Raw water flow requirement sensitivity

[DBBRanger]

I'm expecting to add an Aqualarm flow sensor to my 2008 R25 raw water supply line. On the 110HP Yanmar, the supply line goes aft from the strainer and makes a U-turn and then turns to the port to connect to the engine - all with one 1" hose. I would like to use right angle fittings to make it a cleaner install with the sensor - right angle fittings at the strainer to make that U-turn and also then a right angle fitting coming out of the sensor. But I'm wondering if it will add too much flow resistance and thereby decrease the raw water flow too much, i.e. is the flow that sensitive? Aqualarm only says that the sensor should be 1 foot away from any right angled fittings - I can do that. Any thoughts or words of wisdom? How have others plumbed it on an R25?

 

[SGIDAVE]

I'm expecting to add an Aqualarm flow sensor to my 2008 R25 raw water supply line. On the 110HP Yanmar, the supply line goes aft from the strainer and makes a U-turn and then turns to the port to connect to the engine - all with one 1" hose. I would like to use right angle fittings to make it a cleaner install with the sensor - right angle fittings at the strainer to make that U-turn and also then a right angle fitting coming out of the sensor. But I'm wondering if it will add too much flow resistance and thereby decrease the raw water flow too much, i.e. is the flow that sensitive? Aqualarm only says that the sensor should be 1 foot away from any right angled fittings - I can do that. Any thoughts or words of wisdom? How have others plumbed it on an R25?

Hello DBBR,

I would avoid the right-angle elbows. I realize that would look cleaner, but will add significant extra resistance to flow both because of the right-angle and the reduced internal diameter of the fitting (it must fit INSIDE the 1" ID rubber hose you presently have). Isn't resistance to flow proportional to the cube of the radius?

MY observation with my much-smaller Yanmar 3YM engine is that the raw water flow varies not arithmetically (20, 50, 80% increases) but rather exponentially (or nearly so...raw water intake doubles/triples/quadruples with increased throttle settings) which, to me, explains why it's difficult (impossible?) for these mechanical raw water flow sensors to alarm at "low" flow reliably. Mine alarms at NO flow without delay. I've not noted it alarming at low flow but I could be wrong. My point here is that if it alarms at "low" flow...WHAT flow would that be? At idle the "flow" is quite low but at 1800 rpm it's 5-10X higher...so if you have SOME flow at 1800 rpm but less than "idle" flow...well, that's WAY TOO LITTLE flow, and your exhaust is already going to get WAY TOO HOT really fast.

Sorry, I'm not explaining this very clearly. I think the concept of the Aqualarm "alarming" at low flow is not possible. So, to my thinking, the BEST arrangement is to use BOTH the flow alarm AND the exhaust temp alarm. It is the exhaust temp alarm that will let you know when you have LOW flow more reliably than the flow alarm. Again, this is my thinking which could be faulty. I didn't rest well last night, etc... :?

I CAN envision an electronic alarm giving warning of "low" raw water flow but it would need to know the engine's rpm and coolant temp combined into an algorithm to determine if the flow is truly "low" - since low flow is a moving target depending upon the engine's throttle setting. But this becomes unfeasibly complex and probably too expensive if even available.

I still like my Aqualarm - nothing against it. I don't think it will give "low" flow alarm though. (at anything above idle speed, that is).

dave

 

[R Baker]

You explained your concern clearly enough for me - and, I concur. Not only is the exhaust temp sensor is simplier in concept, it is easier to install. The detailed relationship between water flow and temperature I admit I don't clearly understand. Perhaps a comment from the manufacturer of these devices might provide some insight.

 

[DBBRanger]

I would avoid the right-angle elbows. I realize that would look cleaner, but will add significant extra resistance to flow both because of the right-angle and the reduced internal diameter of the fitting (it must fit INSIDE the 1" ID rubber hose you presently have). Isn't resistance to flow proportional to the cube of the radius?

