Raw Water Flush

drb1025 · Mar 19, 2016

Steve DAntonio said:
Generally speaking I can see no reason not to fresh water flush. The conductivity of seawater and the effect the salt ion has on metal is undeniable, it's why fresh water engine rooms often look like new after 20 years. Keep this in mind, however, for heat exchangers equipped with zinc anodes, when exposed to fresh water zinc anodes, all of them, develop a coating or scale that essentially puts them to sleep, they stop working. The coating can be removed using a stiff, non-metallic brush or Scotchbtite pad. Therefore, if you flush with fresh water and it remains in the heat exchange, the zinc anodes will not work as well, or at all thereafter, unless cleaned or replaced, which could be counterproductive.

The same is true for hull anodes, vessels that operate or are stored in fresh or brackish water will face the same issue. Zinc anodes are designed for salt water use only, magnesium anodes are designed for fresh water use only,. Aluminum anodes can be used in fresh, salt or brackish water. The only caveat, aluminum anodes tend to be more active, they develop a white froth on their surface that does not impede there effectiveness, however, where pencil anodes are concerned this material can make it difficult to remove them.

How long may a vessel operate in fresh water before a zinc becomes ineffective in salt water? I occasionally go from salt water in Puget Sound and through the locks to fresh water in Lake Washington. I recently hauled out in fresh water and had all the zincs replaced. Did the short trip back to salt water render the new zincs ineffective? Thanks

dhays · Mar 19, 2016

drb1025 said:
How long may a vessel operate in fresh water before a zinc becomes ineffective in salt water? I occasionally go from salt water in Puget Sound and through the locks to fresh water in Lake Washington. I recently hauled out in fresh water and had all the zincs replaced. Did the short trip back to salt water render the new zincs ineffective? Thanks

Great question. We have a lot of folks who are moored in rivers and boat in salt water on both coasts.

Tolly Roger · Mar 19, 2016

angus99 said:
I installed these Groco flush fittings on all of my raw water intakes but have not used them yet because we're still on the hard. I'll leave it to others to tell you how foolish I am.

I have these on my engines. I like them. I do not hook up the "dock water" hose to them but instead fill a 5 gal bucket and have a short length of hose from there to the Groco's. To winterize I fill the bucket with pink antifreeze and fill the raw water side. Makes it really easy!

Steve DAntonio · Mar 20, 2016

dhays said:
Thanks Steve, You know more about diesel engines than I ever will.

So I will guess that your answer to;
"Anyone ever use something like this for doing a fresh water flush?" is No.

What about this question and possible hydrolock issues?
"Secondly, I know that some connect a dock hose to the system but I have heard that this can create problems. Seems safer to use non-pressurized water and let the water pump do its job?"

Not necessarily. If your HX has no anodes it's not a problem, some don't, so go ahead and flush. Otherwise, the benefits of a fresh water flush for your heat exchanger as well as the exhaust elbow could outweigh the zinc issue. When you pull the zinc pencil see what it looks like, if it doesn't appear to be consumed, and has a light coating on the surface, then the FW is indeed putting it to sleep. You could periodically clean it off, or you could try an aluminum anode from Performance Metals, mentioned in a later post.

Never, ever, under any circumstances force-feed an engine fresh water unless it's running. Some exhaust systems gravity drain overboard, others gravity drain to the engine (most sailing vessels and many trawlers fall into the latter category). I have nothing against the strainer flushing valves per se, especially for something like an air conditioner, where no harm can be done by force feeding it water. For an engine or genset, my preference is to allow water to flow into, and overflow, an open strainer while the engine is running. Make sure the engine is pumping water from the strainer by checking the exhaust right away. Using this approach there is no way water can run into the exhaust and back up into the engine should it shut down unexpectedly, and the engine only draws in what it's pump can pump, no more. Bottom line, make certain there is no water flow if the engine isn't running.

Steve DAntonio · Mar 20, 2016

drb1025 said:
How long may a vessel operate in fresh water before a zinc becomes ineffective in salt water? I occasionally go from salt water in Puget Sound and through the locks to fresh water in Lake Washington. I recently hauled out in fresh water and had all the zincs replaced. Did the short trip back to salt water render the new zincs ineffective? Thanks

This is a tough question to answer, I haven't done any testing so I can't say at what point the zincs are permanently affected. The proof is, as they say, in the pudding. Check your zincs, are they being consumed as they should be, or are they coated and "dead"?

