Fresh water flushing systems, anyone?

[MapisM]

I'm back onboard after a long winter, thanks God.

While discussing with my mechanic a few final checks before leaving my winter yard, one idea popped to my mind.
The debate started from the pump which picks up sea water to wash the anchor chains, because it got clogged last winter and he had to clean it. Now, since I have quite some fresh water capacity (1.5 T), I wondered if I couldn't fit a T valve on the line where this pump picks up the sea water.
This way, surely not everytime anchors are used, but at least upon the last mooring (and subsequent anchor chain recover) of each cruise, I could switch to fresh water and leave both the circuit/pump and the anchor locker clean, rather than having salt sitting all around.

And from there, I wondered if a similar arrangement wouldn't make sense also for the engines and genset. Again, before leaving the boat, it would be pretty easy to leave her completely flushed with fresh water, just running the engines and genset for a while with the T valve switched to the fresh water circuit.

Am I missing any potential problem of such solution?
On paper, it sounds smart enough to make me wonder why it isn't bult in on any boat...
...then again, maybe there's something I am indeed missing.

Any sensible suggestion will be highly appreciated!

PS: I already envisage some perfectionist suggesting to fit electric valves to control all that from the dashboard. It's worth mentioning that by "sensible suggestion" I mean anything not involving a mortgage...!

 

[Latestarter1]

I wondered if a similar arrangement wouldn't make sense also for the engines and genset. Again, before leaving the boat, it would be pretty easy to leave her completely flushed with fresh water, just running the engines and genset for a while with the T valve switched to the fresh water circuit.

Am I missing any potential problem of such solution?
On paper, it sounds smart enough to make me wonder why it isn't bult in on any boat...
...then again, maybe there's something I am indeed missing.

You are missing NOTHING 100% good sense. Groco and Perko make engine intake water stariners with extra 5/8 port to allow engine fresh water flushing.

As your reasoning is absolutely correct and I'll try to expand on your thoughts.

Leave the seacock open and IF the water flow from the dock is greater than the needs of the engine at an idle (usually is if a good valve/water flow/pressure is at the dock, you have a good hose and 5/8" or bigger plumbing all the way to the "T" in your system,) the engine will only have fresh water in it after a couple of minutes of idling.. Shut off the engine first and the fresh water will just go out the bottom of the boat, as the seacock is STILL open. Since fresh water is lighter than seawater, even after months with the seacock left open, you'll find fresh water still in the system..(I'm not keen on shutting sea cocks as my memory is all used up due to age).

Remember you are also back-flushing the strainer (a lot) when the engine is off..If the owner makes the flush system easy to use (not having to drag a hose though the main saloon) then this type of upgrade to a modern diesel will add years to the life of the entire seawater side of the engine (especially zincs, seawater cooled aftercoolers, etc)..

One more little trick to seawater side longevity is to cut up chunks of your old plate zinc and keep one or two of them in the bottom of your stariner basket.

 

[jfm]

Yup, makes sense, but I'd use the dockside water hose rahter than connect to the boat's freshwater system because you generally have more pressure and flow from the dock. I think that's what LS was suggesting. Ideally you'd want your freshwater flow rate at least to match your engine raw water pump flow rate at idle

Also I agree with LS that you dont need T valves. Just a nipple T-ed into the raw water intake pipe, with a little shut off valve in the line to the nipple, will do

So far as the anchor is concerned I find it just as easy to wash the chain using the dock hose or the deckwash system, squirting into the locker. No need to connect to the actual anchor wash, imho. But for the engines and genset your idea is very attractive

Strictly speaking you're meant to have different anodes (magnesium not zinc) for freshwater. Do you think the zincs in your engine heat exchangers will be ok?

I might add this to the spec of the new boat

 

[MapisM]

Thanks folks, some interesting food for thought here.

Firstly, thanks LS1, I was actually thinking of connecting the fresh water hose before the strainers, but it makes much more sense to have it after them, hence back-flushing them after turning the engines/genset off.
Good point also re.fresh water staying in the circuit with no need to shut the sea cocks.
My memory is not any better than yours in this respect!

