Water strainer - above or below water line?

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KenMcCulloch

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I am improving the water cooling arrangements to my 1GM10 raw water cooled diesel. A remote Vetus water strainer (140 series) will fit in the rather limited space available but it will be below the waterline by some inches rather than above as recommended by Vetus. Will that be perfectly OK or should I anticipate awful problems with such an arrangement? I'd particularly appreciate responses from forumites who have actually tried such an installation.
 
I've got an Vetus strainer as well and it's below the waterline. But I also do close the seawater cock when I leave the boat as a matter of routine.
Engine is a Volvo 2003 with inter-cooling.

Never had any problems for the last few years (since installation) with the setup.
Do keep the seal-ring lubricated with silicone grease though.

Arno
 
On my old Albin Ballad, the vetus strainer had to be fitted below the waterline otherwise the pipwork would airlock with the consequent starvation of coolant.

I tried it in the recommended position, but it just didn't work.
 
The advantage to having the stainer above the waterline is that you can open it up to clean the filter basket without shutting off the seacock. Below the waterline and the same process will result in wet trousers/kilt. I had the luxury of flexibility and so fitted just above the waterline so that water neither drained away nor overflowed making it easy for the pump and the trousers (I tend not to wear the kilt aboard).
 
You would have to shut the seacock to clean the filter but that's probably a minor inconvenience. Also you might get algae etc. growing on the inside of the clear cover. An advantage of having it above the waterline is that you can clearly see the water flowing through it whereas if it was permanently full you wouldn't.

Below the water line the filter chamber is under pressure, if that gets cracked [e.g. by ice] and you weren't aware of it you would get a leak into the boat.

On my boat I could not mount it completely above the water line and still have it in the engine compartment, so it has about 1/2" of water in it, at rest. This works fine. It is also handy when flushing the engine during laying up - just unscrew the top and run fresh water into the filter chamber with the engine running.

If I had not been able to mount it in the engine compartment at that height I would have mounted it outside, or gone for a bronze filter on the seacock.
 
Thanks for those very swift and helpful replies and esp the warning from michael; (I had wondered whether that little impeller would create enough vacuum to sook the water up into the strainer). Given that the only sensible place to mount it is a hand's breadth away from the seacock I don't think I'll have any trouble isolating it on the odd occasion. I wouldn't dream of leaving a boat unattended with the engine seacock open. That is to say I try to avoid it although there has been the odd oversight...
 
I fitted a water strainer above the waterline, but had problems as the impellor wouldn't pull the water through. On investigation the lid seal was leaking air but once screwed up hard it was fine. I had to make a 'lever' to fit the lugs to get extra purchase to fully tighten it. Tightening by hand was not enough. I don't know the make of strainer but I don't think it was Vetus.
 
While mine is not a Vetus device, my strainer is fitted below the waterline. Pisses a fair amount into the boat when the top is removed unless the engine is running when the sook from my admittedly much more testosteroned, machoic 2GM keeps the water level just below the top.

I have the usual paranoid worry about turning it off and double jubilee clips for when I forget - have even be known to row back to the boat to check, though marina berths don't worry me so much with only 0.1m under me at chart datum.
 
No problem whatsoever as long as you switch off the seacock before removing the strainer lid.

AND you seal the lid securely when replacing it.

Iain
 
[ QUOTE ]
vasaline will seal it, dont over tighten if its a plastic lid

[/ QUOTE ]

Having experienced the gritty yellow mess that vaseline can degenerate to when subjected to a marine environment, I have ceased to use it for anything other than battery terminals. Instead I use silicon grease, Molykote 33 Medium to be exact, for 'o'-rings and the like, but I am sure someone will know a reason why this is worse!
 
I fitted my Vetus strainer above the waterline but only just. The water level is about an inch below the lid. It works fine but after some hours motoring, the air gap increases. I have put it down to bubbles being drawn into the intake and accumulating over hours. One problem I did experience was that when sailing well heeled after many hours, the water in the strainer fell out through the intake so when I needed the engine there was only air in the system and the impellor wouldn't draw the water through to the engine. So now, when the engine goes off so does the seacock. I have a Halyard alarm which instantly goes off if I forget to open the seacock.
 
Either work perfectly well, both have certain drawbacks.

Above waterline, have to be perfectly sealed or they gradually lose water resulting in the need to top them up again. Have the advantage of not leaking.

Below waterline self-priming but leak-prone.

Mine is above the waterline, I prefer the peace of mind.
 
I think Charles Reed has it, you need to understand your installation basically.
I would also add from (slightly comic) experience, that it is very useful to be able to clear the skin fitting by poking something (e.g. spare 12" hacksaw blade) right through the (open) seacock to dislodge (e.g.) a plastic bag sucked into the inlet. If the pipework is longer and/or a little curved, some stiffish wire will do it. Having been in this situation, I would want to have a plan for it when sorting out an installation.
By the way, old fashion bronze strainer, if easily accessible is still a good solution and will seal reliably below waterline. The vetus type really come into their own when you have lots of small weed though.
 
Quote: I would also add from (slightly comic) experience, that it is very useful to be able to clear the skin fitting by poking something (e.g. spare 12" hacksaw blade) right through the (open) seacock to dislodge (e.g.) a plastic bag sucked into the inlet.

Agree entirely, every time my cooling water has blocked it has been caused by a glob of something in the inlet skin fitting. The bronze strainer directly on top of the ball valve allows a good poke with a screwdriver to clear it. Just don't do as I once did and use a screwdriver with a handle that fits neatly inside the strainer. It slipped and dropped straight inside at the same time clearing the blockage. I was left with a seacock that couldn't be closed and water flooding into the boat. /forums/images/graemlins/confused.gif It was an anxious few minutes with my hand over the top while directing SWMBO in how to bend up a piece of wire to allow me to hook it out again. Now use a much bigger screwdriver. /forums/images/graemlins/laugh.gif
 
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