your G tanks autofill during extended periods on the water... it may only be an indication your impellors are loosing their form. Remedy? Hit fill for a second to get the fins bent in the other direction before you shut it down. trade off which position it is stored in so the plastic fins maintain their form. or replace them all together and trade off which direction they are stored to maximize their life.

[scarbs]

This is great info. Thanks!