Newbie - More power less speed?

[Martin Megson]

Hi,

I'm new to boating and have just bought a 55ft narrowboat with 35hp Lister Petter engine. On my maiden voyage from Braunston to Napton I found the boat was cruised smoothly at around 3-4 mph at 650 revs with very little prop wash. However at times she slowed and as I applied power to 1000 rpm there was no noticeable increase in speed but a great deal of prop wash, and increased noise. I've read a bit about shallow water affecting boats but I thought that was larger vessels but just thought I'd ask if this Is a natural effect of varying water depth in the canals.

 

Martin

Edited November 6, 2011 by Martin Megson

[bottle]

Simple answer is, yes.

 

You have learnt one of the most important things about canals and boats, pity a few more do not learn it.

 

Edit: your rpm's seem a little odd compared to mine (different engine) may be someone that knows could enlighten.

Edited November 6, 2011 by bottle

[Guest]

Hi,

I'm new to boating and have just bought a 55ft narrowboat with 35hp Lister Petter engine. On my maiden voyage from Braunston to Napton I found the boat was cruised smoothly at around 3-4 mph at 650 revs with very little prop wash. However at times she slowed and as I applied power to 1000 rpm there was no noticeable increase in speed but a great deal of prop wash, and increased noise. I've read a bit about shallow water affecting boats but I thought that was larger vessels but just thought I'd ask if this Is a natural effect of varying water depth in the canals.

 

Martin

 

You are dragging your arse on the bottom or very close to it which slows you down.

[Albion]

You are dragging your arse on the bottom or very close to it which slows you down.

Agreed, and if in that situation you back off the revs slightly you might find the speed improves as the stern rises. By increasing the revs you can often make the stern sit down even more and you end up with a slower boat using more fuel.

Roger

Edited November 6, 2011 by Albion

[steelaway]

You are dragging your arse on the bottom or very close to it which slows you down.

 

What he's saying is because the canal is so shallow as you apply more power it is causing your boat to sink at the stern and rub along the bottom.

Also your propeller cant get enough water from the canal to handle all them revs so it is kinda cavitating.

 

Yes - MJG I am ducking.

 

Alex

 

Hi,

I'm new to boating and have just bought a 55ft narrowboat with 35hp Lister Petter engine. On my maiden voyage from Braunston to Napton I found the boat was cruised smoothly at around 3-4 mph at 650 revs with very little prop wash. However at times she slowed and as I applied power to 1000 rpm there was no noticeable increase in speed but a great deal of prop wash, and increased noise. I've read a bit about shallow water affecting boats but I thought that was larger vessels but just thought I'd ask if this Is a natural effect of varying water depth in the canals.

 

Martin

 

 

 

Where about's was you?

 

Alex

[Chalky]

If you go up Napton onto the South Oxford top pound it's even more pronounced due to it being shallower. 2 to 3 mph is good!

[Higgs]

This time of year you will be picking up leaves on the prop, so if you think this could be the cause of lots of wash and no drive just put in reverse for a second then return to forward drive. And repeat, as necessary.

[alan_fincher]

I'm new to boating and have just bought a 55ft narrowboat with 35hp Lister Petter engine. On my maiden voyage from Braunston to Napton I found the boat was cruised smoothly at around 3-4 mph at 650 revs with very little prop wash.

Whilst agreeing with the logic of the answers given, I'm a bit surprised by your quoted data.

 

You don't say which Lister Petter engine, but I'm kind of assuming something like a "Canal Star".

 

Most modern-ish Lister Petters like that seem to have their tick-over speed quoted as something like 800 to 850 rpm, so I find it genuinely surprising that you can make 3 or 4 mph at 650 rpm, because most would not even ever be running as slowly as 650 rpm, even when not movin the boat.

 

If you are doing over 3 mph at 650 rpm, how do you manage to pass boats slowly, when required, and what speed and rpm do you reckon you are doing then ?

 

If you had reported similar results, but said maybe that you were making good speed at 1000 rpm without much wash, but got excess wash, and little extra speed by increasing to say 1400 rpm, the whole thing would make a lot more sense to me.

 

I'm highly tempted to think your tachometer is nothing like correctly calibrated.

 

Alternativrly you are not using some kind of tacho on the gearbox output or prop-shaft, rather than on actual engine revs are you? Your numbers sound more like prop rpm (after the gearbox reduction) than actual engine speeds!

[Higgs]

Whilst agreeing with the logic of the answers given, I'm a bit surprised by your quoted data.

 

If you are doing over 3 mph at 650 rpm, how do you manage to pass boats slowly, when required, and what speed and rpm do you reckon you are doing then ?

 

 

Is it possible his prop is the wrong size?

[Martin Megson]

Firstly thanks for all the helpful replies - I think I'm going to like this forum.

