Rev Counter not 'Counting'

[jenevers]

It’s a free country, I know, but why do you need a tachometer on a canal boat? Just asking.

[Alan de Enfield]

12 minutes ago, jenevers said:

It’s a free country, I know, but why do you need a tachometer on a canal boat? Just asking.

Assumptions.

 

'Assume' makes an ass out of u & me

 

It is not a canal boat : 4' 6" draft,  and 10' 6"  Air-Draft (with radar arch, VHF and GPS aerials all folded own,) 2000 mile non-refuelling cruising range, twin 6-cylinder engines, 14 foot beam.

 

I just happen to have had it based on the Rivers for the last couple of years whilst we play 'blue-water' cruising with the Big-Cat. (23 foot beam, 1600 square feet of coloured rags & a 58 foot high stick in the middle)

Edited August 21, 2018 by Alan de Enfield

[Alan de Enfield]

Well that didn't go according to plan :

 

G = Good ('working tacho')

B = Bad ('Not working tacho')

 

Disconnected the sensor wire of both G & B tachos.

 

Connected the sensor wire from the B tacho to the G tacho, started engine, tacho not working.

Connected the sensor wire from the G tacho to the B tacho, started engine, tacho not working.

 

Re-connected everything back to original (where one was working and one wasn't) and now have no tachos working.

[Jen-in-Wellies]

13 hours ago, Scholar Gypsy said:

A visiting engineer got a pretty good result using an app on an Android phone called GString. It listens to the bangs made by the exhaust and works out what musical note you are playing.

 

So for example normal cruising speed gave a frequency of 50 Hertz, that is 3,000 bangs a minute (50 x 60), which is 1500 rpm (four stroke 4 cylinder engine, so each cylinder goes bang every two revolutions). 

 

RPM = frequency x 60 x 2 / (no of cylinders)

I've used one of these apps with success. You have to be careful with them. They use the phone microphone to pick up the noise from the engine and this will have a lower limit of frequency that it can pick up. I found that on my phone this was below the sound from a diesel engine at idle. What was being displayed was a harmonic at twice the frequency when at idle, which would then drop to the actual frequency as the engine speed increased. You need to know roughly what the engine speed should be to properly interpret the output from one of these apps. The equation to convert frequency to rpm varies depending on which harmonic you are seeing on the display.

 

Jen

[jenevers]

13 hours ago, Alan de Enfield said:

Assumptions.

 

'Assume' makes an ass out of u & me

 

It is not a canal boat : 4' 6" draft,  and 10' 6"  Air-Draft (with radar arch, VHF and GPS aerials all folded own,) 2000 mile non-refuelling cruising range, twin 6-cylinder engines, 14 foot beam.

 

I just happen to have had it based on the Rivers for the last couple of years whilst we play 'blue-water' cruising with the Big-Cat. (23 foot beam, 1600 square feet of coloured rags & a 58 foot high stick in the middle)

Yes I should have said “Why do people need tachometers on canal boats?” 

[Sir Nibble]

20 hours ago, Alan de Enfield said:

Ok - test with engine running or just ignition turned on ?

 

Back of Rev Counter - which wire would you suggest is the signal wire ?

(with the ignition turned on all terminals are live - even the push-on blade)

 

 

If that's the case and all connections show. "live" then the gnd is open circuit.

and just by the way, those yellow terminals are the wrong size and poorly crimped.

[cuthound]

1 hour ago, jenevers said:

Yes I should have said “Why do people need tachometers on canal boats?” 

 

I use mine as a rough approximation of speed over the ground. 

 

I checked my tacho against an Android app called "Ullysse Speedometer", which has a slow speed (walking) option, and found in moderately deep water 1000rpm equates to 2mph, 1500rpm = 3mph and 2000 rpm = 4mph.

 

However the speedometer app is sensitive enough to see the boat slow down when passing through bridges and shallow sections, even though the revs remain the same.

[Machpoint005]

11 minutes ago, cuthound said:

 

I use mine as a rough approximation of speed over the ground. 

 

I checked my tacho against an Android app called "Ullysse Speedometer", which has a slow speed (walking) option, and found in moderately deep water 1000rpm equates to 2mph, 1500rpm = 3mph and 2000 rpm = 4mph.

 

However the speedometer app is sensitive enough to see the boat slow down when passing through bridges and shallow sections, even though the revs remain the same.

That seems pretty accurate to me. I reckon 1150rev/min is about 2.5mph on a narrow (shallow) canal. and GPS generally says it's between 2.6 and 2.7. Good enough.

[cuthound]

1 hour ago, Machpoint005 said:

That seems pretty accurate to me. I reckon 1150rev/min is about 2.5mph on a narrow (shallow) canal. and GPS generally says it's between 2.6 and 2.7. Good enough.

 

Next year I intend to dock the boat and I'll change the 17" x 11" prop for the 18" x 12" prop, which Beta recommend for a Beta 43 with 2:1 PRM gearbox.

 

I will repeat my speedometer app experiments and see if the revs are reduced for a given speed.

[WotEver]

8 hours ago, Alan de Enfield said:

Well that didn't go according to plan :

 

G = Good ('working tacho')

B = Bad ('Not working tacho')

 

Disconnected the sensor wire of both G & B tachos.

 

Connected the sensor wire from the B tacho to the G tacho, started engine, tacho not working.

Connected the sensor wire from the G tacho to the B tacho, started engine, tacho not working.

 

Re-connected everything back to original (where one was working and one wasn't) and now have no tachos working.

Do both tachos at the other helm work?

[Alan de Enfield]

Just now, WotEver said:

Do both tachos at the other helm work?

