Slowing down

[SiFi]

My slowest speed, according to my fitbit, is roughly 3.5 mph. Recently I was following somebody who was going along much slower and I found it difficult not to run into them.  When I reduced the revs to a minimum the gearbox would disengage and with it my steering. I could not match their slowness. Is there adjustment on the PRM gearboxes? I think I can adjust the Lister a bit lower rpm.

[Arthur Marshall]

My Lister on tickover shoves me along at about 1mph. I only do 3 at best unless I wind it up to full throttle when, downhill and with a following wind, I might hit 4. That's an SR2.

If that's your slowest speed, you must be zooming along at cruising pace, carving out chunks of canal bank as you go. I suspect your fitbit is fibbing a bit.

If I reduce the tickover too far, I don't go out of gear, the engine just stalls. Out of gear is odd, perhaps - Tony Brooks wil know , as will others. Which engine have you got, pushing what size of boat? ?

[SiFi]

The 3.5 mph does seem to tally with people casually walking along the towpath. I don't think I could go much slower.

 

It's a '40hp' Lister LPWS in a 40' nb.

 

 

[MtB]

4 hours ago, SiFi said:

Is there adjustment on the PRM gearboxes?

 

I'll ask to save Tony the trouble of having to.

 

Which model of PRM gearbox is it? They made more than one model over the decades! 

[Mike Tee]

What is the size and pitch of the prop?

[David Mack]

4 hours ago, SiFi said:

My slowest speed, according to my fitbit, is roughly 3.5 mph.

If 3.5 mph is your slowest speed, what is your normal travelling speed and the maximum you can achieve on typical narrow canals?

If this figure is correct I would conclude that much of the time you are going too fast, and you are unable to slow down sufficiently to respond to other craft, moored or moving, or to do any close quarter manoeuvring.

Or perhaps your fit bit is a fib bit. Have you tried verifying it's speed readings? How does it compare with a speedometer app on your phone (find one with a setting for walking rather than car speeds)?

[cuthound]

If you have a smartphone download the Ullysse Speedometer app.

 

It is reasonably accurate at slow speeds, and even shows the boat slowing down in bridge holes and shallow stretches.

 

This will either confirm or disprove the accuracy of your Fitbit's reading.

[Arthur Marshall]

1 hour ago, SiFi said:

The 3.5 mph does seem to tally with people casually walking along the towpath. I don't think I could go much slower.

 

It's a '40hp' Lister LPWS in a 40' nb.

 

 

I've found the best way to measure my boat speed is simply to time the travel between mileposts. I trundle at 3 an hour and still overtake walkers, so I assume they're going at less. All GPS units use algorithms to work out your speed, they aren't measuring it in any real sense, so are notoriously inaccurate at low speeds.

Either way, it's still annoying being stuck behind someone crawling along, though these days I just stop and put the kettle on, make a cuppa and catch them up again later. But I still find it odd that you go out of gear, unless you mean the Morse control drops back into the neutral position because of the cable pull.

[Lily Rose]

2 hours ago, SiFi said:

The 3.5 mph does seem to tally with people casually walking along the towpath. I don't think I could go much slower.

 

It's a '40hp' Lister LPWS in a 40' nb.

 

 

 

If you're matching people casually walking along the towpath then you're not doing 3.5mph.

 

I do quite a lot of "brisk walking" utilising the NHS Active 10 app as well as Runkeeper. When I walk briskly along a decent towpath I catch and overtake narrowboats easily. When I'm away from the towpath, on a road or pavement, I can almost always walk faster but even then I'm still only doing around 3.5mph. On many, if not most, rural towpaths walking at that pace would be very difficult to achieve without risking an unscheduled dip which is why I prefer to get on to a road or a decent public footpath.

 

I reckon most casual towpath walking is about 2.5mph, possibly less, but 3mph at most.

[Rob-M]

I do the same as Arthur and time travel between mile posts and usually manage to maintain an average of 3mph although had it's challenges today on the Shropie with online moorings and a fishing match but glad I'm past the mile after mile between Norbury and Woodeaves that will be full for a fishing match tomorrow.

[Quattrodave]

40hp on a NB does seem a little excessive but it does really depend on gearing and prop, what are your prop dimensions?

 

"When I reduced the revs to a minimum the gearbox would disengage and with it my steering"

 

Rather an odd sentance, I'm assuming Arthur has hit the nail on the head:

13 hours ago, Arthur Marshall said:

But I still find it odd that you go out of gear, unless you mean the Morse control drops back into the neutral position because of the cable pull.

And if you are dropping into neutral then no water is flowing over the rudder so no steering...

 

If indeed you have a morse control then it performs 2 actions, from neutral (generally central position) as you push it forward it selects forward gear then as you keep pushing it increased the engine speed, as you pull it back decreases the engine speed before setting the gearbox back to neutral, pulling backward does exactly the same but for reverse...

