Tachometer readings by measuring an engines sound

[WriterCJ]

I was looking for hand-held tachometers last night to check the Idle / WOT RPM of my 20 HP BE20ELCEM when an i-Phone ad came on the telly.

"Hmmm...," I thought, "I wonder if there's an app for that?"

A quick search of apple's app store revealed the Engine RPM app.

I then went on to find this free download for the PC via Google.

Has anyone tried anything like this this to measure the RPM of their outboard at idle / WOT? How did you get on? Is it a feasible proposition, and can the developers' accuracy claims of +/- 1 RPM really hold up?

Guess at the price it's got to be worth a punt. Would be interested to hear your views / thoughts.

Cheers,

Calvin!

 

[oldcatamount]

Re: Tachometer readings by measuring an engines sound

Interesting...but I don't think I would trust it to much. I'm just old fashioned.

 

[WriterCJ]

Re: Tachometer readings by measuring an engines sound

Couldn't resist... went ahead and got the iPhone app. Think I'll try it out on the petrol strimmer a bit later to see how it works out.

If all goes well I'll give it a try with the outboard next time I'm out on the boat. If I can source one I'll borrow an induction tachometer and compare readings.

C!

 

[oldcatamount]

Re: Tachometer readings by measuring an engines sound

I'll be interested in hearing the results

 

[bob johnson]

Re: Tachometer readings by measuring an engines sound

has to be better than your estimate from hearing it yourself!!!!

and important !!

since its free. , cant go wrong unless you get some virus from the download!!!!!!!!


bob

 

[bob johnson]

Re: Tachometer readings by measuring an engines sound

I found one for my droid that measure the rpm of a two blade model helicopter.

cant be too much longer before someones converts it to outboard motor

http://www.androidzoom.com/android_applications/sports/heliheadspeed_fzff.html

bob

 

[jtexas]

Re: Tachometer readings by measuring an engines sound

the theory is sound. [pun intended]

 

[WriterCJ]

Re: Tachometer readings by measuring an engines sound

It "sounds" great... haven't had chance to try it out properly yet though. Perhaps tomorrow. Will post updates here... would be great to hear how other people find it too.

iPhone version costs ?6 -- around US$8 -- and seems a bit more polished / user friendly than the free PC version. A lot cheaper than getting a tach, as long as it works... and as jtexas points out the theory is "sound" [suppresses audible groan].

C!

 

[jonesg]

Re: Tachometer readings by measuring an engines sound

I found one for my droid that measure the rpm of a two blade model helicopter.

cant be too much longer before someones converts it to outboard motor

http://www.androidzoom.com/android_applications/sports/heliheadspeed_fzff.html

bob

Simple math will recalculate the correct rpm from a 2 blade reading.
I'd post the answer but there isn't enough room.

Jones's last theorum.

 

[WriterCJ]

Re: Tachometer readings by measuring an engines sound

Tested the iPhone app today on the car and after a bit of fiddling about with the setting it worked really well.

Out on the boat this evening I thought I'd give it a try -- I got readings of around 940 RPM at idle in neutral, around 760 RPM at idle in gear and 4,300 at WOT. WOT RPM seems a little low -- I think the recommended range for my engine is 4,500 to 5,500.

Thinking that, as I suspected, the prop pitch is too high for my engine on this boat -- it's a 10" x 13" at the moment... so thinking maybe I should drop to 11" pitch when I change the prop.

BUT -- I dinged the prop recently. Could a slightly damaged prop cause a significant drop in RPM at WOT -- or is it safe to assume low WOT RPM is down to the prop pitch?

Thanks,

Calvin!

 

[Boss Hawg]

Re: Tachometer readings by measuring an engines sound

Tested the iPhone app today on the car and after a bit of fiddling about with the setting it worked really well.

