cooling water loss

[JSulway]

My boat an old Macwester 26 is fitted with a Bukh direct water cooled engine, i have a problem with the water level in the strainer basket when in any kind of a chop, although when in flat water is fine. I believe the boat is lifting out of the sea allowing the water to drain away. Does anyone have a simple solution?

 

[David2452]

Non return valve?

 

[nordic_ranger]

Lower the height of the water strainer.

 

[jerryat]

Sounds to me as if the top/lid of the strainer is leaking as it seems unlikely that the water could 'drain' from it in a sea that quickly. I'm assuming here that the strainer is fitted high up at (roughly) top of engine height or higher.

Even if one of those fitted directly to the seacock, the impeller shouold easily pull the water through, so I'd check that the impeller itself is in good condition.

 

[JSulway]

Thanks for your replies - I had thought about a non return valve but was concerned about restricting flow or easily getting blocked! The strainer on my boat is as you stated high near the top of the engine, i could try lowering it as suggested, as for the impeller even when replaced with a new one, there is no improvement

 

[MoodySabre]

I had the same problem on my Snapdragon with an old petrol engine - against a strong current there was often too little water coming up, resulting in an overheat. i had a one-way valve which probably didn't help. I thought the water was just rushing by and thought about a scoop on the inlet. But when we put in a new Beta 10 the water hit the the top of the strainer like a fountain from Leicester Square. The problem was obviously not enough suction from the water pump (which did not have a replacable impeller).

I'd start with the water pump - and check all the hoses/connections for air leaks. I can't see that lowering the strainer will help as the distance from the sea water inlet to the engine remains constant. You need more lift.

 

[JSulway]

I appreciate your comments, but feel I should add that I have fitted a new pump, so am quite confused

 

[jerryat]

Well it's got to be either an air leak as someone suggested, the strainer is not airtight, or the pump/impeller is faulty.

Could you confirm whether, when the boat is stationary, the water flow is ok? Is it also ok after say, a week without running the engine, when you start it again.

What I'm getting at, is that with all three of the Bukhs I've had, I've never had to prime the water strainer at all. The pump always pulled (and still does) the water through the system with in seconds. If this DOESN'T happen with your engine and assuming you've checked all the hose connections, then I strongly suspect a leak in the strainer - probably via the screw-on lid. For example, have you thoroughly checked the 'O' ring in the (assumed) Vetus type strainer?

One final point. Do check all the hoses throughout their length. I once sorted a similar problem on a friend's boat where I found that the water hoses had chafed against the engine while it was running and worn a tiny hole through it!

 

[Cliveshep]

If your pump is pumping the only way the water in the basket can drain away is if air can get in, so either your inlet is appearing above water or as the other member said you've got an air leak somewhere. As air is easier to lift than water it'll suck air in preference. I don't know your engine or boat, but can't you abandon the water inlet if it broaches clear and put another one in somewhere else that stays submerged?

Also, I would suggest a Jabsco pump if you can rig one, belt driven, as they are quite a positive lift and take replacement impellors (always carry a spare of course). Get the required volume requirement figures from your engine manufacurer and buy a Jabsco with a little more "grunt" than you need.

However, the first and easiest is to look at the most obvious place to start, strip and re-do all connections on the suction side first, looking for air leak possibilities. Check all hoses for cracks or splits, and also check the pump is not leaking from a cover plate. These things in my experience tend to the simpler rather than the most complex solution, human beings often imagine the worst. Is that pain in the chest a heart attack, or trapped wind? Same with any thing mechanical. Pessimism diagnoses the worst case first! Good luck!

 

[JSulway]

To confirm, when the boat is in calm water the flow is fine, also after leaving for a week or more. The water is draining because the inlet is lifting clear of the sea in rough conditions and hence sucking air.

 

[MoodySabre]

Can't see much option but to reposition the inlet, or perhaps have one on each side to keep one in the water. All very odd.

It must get pretty bouncy on your boat /forums/images/graemlins/shocked.gif