Plugged raw water intake

[Stephentrapani]

Hello. Any brilliant tips on unclogging the strainer fitting on my raw water intake, while in the water? It just dribbles water when open. The intake hose connects to a ball valve (1/4" ID I think), then a 90, then through the hull, and then the strainer.
I tried poking up the through the strainer from under the hull, I tried poking a plastic drain snake through the valve from inside the boat, but it wouldn't go around the 90. Anyone dealt with this?

 

[JoeWhite]

I am pretty sure the inside diameter of the through hull is more than 1/4", more like 5/8" or larger.
To unclog, disconnect the hose from the opposite end of the through hull and come up with an adapter that will allow you to connect a garden hose from the shore water supply. Add a valve near you so ypu can turn off the water as needed. Then when you are ready open the water valve slowly so the pressurized water can force watever is clogging to flush out.
Let the water run for 5 minutes fully opened to clear out all the debris. Whatever is closing it entered from outside and it will go back out the same way.

 

[PaulK]

Barnacles clogged the external strainer on our boat. To clear them required cleaning out the inside of the through hull as well as the strainer itself. Barnacles will grow back quickly after you do this because the attachment points they leave behind negate any antifouling you might have used. Not wanting to have to do it again we removed the external strainer. This now allows us to detach the intake hose from the internal strainer and poke a stick down it to clear anything that might be blocking the hose or through hull. Doing this once every three or four weeks prevents any buildup of marine growth and is a lot easier than diving on an external strainer with a toothbrush. Our previous boat had no external strainer and had no issues with this setup for over 25 years.

 

[Captain Larry-DH]

I am pretty sure the inside diameter of the through hull is more than 1/4", more like 5/8" or larger.
To unclog, disconnect the hose from the opposite end of the through hull and come up with an adapter that will allow you to connect a garden hose from the shore water supply. Add a valve near you so ypu can turn off the water as needed. Then when you are ready open the water valve slowly so the pressurized water can force watever is clogging to flush out.
Let the water run for 5 minutes fully opened to clear out all the debris. Whatever is closing it entered from outside and it will go back out the same way.

This is great advice. It usually works.
I recommend you remove the external underwater strainer next time you haul out. Use a conventional seacock with an external mushroom fitting and an interior raw water strainer that can be opened, checked and cleaned as needed.

 

[jssailem]

Whatever is closing it entered from outside and it will go back out the same way.

Well, at least it should.

No telling what it is. A picture of your valve would be helpful.

This is what a typical through-hull valve and 90º full-flow nipple looks like.

The nipple can be unscrewed to give you access to the ball valve. If there is an obstruction, it can often be that a non-full-flow nipple was used, like this one.

The 90º bend is too tight, and stuff gets stuck.

Remove the elbow from the valve.
Clean out the valve and the hose all the way back to the engine.

 

[Ralph Johnstone]

The intake hose connects to a ball valve (1/4" ID I think), then a 90, then through the hull, and then the strainer.

Think you could send a picture of the setup ?

Sounds like this is a bad setup just waiting for a clog, again and again and again. The suspected 1/4" ID valve, if correct, just doesn't work. Too small. The external strainer is also an invitation to clogging and should be removed at the next haul-out.

After several clogs, I finally got around to installing this arrangement :

• When a clog happens, the valve is closed and the top plug is removed.
• A clear vinyl hose about 24" long with a 3/4" X 3/4" hose adapter is attached where the plug was.
• The hose is stood upright.
• The valve is opened and the water slowly rises to the boat's waterline.
• A long 1/8" SS rod is sent down the vinyl tube and through the valve.
• You can see what's coming up through the clear tube when clear.
• Re-assemble when clear and you're ready to fire up the engine.

Your extrnal strainer will cause problems in this operation if you're dealing with barnacles, which was always my misfortune.

 

[dmax]

Courtesy of Stu Jackson: use your dinghy pump with a cone-shaped fitting, stick it in the raw water hose and pump - incredibly powerful.

 

[Stephentrapani]

I am pretty sure the inside diameter of the through hull is more than 1/4", more like 5/8" or larger.
To unclog, disconnect the hose from the opposite end of the through hull and come up with an adapter that will allow you to connect a garden hose from the shore water supply. Add a valve near you so ypu can turn off the water as needed. Then when you are ready open the water valve slowly so the pressurized water can force watever is clogging to flush out.
Let the water run for 5 minutes fully opened to clear out all the debris. Whatever is closing it entered from outside and it will go back out the same way.