Anecdotally short trips probably aren't a problem, if you stayed in FW for a day or more then my guess is that could have an affect, but there are variables like water temp and flow. Best to check your zincs, just make sure they are eroding normally.

angus99 · Mar 20, 2016

I put a bulwark on a 5-gal bucket that allows a hose connection. I used it to gravity-feed propylene glycol through the raw water system for winterizing. Then I drained the system, including the heat exchangers and mufflers, theorizing that any liquid left inside would be heavily concentrated with the PG. It was after removing hoses to do this that I decided I wanted the Groco flush fittings--although I'll still use the bucket to gravity-feed.

rwidman · Mar 20, 2016

I wonder if the US Navy flushes their ship's engines after each use? How about the cruise and cargo ships?

If your engine is raw (seawater) cooled, you should flush if you are running the boat in salt water. If you have a closed cooling system, it's probably not worth the trouble.

If they needed to be flushed after each use, wouldn't they come from the factory with a means for flushing already installed? How are you going to flush when anchored?

angus99 · Mar 20, 2016

WesK said:
I wonder if the US Navy flushes their ship's engines after each use? How about the cruise and cargo ships?

Dunno. If I had the USN's budget--or the amount of metal in their seawater systems--I might not worry about flushing either.

.

WesK said:
If they needed to be flushed after each use, wouldn't they come from the factory with a means for flushing already installed? How are you going to flush when anchored?

When I flush, it will be before leaving the boat for any length of time--not so obsessive that I'll worry about it at anchor. If it keeps one more corrosive element away from engine metal, it's worth the trivial amount of time it takes to flush. For me, it's more about "what harm can it do?" (assuming I have aluminum anodes).

dhays · Mar 20, 2016

Steve DAntonio said:
Not necessarily. If your HX has no anodes it's not a problem, some don't, so go ahead and flush. Otherwise, the benefits of a fresh water flush for your heat exchanger as well as the exhaust elbow could outweigh the zinc issue. When you pull the zinc pencil see what it looks like, if it doesn't appear to be consumed, and has a light coating on the surface, then the FW is indeed putting it to sleep. You could periodically clean it off, or you could try an aluminum anode from Performance Metals, mentioned in a later post.

Thanks Steve. It would seem that swapping the anodes for aluminum could solve the issue of ruining the zincs by letting them sit in fresh water.

I heard somewhere (can't recall where) that if you change to aluminum anodes that all of the anodes should be switched to aluminum. I'd that true? Could just the engine anodes be swapped for aluminum and leave the rest of the anodes on the boat zinc?

Can you tell I am confused by these pesky electrons?

rwidman · Mar 20, 2016

dhays said:
Thanks Steve. It would seem that swapping the anodes for aluminum could solve the issue of ruining the zincs by letting them sit in fresh water.

I heard somewhere (can't recall where) that if you change to aluminum anodes that all of the anodes should be switched to aluminum. I'd that true? Could just the engine anodes be swapped for aluminum and leave the rest of the anodes on the boat zinc?

Can you tell I am confused by these pesky electrons?

I would think all the anodes should be the same metal, otherwise they will be trying to protect each other and will waste away sooner.

My boat is kept in brackish water (on a river) but just a few miles from salt water. Cruising on the AICW involves salt water, brackish water and fresh water. Sometimes we may be in fresh water for a week or two, then back into salt. I would think my situation is not uncommon and I wonder what other people who cruise the AICW do as far as anodes.

I have considered aluminum but everyone else around me is using zinc. If I were to change, I would have to make sure my diver knows and keeps the correct type in stock for my boat.

dhays · Mar 20, 2016

WesK said:
I would think all the anodes should be the same metal, otherwise they will be trying to protect each other and will waste away sooner.[\quote]

That was my thought as well.

My boat is kept in brackish water (on a river) but just a few miles from salt water. Cruising on the AICW involves salt water, brackish water and fresh water. Sometimes we may be in fresh water for a week or two, then back into salt. I would think my situation is not uncommon and I wonder what other people who cruise the AICW do as far as anodes.

I have considered aluminum but everyone else around me is using zinc. If I were to change, I would have to make sure my diver knows and keeps the correct type in stock for my boat.

Click to expand...

As you know, there are folks here that keep there boats in fresh water lakes and lock out to salt water, and some who keep their boats in rivers but cruise primarily in the Salish Sea. So I agree I think it is a common situation. If you are using zinc, have you noticed any unusual galvanic problems or noticed that your anodes are not wasting away?

