Raw Water no-flow alarm

[syoun10]

On my Yanmar diesel, I'm considering installing an alarm that will go off when the raw water flow stops (this could be because "someone" forgot to open the thru-hull (never me!), or because the flow is stopped by a blockage).

There seem to be two types - those that detect high temperature in the exhaust by a band on the exhaust pipe a few inches after the mixing elbow; and those that have an in-line flow detector actually in the water flow (e.g. Aqualarm).

I'm concerned about the temp sensor, as it is placed over a rubber exhaust pipe, so it could get quite hot inside even before the temp on the outside rises sufficiently.

I'm concerned about the flow meter as it might itself be the cause of a blockage.

Does anybody have any experience with either of these approaches?

 

[kloudie1]

#33 in this thread:
http://forums.hunter.sailboatowners.com/showthread.php?p=726098&highlight=Water Flow Alarm
Pretty good discussion.. I don't know if Roger is still using it..

 

[Rob2435]

The alarm is hearing more engine noise, if you don't have water, there is nothing to muffle the sound of the engine via the exhaust.

 

[Benny17441]

No experience with either but consider the infrequency of such ocurrences do not warrant the design, installation and maintenance of such an alarm. I have not gone very far but have spent many hours at sea and only have had three ocurrences of being in a boat that suffered a blockage of the raw water intake. One was catastrophic for the impeller and the other two were partial blockages (ice bags near shore) which caused no damage and just a mere inconvenience. I think the chances of getting hit by lightning are higher.

 

[Rob19574]

[FONT=Calibri, Verdana, Helvetica, Arial]I installed an alert that monitors water flow and it works very well. It does not have an alarm but I was thinking about adding a buzzer. Its has a warning light that illuminates when water flow drops to a reduced flow rate or stops altogether. You can adjust the sensitivity accordingly. I highly recommend adding this to your system and would do such over the high-temp sensor that mounts on the exhaust. My thinking is that the water-flow reduction is one of the first events that will cause an engine to overheat. The temp sensor will work too but that alert goes off after your cooling water has already been restrained – so the water-flow system buys you some time. If your that concerned you can also do both

I installed mine (raw water engine) between the H2o exit line on my block and the injection point on the exhaust riser. I don’t recall the brand — I believe I bought it from Sailors Solutions so google them. Cost ~$80 I recall. I don't think they have any internal mechanical flow-mechanisms, I think it works off sensors inside the device that detect water flow (I am not an engineer). You simply cut your water hose and install in-line with 2 hose-clamps - then wire accordingly.

- Rob[/FONT]

 

[tommays]

Its pretty common in HP outboards to have a water pressure guage which is SIMPLE and will show when the pump starts to get a bit tired and needs service

 

[rardiH36]

No experience with either but consider the infrequency of such ocurrences do not warrant the design, installation and maintenance of such an alarm. I have not gone very far but have spent many hours at sea and only have had three ocurrences of being in a boat that suffered a blockage of the raw water intake. One was catastrophic for the impeller and the other two were partial blockages (ice bags near shore) which caused no damage and just a mere inconvenience. I think the chances of getting hit by lightning are higher.

For me, the greater prospect of no engine raw water flow is being distracted from my normal routine (such as when guests are arriving) and not opening my raw water seacock and also not listening for the sound of splashing water with the exhaust. This did happen to me ONCE --- with the result of a destroyed impeller and steam blowing out of the exchanger pressure cap. Fortunately I have a converted raw water cooling engine (now self contained anti-freeze with heat exchanger) and the over-heat alarm is at 140-150 degrees, rather than the usual 180 or so for most engines. So for me the alarm sounded well below the damage point. My solution was to rig a switch against my seacock lever. If the engine is started with the seacock unopened, the engine warning buzzer will not go off after the usual second or two.

 

[jviss]

The alarm is hearing more engine noise, if you don't have water, there is nothing to muffle the sound of the engine via the exhaust.

That's not so, at least not on my boat. I had a blockage last week and only noticed because I saw clouds of steam at the transom. The strainer on the hull was almost completely blocked.

 

[jviss]

No experience with either but consider the infrequency of such ocurrences do not warrant the design, installation and maintenance of such an alarm. I have not gone very far but have spent many hours at sea and only have had three ocurrences of being in a boat that suffered a blockage of the raw water intake. One was catastrophic for the impeller and the other two were partial blockages (ice bags near shore) which caused no damage and just a mere inconvenience. I think the chances of getting hit by lightning are higher.

How many times have you been hit by lighting? (compared to the three blockages)?