I'm going to try this, except I'm stuck on a buoy. I'm going to rig a hose bib to my fresh water tank/pump and try to blow it out that way. See any problem with that?

 

[azambella]

this will require some industrial force if they are Zebra mussels.
I had a heck of a time clearing this path nd the boat was hauled !
The bronze external strainer makes a perfect hideout for them.

I pressure washed as much as possible (external). They used a Dremel to remove the glue/ dried slime?
then bottom painted as much as I could inside the strainer with a tiny Artists brush.

 

[Stephentrapani]

Courtesy of Stu Jackson: use your dinghy pump with a cone-shaped fitting, stick it in the raw water hose and pump - incredibly powerful.

Are we talking hand pump or motorized? I'll get one!

 

[JoeWhite]

Stephen, I would not try using on board water pump. Try using the pump described in post #7.
If that does not work, close the through hull, remove the hose and extend a hose to outside water so that the raw water pump can draw water from over board, then start your engine and head for the marina so you can clean the clog.
If you can, remove the 90 degree corner so you can clean easily.

 

[Allan12210]

I always disconnected the hose at the strainer and stuck it in the end of my air horn. A couple of honks and you could hear bubbles on the outside of the hull. More often than not it cleared the line.

 

[Captain Larry-DH]

Are we talking hand pump or motorized? I'll get one!

The garden hose idea above works better, and is higher pressure (in most cases)

 

[thinwater]

I've learned that external strainers are needed on things that run constantly while not moving (AC and generator) to keep out the sea grass and avoid sucking up minnows, but they just cause trouble on things that are either intermittent (head) or underway (engine).

Since the AC was the only one with a strainer on my last boat (I installed it after sucking too many fish into the 90), swimming to clean it was not unpleasant. It does take a screw driver, enough vigor to get the hard growth, and a straight shot into the pipe.

 

[dmax]

Are we talking hand pump or motorized? I'll get one!

I've used one of the Bravo foot pumps (easier than a hand pump) but any good pump will do - don't need electric. I was astounded at how effective it is.

 

[Scott T-Bird]

Good luck! I've had the same problem and I sold the boat before I actually corrected it. Replacing the 90 with a straight line or a smoother bend is probably your best ultimate solution. I agree that if it is raw water intake for your engine, remove the external strainer. A lot depends on the matter that is clogging the thru hull. I haven't dealt with barnacles. In my case, it was sea grass that caused the clogs and it also depended on how much loose sea grass was floating in the water. Many years it was not a problem, a few years it was virtually every weekend.

I had little luck trying to poke a screw driver thru the hole while swimming under the boat, but sometimes it was necessary. I had best results with something like a toothbrush or other abrasive material on the end of a rod to draw grass out from inside the hull. Sometimes it was just one strand at a time until a clump finally came out. I didn't have any luck with trying to force water or air thru the assembly. I think the problem was that if the clump leaked enough water thru, then pressure simply wasn't effective. The air or water simply passes thru without removing the clump. I see no way how air or water pressure is going to remove barnacles, if that's your problem.

 

[jssailem]

Stephentrapani, you sail in waters where eelgrass is a big factor. It gets sucked up intakes and finds its way towards the engine, unless it gets hung up along the way. It is the reason the boats I sail on have raw water filters.
This is a typical Groco ARG raw water filter and is the type I have on my boat. The screen will trap eelgrass before it can foul your water pump or destroy your engine.


The other fun flotsam in the water are the white jellyfish that love the Puget Sound.

When these suckers bloom on the waters, boaters beware.


It is like a carpet of goo that stings. You do not want to have to clean them out of your engine.

 

[Scott T-Bird]

I just remembered that I finally found a dental pick that was the most effective way to remove sea grass and it was most effective removing it from inside the boat. Once I discovered the dental pick, I no longer had any need to swim under the hull as I had been doing before to attack from both sides of the clog. Of course I'm talking about sea grass, not something that hardens, like barnacles.

I haven't had this problem for over 5 years because my Catalina has a straight thru-hull fitting with no bends. It's the 90 that is the crux of your problem. With no bends, the sea grass simply collects in the filter, which needs to be emptied periodically when there is floating sea grass in the water.