Dave,

Thanks for the thoughts. I suspect you are right. I'll forgo the right-angles and figure out another way of making it look pretty!

Doug

 

[sheral]

So, to my thinking, the BEST arrangement is to use BOTH the flow alarm AND the exhaust temp alarm. It is the exhaust temp alarm that will let you know when you have LOW flow more reliably than the flow alarm. Again, this is my thinking which could be faulty. dave

Seems to make perfect sense, as usual!

 

[nzfisher]

For those that installed the aqualarm flow meter in the raw water intake line. How loud is the alarm buzzer? I am thinking of mounting it near or on the teak head surround but want to make sure it is audible both from the helm and the cockpit. I probably spend more time in the cockpit with engine running than at the helm.

 

[Lobo]

AQUALARM

BUZZER: Really loud! Overpowers engine alarm. You'll hear it all over the boat.

ALARM LOCATION: I have it on the dashboard. Wired it into one of the instrument panel lights, that makes is live when the ignition is turned on.

UNIT LOCATION ON R25 110 HP: I had earlier replaced hose strainer to engine. Installed hose so that from strainer it looped upward and forward. When I installed alarm I put it on top of loop. Send me a PM and email address and I'll email you a photo.

EFFECTIVENESS: A-1 good! Both in testing and being stupid three weeks ago. You get the alarm in less than 3 seconds from no water. Without alarm could be 5 or more minutes (10 minutes on me one day - idling and low speed out of harbour).

For those of you who don't have this alarm, you should consider it. It's really inexpensive (maybe 15% of a "boat unit") and only ONE time pays for itself.

Dave
Lobo

 

[sheral]

AQUALARM

BUZZER: Really loud! Overpowers engine alarm. You'll hear it all over the boat.

ALARM LOCATION: I have it on the dashboard. Wired it into one of the instrument panel lights, that makes is live when the ignition is turned on.

UNIT LOCATION ON R25 110 HP: I had earlier replaced hose strainer to engine. Installed hose so that from strainer it looped upward and forward. When I installed alarm I put it on top of loop. Send me a PM and email address and I'll email you a photo.

EFFECTIVENESS: A-1 good! Both in testing and being stupid three weeks ago. You get the alarm in less than 3 seconds from no water. Without alarm could be 5 or more minutes (10 minutes on me one day - idling and low speed out of harbour).

For those of you who don't have this alarm, you should consider it. It's really inexpensive (maybe 15% of a "boat unit") and only ONE time pays for itself.

Dave
Lobo

thanks for the review. i have the raw water alarm (and muffler sensor) probably sitting at the border right now. very much looking forward to getting them installed. 🙂

 

[R Baker]

I asked Aqua Alarm the following question :

> How does your Aqua Alarm flow device differentiate between flow at idle rpm
> and reduced flow at high rpm when a flow problem occurs ?

Their response :

Hello , the flow detectors have a set flow rate that must be obtained to keep the flow detector from sounding the alarm. For example the 1" is set approx 3 to 5 gallons per minute. This is usually about 4 gallons per minute. If the flow rate drops below 4 gpm the alarm will sound.
Thanks,
Rodney Morgan
Aqualarm

 

[knotflying]

Does anyone know what the exhaust gas temperature is supposed to be? The Aqualarm literature says it trips at 200 degrees. I am just wondering how close that is compared to the normal constant RPM temperature. The reason I say this is that (now I am using my aircraft experience here) there are several reasons why exhaust gas temperature can rise or fall. Just because you are getting a higher temperature, it may not only be related to your water flow. What happens if for some reason the EGT hits 202 degrees? The alarm will sound, but is it critical to the exhaust components? What are the component's max temperature.
I am just thinking that I would prefer an audible alarm for flow and a temperature gauge for the EGT so I can determine if I have an issue.
At least if my engine blows I won't fall out of the sky. 😀

Just a thought.

