My propeller - thoughts?

[David Horsburgh]

Hi, have had my boat, (now named Pilgrim) for a month or so and have been cruising for a fortnight. I seem to lack thrust ... sure, it poodles along but can only go at walking pace. The assembly seems to be working well, Lister 3 cylinder, Delta 20 gearbox .... I am now on the Oxford which is both shallow and narrow so am aware that this may cause drag, but yesterday I was going into a not very strong headwind and just could not get enough (more) thrust and was going really slowly ... took a photo of the under rear when boat was being blacked - what do you think of my prop? 1997 50ft trad. Looking back I wish I had measured it but looks like a 16 inch .. what do you think? Should/could I upgrade this?

I don't want to thrash along causing tidal waves, just have enough thrust to move it faster when I need to ... seems slow to stop and reverse too, although I can see a lot of prop wash - or perhaps my last boat (20 years ago) had more power and I am comparing to that.

 

 

Edited October 28, 2021 by David Horsburgh

[MtB]

I agree it does look a bit weedy. Even small increases in diameter make a big difference to the power transmitted into the water, provided your engine has that power. Which exact model of three cylinder Lister do you have? There are loads of them all different! 

[Tony Brooks]

What is the reduction ratio in the gearbox? It is that and the engine power that makes the most difference to prop size.

 

If the prop is too small (that could be in either pitch or diameter) then the engine revs like fury but you don't go very fast. Similar applies if the ahead clutch in the gearbox is slipping but in that case less water shoots out behind the boat.

 

If the prop is too large it prevents the engine revving as high as it could so again the boat only goes slowly but at lower revs.

 

So what are the revs that give your engine maximum torque and what revs does it reach. What is the rated engine power and gearbox ratio?

 

 

Edited October 28, 2021 by Tony Brooks

[MtB]

Also, you can still measure the prop radius with the boat in the water, through the weed hatch with a tape measure. 

 

Assuming you have a weed hatch that is. I can't see a weed hatch panel in the uxter plate in your photo!

[David Horsburgh]

Thanks all - is a Lister LPWS3. Gearbox is a PRM Delta TA20. Manual says ahead/astern 1.53:1, 2.09:1, 2.82:1. (why does it have three ratios? - no idea)

New gear/engine cables, properly adjusted, no slack. Full revs is normally 1500 but sometimes goes up to nearly 1800 (deep water or downwind I guess). I didn't have this on the Grand Union, or never noticed it, so my thoughts is either shallow narrow water creating drag or there is some slip in the gearbox. Prop has no fouling and isn't slipping. (Yes, lovely big weed hatch - good point, will measure it).

Maybe the original set upback in '75 just wasn't powerful enough? Just that when I was thinking about the whole drive train, well, that prop looked a little small for a 50 footer to me - but what do I know?? 
Looking at the manual and is says that minimum full load speed is 1500r/min so I think I will look at the max setting on the speed adjustment too.

Edited October 28, 2021 by David Horsburgh

[OldGoat]

 Wrong...

Edited October 28, 2021 by OldGoat

[Tony Brooks]

The two forward gears thing probably means that you could get the box in either a 2:1 or 3:1 reduction ratio (2.09 or 2.82). Before we can enter your data into a prop calculator we need to know the actual ratio. If its a mechanical box put it in gear, mark the engine crankshaft pulley and the shaft coupling, and the turn the engine manually counting the turns needed to bring the mark on the coupling back to the start.

Just seen its a hydraulic box so no good.

 

 

Edited October 28, 2021 by Tony Brooks

[nicknorman]

I’m no expert but surely the LPWS3 should rev to a lot more than 1500 on full throttle? This suggests that it is either over-propped (a bit like trying to drive a car uphill in too high a gear) or the engine is way down on power. Or both.

 

At full throttle, do you get any black smoke? If not I would suspect there is something wrong with the fuel flow or the throttle lever adjustment.

 

Having a larger diameter prop (but you need to keep a minimum of 2” clearance between prop blades and bottom of boat/skeg) with a finer pitch will give more punchy response to both setting off and stopping.

Edited October 28, 2021 by nicknorman

[David Horsburgh]

Agree re the 1500 as max hp is listed at 2,500 ... so will adjust  the fixed speed adjuster upwards, see if that makes a difference. Yes, it is smoky at full revs ... hhmmm .... old engine, probably needs rebuilding!

