Raw water flow sensors

[Sean B]

I've got raw water flow sensors and alarms on my boat, installed from the factory. The sensors are installed just after the strainers, and before the water pump.



I need to work on that area, and am thinking about moving the flow sensors to the line leading to the exhaust elbow (deisel engine).

My main reason would be to eliminate four clamped joints below the waterline, and also to put the sensors in a spot where I can get to them easier.

By moving these, I would be monitoring raw water flow exiting the engine, rather than entering it. Seems like the sensor would detect more types of failures this way too.

Does anyone see any reason I should not make this change?

[Harry Babb]

Sean
It makes perfectly good sense to me. If the water cannot come in it cannot go out.....and if it cannot get out it cannot come in.....seems like a pressure gage would be a good compliment to the flow sensor.

hb

[In Memory Walter K]

I would think they'd be of greater value where they are or just before the raw water pump. If it tells you of a shortage of raw water before the pump it might save you an impeller. If it's after, the pump/impeller might be fried or damaged by the time there's exhaust flow (or lack of it). I've sometimes had prime problems at the beginning of the season and have learned to feel my pumps the first time I'm going to leave the slip. If they're cold, fine. Warm, no go. How do these sensors work? To a gauge on your bridge? Sound alarm?

[Sean B]

How do these sensors work? To a gauge on your bridge? Sound alarm?

They go to a warning alarm control box, which is connected to a very loud bell. Indicator lights tell you what set the alarm off.

The Bertram factory alarm system came with no raw water flow, low oil pressure, high engine temp, high bilge water, and high gear oil temp alarms. Yeah really - gear oil temp alarms... seems weird but I have freshwater gear oil coolers, so I'm supposing that why these are there. Also when I had a small coolant leak a while back, the gear temp alarm warned me before the engine ever experienced any temp increase, and I sure did like that.

Aqua Alarm makes indicator panels and alarm control systems similiar to the one my boat came with, and I'm thinking about putting one in soon to replace my 24 year old panel that is getting a little crusty.

The new panels look like this:





Twice in six years the raw water flow alarm has alerted me to a flow restriction. Both times I was running slow, and both times I backed down the boat to successfully blast away the restriction. One of those times I actually saw the plastic bag float off in the prop wash. Those sensors are good things to have.

They will make custom panels and I'll have to get one of those, because of the gear oil temp sensors. I'm also thinking of adding bilge pump counters too. Boat sits in the water year round here, and it's nice to know about any leaks before they are big ones

[Rawleigh]

Sean: Are they rated for the temperature they will be getting on the outflow side?

[Sean B]

Good thought, and I thought about that too.... the flow sensors are CPVC and are rated for continuous running at maximum 210 degrees.

My engines themselves run at around 195-205, and I've been thinking that the raw cooling water coming out of the heat exchangers would be much cooler than that. My local diesel guru tells me that is so, but I also plan to verify that fact with a pyrometer during my next boat ride, before I start making any modifications. These are 3208T engines.

There is short length of thin walled copper tubing along the outflow raw water circuit on which I should be able to take an accurate raw water temp reading, once I have the puppies warmed up and at cruising speed. Actually I think I'll do it at WOT, just to know how hot it can get

[randall]

my boat has a flush out system which i dont use because its past the impeller. but its great for checking water flow. unintended consequences.

i like the idea of removing below waterline clamps....if possible i would do that.