Freshwater flush

I was on my surveyors boat on Thursday and he had rigged a freshwater flush system by tapping the top of his groco sea strainer adding a nipple, a valve and a quick disconnect garden hose adapter. Interesting idea, especially if you aren't going to be on the boat for a few weeks.

I know groco sells a whole new sea strainer with an adapter but has anyone ever rigged one?

Pro/con for flushing?

Baggiolini said:

I was on my surveyors boat on Thursday and he had rigged a freshwater flush system by tapping the top of his groco sea strainer adding a nipple, a valve and a quick disconnect garden hose adapter. Interesting idea, especially if you aren't going to be on the boat for a few weeks.

I know groco sells a whole new sea strainer with an adapter but has anyone ever rigged one?

Pro/con for flushing?

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Well, we have installed recently a fresh water flush system on our trawler style motor yacht which has a Caterpillar 3208NA diesel.. The flush system tees into the water intake just before the raw water strainer. This has its own seacock. We connect a 3/4 inch hose to the marina water supply and turn this on when we have docked with the engine still running. Then turn off the raw water intake and run the engine on fresh water for about 10 minutes. The system has flapper valves which divert the fresh water out the transom if the valve is closed or the engine is not running. All the raw water channels in the engine are flushed through with fresh water.

We expect much reduced maintenance on the heat exchanger, on the raw water impellor and most of all on the recently replaced ( very expensive) exhaust risers.

Most boats already have marine parts that can accept living in sea water .

On an aluminum IO or outboard it might be worth the effort , or on a boat where sea water is in the block it could be a help for engine longevity .

Direct sea water cooling is not common today even on IO boats.

FF said:

Most boats already have marine parts that can accept living in sea water .

On an aluminum IO or outboard it might be worth the effort , or on a boat where sea water is in the block it could be a help for engine longevity .

Direct sea water cooling is not common today even on IO boats.

Click to expand...

Agreed...having toyed with idea a long time...not sure how much it really helps.

Now if you ran anti-corrosion stuff through it...maybe a different story.

Through the years I have experimented with our trash pumps we use in salvage. Fresh water washes don't seem to help as much as after I run a bit of antifreeze through them and let it sit in there. Ideally...if you could keep it full of something like antifreeze without air would be the ticket I think....then the rubber impeller would have issues I suspect (probably nitrile ones would do better).

When I was dowin in Key West Fourth of July my brother was installing Groco flush fittings on strainers he was servicing that were cast bronze nipples which had a plugged tee on one side. He just replaced the hose barb on one side of the strainer with the new flush fitting. To use them you close the seacock remove, the plug and install a hose adapter. Not inexpensive but probably less than a whole strainer assembly. The fittings were heavy duty cast bronze.

Baggiolini said:

I was on my surveyors boat on Thursday and he had rigged a freshwater flush system by tapping the top of his groco sea strainer adding a nipple, a valve and a quick disconnect garden hose adapter. Interesting idea, especially if you aren't going to be on the boat for a few weeks.

I know groco sells a whole new sea strainer with an adapter but has anyone ever rigged one?

Pro/con for flushing?

Click to expand...

I have a engine and genset fresh water flush system I installed when I bought the boat. It's a simple system where I had my mechanic drill a hole into the caps of the stainer and install a ball type brass valve with a hose fitting. I open the valve to flush and close the raw water sea cock. Run the engine for about 10-15 minutes at idle. Make sure the hose doesn't collapse because the engine is sucking too much water. Don't let the water continue to run after you shut the engine down as you might force water back into the engine exhaust manifold.

There is no doubt you will have cleaner raw water components if you are consistent about flushing. The guru's on boatdiesel recommend it and it's partly why fresh water boats bring a premium. Don't you flush your O/B at season's end?

timjet said:

I have a engine and genset fresh water flush system I installed when I bought the boat. It's a simple system where I had my mechanic drill a hole into the caps of the stainer and install a ball type brass valve with a hose fitting. I open the valve to flush and close the raw water sea cock. Run the engine for about 10-15 minutes at idle. Make sure the hose doesn't collapse because the engine is sucking too much water. Don't let the water continue to run after you shut the engine down as you might force water back into the engine exhaust manifold.

There is no doubt you will have cleaner raw water components if you are consistent about flushing. The guru's on boatdiesel recommend it and it's partly why fresh water boats bring a premium. Don't you flush your O/B at season's end?