Re.using the dock hose rather than the boat circuit (as also jfm suggests), I was actually thinking of integrating both.
In fact, I already have a direct connection in the cockpit for the dock hose, and that's what I'm already using when moored, cutting off automatically the onboard pump because the dock line pressure is higher.
Therefore, if I arrange fixed hoses from the boat fresh water circuit to the engines/genset/anchor chains, I can run all of them on fresh water from either the boat tank or the dock line.

Actually, that's not so relevant for engines/genset, because a final flush before leaving the boat will be by definition with the boat moored, hence with the dock hose connected.
But I beg to disagree on the anchor chains, J.
It's much more effective to have the chain wash pump working with fresh water upon the last anchor recovery at the end of a cruise.
Though that depends also on the chains/anchors arrangement, which is the "ship-like" system (for my own lack of better wording) on my boat, as opposed to the typical bow anchor. I'm afraid you'll have to either change type of boat or further step up to the P95 for such proper ground tackle...

Fully agreed on nipple plus shut off valve, rather than T valve.

Good point also re.magnesium anodes.
Mmm.... that's a tricky one. Obviously engines and genset would run on salt water 99% of the time. It's just at rest that they would have fresh water in the circuit. So, timewise, they would have fresh water inside for much longer periods. I guess magnesium would make sense in this respect, but I'm afraid that the anodes could disappear very quickly during usage with sea water...

Any anodes expert around?

 

[Trundlebug]

Aluminium!

I'm not an "anode expert" but I do know Aluminium anodes are used for brackish environments.

I currently have them fitted to our boat, we spend most of the time on the Trent but try to get out on the Humber or the Wash and further afield when time and weather permit.

They're generally cheaper than either Mag or Zn anodes, and seem to work quite well.

Being a compromise they do of course erode faster than ZN in salt water, but not a fast as Mag.

I'm not sure though how the mixture of anode materials would affect things overall, if at all? i.e. Zn anodes underneath but Al anodes in the engine. Would that lead to faster erosion of the Al than normal?

 

[scubaman]

Since fresh water is lighter than seawater, even after months with the seacock left open, you'll find fresh water still in the system..(I'm not keen on shutting sea cocks as my memory is all used up due to age).

Although this is true, I would expect the fresh water to 'absorb' salt from the seawater due to osmosis. I would expect this to be fairly quick process as well. Of course this would increase the salinity only as far as the water pump. The rest should be okay?

 

[MapisM]

I'm not sure though how the mixture of anode materials would affect things overall, if at all? i.e. Zn anodes underneath but Al anodes in the engine. Would that lead to faster erosion of the Al than normal?

Very good question.
I'm afraid I don't have an answer, but hopefully someone has a sensible one...

 

[AndieMac]

Very good question.
I'm afraid I don't have an answer, but hopefully someone has a sensible one...

You keep making reference to sensible answers MM........what are trying to say??

 

[MapisM]

You keep making reference to sensible answers MM........what are trying to say??

Well, nothing special really. Surely not that the replies I got so far weren't sensible, if that was your impression.
Anyway, apologies if the use of the adjective wasn't.... sensible!

 

[MapisM]

I discussed further the anodes choice with my mechanic.
In his view, the inside protection granted by the anodes is mainly effective upon engines/genset usage.
When they are at rest (which is when they would be filled with fresh water), it's just the salt corrosion which is harmful.
Therefore, zinc anodes would still be the best choice, also with the fresh water flushing system we're talking about.

Happy to hear different views, if any.
And of course also the reasons for them!

 

[Latestarter1]

Seems a little odd that the little trick of throwing used anodes in the strainer has attracted far more attention than the absolute benifits of flushing.

Remember that when motors are running little pieces of zinc are protecting your strainer basket. People obviously have never had a strainer basket fall to pieces due to electrolytic corrosion.

Never thought of having my work peer reviewed by a mechanic before.....

 

[MapisM]

Seems a little odd that the little trick of throwing used anodes in the strainer has attracted far more attention than the absolute benifits of flushing.

Nope, actually my concern wasn't for the strainer anode. Btw, I was already aware of that trick, though it's actually useless, at least in my boat, because the anodes on the bottom of my strainers are 6 or 7 years old and still almost as new.
Anyway, what I was talking about were the internal engine anodes, those meant to protect the heat exchanger and the whole raw water circuit. And those are obviously affected by having to deal with salt and/or fresh water.

