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gregabbiss · 10-03-2022, 07:20

Right, not sure if this is asking for help, advice or just giving you all a laugh, hopefully not just at me.

When we bought our boat, a 2018 Lagoon 450S, I installed a watermaker under the port forward bed base (not the bed because we turned the port forward cabin into a closet).

I used the thru hull for the air-conditioning units, which enters in by the bilge and the outlet from the port forward sink for the brine outlet. The fresh water is routed to the rear “water” cabinet where the fresh water pump is located, to a manifold that allows me to divert the water to Starboard, port tanks or out through a faucet in the aft cabin.

The watermaker has worked faultlessly, bar one minor issue, for the whole of last season. The minor issue is that it takes in a small amount of air and so I need to stop the watermaker high pressure pump every 30mins or so and bleed the system.

I have chased down every possible place that the air is making its way into the system and have now confirmed exactly where it is coming from, which in itself raises a few questions.

Rather than just tell you, lets go through, quickly and see if YOU can work it out. I finally got to the bottom of it this week whilst hunkered down in storm weather in the Aegean and making water without any other distractions.

So the whole system was checked, retaped, re-checked and I could not find anywhere where there might be a leak. It appeared? That if I tighten the filter holders really tight then the air leak slowed.

The low pressure pump, that lifts raw water from the thru hull to the filters and onto the high pressure pump, did not manage to make much pressure, less than 2-3psi after the filters and below zero when the high pressure pump was turned on.

From this I concluded that the problem lay in a vacuum being created in the filters and the high pressure pump literally pulling air in through the filter seals.

I duly replaced the primary pump with something a bit more robust and started to get 25psi after the filters until the high pressure pump was turned on and then it fell to zero again. But perhaps not so negative.

During this I noticed, now that the primary pump was pulling water with more vigour that the port forward head was sucking air through it, and now, loudly activating the macerator as it went.

Aha… air must be being pulled through the head, along the hull and into the thru hull for the watermaker. Unexpected given that the exit for the port forward head was at least 5’ forward of the inlet, but seemed to be the case.

So you close off the valve to the port forward holding tank dump, the circuit being head to holding tank, to outlet.

Strangely, very strangely, the port aft head was not being affected at all by this and yet its outlet was just inches ahead of the forward outlet?? Very bizzare.

But it gets worse.

Close of the holding tank dump, therefore effectively isolating the tank and head from the outside of the boat and it made no difference.

In fact if I filled the head with sea water it was drained out whilst I ran the watermaker. Hmmmm?

Ok, block the damn thing completely using a plunger and filled bowl to make it air tight.

Water stopped being drained out of the head bowl. Win!!! Not so fast.. the air problem got worse, considerably worse. It was sucking in air much faster now than it had been and the primary pump could no longer get up to 25psi when run alone??????

Ok… open it back up, bleed the system, fill the head with water and keep it filled using the electric pump of the head.

Problem solved. No air sucked into the watermaker, until of course I allowed It to empty.

But if I then filled it and kept it filled the air was slowly pushed out and the system recovered.

Ok, I could now run the watermaker for extended periods without having to stop to bleed the air. But what the F(&K!!!!!

So Conclusions: The primary pump is creating a low pressure zone under the boat. Presumably near the keel. This low pressure zone is creating a suction on the forward head holding tank outlet, presumably along the angle of the keel and that outlet is not air tight/water tight even when closed.. perhaps only when empty?? (we don’t use this head) or perhaps just when under vacuum from outside?

Questions still to be answered: Why did it get worse when I closed this off, presumably the pressure gradient pulled air down from above the water line?? Not sure of that one.

Why did this not affect the aft head? Even when the forward was blocked off … you’d think the easiest path of resistance was there not the waterline above ???

What might happen if I use a different thru hull? The rest are actually closer to the head outlets, but also slightly higher on the hull?? mIght give this a try at some stage.

So, as I started to say, not sure if I was asking for help, comment or just wanting to amuse you. But certainly comes under the joy of cruising .

All comments suggestions and qualifications accepted and no doubt laughed at.... Be kind

.

dcondit · 10-03-2022, 07:34

Are you 100% sure that the only thing fed by the thru hull you tapped is the ACs? Regardless of design specs, I've seen a few instances of factory-tapped lines that surprised me. If that thru hull feeds other things it could be drawing hoses in reverse with the water maker pull. Just a thought...

**tkeithlu** · 10-03-2022, 07:34

No reason to laugh at you. You faced one of those super mysteries and solved it. Congratulations. Most of us have faced those once or twice, and they show up on the forum frequently. What follows then is often a board game of questions and proposals of solutions. 25 posts later the original poster has solved the problem, and it was something no one thought of....

Weatherbird · 10-03-2022, 09:14

When your water maker is flushing your toilet it's time to forget everything you think you know and start running hoses.

goboatingnow · 10-03-2022, 12:15

I find it most improbable that a conventional water maker could create such a zone of suction. I mean I owned a big twin Mobo
It pulled tons of water from around the boat but never emptied the direct plumbed sea toilet.

flee27 · 10-03-2022, 13:04

Not saying your wrong but this sounds crazy if I am correct in my understanding of your findings.

Are you saying that your water maker is sucking your toilet dry through an adjacent through hull? So when all the water has been sucked out it is pulling air out the through hull and back into the through hull that is the water maker input.

If so I would love to see video of this happening from under the boat. That would be crazy for sure.

Foster

Lodesman · 10-03-2022, 13:10

Quote:

Originally Posted by dcondit

Are you 100% sure that the only thing fed by the thru hull you tapped is the ACs? Regardless of design specs, I've seen a few instances of factory-tapped lines that surprised me. If that thru hull feeds other things it could be drawing hoses in reverse with the water maker pull. Just a thought...