Out on the boat this evening I thought I'd give it a try -- I got readings of around 940 RPM at idle in neutral, around 760 RPM at idle in gear and 4,300 at WOT. WOT RPM seems a little low -- I think the recommended range for my engine is 4,500 to 5,500.

Thinking that, as I suspected, the prop pitch is too high for my engine on this boat -- it's a 10" x 13" at the moment... so thinking maybe I should drop to 11" pitch when I change the prop.

BUT -- I dinged the prop recently. Could a slightly damaged prop cause a significant drop in RPM at WOT -- or is it safe to assume low WOT RPM is down to the prop pitch?

Thanks,

Calvin!

Up to you but i would'nt buy a new prop based on that

 

[Willyclay]

Re: Tachometer readings by measuring an engines sound

Could the cause of low WOT RPM's be motor performance less than optimum due to carbon build-up in the cylinders/ports/rings, ethanol deposits in the fuel system/carb, link&sync issues, weak spark, etc.? If the motor has been "lugging" because it is over-propped, then carbon deposit build-up is highly likely. What is your history with this motor?

 

[WriterCJ]

Re: Tachometer readings by measuring an engines sound

Hi Boss Hawg,

I need a replacement prop anyway... just wondering whether to drop a couple of inches in pitch.

I've tested the Engine RPM app on a couple of cars with installed tachs and when it's set up right the reading is spot on (you can dowmload a detailed PDF Manual -- it all seems to make sense).

Trying to get hold of a tach with induction pick-up to verify the readings before deciding on the prop, and will re-check the engine for other things that could be affecting the performance.

Cheers,

Calvin!

 

[WriterCJ]

Re: Tachometer readings by measuring an engines sound

Hi Willy Clay,

Thanks for the input.

You're absolutely right of course... there could be a host of things causing the drop in performance / WOT RPM.

I'm new to outboards, but learning fast thanks in no small part to the people and information available through this forum.

Only got the boat in the water recently. The engine was not running or idling properly. Seemed to have a decent spark, but I installed new spark plugs anyway just to be on the safe side; checked the fuel system for air ingress, leaks, blockages, etc.; stripped and cleaned the carb (there was gunk in the high speed jet), put it all back together, followed the link and sync instructions and idle adjustment procedure in the manual I have and she seemed to run sweet as a nut.

At that point she was pushing the boat up onto a plane at 9-10kt and topping out at 16-17kt with just me on board (which was way better than I was expecting from an old 20HP on this 17ft boat, to be honest).

At the time I had no way of measuring RPM, so don't have any readings from when the engine was performing at that level . To the untrained ear it never "sounded" like it was revving any higher than it is now -- but that's purely speculation.

I have no way of checking compression at the moment, but suspect it is (or at least was) OK, as I doubt the 20HP could push my boat to 16kt running on one cylinder (but then I could be way off base with that assumption -- going largely by gut feeling here).

How quickly can carbon deposits affect an engine? I've only been out a couple of times since I clocked the 16kt top end on my GPS. Is that enough?

I'm trying to find someone who can lend me a compression gauge and proper spark tester, and have ordered myself a digital multimeter so I can test the electrics/ignition system properly. Plan to give the whole engine a thorough overhaul when I pull the boat out of the water at the end of the season, but hoping to get a few more good weeks out of her before the weather breaks.

The reason I'm looking to the prop is that the drop in performance followed soon after I hit the bottom with the prop at low speed (around 4kt) returning to the mooring on a lowish tide. There's not much damage... a bit to the periphery of the blades, and everything else seems OK. Prop is straight, turns freely in neutral, and there's no obvious increase in vibration when under way.

At first performance seemed OK, so I thought little of it, but the last couple of times out she's definitely not performing optimally. She starts and idles fine -- first turn of the key -- and gets going without any trouble, but she barely gets on a plane and bogs down at 10-11kt.

As you say it Could have nothing to do with the prop -- I'm just looking for a bit of experienced guidance. Is slight prop damage likely to cause the drop in performance I'm seeing, or should I focus on the engine?

