Darn raw water intake blocked again

[Dr. D]

My boat was splashed this morning and put back in the slip. In the afternoon I go aboard to get a few things done. Most went fine and I was glad to see the batteries had not lost any charge after over three months disconnected.

What is not good is this: I opened the raw water intake on the sail drive. Then I looked into the raw water filter and it remained full. As the filter is above the waterline it should have drained. Another blockage. Must be some insect made a nest. Can‘t be another fish swimming up the sail drive. I hope.

 

[Justin_NSA]

Should it have drained? Mine is above the waterline but it doesn't.

 

[Don S/V ILLusion]

Is it impractical to test by lowering the filter temporarily just to validate your ‘diagnosis’?

 

[Dr. D]

Should it have drained? Mine is above the waterline but it doesn't.

I thought perhaps the entire system was sealed, so the level would stay the same. But I took off the cover of the filter and the level did not change.

 

[Davidasailor26]

Maybe try something like a dinghy air pump to push whatever is causing the blockage back down and out? I’ve had success with that to fix a plastic bag over the AC intake.

 

[JohnShannon]

The symptom would be overheating? Easy to verify?

 

[Dr. D]

No, no way I am starting the engine until I am certain raw water is going through the engine.

I'll be over at the boat on Saturday and investigate further. Opening the raw water intake valve was the last thing I did on Tuesday and I was too tired to look into the problem then.

1: Make sure valve is open (I believe I left it open)
2: Disconnect the hose from the filter to the intake at the filter to make sure the filter isn't blocked.
3: Blow hard into the hose to see if air will pass through it. If that doesn't work, then try air horn.
4: If no air passing, then disconnect the hose at the intake and check if the hose is blocked.
5: If the hose is clear, the block is inside the sail drive. Last time I used dock water to clear the intake, but the dock water isn't turned on.

Justin, Don: The filter was full to the top with antifreeze and it stays there when I remove the cover. From the last blockage and investigation, I know the filter is above the waterline. So if the pathway to the water is clear (valve is open and no blockage), the level in the pathway will fall to the waterline level.

 

[Justin_NSA]

Justin, Don: The filter was full to the top with antifreeze and it stays there when I remove the cover. From the last blockage and investigation, I know the filter is above the waterline. So if the pathway to the water is clear (valve is open and no blockage), the level in the pathway will fall to the waterline level.

True dat. Sounds like you really do have a blockage. The only thing you can do in the water is try to backflush it with air. Maybe fish a wire down and see what you pull out. Is your hull intake screened? That could be good or bad from what has been discussed here in the past.

 

[Don S/V ILLusion]

.

Justin, Don: The filter was full to the top with antifreeze and it stays there when I remove the cover. From the last blockage and investigation, I know the filter is above the waterline. So if the pathway to the water is clear (valve is open and no blockage), the level in the pathway will fall to the waterline level.

That’s logical, however, remember that the rate at which the filter empties depends on the head (above the WL) so it can be a slow process you might miss if you are looking momentarily

 

[Dr. D]

Aboard the boat. When I arrived the level in the filter had not changed. I decided removing the hose from the bottom of the filter would result in too much antifreeze sprayed around until I got a container under it. So I got a syringe and began sucking the antifreeze out and squirting it into the container.
After the third syringe full, there was a loud gurgling and the filter drained.
I poured about two gallons of water through the filter to make sure whatever was causing the blockage was cleared. Then I started the engine. Everything went fine.
Still don’t know what was the cause of the blockage. Perhaps in the pathway through the sail drive there is a slight rise, so when the boat was splashed a bubble got trapped and formed a vapor lock. Oh, well......