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I've always flushed my outboards after EVERY use (except while cruising and the motor stays on the boat in the water)....

But after taking apart multiple outboards through the years and seeing the mechs at my marina work on hundreds more...not sure that flushing does much more than keep passageways unclogged from salt...there is always significant corrosion in them no matter what. Although newer outboards are doing better.

So the saga of life continues....experts recommend....just like doctors and people seem to still die at all different ages no matter what doctor's advice they follow (I think motors have similar genes...)...Flushing doesn't hurt (unless you fill up your cylinders after the muffler so new to flushing...be careful).....but my jury is still out in how much it helps.

I may do the same...especially as long as I sit during the summer months...and like I said about flushing with some sort of anti-corrosive stuff...might try that as well as plugging the injection to the exhaust so I can keep the system full.

As to fresh water boats bringing a premium...it's for a lot more than just a few internal engine parts...

I have also considered building a flushing system, but or that past several years I have been hauling the boat several hours run up a freshwater river (Ct River) so the systems get a really good final flushing beforenstorage. I run the genset too. I also take the raw water system apart every 2 or 3 years.
As far as freshwater boats getting a premium....every boater I talk to thinks they are better...so it is a selling point to most be it justified or not

Paul does have a point; can anyone conclusively prove fresh water flushing is helpful?
Someone probably can, but in the mean time it just makes sense to me that flushing with fresh water can't hurt and probably helps. After all we fresh water flush all our stainless on the boat and dive gear.

timjet said:

Paul does have a point; can anyone conclusively prove fresh water flushing is helpful?
Someone probably can, but in the mean time it just makes sense to me that flushing with fresh water can't hurt and probably helps. After all we fresh water flush all our stainless on the boat and dive gear.

Click to expand...

I guess the longer I'm around and the more goofy stuff I see...the harder it gets to say anything is right/wrong/black/white.

2 good examples...I was sick of seeing how much room my steel fuel tanks took up and how hard it would be to do almost anything to really get a good look at their complete condition...they were VERY rusty on the outside and very black on the inside. With the horror stories of pinhole leaks and me needing more storage room plus accepting less fuel carried around...I decided to replace the tanks with smaller plastic ones. After I cut one out and went over it carefully in the parking lot...well lets just say it might have lasted another 25 years...but the decision was made and out they came.

Second example was a broken brake line on my truck this week...perfect condition, all 11 feet of it, except for one pinhole and a rusty area the size of a dime...but it made the line worthless and repairing the line was not even in the cards.

So the same for me goes with some boat maintenance ideas....you can get carried away with ideas that may or may not extend the life of a system. Sometimes systems get changed out because of wear and tear, sometimes because of totally external damage, etc...etc..

I think flushing is generally a minimal cost and effort type of operation. If it extends the life of a component a year or so is probably worth the effort. Although again as FF pointed out, a well made cooling system is generally saltwater resistant...more likely to suffer from galvanic or stray current corrosion. The expense (pieces and parts), can be useful for winterizing, trouble shooting or emergencies...such as hooking up a salt water washdown hose to the saltwater system in such a fashion that it could help cool if the regular saltwater pump starts to or totally fails.

With PSN
My first cruising boat was a 30 ft sailer built for me in 1977. The engine was raw water cooled and never had a flush. Well after I sold the boat I ran across it again, in 2007 and had a chat with the owner. He had recently replaced the old yanmar with a larger one that was fresh water cooled. He reported that the old engine, on inspection, had no issues with the salt water cooling, despite 30 yrs of never being flushed, always kept in the salt. So I don't concern myself with flushing.

I thought about modifying my last sailboat engine cooling system to allow for FW flush....Then I was concerned about the fact that my zinc anodes would be setting in fresh water the majority of the time, which is where one should be using aluminum anodes.....Decided to not go against the grain of decades of marine design for a "might help" benefit..... JMHO

Picture of fresh water flush system

I installed something similar on my Perko strainer. This is the setup that Tony Athens recommends. There is no doubt that fresh water is less conductive than salt water and at the very least will reduce zinc usage and maybe corrosion.

I drilled and tapped the cover for 1/2" NPT and threaded a street el, a couple of close nipples, a 1/2" ball valve, a 3/4x1/2" bushing and a female hose adapter. Parts cost was about $25.