And re. checking some ideas with a mechanic, why not?
If he's a good one, he must have some knowledge of the subject.
And if he isn't, it's better to look for another one, rather than just refrain from asking his opinion...

 

[jfm]

Seems a little odd that the little trick of throwing used anodes in the strainer has attracted far more attention than the absolute benifits of flushing.

Remember that when motors are running little pieces of zinc are protecting your strainer basket. People obviously have never had a strainer basket fall to pieces due to electrolytic corrosion.

Never thought of having my work peer reviewed by a mechanic before.....

Yup, the anodes thing is perhaps overall insignificant and has been done to death. The general plan seems a smart one. I reckon the way to go is this: fit a T'ed nipple hosepipe connector above the raw water intake seacock, with isolator valve. When parking up the boat for any longish period, just connect the hose and flush freshwater in there. Whether to shut the seacock is a personal choice - I would (and I'd stick a label over the engine isolator switches to remind me), and this avoids the salt osmosis thing that Scubaman mentioned (I think it's diffusion not osmosis, but no worries!). And I'd just leave the zinc anodes in the engine and gearbox heat exchangers, and not worry about it.

Overall, for a pair of engines you want to keep a long time, and to keep the heat exchangers nice and clean, this seems a very smart and simple/easy/cheap idea

I have one niggling worry though. The flushing water will enter the exhaust elbows in the usual place, but with the engines NOT running. You are relying on a perfect hydrodynamic design here to ensure no water dribbles back the wrong way, which would be a disaster, even if fresh water not salt. How big this risk is depends on the exact design, which is specific to each boat type so we can't generalise, but it is a worry. The designer will have assumed the engines to be running in designing the water entry at the elbow, and so the designer might (justifiably) have been lazy and not tested too hard to be sure of the behaviour of the water.

Of course it would be possible to alter the plumbing there too, and fit vlaves to take the flush water to somewhere other than the elbow, eg enter the exhaust system much lower down or go overboard somewhere else

If I can overcome this point I will be making this flushing mod to my next boat

 

[MapisM]

I reckon the way to go is this: fit a T'ed nipple hosepipe connector above the raw water intake seacock, with isolator valve. When parking up the boat for any longish period, just connect the hose and flush freshwater in there.

A couple of further thoughts:
Firstly, as previously mentioned, I'd fit the nipples after the strainers, as in my understanding also LS1 suggested. This way, it's also possible to backflush/clean the strainers.
Secondly, I was thinking to run the engines at idle while flushing them. This should allow a better flow/distribution of fresh water in the whole circuit, and avoid the risk you mention. 'Course a good flow from the hose would be required. No big deal with my engines, but I'm not sure with 32 liters monsters...

 

[jfm]

A couple of further thoughts:
Firstly, as previously mentioned, I'd fit the nipples after the strainers, as in my understanding also LS1 suggested. This way, it's also possible to backflush/clean the strainers.
Secondly, I was thinking to run the engines at idle while flushing them. This should allow a better flow/distribution of fresh water in the whole circuit, and avoid the risk you mention. 'Course a good flow from the hose would be required. No big deal with my engines, but I'm not sure with 32 liters monsters...

Yep, i guess that's the answer. thanks. Run the engines, then there cannot be any exhaust problem. I have no idea how the flow rate from the dock hose matches up to the flow rate of a Cat C32 water pump at idle rpm, but will find out. I suppose the hosepipe will be sucked flat if the flow isn't enough (and if I shut the seacock)! Alternatively, I might use the boat's water tank as you originally suggested, then the C32 pumps can just suck the water, ie not rely on the boat's freshwater pump to deliver the flow rate

Indeed, the Sq78 btw has water hose in the engine room on a curly pipe, which will make this even easier - see below pic. Anyway, thanks for the overall idea. It's a good one.