[nicknorman]

1 minute ago, David Horsburgh said:

Agree re the 1500 as max hp is listed at 2,500 ... so will adjust  the fixed speed adjuster upwards, see if that makes a difference. Yes, it is smoky at full revs ... hhmmm .... old engine, probably needs rebuilding!

If it is black smoky, adjusting the high speed stop won’t help as fuel flow is already at a maximum. You will probably find that the 1500 is reached well before the lever is all the way forward, and subsequent movement of the lever doesn’t do anything because the fuel flow is already at maximum. Anyway, it is certainly over-propped (pitch too coarse) for the available engine power. But before messing about with different props I’d get the compressions checked etc.

[Slim]

 I think you summed up the problem when you mentioned the S Oxford. You don't cruise it you plow it. What part were you on when you were struggling? My 55' with a 17x12 prop, BMC 1.8, 1.9:1 box can and does drop to a crawl on much of it. Find deep water (Napton to Braunston? ) and see what happens there. 

 

 

[nicknorman]

4 minutes ago, Slim said:

 I think you summed up the problem when you mentioned the S Oxford. You don't cruise it you plow it. What part were you on when you were struggling? My 55' with a 17x12 prop, BMC 1.8, 1.9:1 box can and does drop to a crawl on much of it. Find deep water (Napton to Braunston? ) and see what happens there. 

 

It’s true that this is a very shallow canal and one is never going to get anywhere near 4mph, however that doesn’t explain the maximum of 1500rpm. The limiting factor should be the amount of wash, not the engine rpm.

[Slim]

53 minutes ago, nicknorman said:

It’s true that this is a very shallow canal and one is never going to get anywhere near 4mph, however that doesn’t explain the maximum of 1500rpm. The limiting factor should be the amount of wash, not the engine rpm.

Recent, practical experience (mine) has shown that it's so shallow and the bottom so glutinous that revs drop down regardless of throttle. I'm sure others on this forum have experienced the same. 

Should add that it's my 'home' canal so I'm quite used to it's issues.

Edited October 28, 2021 by Slim

[David Mack]

2 hours ago, David Horsburgh said:

Gearbox is a PRM Delta TA20. Manual says ahead/astern 1.53:1, 2.09:1, 2.82:1. (why does it have three ratios? - no idea)

Gearbox was available with three different ratios. If you look at the manual it would appear that the '20' refers to the 2:1 (actually 2.09:1) variant.

[Cheshire cat]

Going back to the original post it looks to me like the prop shaft would need to be lengthened to fit a larger propeller.

Currently there's not much clearance between the prop and the skeg support.

[David Horsburgh]

Thanks for all the info above. I went through a different section this morning and max revs became 2000 (didn't keep it there as caused that side wave on the bank) and it went well again - I think it is the canal that brought the problems that worried me.

and thanks re fuel flow and revs - interesting. Shall leave it all as it is - now I know more about gearbox, engine (flow and revs) and the shallow muddy nature of the Oxford-  thought something had gone wrong as it was ok on the Grand Union

 

[David Mack]

Having just taken a 3ft+ draft ex working boat up the Ashby, which has been notoriously shallow for years, the answer is not to try and push it in shallower waters. Just ease off on the revs, reduce your fuel consumption, noise and wash, and you will find you are going no slower. If you don't believe me, try a walking speed app on your phone at different engine speeds.  We were doing around 2.6-2.9 mph on tickover, and we don't get much faster on deeper canals, until you get onto wider river navigations. The speed app also shows how much you slow down going through bridges - the difference is greater than you think!

[dmr]

13 minutes ago, Cheshire cat said:

Going back to the original post it looks to me like the prop shaft would need to be lengthened to fit a larger propeller.

Currently there's not much clearance between the prop and the skeg support.

 

Thats a good observation, could that even be part of the problem?  and potential for some tricky prop fouls too.

[Bod]

13 hours ago, David Horsburgh said:

Hi, have had my boat, (now named Pilgrim) for a month or so and have been cruising for a fortnight. I seem to lack thrust ... sure, it poodles along but can only go at walking pace. The assembly seems to be working well, Lister 3 cylinder, Delta 20 gearbox .... I am now on the Oxford which is both shallow and narrow so am aware that this may cause drag, but yesterday I was going into a not very strong headwind and just could not get enough (more) thrust and was going really slowly ... took a photo of the under rear when boat was being blacked - what do you think of my prop? 1997 50ft trad. Looking back I wish I had measured it but looks like a 16 inch .. what do you think? Should/could I upgrade this?

