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Old 09-16-2018, 09:45 PM   #21
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Although quite expensive these people have some very nice kits you can install to flush your engines. https://aditmarine.com.au/

Some friends of our have one of their products installed and are very happy with it. I used to flush our little 40 series Volvo's using just the dock hose through a tee fitting and turning the seacock's off but our Cummins were never shut down long enough to have a great benefit.
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Old 09-16-2018, 10:20 PM   #22
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Those two concerns you mention are concerns that I shared. I discovered that my dock hose won’t supply too much water for the engine if the seacock is closed. However, that leaves the second concern.

Your PO said that he simultaneously turned on the hose and started the engine and did the reverse when finished. I want to be able to do it solo, which means that I can’t simultaneously close or open the hose bib while starting or shutting down the engine.
My concern with the seacock closed would be pressurizing the raw water system with 80 psi city main pressure. The PO of my boat always had his wife to help. I like the sequence described by David above.

I'm not too worried about undersupply of water at idle. It doesn't seem to hurt the pump to even have the seacock closed for periods of time, and a hose surely supplies enough to cool at idle - but you could watch the temp and see.
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Old 09-16-2018, 10:27 PM   #23
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How much hose pressure would a raw water pump need, for any damage to occur? Next time I have the pressure washer revved up I will try to find a Raw water impeller and some way to immobilize it so I can see if 3200# pressure is enough.
Somehow I doubt 60# street pressure will do anything at all.
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Old 09-17-2018, 12:24 AM   #24
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Save you the work Dave.
12 gal 1/2 in @40# 50ft. 25 gal 1/2 in 25 ft
22 gal 5/8. 44 gal 5/8
36 gal 3/4. 72 gal


Thanks Dan.
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Old 09-17-2018, 12:31 AM   #25
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Dave:

This is how I do it single handed:

Start the engine with the hose connected to the flush fitting with the water valve on and the seacock open. Close the sea cock. The hose collapses a bit as the raw water pump pulls more than the hose can supply, but plenty enough to keep the engine cool at idle. Run the engine for 5 minutes. Close the hose water valve and immediately shut down the engine. Open the seacock.

This flushes the engine and never puts excessive water pressure on the raw water pump. The 10-20 seconds that it takes me to close the engine room hatch (I need to close it to get to the helm) and shut down the engine doesn't hurt a thing.

In my case the engine can pull something like twice the volume of water as the hose can supply. So if you left the seacock open and tried to flush it that way, it would get a mixture of 50/50 sea and fresh water. Not so good. This way you get 100% fresh water and after 5 minutes all of he sea water has been displaced from the engine. I have tested this by pulling zincs at various places along the water path and all tasted fresh.

I have even flushed at a mooring with no dock water available by using the potable water system. The potable water pump puts out even less water so I run it a bit longer, maybe ten minutes to displace all of the sea water.

David


Thanks David. That is what I needed to know. It would be easier if I had an engine shut off there in the ER, then I could just shut the engine off and open the seacock at the same time.
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Old 09-17-2018, 12:35 AM   #26
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How much hose pressure would a raw water pump need, for any damage to occur? Next time I have the pressure washer revved up I will try to find a Raw water impeller and some way to immobilize it so I can see if 3200# pressure is enough.

Somehow I doubt 60# street pressure will do anything at all.


I don’t think it is a problem on the impeller, but I really don’t know. Maybe David or some of the other smart diesel folks can tell us?
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Old 09-17-2018, 06:39 AM   #27
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I don’t think it is a problem on the impeller, but I really don’t know. Maybe David or some of the other smart diesel folks can tell us?

Since the raw water pump seal is designed to operate at a slight vacuum, I think any positive pressure could blow out the seal.