Steve DAntonio · Mar 21, 2016

dhays said:
Thanks Steve. It would seem that swapping the anodes for aluminum could solve the issue of ruining the zincs by letting them sit in fresh water.

I heard somewhere (can't recall where) that if you change to aluminum anodes that all of the anodes should be switched to aluminum. I'd that true? Could just the engine anodes be swapped for aluminum and leave the rest of the anodes on the boat zinc?

Can you tell I am confused by these pesky electrons?

Ideally, yes, if you switch to AL anodes, then all should be switched because, as another member pointed out, the Al anodes will protect the Zn anodes. Keep in mind, however, the anodes that are inside the boat, in the gen or propulsion engine HX, are considered to be in a different body of water than those attached to the hull or running gear, they have no effect on each other what so ever. So engine pencil anodes aren't protecting the prop, and hull anodes aren't protecting the HX, regardless of the level of bonding between the two.

dhays · Mar 21, 2016

Steve DAntonio said:
Ideally, yes, if you switch to AL anodes, then all should be switched because, as another member pointed out, the Al anodes will protect the Zn anodes. Keep in mind, however, the anodes that are inside the boat, in the gen or propulsion engine HX, are considered to be in a different body of water than those attached to the hull or running gear, they have no effect on each other what so ever. So engine pencil anodes aren't protecting the prop, and hull anodes aren't protecting the HX, regardless of the level of bonding between the two.

That makes sense. If I do that I will try to ensure that the two bodies of water remain separate. Of course if they do combine, galvanic corrosion won't be my first concern. :whistling:

rwidman · Mar 21, 2016

dhays said:
WesK said:

.......... If you are using zinc, have you noticed any unusual galvanic problems or noticed that your anodes are not wasting away?

Click to expand...

I have noticed nothing unusual but I only see them when the boat is hauled and that's typically just every few years for bottom painting. The diver takes care of them in the meantime and they do deteriorate.

Steve DAntonio · Mar 22, 2016

WesK said:
dhays said:

I have noticed nothing unusual but I only see them when the boat is hauled and that's typically just every few years for bottom painting. The diver takes care of them in the meantime and they do deteriorate.

Click to expand...

If the anodes are being consumed, then they are working, so likely not an issue for you.

rwidman · Mar 22, 2016

Steve DAntonio said:
WesK said:

If the anodes are being consumed, then they are working, so likely not an issue for you.

Click to expand...

Thanks.

timjet · Mar 22, 2016

I've had a fresh water flush since I bought the boat. Dock hose connected to the strainer top. I flush with full pressure from the dock hose connection. When I first installed the flush system, I had a cheap dock hose and found the suction from the engine raw water pump collapsed the hose, had to upgrade the hose.

When flushing is complete (about 10 minutes) my wife shuts down the engine and at the same time I close the dock water valve on the strainer. If my wife is not available I shut off the water and then rush to the helm and shut down the engine (about 5 sec). I never leave the boat while flushing is in progress.

After 2 years and 400 hrs, on inspection my new Cummins reman aftercooler looked new. My other original engine had some blow by (green gunk) on the air fins but did not affect the boost pressure. Boost pressure on both engines had not changed over the 2 yr period.

TDunn · Mar 22, 2016

I simply pull the hose to the thru-hull off my raw water pump and replace it with one that I stick into a bucket. I then put a garden hose in the bucket. Fire up the engine and adjust the garden hose flow to keep water in the bucket. No risk that way and you can flush for as long as you want.

MRRiley · Mar 22, 2016

WesK said:
I wonder if the US Navy flushes their ship's engines after each use? How about the cruise and cargo ships?

Generally speaking, if we had a chance to run freshwater through the main salt water systems on board we did. Things like the fire main, main and secondary drain, ballasting, and of course the sea water strainers would be flushed when we had the chance which was limited by location.

Small boats, if being properly maintained, would be run periodically even while deployed and their use limited. This would necessitate cooling and fresh water would be used, so they too would effectively be flushed during the maintenance process.

Of course most Navy ships are running gas turbines these days so not too much demand for freshwater there, in the days of steam, we made our own condensate with pretty specific limits for salt anyway.

It would be interesting to see if the limited underway time outside of deployments these days is having any maintenance effect on cooling systems etc. I'd guess the folks at NAVSEA could pull the numbers.

PS - The sheer volume of water required to operate the installed systems precludes the regular use of fresh water for flushing. I'd say, if we had the fresh water available, we'd use it.

Raw Water Flush

Guru

Guru

Senior Member

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Senior Member

Similar threads