fitting a raw water strainer, above or below the water line?

[Dellquay13]

my current raw water strainer is a bronze lumpen thing built into the head of the sea cock, and is hard to get to and clean out. I have bought an inline strainer with a clear lid, which will let me see what is going through, and also pour fresh water in to flush the 1gm10 or run it while ashore.
Do i have to install it above the water line (awkward) or can it go at or a little below the water line?
I know I would have to be very careful to close the seacock before opening the strainer if below the water line. I would remove the basket from the original strainer once the inline strainer is fitted.

 

[Dellquay13]

 

[Dellquay13]

 

[Graham376]

Best to fit it level with or just above waterline so if you need to rod a blockage, it's not flooding.

 

[penfold]

I've seen them installed both above and below the waterline, there are pros and cons for both; below self-bleeds a lot easier, above means you can clean it without closing the seacock. For that style of housing Vetus say above. The main thing about installing below the waterline is that it becomes a good idea to carry a spare seal for the lid, or even a spare lid if you are of a nervous disposition.

What state is the valve and throughhull? The rust suggests the adaptor between the strainer and the valve is stainless steel, I'd be changing that as a matter of priority due to the galvanic corrosion.

 

[garymalmgren]

The installation diagram has the base of the filter 6 inches / 15 cm above the water line.
This means that the water pump will have to pull a vacuum in the system to fill the filter.
It guarantees the safety of the filter and connections as they are above the water line.

That being said there are plenty of these units fitted below the waterline.
So, fit it where ever it is easiest to fit and access.

I would remove the basket from the original strainer once the inline strainer is fitted.

As Atom has suggested, you would be better to remove the stainless nipple and replace it with a bronze elbow barb or straight barb fitting.
I think the horizontal fitting coming out of your present filter could screw straight into your sea cock.

gary

 

[Halo]

Keep the lumpen thing. You can rod out the sea cock from inside if it blocks.
Those vetus type strainers like the one you show are prone to leaks around the seal. I would not put one below the water line.

 

[Bristolfashion]

This is exactly my set up. I have kept the bronze strainer & installed the versus above the waterline as per the instructions. It works very well.

 

[Keith-i]

I also have a similar Vetus strainer and although mounted as high as possible the water line is midway up the filter. This seems a very good compromise and has been fine for the last 10 yrs.

 

[RichardS]

I have two engine strainers above the water-line and two toilet strainers below the water-line and no particular problems with either configuration.

Richard

 

[Bergamot]

My similar strainer is above the water line as per the instructions above. However an old salt at the marina mounted his with the waterline just above the intake to the engine but below the top of the bowl so it self primes rather than relying on the impeller pump generating sufficient suction to start the flow. His approach also allows him to remove the lid to rod it through if the seacock is clogged without flooding the boat. His approach makes a lot of sense .

 

[Gary Fox]

Keep the lumpen thing. You can rod out the sea cock from inside if it blocks.
Those vetus type strainers like the one you show are prone to leaks around the seal. I would not put one below the water line.

The 'lumpen things' can be rodded straight through, if, repeat if, you have easy access. That's their only advantage though.

Pardon for contradicting you but: it is nonsense to suggest Vetus strainers are '..prone to leaks around the seal.' You would have to be extremely determined to make one leak, either by cross-threading the lid or leaving it loose, or omitting the seal entirely; although with a correct installation, (sea level under below the inside of the lid, but possible to check by touching if not looking), the inside of the lid is at atmospheric pressure when the engine isn't running, or a slight vacuum from the jabsco when running.

 

[JumbleDuck]

The installation diagram has the base of the filter 6 inches / 15 cm above the water line.

That's how my Vetus one was fitted by the yard when they changed the engine.

 

[Dellquay13]

thanks everyone, especially for pointing out the corrosion. I've spoken to my local marine engineer about the corrosion and he will sort it out properly when the boat next comes ashore, I know I would most likely end up with a right mess and constant fear of sea cock failure if I tried parting those old joints myself.
I'm confident about fitting the new strainer though.

 

[Sandy]

You don't mention what vessel you have.

What is with this strainer thing, asks man who has never had one.

 

[TernVI]

Ideally, I'd have the Vetus one, on the waterline, with the inlet hose straight for rodding through.
But the main thing is IMHO, it must be possible to poke it through, bit of water in the bilge is nice to avoid but survivable.
Being able to clear a plastic bag or weed off the inlet quickly might be important one day. Had both, got away with it!

 

[Ian_Rob]

I am about to fit a Vetus Strainer. Vetus recommend that is a minimum of 150mm above water level but to have it an accessible position I need to have it at 300mm. I assume that the additional height will not matter?

 

[RichardS]

I am about to fit a Vetus Strainer. Vetus recommend that is a minimum of 150mm above water level but to have it an accessible position I need to have it at 300mm. I assume that the additional height will not matter?

The water pump will have to work a little harder to self-prime but once it's done, then provided the top is properly sealed with silicone grease, it will be fine. I would guess that mine are something like 300mm above the water line.

Richard

 

[TernVI]

The water pump will have to work a little harder to self-prime but once it's done, then provided the top is properly sealed with silicone grease, it will be fine. I would guess that mine are something like 300mm above the water line.

Richard

If it struggles to self prime, just shut the seacock and fill the strainer with water. Put the lid on and open the seacock. Some raw water pumps are not good at sucking air, it's not what they are for.

 

[RichardS]

If it struggles to self prime, just shut the seacock and fill the strainer with water. Put the lid on and open the seacock. Some raw water pumps are not good at sucking air, it's not what they are for.

I know .... and no need to shut the seacock if the strainer is above the waterline. If it's below the waterline you just need to crack open the lid a little but it will almost certainly prime perfectly anyway.

Richard