To use it, you run the engine in idle, connect up a water hose and with the thru hull valve open you open the fresh water flow. The theory is that the fresh water displaces the salt water and only fresh water gets sucked up into the engine.

Well, with our low slip fresh water flow it didn't work that way. After idling for 5 minutes I pulled a zinc and the water still tasted brackish (our water is always brackish). Maybe it would work better with stronger flow. And it would certainly work if I shut off the thruhull, but I am hesitant to do that.

Here is the picture:

djmarchand said:

I installed something similar on my Perko strainer. This is the setup that Tony Athens recommends. There is no doubt that fresh water is less conductive than salt water and at the very least will reduce zinc usage and maybe corrosion.

I drilled and tapped the cover for 1/2" NPT and threaded a street el, a couple of close nipples, a 1/2" ball valve, a 3/4x1/2" bushing and a female hose adapter. Parts cost was about $25.

To use it, you run the engine in idle, connect up a water hose and with the thru hull valve open you open the fresh water flow. The theory is that the fresh water displaces the salt water and only fresh water gets sucked up into the engine.

Well, with our low slip fresh water flow it didn't work that way. After idling for 5 minutes I pulled a zinc and the water still tasted brackish (our water is always brackish). Maybe it would work better with stronger flow. And it would certainly work if I shut off the thruhull, but I am hesitant to do that.

Here is the picture:

Click to expand...

greysailor makes a good point...if you don't use aluminum "zinc" anodes are you really doing a disservice to your cooling system metals if you flush?

psneeld said:

greysailor makes a good point...if you don't use aluminum "zinc" anodes are you really doing a disservice to your cooling system metals if you flush?

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Hardly, zinc and aluminum are so close together on the galvanic table that it makes no difference in the application described.

I put this issue in with the "what should I worry about when I have absolutely nothing else to do or think about on my boat" class of self induced concerns.

RickB said:

Hardly, zinc and aluminum are so close together on the galvanic table that it makes no difference in the application described.

I put this issue in with the "what should I worry about when I have absolutely nothing else to do or think about on my boat" class of self induced concerns.

Click to expand...

Is that true for external zincs too? (shaft, rudder, tabs, etc)

I drilled and tapped the cover for 1/2" NPT and threaded a street el, a couple of close nipples, a 1/2" ball valve, a 3/4x1/2" bushing and a female hose adapter. Parts cost was about $25.

Most of the top covers I have seen are fairly thin. I would either add a nut inside or braze the street el in place.

psneeld said:

Is that true for external zincs too? (shaft, rudder, tabs, etc)

Click to expand...

The OP mentioned not using the boat "for a few weeks." Even if it were for a few months it would make little difference. There are plenty of boats that move from salt to fresh water all the time, they don't change anode material for each transition as it is really really silly.

Look around Lake Union at the fishing fleet and the coastal freighters. Few of them use an impressed current protection system, they use zincs just like the rest of us. They have steel hulls, fiberglass hulls, aluminum hulls, wooden hulls, engines that use zincs, engines that don't use zincs, some use shaft zincs, some don't ... they all share one thing in common - they don't haul the boat and change from zinc to aluminum or magnesium anodes or back after passing the locks. They don't dissolve at the dock either.

Those who are really concerned about mooring in fresh or brackish water for extended periods can use a magnesium version of the fish or grouper style zinc on a wire hanging over the side.

FF said:

Most of the top covers I have seen are fairly thin. I would either add a nut inside or braze the street el in place.

Click to expand...

FF made a good observation. In my case the mechanic had to use a backing nut and I treat the whole fixture gently.

FF said:

Most of the top covers I have seen are fairly thin. I would either add a nut inside or braze the street el in place.

Click to expand...

I was concerned about the thickness and was expecting to have to braze it. But I found that the cover was about 1/4" thick near the edge and I caught about 4 threads. I made sure that the threads were full depth and at the beginning of the taper so it made up tight. It feels solid.

David

We inserted a "T ' fitting into the raw intake hose just before the raw water filter i.e between the hull intake skin fitting and the raw filter.
The fresh water flush pipe (which is a reinforced hose) runs from a quick connect fitting near the transom and then forward through the bilge to a seacock mounted at the "T' connection. Thus we avoid any drilling or tapping into the filter body.

