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DavidPeckham

Engine Revs

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Hi all, got a question about revs,I cruise at around 2000 but everyone passes me, is it normal to regularly go above this? I've got a Vetus 3.10 on a 33ft narrow boat. many thanks for any advice.

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If I had my boat at 2000 revs I would be on the plane, in fact it will not reach 2000 on a shallow canal. I think it GREATLY depends on your gearbox ratio and prop size amongst other things so no one will be able to give you a conclusive reply as to your engine revs for your situation.

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Just now, DavidPeckham said:

Hi all, got a question about revs,I cruise at around 2000 but everyone passes me, is it normal to regularly go above this? I've got a Vetus 3.10 on a 33ft narrow boat. many thanks for any advice.

RPM as shown by the normal inaccurate tacho means nothing. You cruise at whatever speed you feel comfortable with, under 4mph, providing you make no breaking wash and don't annoy others.

Too many motorway cruisers these days, that's why they pass you.

Its them not you.

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6 minutes ago, DavidPeckham said:

Hi all, got a question about revs,I cruise at around 2000 but everyone passes me, is it normal to regularly go above this? I've got a Vetus 3.10 on a 33ft narrow boat. many thanks for any advice.

 

RPM is no help at all as speed for a given RPM varies according to the width and depth of the channel you are cruising in.

 

How does your speed compare with towpath walkers? You ought to be about the same speed as someone walking walking steadily but not necessarily briskly.

 

 

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Cheers all, thought it might be a bit of a vague question, I'm going just slower than  tow path walkers and the engine seems comfortable enough.

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3 minutes ago, DavidPeckham said:

Cheers all, thought it might be a bit of a vague question, I'm going just slower than  tow path walkers and the engine seems comfortable enough.

 

In that case I suspect you have a slipping clutch or an undersized prop.

 

In all of my boats I tend to slowly catch up the amblers on the towpath and none of my boats is fast. 

 

 

 

  • Greenie 1

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If you have a  Smart phone, you can download a speedometer app. Get one with a slow speed setting like the Ullysse app and you will get an idea of how your revs relate to your speed over the water.

 

You will also see the boat slow down through bridgeholes and shallow bits.

 

Armed with this information you can decide whether it is worth having your propeller replaced.

 

I am having mine changed as we speak, at present my boat does 1500rpm at 3mph in relatively deep water, and I wish to reduce this to perhaps 1200rpm.

Edited by cuthound
Spillung
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WotEver was 34ft with a Vetus M3.10 and usual cruising speed was about 1900 rpm at which speed we’d be travelling a little faster than ambling walkers. I suspect that the OP is under-propped. 

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16 minutes ago, WotEver said:

WotEver was 34ft with a Vetus M3.10 and usual cruising speed was about 1900 rpm at which speed we’d be travelling a little faster than ambling walkers. I suspect that the OP is under-propped. 

It may be a silly comment - but a small amount of 'stuff' around the propellor can slow the boat down considreably.

 (There is no info: from the OP about his experiemce or boat or anything....)

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9 minutes ago, Kudzucraft said:

Possible that the tachometer it wrong. Probably not but it is possible.

That’s quite possible, as is OldGoat’s suggestion of a fouled prop. We really need OP to tell us a bit more. 

 

As an aside... Judging from my singular experience of just one M3.10 it was very happy at 1800-1900 rpm, at 2000 rpm it was working a bit harder, and at 2200 rpm it was going like the clappers. I’d never have dreamt of taking it to its max of 3600 rpm. 

Edited by WotEver
Fouled, not foiled!

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2 hours ago, DavidPeckham said:

Hi all, got a question about revs,I cruise at around 2000 but everyone passes me, is it normal to regularly go above this? I've got a Vetus 3.10 on a 33ft narrow boat. many thanks for any advice.

Whatever anyone says about your prop and any thing else mechanical, you need to identify your speed. 

 

Once you know your speed at 2000 revs on a canal where width and depth don't affect your speed, you will be in a position to discuss things further,

Edited by Richard10002

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Something is not right, at 2000 rpm towpath walkers should not be outpacing you, at 2000 revs my waterskiier would be clinging on for dear life.

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2 hours ago, cuthound said:

If you have a  Smart phone, you can download a speedometer app. Get one with a slow speed setting like the Ullysse app and you will get an idea of how your revs relate to your speed over the water.

Another useful smartphone app is one that measures sound frequency. The loudest noise spike it picks up will be related to the engine speed. Do it at your usual cruising revs, rather than idle. It needs a bit of calculation to relate this to engine revs, but not hard. Ask on here if you need any help. Not unlikely that your tacho isn't calibrated properly. Not unusual. Go with ground speed, "feel", and relate that to indicated engine revs, or calibrate the tacho to the altenator W signal.

