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Old 23-12-2015, 18:40   #1
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Intake water Problem

Our Outremer 45 with 3gm30s is fitted with vetus raw water strainers mounted above the waterline and the intake is covered with the scoop style strainer with the cup facing forward.
After sailing fast or in rough seas the strainer is empty and the no water gets pumped . The impellers where new last year and when I fill the strainer going everything works properly. I was going to turn the scoops around but was advised against that as it can send water into the engine when sailing. One solution would be to drop the strainers to just above the water line and install a vented loop. I have inspected and lubed the O ring .The strainers will hold water for weeks when sitting . Is this A WATER PUMP PROBLEM
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Old 23-12-2015, 19:01   #2
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Re: Intake water Problem

If your strainers are mounted about the waterline as I am reading, how on earth would 1 expect to get water to the engine?! I will admit I don't know much about Cats or tris. but logic would dictate that the water intake have to be under water, at all times to function properly!
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Old 23-12-2015, 19:03   #3
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Re: Intake water Problem

1. Where would you install vented loops if you lower the strainers?

2. Why not just remove the scoops?


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Old 23-12-2015, 19:03   #4
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Re: Intake water Problem

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Originally Posted by mike d. View Post
If your strainers are mounted about the waterline as I am reading, how on earth would 1 expect to get water to the engine?! I will admit I don't know much about Cats or tris. but logic would dictate that the water intake have to be under water, at all times to function properly!

Their strainers are baskets, with scoops on the thru hulls below the water


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Old 23-12-2015, 19:08   #5
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Re: Intake water Problem

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Originally Posted by admiralslater View Post
.............................
.................. After sailing fast or in rough seas the strainer is empty and the no water gets pumped. ..................
.................. I fill the strainer going everything works properly. .............
I am not clearly understanding these two statements. For the first statement, are you saying that the strainer fills with air while you are sailing (not motoring)? Is the through hull valve closed or open when this occurs? When the seacock is opened does seawater flow in to fill the strainer?

When you say that you fill the strainer, in the second statement, Are you opening the top of the strainer to manually fill it? Are you opening the top of the strainer with the sea cock open to fill it? When you open the system between the through hull and the raw water pump, does water flow in at a fast rate?

I think important information would be added if you determine that the water is not lost from the strainer if the sea cock is closed while sailing.
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Old 23-12-2015, 19:14   #6
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Re: Intake water Problem

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I am not clearly understanding these two statements. For the first statement, are you saying that the strainer fills with air while you are sailing (not motoring)? Is the through hull valve closed or open when this occurs? When the seacock is opened does seawater flow in to fill the strainer?



When you say that you fill the strainer, in the second statement, Are you opening the top of the strainer to manually fill it? Are you opening the top of the strainer with the sea cock open to fill it? When you open the system between the through hull and the raw water pump, does water flow in at a fast rate?



I think important information would be added if you determine that the water is not lost from the strainer if the sea cock is closed while sailing.

Their strainers are above the waterline, as is quite common with these plastic strainers, also the boat I fitted with aft facing scoops and is quite fast, so the water is being drawn out of the strainers.....

As least that's what I gathered......from the op.


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Old 23-12-2015, 21:17   #7
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Re: Intake water Problem

Sorry for the confusion . The intake thru hull is covered with a cup strainer, that had the solid part facing forward and it is mounted well below the waterline. The inline vetus strainer is above the WL. I think what happens at speed is that the solid cup in the water pulls a vacuum and empties the entire line back to the water or thereabouts and the pump is sitting in air. I would put the vented loop after the vetus to stop any siphon action while sailing.

I want to lower the strainer to the point that it is at WL.
When this happened last year I had to close the sea cock take the lid off the Vetus, fill it with water, put the lid on and open the seacock again, and that work everytime. It occurs to me that just releasing the cap and letting the pressure out may have been enough
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Old 24-12-2015, 05:53   #8
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Re: Intake water Problem

I was unsure with the use of the strainer term for both the strainer basket and the strainer outside the through-hull, but as I understand now, the speed of the water passing over the exterior scooped strainer is creating a vacuum pulling air through the raw water cooling system to empty the water from the strainer basket.

It seems to me that there are two possible solutions. One would be to block the flow out of the system and the other would be to alter the exterior strainer to keep a neutral flow at speed.

The first solution could either rely on manually closing the system when not motoring (kingston valve) or adding some type of one-way valve. I would not favor the task of manually operating the valves before and after motoring and I would not want the potential blockage/leakage with an added valve in the raw water flow.

I would consider using the exterior strainers with slotted openings that extend fore and aft with no "scoop" that would promote the vacuum. I can understand the risk of the reverse action where the fast moving water would flood into the cooling system while the engine is not running. Maybe the best assurance for a neutral flow of water would be fitting the exterior strainer with the slots positioned athwartship.
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Old 24-12-2015, 06:11   #9
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Re: Intake water Problem

Interesting predicament admiral man....

So let's go with our presumptions....

1. The reversed clamshell is pulling a vacuum from your raw water inlet at speed...

2. We can't very well "force" positive pressure by reversing said inlets...

3. A vented loop would seem to do almost the exact same thing as is currently happening by introducing air into the line... BUT located pre-stainer... your strainer should remain full, thereby instantly creating your pre-strainer prime...

4. Bouncing a thought to vent the inlet (tee) with another restricted orifice raw water source pre-strainer?
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Old 24-12-2015, 06:21   #10
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Re: Intake water Problem

I wouldn't put the vented loop in after the strainer, that will at best aerate the engine cooling water, at worstake it possible for the engine to pull water.

Personally I'd either remove the scoop completely, or put bronze strainers below the waterline (I'm not so sure those plastic vetus strainers are meant to go below the wl)


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Old 24-12-2015, 06:36   #11
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Re: Intake water Problem

Maybe there's another approach to solving the problem with the use of a "sea chest" or larger internal water reservoir.
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Old 24-12-2015, 07:03   #12
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Re: Intake water Problem

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Maybe there's another approach to solving the problem with the use of a "sea chest" or larger internal water reservoir.
Awesome idea Hudman... Like an accumulator...
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Old 24-12-2015, 09:15   #13
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Re: Intake water Problem

Sounds like an amateur installed engine intake. A proper sea strainer should be installed below the waterline, with its plumbing a continuous rise to the pump. Eliminate the reverse-facing intake screen.
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Old 24-12-2015, 11:41   #14
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Re: Intake water Problem

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Sounds like an amateur installed engine intake. A proper sea strainer should be installed below the waterline, with its plumbing a continuous rise to the pump. Eliminate the reverse-facing intake screen.

I've been on dozens of boats with this "amateur" install, forespar and vetus strainers are almost universally installed above the waterline......for good reason.

I believe the real root of the problem is the aft facing scoops and the high speed obtained by an outremer catamaran.


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Old 24-12-2015, 12:03   #15
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Re: Intake water Problem

I recently installed a solar controller in the port engine room of 1 of these recently. Certainly don't recall noticing any of the cooling system looking out of the ordinary, certainly not above the w/line.
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