 

[SGIDAVE]

Does anyone know what the exhaust gas temperature is supposed to be? The Aqualarm literature says it trips at 200 degrees. I am just wondering how close that is compared to the normal constant RPM temperature. The reason I say this is that (now I am using my aircraft experience here) there are several reasons why exhaust gas temperature can rise or fall. Just because you are getting a higher temperature, it may not only be related to your water flow. What happens if for some reason the EGT hits 202 degrees? The alarm will sound, but is it critical to the exhaust components? What are the component's max temperature.
I am just thinking that I would prefer an audible alarm for flow and a temperature gauge for the EGT so I can determine if I have an issue.
At least if my engine blows I won't fall out of the sky. 😀

Just a thought.

Hello Mike,

I think 'normal' exhaust temps are well below 200 F. Remember, this is "exhaust temperature" in contrast to exhaust GAS temperature as pilots of 'complex' aircraft would monitor. I've been checking my exhaust HOSE temp grossly (feeling with my hand) lately. At normal cruise speeds (2000-2400 rpm) as well as WOT for a few minutes - the exhaust hose temp just before it dumps overboard is nice and "warm" but definitely not 'hot,' so I believe a sensor with a 200* alarm level would be fine. I think the hose and muffler assembly is rated around 250-300*F (?). This is on my naturally aspirated Yanmar 3YM30 engine. I'd wonder if the TA engines in the big boy tugs like yours produce a 'hotter' exhaust? Still, with raw water mixing, it can't get too hot, right?

dave

 

[knotflying]

The next time I am running I will check the temperature with my infrared thermometer. Unfortunately it won't be until February.

 

[baz]

For those that installed the aqualarm flow meter in the raw water intake line. How loud is the alarm buzzer? I am thinking of mounting it near or on the teak head surround but want to make sure it is audible both from the helm and the cockpit. I probably spend more time in the cockpit with engine running than at the helm.

The buzzer I received from Aqualarm is rated at 85 dB, and that is very loud noise level. For this reason I'm apt to install the buzzer on the engine box side and not inside the cabin of my R-21EC. I will have to have some wire slack so the wiring isn't stretched dangerously when the engine box is rotated up. 😱

For reading buffs http://www.dangerousdecibels.org/education/information-center/noise-induced-hearing-loss/

"Sound pressure is measured in decibels (dB). Like a temperature scale, the decibel scale goes below zero. The average person can hear sounds down to about 0 dB, the level of rustling leaves. Some people with very good hearing can hear sounds down to -15 dB. If a sound reaches 85 dB or stronger, it can cause permanent damage to your hearing. The amount of time you listen to a sound affects how much damage it will cause. The quieter the sound, the longer you can listen to it safely. If the sound is very quiet, it will not cause damage even if you listen to it for a very long time; however, exposure to some common sounds can cause permanent damage. With extended exposure, noises that reach a decibel level of 85 can cause permanent damage to the hair cells in the inner ear, leading to hearing loss. Many common sounds may be louder than you think…"

 

[SGIDAVE]

For those that installed the aqualarm flow meter in the raw water intake line. How loud is the alarm buzzer? I am thinking of mounting it near or on the teak head surround but want to make sure it is audible both from the helm and the cockpit. I probably spend more time in the cockpit with engine running than at the helm.

The buzzer I received from Aqualarm is rated at 85 dB, and that is very loud noise level. For this reason I'm apt to install the buzzer on the engine box side and not inside the cabin of my R-21EC. I will have to have some wire slack so the wiring isn't stretched dangerously when the engine box is rotated up. 😱

To my ears the Aqualarm buzzer is not much louder than the buzzer in the Yanmar engine "display." I mounted mine behind the steering wheel. The AQ alarm can be wired to "buzz" continuous (like the engine alarm) or intermittent. I set mine up to intermittent beeping so I can easily differentiate it from the ENGINE ((oil, temp, etc) alarm which is continuous) 'by ear.'

dave