Sea strainer water level

[Bajavet]

Hello all. I have a Beneteau Swift Trawler with twin Volvo D4 300’s. The boat is only 5 months old so I am still figuring things out.

I cleaned the sea strainers out which I have done several times before. This time, after removing the top on the port side engine strainer the water level slowly dropped to about 1/2 way down the strainer. The seacock was definitely closed. I cleaned the basket and tried to refill the strainer by adding water but the level kept dropping to about the halfway mark. I tried a couple of times. Finally, I put the cover on the strainer and ran the engine. There was water pumping and the engine did not overheat but the sea strainer did not fill up.

The starboard strainer was normal and the water level did not drop with the top off. This is the first time this has happened with port strainer, the other times were normal. The intake line has an above the waterline loop in it.

Is this normal? Where is the water going? How concerned should I be? We are currently in a marina in Key West and getting ready to make the 300 mile trip home this week.

Thank you all very much.

 

[RT Firefly]

Greetings,
Welcome aboard.

 

[diver dave]

RW strainers are a funny thing. Engines don't want air in any circulating coolant, since air is a poor thermal conductor.
But, the typical RW strainer has its output at the bottom of the bowl, and the input is higher, forcing flow down. Therefore, as long as there is continuous water at the bottom third or so (no whirlpool) there will be no air flow out. If you think about it, to rid the bowl of air, means that air must leave the output side. Bottom line, I'm good with 1/2 full bowls.

On you second question about engine OFF flow thru the strainer;
Usually slight wear on the impellor can allow some flow thru the engine, if the RW strainer is mounted high and the RW top is off.

 

[ScottC]

I agree with Diver Dave, that this is likely nothing to worry about. Mine is not always completely full, but still plenty of water coming in at the top and going out at the bottom. By way of possible explanation...as water seeks its own level, perhaps it could have something to do with the positioning of the hoses?

 

[Comodave]

Welcome aboard and congrats on your new boat.

 

[Bajavet]

Thank you all very much for the information and the welcomes. I’m looking forward to cruising.

 

[SteveK]

Where would the water go? Assuming the RW strainer is below the exhaust elbow where the water exits after going through heat exchangers, where would it go even after water being added with a closed thru hull?

 

[diver dave]

Where would the water go? Assuming the RW strainer is below the exhaust elbow where the water exits after going through heat exchangers, where would it go even after water being added with a closed thru hull?

Here is an experiment. At engine shutdown, does water stop flowing out the exhaust thru hull instantly?

 

[SteveK]

Here is an experiment. At engine shutdown, does water stop flowing out the exhaust thru hull instantly?

gravity will drain water out exhaust but not from the strainer unless it is higher. any water left in exhaust hose will drain.
RW from strainer exits at the exhaust elbow at the end of the exhaust manifold to mix with and cool the exhaust. Up to that point none should leak out. There should not be any gravity drop of water from the strainer unless it is above that point, even then the impeller should hold it back unless housing is worn. If the strainer is above outside water line and the thru hull does not completely close it could drain out the inlet. IMO

 

[kapnd]

I prefer to orient a raw water strainer so that the waterline is just below the top of the strainer, so that it is always full, but will not overflow when opened.