 

The other thing that springs to mind is your engine tickover, its possible that its incorrectly set or stuck... can you post a short video or audio clip of it at tickover in neutral and say engine you have pls....

Edited September 1 by Quattrodave

[MtB]

49 minutes ago, Quattrodave said:

The other thing that springs to mind is your engine tickover, its possible that its incorrectly set or stuck... can you post a short video or audio clip of it at tickover in neutral and say engine you have pls....

 

The OP says "It's a '40hp' Lister LPWS in a 40' nb."

 

40HP in a 40ft boat??!!!

 

One might surmise the prop might be sized 'to suit' a 40hp engine too, so yes this over-engined small boat could easily fly along at tickover. I'd suggest a shorter pitched blade might be the solution. 

 

 

[David Mack]

14 hours ago, Arthur Marshall said:

All GPS units use algorithms to work out your speed, they aren't measuring it in any real sense, so are notoriously inaccurate at low speeds.

It's inherent in the technology. The GPS calculates your position at successive time points then calculates your speed from the difference in position and time between successive locations. At low speeds a small error in the location calculation is proportionately bigger in relation to the distance travelled between successive points than at higher speeds, and hence the calculated speed is less accurate. I have noticed that the Ullysse app speed jumps around quite a bit when I use it boating.

[Laurie Booth]

21 hours ago, SiFi said:

My slowest speed, according to my fitbit, is roughly 3.5 mph. Recently I was following somebody who was going along much slower and I found it difficult not to run into them.  When I reduced the revs to a minimum the gearbox would disengage and with it my steering. I could not match their slowness. Is there adjustment on the PRM gearboxes? I think I can adjust the Lister a bit lower rpm.

3.5 mph is stupidly too fast.

[MtB]

39 minutes ago, Laurie Booth said:

3.5 mph is stupidly too fast.

 

Indeed it is. I dream of getting up to such speeds without creating a breaking wash.

 

The OP's boat is clearly over-propped, as I said earlier. A shorter pitched blade will fix it. 

 

 

[SiFi]

I accept that my 'fit bit' is likely over estimating my slowest speed but nevertheless I would still like to be able to go slower even if I can't  'creep' along as and when. Fitting a different propeller is not worth it for me.

 

I have disconnected the throttle cable and found that the engine (Lister LPWS4) is already against its lowest stop. Is there any other way to reduce the tickover, it sounds on the high side to me.

 

[I now realise that the gearbox (PRM Delte20) is not the issue, it engages before the throttle increases.]

[nicknorman]

20 minutes ago, SiFi said:

I accept that my 'fit bit' is likely over estimating my slowest speed but nevertheless I would still like to be able to go slower even if I can't  'creep' along as and when. Fitting a different propeller is not worth it for me.

 

I have disconnected the throttle cable and found that the engine (Lister LPWS4) is already against its lowest stop. Is there any other way to reduce the tickover, it sounds on the high side to me.

 

[I now realise that the gearbox (PRM Delte20) is not the issue, it engages before the throttle increases.]

It might be possible to reduce the idle speed a bit if there is eg a stop screw. However one shouldn’t reduce the idle speed below the manufacturer’s specified idle speed as it is bad for the engine - oil pressure too low, big momentary speed fluctuations as each cylinder goes over compression causing torque stress etc. You really need to measure the idle and compare it with the manual’s spec. Do you not have a tachometer?

 

There are some boats around with tiny propellers capable of barely moving whilst still being in gear, and some people seem to find virtue in going as slowly as possible, holding everyone up whilst chanting the mantra “you mustn’t be in a rush on the canals”.

 

So I think that unless your boat causes annoyance to moored boats (the ones that are tied up properly) I would leave well alone. There will always be a boat that is capable of going slower than yours. When you occasionally come up behind the slow-virtue-signalling selfish people, either ram them into the trees or stop for a relaxing cup of tea.

[SiFi]

Thanks nicknorman ... it does look like I have to agree with your sentiment on this one.

 

[Tony Brooks]

On 31/08/2024 at 14:58, SiFi said:

When I reduced the revs to a minimum the gearbox would disengage and with it my steering. I could not match their slowness. I

 

I did not look at this because I thought the tile was another whinge about overly fast or slow boats. sorry.

 

The above quote worries me, if it means what it says. There is no way a gearbox (I assume hydraulic PRM -noted that question was not answered) should disengage at minimum revs UNLESS the setting it to idle also puts the box into neutral or there is a gearbox fault.

 

First, check is to look at the lever on the gearbox as you put the control to slow speed. The gearbox lever should not move. If it does, then the cable adjustment is faulty. Counterintuitive as it may seem, I would suspect the throttle cable adjustment first. Adjust the throttle cable so one of the ends slips into the relevant holes when the engine lever is against the idle stop AND the control is in slow ahead or astern. That allows the mechanism to go to idle without disengaging the gear. The actual mechanism varies, but it is often a spring-loaded outer anchor for the throttle cable that moves as you push the lever from slow ahead/astern to neutral.