 

The engines is a Lister-Petter Canal Star 36HP with a PRM150 gearbox. The revs were taken from the tacho on the engine control panel, I'm guessing it is engine speed as it reads with the drive disengaged. The calibration could be wrong. I'll read the manual when I'm next on board.

 

Regarding holding a slow speed while passing boats I found that on the short stretch from Braunston Marina to Braunston Turn (which must be deeper) I was struggling to keep the speed down to about 2 mph and actually dropped her out of gear a couple of times.

 

Martin

[alan_fincher]

The engines is a Lister-Petter Canal Star 36HP with a PRM150 gearbox. The revs were taken from the tacho on the engine control panel, I'm guessing it is engine speed as it reads with the drive disengaged. The calibration could be wrong. I'll read the manual when I'm next on board.

My strong hunch is that the tacho is reading well low.

 

What speed does the tacho indicate when the engine is just idling, please ?

 

A book I am looking at here says that number should be about 800 rpm, so hard to see how you are only indicating 650 rpm when well under way, (unless the boat is massively over-propped, and putting it in gear heavily slows the engine - but then I'd expect the engine to be making black smoke).

 

Most boat diesel tachos drive from a terminal on the alternator, and have to be calibrated to allow for the type of alternator in use, (how many "poles" it has), as well as the step up ratio in the pulley on each end of the fan belt driving it.

 

If someone has changed the alternator, or alternator drive arrangements on your boat, without recalibrating the tacho, that could explain the apparently very low readings. Or even that a faulty tacho has been replaced, and the replacement not calibrated to suit your set-up.

 

I'd be surprised if you are not actually using rpm numbers at least 50% higher than what your tacho is currently saying.

 

Doesn't alter the answers given to your basic question, but your actual data sounds suspect, (to me!).

[Martin Megson]

My strong hunch is that the tacho is reading well low.

 

What speed does the tacho indicate when the engine is just idling, please ?

 

A book I am looking at here says that number should be about 800 rpm, so hard to see how you are only indicating 650 rpm when well under way, (unless the boat is massively over-propped, and putting it in gear heavily slows the engine - but then I'd expect the engine to be making black smoke).

 

Most boat diesel tachos drive from a terminal on the alternator, and have to be calibrated to allow for the type of alternator in use, (how many "poles" it has), as well as the step up ratio in the pulley on each end of the fan belt driving it.

 

If someone has changed the alternator, or alternator drive arrangements on your boat, without recalibrating the tacho, that could explain the apparently very low readings. Or even that a faulty tacho has been replaced, and the replacement not calibrated to suit your set-up.

 

I'd be surprised if you are not actually using rpm numbers at least 50% higher than what your tacho is currently saying.

 

Doesn't alter the answers given to your basic question, but your actual data sounds suspect, (to me!).

 

Thanks for the additional info. I agree that the reading must be low, I found the spec on-line and the idle speed is quoted at 800 as you said.

The tacho was reading nearer 500 which suggests its showing almost half the true speed. I don't think its an over prop problem as the engine speed hardly drops as I engage gear and there is no black smoke. I'll have a look at the tacho to see if I can find any adjustment or failing that get the marina to look at it.

 

The good news is that you've put my mind at rest as there is nothing seriously wrong with the boat.

 

Thanks

 

Martin

[alan_fincher]

Thanks for the additional info. I agree that the reading must be low, I found the spec on-line and the idle speed is quoted at 800 as you said.

The tacho was reading nearer 500 which suggests its showing almost half the true speed.

So, assuming engine idle correctly set, 800 rpm is actually indicated as 500 rpm, (approximately, I'm guessing).

 

So, multiply indicated reading by 1.6 to get the real(ish) number ???

 

In which case we could re-write the appropriate part of your original post as......

 

I'm new to boating and have just bought a 55ft narrowboat with 35hp Lister Petter engine. On my maiden voyage from Braunston to Napton I found the boat was cruised smoothly at around 3-4 mph at about 1040 revs with very little prop wash. However at times she slowed and as I applied power to about 1600 rpm there was no noticeable increase in speed but a great deal of prop wash, and increased noise.

 

Now that sounds far more likely for the boat/engine/canal combination you are describing to me, and all makes perfect sense.

 

If we can accept that the tacho value needs multiplying by about 1.6, then I agree with the answers you have already been given. All quite normal, and as expected!

 

You can use a cheap (under £10) cyclo computer to calibrate an alternator driven tacho correctly, provided it is one that lets you set an appropriate "wheel size".

 

Several old threads on this if you search, but this one is probably as good as most.

[PhilR]

It might be helpful to hear how the OP is measuring the boat speed.

 

Regarding the tacho readings I am inclined to agree with Alan's post

[Higgs]

With the tacho and calibration sorted and tickover set:

 

If the boat still won't handle the slowing down, is there anything else but prop size to explain this?