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Old 09-17-2018, 09:25 AM   #28
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Thanks David. That is what I needed to know. It would be easier if I had an engine shut off there in the ER, then I could just shut the engine off and open the seacock at the same time.
Dave:

I don't know about your Cummins, but my Volvos shut down if I grab the throttle at the high pressure pump and hold it closed. No fuel and it shuts right down. I could reach the throttle with one hand and the seacock with the other. Doesn't work for startup of course, but then startup is less time sensitive.
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Old 09-17-2018, 10:01 AM   #29
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How much hose pressure would a raw water pump need, for any damage to occur? Next time I have the pressure washer revved up I will try to find a Raw water impeller and some way to immobilize it so I can see if 3200# pressure is enough.
Somehow I doubt 60# street pressure will do anything at all.
I'm not worried about the pump though you could blow the seal. But you are pressurizing the entire raw water circuit to 60 or 80 psi. Strainer, hoses, heat exchangers, exhaust elbow, muffler. It is certainly not built to take that pressure, and you might find out that it won't. Now, it is open at the far end and there are some restrictions on the near end which will reduce the pressure some, maybe a lot, and that *might* mitigate the pressure depending on the boat.

In addition, you are adding water in an uncontrolled amount to the muffler. If the engine stops, you are still adding water. It doesn't take long for a waterlift muffler to fill up, after which it fills the turbo, exhaust manifold, and cylinders. Then the oil sump.

I'd much rather see the engine somewhat starved for water in this scenario than have too much. If it is starved, you will see the temperature climb slowly. With too much, you may not know until something is very wrong.

The sequence David described eliminates many of these concerns. With the seacock open, excess pressure will exit the thru hull. Turn on the hose, then turn off the seacock with the engine running.
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Old 09-18-2018, 08:24 AM   #30
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I don’t think the system would see those pressures, the water from say a 3/4 inch hose is free to exit out of a much larger exhaust. If you plugged the exhaust, you would have that problem after it filled several cylinders with water!.
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Old 09-21-2018, 01:40 PM   #31
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My first power boat had a unique flush system. The previous owner had converted the salt water anchor wash to a fresh water flush line as the through hull came from the engine room. Then he had an alternate system the drew from the fresh water tanks. He could flush at anchor and at the dock. My thinking is, just draw from the fresh water tanks and refill them at the dock. The sequence was, start the engines, turn on the water, close the sea cocks, turn off the water, stop the engines, open the sea cocks or not. I don't remember if I did both engines at the same time or individually. I think it was both. That boat held 300 gallons of fresh water so we could flush at anchor but I never did.

My new boat has no flush. I'm going to tap into the fresh water tanks and refill at the docks.
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Old 09-21-2018, 09:58 PM   #32
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My first power boat had a unique flush system. The previous owner had converted the salt water anchor wash to a fresh water flush line as the through hull came from the engine room. Then he had an alternate system the drew from the fresh water tanks. He could flush at anchor and at the dock. My thinking is, just draw from the fresh water tanks and refill them at the dock. The sequence was, start the engines, turn on the water, close the sea cocks, turn off the water, stop the engines, open the sea cocks or not. I don't remember if I did both engines at the same time or individually. I think it was both. That boat held 300 gallons of fresh water so we could flush at anchor but I never did.

My new boat has no flush. I'm going to tap into the fresh water tanks and refill at the docks.


Interesting. I can switch from raw water to fresh water on my washdown pump. However, my system doesn’t have the same comparable fresh water flow that even my wimpy dock hose has.

However, I can see a couple of possibilities for using the fresh water from my tanks...
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Old 09-21-2018, 11:08 PM   #33
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I just used the fresh water flush on the hard to test the engine and new cutlass bearings. With the hose on (and good pressure from the mains) at idle the suction from the engine collapsed the hose. So no worries about it providing too much pressure. I turned the hose on with the seacock open, started the engine, then shut the seacock.
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Old 09-22-2018, 03:25 AM   #34
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I dealt with this on a previous boat. A little different situation because I was winderizing, but the same in that I needed to replace the sea water circuit with something other than sea water.


I used the same type of strainer cap with a hose fitting, except it was before Groco offered them and I had to make it myself from a replacement bronze cap.


I also made a general purpose "service" bucket that has come in hand over and over again. It's just a 5 gal bucket, and I installed a fitting and shutoff valve through the side of the bucket as close to the bottom as possible. That allows water to be drawn from teh bottom of the bucket rahter than pulled up over the top. for flushing something like an HVAC pump that has no lift capability, it allows you to gravity feed it.