I don't want to thrash along causing tidal waves, just have enough thrust to move it faster when I need to ... seems slow to stop and reverse too, although I can see a lot of prop wash - or perhaps my last boat (20 years ago) had more power and I am comparing to that.

 

 

 

Leaves on the prop.

This time of year, as the leaves die and fall into the water, as you pass over/through, the leaves gather around the prop, reducing it's efficiency, to the point of being almost useless.

As this build up is noticable, the easy cure is to go into reverse for a short burst, the leaves will fall away, and all will be good till the next build up.

 

Bod

[MtB]

37 minutes ago, Bod said:

 

Leaves on the prop.

This time of year, as the leaves die and fall into the water, as you pass over/through, the leaves gather around the prop, reducing it's efficiency, to the point of being almost useless.

As this build up is noticable, the easy cure is to go into reverse for a short burst, the leaves will fall away, and all will be good till the next build up.

 

Bod

 

Good call, but I think it's a bit too early in the leaf-dropping season for this to be having much effect yet. Especially in the south....

 

 

[Mad Harold]

12 hours ago, Bod said:

 

Leaves on the prop.

This time of year, as the leaves die and fall into the water, as you pass over/through, the leaves gather around the prop, reducing it's efficiency, to the point of being almost useless.

As this build up is noticable, the easy cure is to go into reverse for a short burst, the leaves will fall away, and all will be good till the next build up.

 

Bod

Was moored on the Upper Peak Forest for some time and in Autumn it is a carpet of leaves.

They not only get around your prop,but you can find yourself shunting a huge pile of leaves on the bow.

[doratheexplorer]

If you're doing walking pace on the south oxford, that's about right.  I'm not sure what you think the problem is?

 

I wouldn't get too hung up on rpm either; for all we know your gauge doesn't read accurately anyway.

 

If you're making steady progress and, crucially, the steering is responsive, then carry on as normal.  If the steering starts to go vague and the speed drops off, then you probably have something round your prop, and right now that's probably leaves.  Give a blast of reverse and you'll blow them off.

 

How much narrowboating experience did you have before buying yours?  Methinks you may be expecting something which isn't realistic.

[blackrose]

On 28/10/2021 at 08:52, David Horsburgh said:

Hi, have had my boat, (now named Pilgrim) for a month or so and have been cruising for a fortnight. I seem to lack thrust ... sure, it poodles along but can only go at walking pace.

 

 

Poodles along?

 

 

I think we all knew what you meant... 😂

[David Horsburgh]

On 29/10/2021 at 12:13, doratheexplorer said:

If you're doing walking pace on the south oxford, that's about right.  I'm not sure what you think the problem is?

 

I wouldn't get too hung up on rpm either; for all we know your gauge doesn't read accurately anyway.

 

If you're making steady progress and, crucially, the steering is responsive, then carry on as normal.  If the steering starts to go vague and the speed drops off, then you probably have something round your prop, and right now that's probably leaves.  Give a blast of reverse and you'll blow them off.

 

How much narrowboating experience did you have before buying yours?  Methinks you may be expecting something which isn't realistic.

 

Experience? Well, back in the day I was assistant operations manager of a 16 boat hire fleet and shared all servicing and repairs with the ops manager. I owned a 65' trad Colecraft and navigated the Kennet & Avon, the Thames, Oxford, Grand Union .... I would say that I have sufficient experience .... was a genuine query, now answered as I now know how shallow and muddy the Oxford can be and how it can really slow a boat in certain areas.

[Alan de Enfield]

9 minutes ago, David Horsburgh said:

 

Experience? Well, back in the day I was assistant operations manager of a 16 boat hire fleet and shared all servicing and repairs with the ops manager. I owned a 65' trad Colecraft and navigated the Kennet & Avon, the Thames, Oxford, Grand Union .... I would say that I have sufficient experience .... was a genuine query, now answered as I now know how shallow and muddy the Oxford can be and how it can really slow a boat in certain areas.

 

But unless you state that, no one is going to know what your level of experience is, folks go to a great deal of effort to try and explain why & what is happening (assuming that by the question you have little experience) when all along you probably have 1000's of hours of Narrowboating on Rivers / Big canals but just not used to the damp, muddy ditches.