 

[PaulGooch]

Yep, i guess that's the answer. thanks. Run the engines, then there cannot be any exhaust problem. I have no idea how the flow rate from the dock hose matches up to the flow rate of a Cat C32 water pump at idle rpm, but will find out. I suppose the hosepipe will be sucked flat if the flow isn't enough (and if I shut the seacock)! Alternatively, I might use the boat's water tank as you originally suggested, then the C32 pumps can just suck the water, ie not rely on the boat's freshwater pump to deliver the flow rate

Indeed, the Sq78 btw has water hose in the engine room on a curly pipe, which will make this even easier - see below pic. Anyway, thanks for the overall idea. It's a good one.

With the large tanks your boat will be fitted with, i'd think the best bet would be for the engine to be idling, sucking whatever water it needs from the onboard tanks. Onboard tanks can also be connected to the dock hose whilst you're doing it. I certainly wouldn't want to run my engine from the dock hose alone.

I agree with you about closing the seacock. Those who think it's a good idea to NOT close the seacock in case they forget to open it might want to check their raw water systems for the ability to syphon. For instance, my raw water strainer is mounted higher than the engine, a leak in the system after the strainer will continue to let water in after the engine is stopped. I ALWAYS turn off all seacocks as we leave the boat and turn them all back on when we arrive next time.

 

[ChrisKaye]

"I have no idea how the flow rate from the dock hose matches up to the flow rate of a Cat C32 water pump at idle rpm, but will find out."

John, I really don't think thats a good idea.............I looked into this some time ago with my 7litre CAT 3126'sengines and I was amazed at the amount of water the sherwood pump sucks up i.e. @ 120Litres / minute at 650RPM idle speed and I doubted that the pontoon water could keep up. Bet your pump's flowrate is much much more

 

[jfm]

"I have no idea how the flow rate from the dock hose matches up to the flow rate of a Cat C32 water pump at idle rpm, but will find out."

John, I really don't think thats a good idea.............I looked into this some time ago with my 7litre CAT 3126'sengines and I was amazed at the amount of water the sherwood pump sucks up i.e. @ 120Litres / minute at 650RPM idle speed and I doubted that the pontoon water could keep up. Bet your pump's flowrate is much much more

Paul/Chris, thanks. Ok, noted re engine raw water pump flow rate Chris! I think then the answer is to use the boat's water tank. In my case it will be quite near the engines, so I could just have a temporary big-bore link hose or something, if the normal narrow-bore domestic water piping isn't enough. There is a pretty humungous freshwater delivery pump on the Sq78, so it might do the trick - I'll get its specs, but the boat has 4 showers and a bath for starters. I'll think about it and experiment - the basic idea here of getting freshwater into the engine/gen raw water circuits is worth shooting for

 

[Trundlebug]

I think the idea of letting the engines suck the water direct from the tank is both simple, effective and sound from an engineering viewpoint.

Essential to fit an in-line check valve though, to prevent any possibility of back flow to the water tank. Also an isolator valve upstream (tank side of) check valve to enable subsequent maintenance.

Would you need another take -off from the water tank? Quite possibly with the flow rates required.

Also worth thinking about some kind of warning light / buzzer / indicator to ensure you don't accidentally leave the engines switched over to fresh water cooling without being aware of it.

Perhaps that's where the idea of solenoid operated valves etc come in, as referred to in the original suggestion...Pressing a button on the dash (labelled "Engine Flush" or similar) opens the fresh water solenoid valve for x seconds before closing automatically..."the possibilities are endless"

Go on JFM, you're dying to do it properly, you know you are...

 

[MapisM]

I think then the answer is to use the boat's water tank. In my case it will be quite near the engines, so I could just have a temporary big-bore link hose or something, if the normal narrow-bore domestic water piping isn't enough. There is a pretty humungous freshwater delivery pump on the Sq78, so it might do the trick

Yup, that's the smarter way to do it imho.
And I wouldn't even bother about the freshwater pump capacity. The big-bore hose could bypass it, picking freshwater directly from the tank. The engine pump will take care of sucking whatever needed - as it normally does.

Btw, didn't you fit a water softener to the filling hose of the freshwater tanks in the 58? If so, I guess you'll do the same on the 78.
Go figure, engines and genset treated to fresh and de-calcified water!
It can't get any better, even on a lake...

Oops, trundlebug beated me to the first of my comment above!