Non return on engine water intake

[ghostlymoron]

At present, I have no strainer on my raw water intake. This is a BAD THING as my boat will reside on a drying mooring. I have bought a basket type strainer but can't mount it close to the intake so there will be a 3' (ish) hose from the intake to the strainer and a similar length back to the water pump. Question is 1. Will this cause the pump to run dry for too long before it primes? and 2. Would the situation be improved by fitting a non return valve on the hose where it joins the intake?
My thinking is that, in the latter case, I could prime the pipe via the strainer if the boat has been standing for a while.

 

[johnalison]

Although I'm not in mud, my Vetus strainer is above the engine and has no trouble priming. If you have a strainer above the waterline, you have the advantage of being able to use a dinghy pump to blow any blockage back out, and this could be useful in a mud berth.

 

[Keith-i]

It's good practice AFAIK to mount the strainer above the water line. This means the pipe to the pump will be downhill and always have water sitting in it. Assuming you have a valve/seacock at the skin fitting then you can close this off after any trip and the pipes will stay full. Even so, with a little water in the pipework I have never had a problem with my system priming and I have close on 6 feet of pipe from strainer to pump and about 18" from intake vertically up to strainer.

 

[charles_reed]

At present, I have no strainer on my raw water intake. This is a BAD THING as my boat will reside on a drying mooring. I have bought a basket type strainer but can't mount it close to the intake so there will be a 3' (ish) hose from the intake to the strainer and a similar length back to the water pump. Question is 1. Will this cause the pump to run dry for too long before it primes? and 2. Would the situation be improved by fitting a non return valve on the hose where it joins the intake?
My thinking is that, in the latter case, I could prime the pipe via the strainer if the boat has been standing for a while.

With my boat, the strainer is mounted above the WL and about 450mm from the water pump.
Under normal circumstances, once I have filled the filter, there is no problem with the pump self-priming. Usually a failure to do so is due to a faulty raw-water pump (either impeller or seals). I do always make sure the filter is filled after beaching.

 

[vyv_cox]

As shown in the photo, the hose from the seacock (not in photo, in adjacent compartment) to the strainer on my boat is at least 3 feet in length. Provided there are no air leaks in either the strainer lid or the pump seal, the pump primes perfectly well.

I have fitted a NRV at the seacock when using the old fitting that had the strainer at the seacock. After sailing in choppy conditions the pump would not prime and I hoped that a NRV would preventing water from draining back. It didn't but the problem was completely resolved when the old pump seal failed and I replaced it.

 

[pvb]

Most basket-type strainers are designed so that they remain fairly full of water when the boat dries out, thus giving the pump a good chance to work effectively when the engine starts. To achieve this, it's essential to plumb the inlet and outlet correctly, according to the strainer instructions.

 

[ghostlymoron]

That's very good news. I'll try without a nrv and turn off the sea cock after use. (Good practice anyway).