^^^ This!

mrh123 · 10-03-2022, 17:20

I had a deckwash pump feed that came off the same thru hull as the head and it could suck the head dry even though the pump and fed were all below the water line with a much larger diameter thru hull that the hose to the head or the deckwash. So shared thru hulls are an issue and probably the cause of your flow problems.

**Madehn** · 10-03-2022, 18:34

You are not sucking water out of the head from an adjacent thru hull- not possible. you have two things happening yes the head is draining and yes the watermaker is sucking air but they are not cause and effect. my guess is that you are actually pulling air back thru your AC from where your cooling water exits the hull which is above the water line and exposed to air. My watermaker was emphatic that it needed its own thru hull and not a shared one-- good news is that it is easy to fix-- put an inline valve with a couple of hose barbs in the line between the thru hull and your AC- close this when making water and i am going to bet that fixes your issue-- certainly cheap enough and easy to try. also agree that you need to check your hose routing-- if i read your post incorrectly i apologize in advance as i read thru rapidly-- bottom line make sure you isolate your watermaker thru hull - it should not be connected to any other device while your watermaker is running. think horse not zebra when you hear hoof beats!

:smile putting in my watermaker which i built from new and used parts was a project that absolutely was defied by aggravation and frustration while taking 4x as long as i thought it would fair winds to you my friend we have all been there. incidently is our thru hull supply low enough that it never getting exposed to the air from rolling/pitching- that too can introduce air in the system intermittently making troubleshooting a real witch with a B. (ask me how i know)

gregabbiss · 10-03-2022, 23:34

Quote:

Originally Posted by dcondit

Are you 100% sure that the only thing fed by the thru hull you tapped is the ACs? Regardless of design specs, I've seen a few instances of factory-tapped lines that surprised me. If that thru hull feeds other things it could be drawing hoses in reverse with the water maker pull. Just a thought...

Good thought. I have checked a number of times and traced lines. So pretty sure.

I pretend I am pretty good at this stuff but this one just has me laughing my socks off at the idiocy of it.

gregabbiss · 10-03-2022, 23:39

Quote:

Originally Posted by flee27

Not saying your wrong but this sounds crazy if I am correct in my understanding of your findings.

Are you saying that your water maker is sucking your toilet dry through an adjacent through hull? So when all the water has been sucked out it is pulling air out the through hull and back into the through hull that is the water maker input.

If so I would love to see video of this happening from under the boat. That would be crazy for sure.

Foster

Yep that is what `i am saying and yes agree it is crazy. Especially given that the two thru hulls are about 5' apart.

I'd video this but at the moment we have snow in Mykonos.. yeah I know... I'm beginning to think I might wake up any moment and find its all a silly dream, but with snow in March in the Aegean, I'm not getting into the water

gregabbiss · 10-03-2022, 23:46

Quote:

Originally Posted by Madehn

You are not sucking water out of the head from an adjacent thru hull- not possible. you have two things happening yes the head is draining and yes the watermaker is sucking air but they are not cause and effect. my guess is that you are actually pulling air back thru your AC from where your cooling water exits the hull which is above the water line and exposed to air. My watermaker was emphatic that it needed its own thru hull and not a shared one-- good news is that it is easy to fix-- put an inline valve with a couple of hose barbs in the line between the thru hull and your AC- close this when making water and i am going to bet that fixes your issue-- certainly cheap enough and easy to try. also agree that you need to check your hose routing-- if i read your post incorrectly i apologize in advance as i read thru rapidly-- bottom line make sure you isolate your watermaker thru hull - it should not be connected to any other device while your watermaker is running. think horse not zebra when you hear hoof beats!

:smile putting in my watermaker which i built from new and used parts was a project that absolutely was defied by aggravation and frustration while taking 4x as long as i thought it would fair winds to you my friend we have all been there. incidently is our thru hull supply low enough that it never getting exposed to the air from rolling/pitching- that too can introduce air in the system intermittently making troubleshooting a real witch with a B. (ask me how i know)

I'd agree with you, BUT, explain this:

I keep the head full of water and no air is sucked into watermaker. If it was the AC this would not be the case true?
I already have a oneway valve between the AC and the Thru Hull junction sot that it can't pull backward through the AC. I have tested this as very early on I thought this was probably faulty.
I can actually observe positive flow OUTWARD from the boat out the AC outlet at the same time by turnign on pump and still see same behaviour with regards to air and head, infact gets worse, presumably with extra suction of thru hull.

You've got to enjoy the silliness of this don't you 😇😇😇.

gregabbiss · 11-03-2022, 01:04

SOLVED SOLVED SOLVED.

Guys you are a brilliant lot. As often happens throwing thoughts out there and chasing solutions takes you on a rollercoaster through all the things that you have already gone over and thrashed to death.

Makes you reassess things that just shouldn't be possibly.

So I started thinking, the head pump is not running, or is it? it certainly isn't running normally so I have assumed that It was spinning because of the vacuum.

But what it if was not hydraulic but electrical? what if somewhere along the lines there was a short and this was activating the head macerator pump, albeit very slowly and perhaps also draining current from the primary pump so making it work less efficiently.

Well after an hour tracking down... yep that is exactly what has happened. The wiring loom had a slight short in it and when turning on the primary pump we were also powering (just a little) the head macerator pump. This was pulling air down into the boat and being sucked up by the thru hull for the watermaker.

Now fixed I have much better pressure during the high pressure pump activation, 15psi instead of near zero. I have no activation of the head macerator pump and there is NO air coming in.

Bloody brilliant. Thanks guys for your challenging me and making me think of different explanations.

So air in the watermaker is from a short across the loom that is causing the port forward head macerator to activate and pump air under the hull.

GO FIGURE!!!!!!!!