Didn't look.

They did, but not now on the boat (on the way to Plymouth for a couple of weeks sailing).

[blackrose]

6 hours ago, jenevers said:

Yes I should have said “Why do people need tachometers on canal boats?” 

Lots of people take canal boats onto rivers where knowing your engine revs can be useful in terms of what the boat is doing going with or against the current. My engine revs to 3000rpm, but in gear it used to only rev to 1950rpm because it was over-propped. I had the prop re-pitched and regained some revs which has resulted in a lot more power for use on rivers, but I wouldn't have known anything about it if I hadn't had a rev-counter.

Edited August 22, 2018 by blackrose

[WotEver]

20 minutes ago, Alan de Enfield said:

Didn't look.

They did, but not now on the boat (on the way to Plymouth for a couple of weeks sailing).

When you get back, resurrect this thread with the answer

[rusty69]

25 minutes ago, Alan de Enfield said:

Didn't look.

They did, but not now on the boat (on the way to Plymouth for a couple of weeks sailing).

Sorry Alan. You said I could have the cat this week. Currently enroute to St Peters Port! Thanks for the beer. 

[Alan de Enfield]

16 minutes ago, WotEver said:

When you get back, resurrect this thread with the answer

Will do - planning on 3 weeks or so on the Cruiser (the boat with the dicky tacho) from Mid September, so plenty of time to 'play about'.

[Mike Todd]

6 hours ago, Machpoint005 said:

That seems pretty accurate to me. I reckon 1150rev/min is about 2.5mph on a narrow (shallow) canal. and GPS generally says it's between 2.6 and 2.7. Good enough.

The speed over the ground is very much a function of the water conditions, especially depth and width. In our case, 1200 can result in anything between 2 (or less) and 3.5 mph (probably even more in virtually open water, eg a still-ish river) In some contexts, increasing rpm can result in a decrease in speed. Hence Your basic model is invalid. I doubt whether anyone can reliably predict speed over the ground from rpm on anything like our canals. (Unless, of course, you only even go up and down the sane restricted length)

[Alan de Enfield]

On ‎22‎/‎08‎/‎2018 at 19:04, WotEver said:

When you get back, resurrect this thread with the answer

All sorted.

Went thru fault finding exercise again.

Long story short : Alternator tests needed both the sender wire AND the positive supply from its own starter battery moving to the other tacho, (the Gnd was common). Found the wiring was fine, the 'faulty' ammeter WAS faulty.

 

Replaced ammeter (£80 from ASAP) and works perfectly, just needs calibrating now - got it 'close' but need to get / borrow an optical rev counter.

 

Thanks all for the guidance.

[Scholar Gypsy]

I use a free app Gstring to listen to the engine exhaust note.

 

50 Hz x 30 = 1500 rpm for a 4 cylinder 4 stroke engine. 

[Alan de Enfield]

8 minutes ago, Scholar Gypsy said:

I use a free app Gstring to listen to the engine exhaust note.

 

50 Hz x 30 = 1500 rpm for a 4 cylinder 4 stroke engine. 

Thanks for the suggestion, but the problem I would have is that there would be a lot of re-bound noise, they are big 6 litre, 6 cylinder engines in a 'hard wall, hard floor and hard roof' engine space, I would doubt (but maybe worth a try) that it would pick out the correct note without any harmonics / reflections interfering.

[Mike Todd]

5 minutes ago, Alan de Enfield said:

Thanks for the suggestion, but the problem I would have is that there would be a lot of re-bound noise, they are big 6 litre, 6 cylinder engines in a 'hard wall, hard floor and hard roof' engine space, I would doubt (but maybe worth a try) that it would pick out the correct note without any harmonics / reflections interfering.

Classic measurement scenario when you know that you are approximately in the right ball park. You only have to get it to read the frequency close to where you want to be - commonsense helps you reject readings much further away.

[TheBiscuits]

40 minutes ago, Mike Todd said:

Classic measurement scenario when you know that you are approximately in the right ball park. You only have to get it to read the frequency close to where you want to be - commonsense helps you reject readings much further away.

Stick the phone in a padded box and point the open end of the box straight at the engine.

[frahkn]

On 22/08/2018 at 15:24, cuthound said:

 

Next year I intend to dock the boat and I'll change the 17" x 11" prop for the 18" x 12" prop, which Beta recommend for a Beta 43 with 2:1 PRM gearbox.

 

I will repeat my speedometer app experiments and see if the revs are reduced for a given speed.

 

My prop (on a Beta 43 with a 2:1 PRM) is 23" - I'm not certain of the pitch.

 

I have been advised to change it but I asked Beta, they said that while it's not recommended, it's probably doing no harm.

[Alan de Enfield]

6 hours ago, frahkn said:

 

My prop (on a Beta 43 with a 2:1 PRM) is 23" - I'm not certain of the pitch.

 

I have been advised to change it but I asked Beta, they said that while it's not recommended, it's probably doing no harm.

I suppose I could use the prop but I'm not sure it would work - how would I calibrate it to the engine revs ?

[frahkn]

2 hours ago, Alan de Enfield said:

I suppose I could use the prop but I'm not sure it would work - how would I calibrate it to the engine revs ?

 

A good question, perhaps Cuthound (whose post I was responding to) can answer it - I certainly cannot!

[cuthound]

2 hours ago, frahkn said:

 

A good question, perhaps Cuthound (whose post I was responding to) can answer it - I certainly cannot!

 

I used an app on my Android phone, Ullysse Speedometer, which has a slow speed option.

 

At with the engine  in gear and in reasonably deep water, I noted the speed at 1000rpm, 1500rpm and 2000rpm.