A key feature of this system is the flapper valve diversion which directs the fresh water out through the transom when the sea cock is shut or if the motor is not running. Thereby avoiding the possibility of a water lock in the engine.

The fresh water flush hose is 3/4 inch from marina tap to provide sufficient water volume for the Cat 3208 NA.

FF said:

Most boats already have marine parts that can accept living in sea water .

On an aluminum IO or outboard it might be worth the effort , or on a boat where sea water is in the block it could be a help for engine longevity .

Direct sea water cooling is not common today even on IO boats.

Click to expand...

Cast iron risers on Caterpillar 3208 only last 3 or 4 years we are told. Just replaced at over $NZ 3500 each plus installation.

The fresh water flush will add significantly to the life of these risers - we are advised.

Most inclined to agree but guess time will tell.

Cast iron risers on Caterpillar 3208 only last 3 or 4 years we are told. Just replaced at over $NZ 3500 each plus installation.

Check with other suppliers cast SS should not be much more,

heck with
Marine Exhaust Systems of Alabama, Inc.

www.[B]mesamarine[/B].com/‎

djmarchand said:

I installed something similar on my Perko strainer. This is the setup that Tony Athens recommends. There is no doubt that fresh water is less conductive than salt water and at the very least will reduce zinc usage and maybe corrosion.

I drilled and tapped the cover for 1/2" NPT and threaded a street el, a couple of close nipples, a 1/2" ball valve, a 3/4x1/2" bushing and a female hose adapter. Parts cost was about $25.

To use it, you run the engine in idle, connect up a water hose and with the thru hull valve open you open the fresh water flow. The theory is that the fresh water displaces the salt water and only fresh water gets sucked up into the engine.

Well, with our low slip fresh water flow it didn't work that way. After idling for 5 minutes I pulled a zinc and the water still tasted brackish (our water is always brackish). Maybe it would work better with stronger flow. And it would certainly work if I shut off the thruhull, but I am hesitant to do that.

Here is the picture:

Click to expand...

David, I did a very similar thing to the raw water strainer for my air conditioning system. There was a problem with air locks after the boat had been out and put back in the water. Open the valve to let the air out. I put a hose connection on it to flush out that system with fresh water or cleaning mixture. Works like a charm.

Moonstruck said:

I put a hose connection on it to flush out that system with fresh water or cleaning mixture. Works like a charm.

Click to expand...

Don, do you not leave the Air Conditioning on while unattended at the dock?

timjet said:

Don, do you not leave the Air Conditioning on while unattended at the dock?

Click to expand...

No, Tim. I am afraid of a line breaking, and sinking the boat. The air lock only occurs after the boat is hauled, so it's not a major problem. Just wanted a method that made it easier to bleed the line. I have a captain that keeps an eye on the boat for me. I pay him monthly to check the bilges, and air the boat out. He has the charter boat, Last Mango, in the slip next to me; and can hear the alarms if they go off in the boat. I just don't trust fittings enough to leave the a/c pump running. I may be away for a month or two at a time. I also turn off and clean out the ice maker and refrigerator in case the power goes out. I turn off the inverter. I don't want anything to run the batteries down. I turn off everything on the boat except the battery charger and the 24 hr things like bilge pumps, stereo memory, etc. Is that anal?

Moonstruck said:

No, Tim. I am afraid of a line breaking, and sinking the boat.
Is that anal?

Click to expand...

No I don't think so.

I worry about a line breaking and sinking the boat too. The admiral worries about mildew and claims the vinyl liner will sag if it gets too hot.

So far I've run the AC 24/7 but again I worry about a line breaking.

I have a siren connected to a high water bilge alarm that I hope someone would react to. But a broken AC line would probably sink the boat before anyone could do anything.

timjet said:

No I don't think so.

I worry about a line breaking and sinking the boat too. The admiral worries about mildew and claims the vinyl liner will sag if it gets too hot.

So far I've run the AC 24/7 but again I worry about a line breaking.

I have a siren connected to a high water bilge alarm that I hope someone would react to. But a broken AC line would probably sink the boat before anyone could do anything.

Click to expand...

We only had a mildew problem one time. Guess what? An air conditioning condensate line had seeped water into the bilge under the saloon area. We unloaded the whole boat. Cleaned, disinfected, aired, and sun dried it all. No problems since. It doesn't take much water in a bilge to get condensation. Airing the boat out occasionally seems to keep it in check.