Guess it's no harm checking everything again -- spark, compression, fuel system, link and sync. Of course I could just get a 40-50HP engine that's better suited to the boat, but that will have to wait until I've saved up for a while .

Thanks again for your help.

Cheers,

Calvin!

 

[Chinewalker]

Re: Tachometer readings by measuring an engines sound

Over 40 years ago, back when my Dad was racing boats he borrowed his brother-in-law's oscilloscope and a mic and rigged it up so he could tell engine RPM from shore. Something with the harmonics & vibrations, etc. He was usually pretty close to dead-on. He could also tell what other racers' engines were running...

 

[WriterCJ]

Re: Tachometer readings by measuring an engines sound

Apparently before they introduced an upper rev limit in Formula 1 pit crews used to use the same technique to analyse competitors engines from the pit lane. Amazing what you can find on the internet!

 

[d.boat]

Re: Tachometer readings by measuring an engines sound

Tested the iPhone app today on the car and after a bit of fiddling about with the setting it worked really well.

I dont' think you can say that unless you can compare its readings to actual tachometer readings.

I noticed in another post you mentioned a lot of tools and instruments you plan on buying (all sound pretty good to me). Why don't you buy and install a tachometer? It's cheap and easy.

 

[WriterCJ]

Re: Tachometer readings by measuring an engines sound

I dont' think you can say that unless you can compare its readings to actual tachometer readings.

I did with the cars... both had actual tachometers and the app was spot on.

I noticed in another post you mentioned a lot of tools and instruments you plan on buying (all sound pretty good to me). Why don't you buy and install a tachometer? It's cheap and easy.

I was researching options for hand held tachometers when I came across the iPhone app and thought it was worth giving it a try. I don't think I need to install a fixed tacho on the boat -- I'll only need to monitor RPM occasionally (like when I'm trying to work out what pitch prop I need).

I've never done much mechanical/electrical work, and I'm just getting started with the outboard. That means I don't currently have gadgets like compression gauges, feeler gauges, spark testers, multimeters, etc., etc. in the toolbox.

I'm happy to invest in tools I'll use regularly for DIY outboard troubleshooting / maintenance when I need them -- but don't want to spend a fortune on stuff I'll use once in a blue moon either.

Not sure what it's like in the US but here in Ireland anything "marine" or even remotely related to boats is really expensive -- which means the boat is already eking more than its fair share of the household budget. .

Cheers,

Calvin!

 

[Willyclay]

Re: Tachometer readings by measuring an engines sound

At first performance seemed OK, so I thought little of it, but the last couple of times out she's definitely not performing optimally. She starts and idles fine -- first turn of the key -- and gets going without any trouble, but she barely gets on a plane and bogs down at 10-11kt.

Since the performance has degraded after the prop damage, that makes a pretty strong case. However, it could just be coincidence. Verify boat speed and RPM's at the first chance you get. That should tell you if the motor is not performing correctly. While you are out, try pumping the fuel hose primer bulb and see if the engine speeds up. If yes, that would indicate a weak fuel pump. After that test, try engaging the choke/carb primer while it is bogging and see if that has any affect on the engine. If yes, that would indicate trash/blockage of the high-speed carburetor jet. You may be able to squeeze out a few more horsepower with a carb/manifold swap. I'll look for that thread and add it later. Good luck!

EDIT: The link below discusses some opportunities to gain horsepower by swapping carbs.

http://forums.iboats.com/showthread.php?t=274566

 

[keefallan]

Re: Tachometer readings by measuring an engines sound

You mentioned tools you can use, well, I had to buy a new timing light because my one from sears was 20 years old and I had to wiggle the cord to get it to work. So I bought one fro Actron with a digital readout on the back. It came with settings for 2/4 stroke and a Tach. It was a 100 bucks. Just thought I'd pass it on. i used it to verify the tach I installed on my boat.