DavidPeckham Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
Chris Williams Posted August 15, 2019 Report Share Posted August 15, 2019 Have you got the right propellor ? Link to comment Share on other sites More sharing options...
mrsmelly Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
Boater Sam Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
MtB Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
DavidPeckham Posted August 15, 2019 Author Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
MtB Posted August 15, 2019 Report Share Posted August 15, 2019 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. 1 Link to comment Share on other sites More sharing options...
cuthound Posted August 15, 2019 Report Share Posted August 15, 2019 (edited) 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 August 15, 2019 by cuthound Spillung 1 Link to comment Share on other sites More sharing options...
WotEver Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
OldGoat Posted August 15, 2019 Report Share Posted August 15, 2019 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....) Link to comment Share on other sites More sharing options...
Kudzucraft Posted August 15, 2019 Report Share Posted August 15, 2019 (edited) Possible that the tachometer it wrong. Probably not but it is possible. But I lean toward with Mike the Boilerman ideas. Edited August 15, 2019 by Kudzucraft Link to comment Share on other sites More sharing options...
WotEver Posted August 15, 2019 Report Share Posted August 15, 2019 (edited) 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 August 15, 2019 by WotEver Fouled, not foiled! Link to comment Share on other sites More sharing options...
Richard10002 Posted August 15, 2019 Report Share Posted August 15, 2019 (edited) 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 August 15, 2019 by Richard10002 Link to comment Share on other sites More sharing options...
Rickent Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
DavidPeckham Posted August 15, 2019 Author Report Share Posted August 15, 2019 Cheers all, will follow those things up. Link to comment Share on other sites More sharing options...
Jen-in-Wellies Posted August 15, 2019 Report Share Posted August 15, 2019 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 Link to comment Share on other sites More sharing options...
Bee Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
blackrose Posted August 15, 2019 Report Share Posted August 15, 2019 (edited) 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 August 15, 2019 by blackrose Link to comment Share on other sites More sharing options...
Cheshire cat Posted August 15, 2019 Report Share Posted August 15, 2019 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? Link to comment Share on other sites More sharing options...
blackrose Posted August 15, 2019 Report Share Posted August 15, 2019 (edited) 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 August 15, 2019 by blackrose Link to comment Share on other sites More sharing options...
Alan de Enfield Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
Cheshire cat Posted August 15, 2019 Report Share Posted August 15, 2019 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 Link to comment Share on other sites More sharing options...
nb Innisfree Posted August 15, 2019 Report Share Posted August 15, 2019 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. Link to comment Share on other sites More sharing options...
Tony Brooks Posted August 16, 2019 Report Share Posted August 16, 2019 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. Link to comment Share on other sites More sharing options...
Grassman Posted August 16, 2019 Report Share Posted August 16, 2019 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! Link to comment Share on other sites More sharing options...
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