[ditchcrawler]

Hi,

I'm new to boating and have just bought a 55ft narrowboat with 35hp Lister Petter engine. On my maiden voyage from Braunston to Napton I found the boat was cruised smoothly at around 3-4 mph at 650 revs with very little prop wash. However at times she slowed and as I applied power to 1000 rpm there was no noticeable increase in speed but a great deal of prop wash, and increased noise. I've read a bit about shallow water affecting boats but I thought that was larger vessels but just thought I'd ask if this Is a natural effect of varying water depth in the canals.

 

Martin

Is it THIS one?

[PhilR]

With the tacho and calibration sorted and tickover set:

 

If the boat still won't handle the slowing down, is there anything else but prop size to explain this?

 

Slowing down doesn't seem to be the reported problem. But we will wait to hear how the OP is measuring boat speed and how accurate that is.

[Martin Megson]

Is it THIS one?

 

Yes it is! Do you know her?

 

PhilR & Higgs. I used an iPhone app to measure speed. The problem of slowing may be driver error. I guess the drag effect in shallow water means the boat will slow quicker when power is reduced and when I'm in deep water I need to reduce power earlier to let her slow over a longer distance.

Edited November 7, 2011 by Martin Megson

[alan_fincher]

Is it THIS one?

 

Yes it is! Do you know her?

 

Ah! - Didn't spot a boat name.

 

I think that looks like the boat of that name, (for there are several!), that used to be based at Cow Roast on the Grand Union ?

 

If so, I seriously doubt there will be anything wrong with the actual engine/gearbox/prop sizing department, unless it has been tampered with since we have shared locks with it in the past.

 

It seemed to be a very well set up (and fast!) boat, and it's owner claimed that they used to regularly go for "fastest time down the Marsworth flight", when nobody else was using the locks, and they had a big enough crew......

 

However, if it's not that "Mr Bunbury", then ignore these ramblings!

 

Whilst diverting us to "is the tacho reading right ?" issues, I have allowed the leaf fall suggestion to drop of the radar. If the boat is generally moving well, (whatever the rev counter says!), but does sometimes start to slow down for no obvious reason, then at this time of year a ball of laeves gathered around the prop is more than a distinct possibility. If you suspect this, try a sharp burst of reverse or two, (at which point leaves being thrown out from underneath could be very apparent), then try going forward again, but at the original throttle setting, not piling on any more revs.

[Martin Megson]

Ah! - Didn't spot a boat name.

 

I think that looks like the boat of that name, (for there are several!), that used to be based at Cow Roast on the Grand Union ?

 

If so, I seriously doubt there will be anything wrong with the actual engine/gearbox/prop sizing department, unless it has been tampered with since we have shared locks with it in the past.

 

It seemed to be a very well set up (and fast!) boat, and it's owner claimed that they used to regularly go for "fastest time down the Marsworth flight", when nobody else was using the locks, and they had a big enough crew......

 

However, if it's not that "Mr Bunbury", then ignore these ramblings!

 

Whilst diverting us to "is the tacho reading right ?" issues, I have allowed the leaf fall suggestion to drop of the radar. If the boat is generally moving well, (whatever the rev counter says!), but does sometimes start to slow down for no obvious reason, then at this time of year a ball of laeves gathered around the prop is more than a distinct possibility. If you suspect this, try a sharp burst of reverse or two, (at which point leaves being thrown out from underneath could be very apparent), then try going forward again, but at the original throttle setting, not piling on any more revs.

 

Could be the same boat. The name painted on the side is Mr Bunbury No 2. It was built at Braunston in 2003 and the original owner kept it until Oct 10. I'm not sure of mooring location but the she has certainly been based in the area for a long time.

 

Martin

[sociable_hermit]

I guess the drag effect in shallow water means the boat will slow quicker when power is reduced and when I'm in deep water I need to reduce power earlier to let her slow over a longer distance.

Well, yes.... but then again no.

 

If she's already sitting down at the stern on a shallow stretch of canal, backing off the power could actually make her go faster, as the back end comes up!

 

The main reason for backing off earlier when in deep water is the fact you'll be going that bit quicker in the first place.

 

It has to be VERY shallow before tickover-style low revs start increasing drag, and backing off further is helpful. Indeed you can lose the steering if you back off too much. It is useful sometimes, though - for example, taking the power right off when you feel the boat running aground can often allow you to coast over the top of the obstruction.

 

Like everything with boating, it's all about context!

[ploddy]

what iphone app can you use to measure speed?

[Martin Megson]

what iphone app can you use to measure speed?

 

There are a few that use the GPS signal. The one I used is a freebie called dashboard - its actually meant for a car but it has a digital speedometer which was a cheap way to check.

[Radiomariner]

what iphone app can you use to measure speed?

 

Crew member in the bow throws iphone into the cut. If it has not sunk by the time the steerer passes the spot then your going too fast

[The Pipe]

Crew member in the bow throws iphone into the cut. If it has not sunk by the time the steerer passes the spot then your going too fast

Wrong.. Throws iphone user in cut.