OK, with that aside, I needed to flush prop glycol through the system, not just water, but the approach is the same. I did as you and closed the thruhull and filled the bucket. Then start and run the engine which would drain the bucket down very fast. Stop when the bucket is empty, refill, and repeat.


That flushes with 100% of whatever you put in the bucket. Getting back to your original question, my engines were QSCs, not QSBs, so a bit larger. And I also needed to get glycol into the muffer, not just the engine. So I needed more juice than you need to just get fresh water into the engine and the injection ring. I needed 15 gal per engine, and I think a significant part of that was the mufflers. So I would think 5 gal would probably be plenty for you, and 10 gal would be certain beyond any doubt.


I would not operate with the thruhull open. That just defeats the whole purpose.


You could run the hose to keep filling the bucket while draining, but that makes for a very difficult one man job. If you fill the bucket, shut off the hose, go start and run the engine long enough to drain the bucket, then go fill up again, it's an easy one man job. I always did it myself on our boat.


I would also let the engine pull water from the bucket, and never connect the hose such that the raw water system is pressurized. Not only do you risk damage to teh impeller, but you can full the muffler (assuming a water muffler) more than expected and risk back flooding the engine. It's not a certain problem, but an opportunity to make mistakes, forget to turn off the water, or whatever.
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Old 09-22-2018, 03:39 AM   #35
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Hi,


Have you seen this video where QSB built fluch system?





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Old 09-22-2018, 10:37 AM   #36
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Hi,


Have you seen this video where QSB built fluch system?





NBs


Thanks for that NB. Looks like they just stuck a hose in a large diameter hose. That avoids any risk of pressurizing the system.

I was surprised that they were running the engine at 760 rpm. Idle for these engines is 600 rpm. I don’t see any reason for flushing the engines at higher than idle.
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Old 09-22-2018, 10:56 AM   #37
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Twisted, thanks for your experience. What you did was pretty similar to what I ended up doing and I think will likely continue to do for the mean time.

Part of the issue I have is that I need to make the process as quick and convenient as possible. Unfortunately, getting access to the front of the engine means flipping up the stairs thereby blocking the way to the pilothouse. So I have attached a line that I can use to lift the stairs from above.

If I had an engine shut-off in the ER, near the front of the engine, it would be easy. I could attached the hose directly to the filter cap with the thru hull open. Turn on the hose, then turn on the engine. I could then open the thru hull and turn off the engine from the ER. Unfortunatley, I can’t do that.

So...
- attach short hose to the filter with the end placed in the bottom of a 5 gallon bucket.
- Place the end of the dock hose in the bucket.
- close the stairway access, climb the stairs, pull the line to open the stairs (I can now see down directly into the bucket in the ER)
- get off the boat and open the dock water valve
- quickly reboard the boat and stand at the back of the PH and look down at the bucket.
- start the engine when the bucket is full.
- watch the bucket and stop the engine as the bucket approaches empty.
- turn the engine on again when the bucket is almost full and again turn it off when the bucket is almost empty.
- quickly exit the boat and close the dock water valve.
- open the engine thru-hull

I just need to be quick enough to turn off the dock water before the bucket overfills and gives my bilge a fresh water flush.

As in the video that was posted, I could put another hose section and in-line shut off in the line, but that would decrease the flow from the hose.
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Old 09-30-2018, 09:44 PM   #38
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Not that anyone is all that interested, but I tried the above today.

I attached the hose directly to the filter with a shut-off near the helm. I closed the seacock, started the engine, and turned on the hose and let the engine run for 5 minutes or so. Then turned off the hose and shut the engine down.

The hose didn’t collapse but was very “soft”. With just my thumb and forefinger I was able to squeeze the hose closed. So my ignorant assumption is that the hose wasn’t quite able to keep up with the water demand from the engine water pump but not enough of a water deficit to collapse the hose.
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Old 10-01-2018, 11:22 PM   #39
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That's just what mine does. I don't think you are actually going to cut off water to it, after all there is still pressure in one end of the hose. Just a lot of pressure drop by the time it gets to the end.
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