Rescued - Engine water strainer position above the waterline causes exhaust and engine overheating.

[Red]

I had to replace and reposition a plastic Vetus water strainer to a metal unit and mount it above the waterline. This was a requirement of a vessel survey carried out for for MCA. Yesterday I had to be rescued, the Vetus waterlock burst and the engine overheated crossing Portsmouth Harbour, luckily I was able to secure a buoy, assess the situation and arrange for a tow back to my mooring. The impeller on the Jabsco pump, which was only recently fitted was shredded, and there are 3 large burst holes on the Vetus waterlock. I can see the advantage of being able to clean the water strainer without needing to turn the sea clock off with the current position above the waterline, however I was always concerned that one creates air in the system and the pump would be sucking air through the system until it then sucks water. The engine is a Beta 38 which has a small pump and now as recommended a large metal strainer. I am now planning to reposition the strainer at the waterline so as not to create a large waterlock, has anyone any recommendations or knowledge on this matter. The MCA requirement of mounting the strainer above the waterline is standard recommendation however I have been told that some or their recommendations are not always good.

 

[scottie]

One of the disadvantages of using “plastic “ in exhaust systems
You should also examine the exhaust hose from the engine as it is also likely to be damaged internally
GRP components are available which are more heat resistant along with overheat alarms plus the basic checking of water flow at the outlet especially after changing an impeller and before casting off

 

[Poignard]

My plastic Vetus strainer is mounted so that its base is just about at the water line and it works fine there.

The O-ring in the lid is kept lightly greased.

 

[LittleSister]

My Beta 14 had no trouble sucking water (and air to start with) through a large plastic Vetus strainer positioned similar to Poignard's. (I did always wet the impeller and pump with water at the start of the season to ensure there was sufficient sealing and lubrication to get it started.)

 

[Refueler]

I honestly think that some recommendations should be re-assessed or questioned.

Lets consider water strainer to engine cooling.

1. It should be fit for purpose meaning over-engineered to give long term reliability. That makes me very happy - I have a traditional bronze unit. I would never fit plastic.
2. It should have valve control so that it can be closed and strainer cleaned / serviced ... that water flow can be regulated for raw water systems.
3. Should be positively fed to assist the engine water pump - ie at or below waterline.

Those are MY personal views on it and seem to ally with many boats installations (older of course) - I am not suggesting todays builds are same.

 

[davidej]

We have a strainer above the waterline. When cleaning it, I occasionally found the water-pump would not overcome the airlock . So now, I close the seacock and fill it up before replacing the lid. Then start the engine and immediately open the cock

 

[colhel]

We have a strainer above the waterline. When cleaning it, I occasionally found the water-pump would not overcome the airlock . So now, I close the seacock and fill it up before replacing the lid. Then start the engine and immediately open the cock

Andy59 of this forum explained this method to me when we first got our mobo. It didn't occur to me, until he explained it, the importance of everything in the system being air tight. I'm still grateful for the time he spent with me that day when i was getting those frustrating new boat niggles.

 

[PCUK]

30 years with plastic Venus strainer 500mm above water-line.

 

[James L]

30 years with plastic Venus strainer 500mm above water-line.

At least in my case the pump is before the strainer, so the strainer location has no effect on the pump getting water.
However what I do find after launching is I need to open the strainers to allow the water to reach the pump. Otherwise the pumps may fail to prime. Once the pump gets water the locations after that have no effect.

 

[LittleSister]

At least in my case the pump is before the strainer, so the strainer location has no effect on the pump getting water.

Isn't the main point of a strainer to prevent (most) debris from getting to the pump, where it would prematurely wear and potentially block it? Doesn't your arrangement negate that?

 

[James L]

Isn't the main point of a strainer to prevent (most) debris from getting to the pump, where it would prematurely wear and potentially block it? Doesn't your arrangement negate that?

The openings on the inlet of the outdrives would prevent anything big enough to damage the pump from entering. The strainer is to catch the smaller stuff that would cause problems further on.

 

[scottie]

Check the vertical hole in the nose if there is one?

 

[chillee]

have the same problem. Since bring dry stacked I seem to get airlocked everytime I go back in the water. Have to fill her up from the Venus strainer to reprime it. Really annoying.

 

[Refueler]

I'm surprised at the airlocks ... most water pumps on engines I've seen are rotary vane type ... that basically the vanes create a near rotary engine type pumping motion .. what we call positive displacement ... I know my water pump on front of my Perkins has no problem at all drawing up from the strainer ... I admit that my pump is only maybe 6" above waterline ...

If I had to prime my engine system each time, even though it may be only a few x's a year .. I think I would look to find a solution .. especially if on a drying mooring !