 

If that does not work then looks at gear cable. With the gearbox lever and control lever in neutral, the trunions that attach the cable to the levers should just drop into place. If not screw them up or down the cable threads to ensure they do.

 

Then we are thinking about lack of gearbox oil pressure at slow speed, so check the oil level and type in the box. It should be engine oil so 20W50 or 15W40. Not gearbox oil, or ATF, although I doubt the latter would cause much of a problem.

 

Finally check the oil pressure in the box because ere is an adjustable PRV I think, but this is unlikely.

 

I agree that it sounds like too much pitch on the prop for the size of boat if the above does not sort it.

 

 

 

 

 

 

[carlt]

14 hours ago, nicknorman said:

 

 

There are some boats around with tiny propellers capable of barely moving whilst still being in gear, and some people seem to find virtue in going as slowly as possible, holding everyone up whilst chanting the mantra “you mustn’t be in a rush on the canals”.

 

As one of the ones who was happy to plod along at a couple of mph I could never understand the motives of my fellow snails who refused to pull over to let folk pass.

 

Never being in a rush I found bunging it into the bank occasionally to let someone overtake was a good excuse to make a coffee or roll a fag.

[blackrose]

23 hours ago, MtB said:

The OP's boat is clearly over-propped, as I said earlier. A shorter pitched blade will fix it. 

 

My overpropped widebeam has always been able to creep along pretty slowly and it's handy to be able to do that in certain situations. 

 

I had the prop repitched to reduce the pitch from 13" to 11.5" and they also took half an inch off the 19" diameter. While freeing up more engine revs and resulting in more speed in deep water (the reason I had it done), the repitch also resulted in slower speeds at idling while still being able to maintain steering. 

 

If I was the OP, after going through Tony's suggestions I'd find out what size prop you've got and do some calculations on a couple of online prop size calculators.

Edited September 2 by blackrose

[bizzard]

Bit like big variable pitch prop driven aircraft. Take off on fine and cruise on course. Once on holiday in Newquay Cornwall staying at a pub. The owner told me a tale about when he was a lad during ww2 he watched and American Liberator take off from RAF St Mawgan, it stalled and crashed into a cliff. The investigation found the prop pitch control was in course pitch which caused the stall.  The pilot could of course take off in fine pitch but changed to course pitch far too early, who knows.

Edited September 2 by bizzard

[SiFi]

4 hours ago, Tony Brooks said:

 

I did not look at this because I thought the tile was another whinge about overly fast or slow boats. sorry.

 

The above quote worries me, if it means what it says. There is no way a gearbox (I assume hydraulic PRM -noted that question was not answered) should disengage at minimum revs UNLESS the setting it to idle also puts the box into neutral or there is a gearbox fault.

 

First, check is to look at the lever on the gearbox as you put the control to slow speed. The gearbox lever should not move. If it does, then the cable adjustment is faulty. Counterintuitive as it may seem, I would suspect the throttle cable adjustment first. Adjust the throttle cable so one of the ends slips into the relevant holes when the engine lever is against the idle stop AND the control is in slow ahead or astern. That allows the mechanism to go to idle without disengaging the gear. The actual mechanism varies, but it is often a spring-loaded outer anchor for the throttle cable that moves as you push the lever from slow ahead/astern to neutral.

 

If that does not work then looks at gear cable. With the gearbox lever and control lever in neutral, the trunions that attach the cable to the levers should just drop into place. If not screw them up or down the cable threads to ensure they do.

 

Then we are thinking about lack of gearbox oil pressure at slow speed, so check the oil level and type in the box. It should be engine oil so 20W50 or 15W40. Not gearbox oil, or ATF, although I doubt the latter would cause much of a problem.

 

Finally check the oil pressure in the box because ere is an adjustable PRV I think, but this is unlikely.

 

I agree that it sounds like too much pitch on the prop for the size of boat if the above does not sort it.

 

 

 

 

 

 

I think I did mention somewhere later that its a PRM Delta 20 gearbox.  I spent some time yesterday understanding how things are working.  As I reduce the throttle (Morse) it does stay engaged down to the (LPWS4) engine's tick-over and only disengages once the throttle reaches 'neutral'.  The engine tick-over does seem to be on the high side but I think I have run out of adjustment.

 

Thanks everyone for you responses ... a new propellor or modification of what I have will have to wait.

 

 

[Tony Brooks]

6 minutes ago, SiFi said:

The engine tick-over does seem to be on the high side but I think I have run out of adjustment.

 

Is that cable adjustment or throttle stop (idle speed) adjustment on the engine? If the former, you may find more adjustment at the othered of the cable.

 

When the lever goes to slow ahead or astern, does the lever on the engine actually hit the throttle stop screw?

[SiFi]

Throttle stop, I disconnected the cable.  I need to have a closer look as I don't remember a tick over adjuster stop.