 

Jen

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So many variables..... 2000rpm is pretty fast. Gearbox is 2:1 ??? so shaft speed is 1000rpm??? you need to find the dia. of your prop and the pitch and then find the recommended size for your engine/gearbox/boat. You might just have the right size already in which case the problem might be with the shape of the boat. Shorter boats tend to have quite blunt ends and have lower max speeds than long boats but there are many exceptions and ifs and buts to that rule.  If water flow to the prop is not smooth and easy the prop will struggle.

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2 hours ago, Kudzucraft said:

Possible that the tachometer it wrong. Probably not but it is possible.

 

 

I found out mine was wrong, displaying about 400 RPM less than it should. I used one of these handheld IR tachometers to calibrate it. Put the reflective tape on the main flywheel and measure at different RPM. But be careful in the engine space with hands near spinning parts and moving belts.

 

https://www.amazon.co.uk/KKmoon-Digital-Tachometer-Engine-Non-contact/dp/B00HWLTW90/ref=mp_s_a_1_12?keywords=handheld+tachometer&qid=1565898455&s=gateway&sr=8-12

 

Edited by blackrose

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I'd have thought that at 2000 revs the engine would be a bit vocal unless it's not really working very hard. How many revs will it do in gear if you run it (briefly) flat out?

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1 hour ago, Cheshire cat said:

I'd have thought that at 2000 revs the engine would be a bit vocal unless it's not really working very hard. How many revs will it do in gear if you run it (briefly) flat out?

 

That would depend on the depth of water. If you're on a typical canal you won't get the maximum in gear. 

Edited by blackrose

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5 hours ago, mrsmelly said:

If I had my boat at 2000 revs I would be on the plane, in fact it will not reach 2000 on a shallow canal. I think it GREATLY depends on your gearbox ratio and prop size amongst other things so no one will be able to give you a conclusive reply as to your engine revs for your situation.

One of our NB's was an ex-hire boat, It had a PRM150 3:1 gearbox onto the Lister LPWS4 engine.

The engine was running at high revs to produce much less speed than a similar boat with a 2:1 gearbox.

 

So at 1500 Engine rpm the prop was only making 500 RPM, but with a 2:1 gearbox the prop would have been making 750 RPM

 

I can only assume that the hire company (Weltonfield) had fitted the 3:1 gearbox so that the engine 'made more noise' and sounded as if it was going faster than it was so that the hirers would not speed down the canal.

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1 hour ago, blackrose said:

 

That would depend on the depth of water. If you're on a typical canal you won't get the maximum in gear. 

I agree that depth of water  will affect things to some extent but if it can only do 2400 flat out that would tell me the engine is trying really hard at 2000.

 

I think my engine is buzzy when it is turning at 1500. In theory the maximum is 2800 but on the canal it won't go above 2100

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1 hour ago, Alan de Enfield said:

One of our NB's was an ex-hire boat, It had a PRM150 3:1 gearbox onto the Lister LPWS4 engine.

The engine was running at high revs to produce much less speed than a similar boat with a 2:1 gearbox.

 

So at 1500 Engine rpm the prop was only making 500 RPM, but with a 2:1 gearbox the prop would have been making 750 RPM

 

I can only assume that the hire company (Weltonfield) had fitted the 3:1 gearbox so that the engine 'made more noise' and sounded as if it was going faster than it was so that the hirers would not speed down the canal.

Innisfree's original engine was 2.45 lts & 33bhp @2k rpm, 2:1 box and the Crowther prop made to measure was spot on. When I swapped for a LPWS4 40 bhp @ 3k rpm with a 2:1 PRM. I foolishly had the prop reprofiled but it wasn't the same, instead I should have forked out for a 3:1 PRM, it would have been nearly ideal. 

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8 hours ago, Alan de Enfield said:

One of our NB's was an ex-hire boat, It had a PRM150 3:1 gearbox onto the Lister LPWS4 engine.

The engine was running at high revs to produce much less speed than a similar boat with a 2:1 gearbox.

 

So at 1500 Engine rpm the prop was only making 500 RPM, but with a 2:1 gearbox the prop would have been making 750 RPM

 

I can only assume that the hire company (Weltonfield) had fitted the 3:1 gearbox so that the engine 'made more noise' and sounded as if it was going faster than it was so that the hirers would not speed down the canal.

 

I think some hire fleets under prop to give high alternator revs and thus a higher initial charge rate.

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My BMC 1.8 (38bhp) in my 60ft nb shows 1800 rpm at 3 mph (given a reasonable depth and width of canal and a clear prop). At 2000 rpm it does about 4mph.

 

On rivers I often have it up to 2200 depending on the strength of the flow and often for long periods at a time.

 

I used to worry about the revs seeming so high because the hire and share boats I'd used previously needed less rpm, probably about 300 or so less than this.

 

But at these revs the pitch of my engine noise didn't seem to be any higher than those previous boats and the engine didn't appear to be working any harder, so I gave up worrying about it.

 

And now 6 years on it's still doing fine, touch wood!

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