Propeller clearance

[Maudesmaster]

Eventually ordered a Left hand 21”x 18 pitch Propeller 3 years ago  was ok but lacking thrust so had it remodelled to 21”x21 pitch 1 year ago worked fine but hectic on right hand bends until got used to the stern pushing to the right 

Now then I have a throw of 12” ie 24” between skeg and uxter plate 

Up on Leeds Liverpool just west of Wigan flight top lock picked up a big rock or something winding all three blade ends are like the top of an “r”

I am wondering if better to have 1” gap top and bottom and going for a 22” prop 

62’ with a Gardner 3LW 

not done anything about it yet as needed to descend the flight before it closed

 

[bizzard]

6 minutes ago, Maudesmaster said:

Eventually ordered a Left hand 21”x 18 pitch Propeller 3 years ago  was ok but lacking thrust so had it remodelled to 21”x21 pitch 1 year ago worked fine but hectic on right hand bends until got used to the stern pushing to the right 

Now then I have a throw of 12” ie 24” between skeg and uxter plate 

Up on Leeds Liverpool just west of Wigan flight top lock picked up a big rock or something winding all three blade ends are like the top of an “r”

I am wondering if better to have 1” gap top and bottom and going for a 22” prop 

62’ with a Gardner 3LW 

not done anything about it yet as needed to descend the flight before it closed

 

You need a repeller instead od a propeller.

[dmr]

I suspect a 3LW could handle something much bigger than a 21x21, but with only 24" of space going any bigger than 21" might give problems, but chances are it would be ok.

A new 22" inch prop will cost a bit but if you have the money it would be nice to try it.

I assume it could be reworked down to 21 if it doesn't work out?

Are you happy with your current tickover speed and maximum speed?

 

You must have hit something big and hard to do the damage. I suppose a bigger prop very slightly increases the risk of it happening again, but its such a rare event its probably not worth worrying.

[BEngo]

Increasing the diameter and reducing the clearance will make the prop walk even greater.

 

Reducing the gap will also make it more likely that something will get stuck. between the bats and the counter.

 

In an ideal world you are looking for a gap of at least 10% of prop diameter.

 

If you are happy with the existing blade It might be worth getting a prop repair company to sort it.  Crowthers would  have been handy....  Maybe someone can suggest a suitable fixer.  Norris are a long way sarf.  Not sure where Clements (Crowthers reccomend) are.

 

N

 

[IanD]

3 minutes ago, BEngo said:

Increasing the diameter and reducing the clearance will make the prop walk even greater.

 

Reducing the gap will also make it more likely that something will get stuck. between the bats and the counter.

 

In an ideal world you are looking for a gap of at least 10% of prop diameter.

 

If you are happy with the existing blade It might be worth getting a prop repair company to sort it.  Crowthers would  have been handy....  Maybe someone can suggest a suitable fixer.  Norris are a long way sarf.  Not sure where Clements (Crowthers reccomend) are.

 

N

 

 

Since you're diameter limited, a 4-blade prop might be a better choice, but this would mean shelling out for a new one...

[Alan de Enfield]

10 minutes ago, BEngo said:

Norris are a long way sarf

 

 

I'd certainly recommend Norris

 

T. Norris Marine Ltd

Unit 17 St. James Industrial Estate

Westhampnett Road

Chichester

West Sussex

PO19 7JU

Tel: 01243 716205

Email: sales@tnorrismarine.co.uk

 

Supplier of Propellers, Stern Gear & Marine Equipment. Supply - Manufacture - Repair Since 1950 Propellers & Stern Gear Bronze Propellers

 

Bronze Propellers — T.Norris Marine (tnorrismarine.co.uk)

 

PROPELLER RECONDITIONING and RE-PITCHING SERVICE

We can recondition Manganese bronze, Aluminium bronze and Aluminium (outboard and outdrive propellers). All Propellers are Re-welded if required and then polished, balanced, re-tracked and Aluminium Propellers are re-painted. The price depends on the size, material and amount of work required. Bronze propellers can also be re-pitched. It would be wise to contact us prior to sending or delivering a Propeller to check viability and get an estimate of cost. Some propellers can be bent beyond “the point of no return”, and if a propeller has severe electrolysis repair is not possible. As a good guide, if a propeller is held at the boss and a blade is tapped with a metal object, it should “ring”. If a dull thud results it is most likely beyond repair.

Edited November 12, 2023 by Alan de Enfield

[dmr]

4 minutes ago, BEngo said:

Increasing the diameter and reducing the clearance will make the prop walk even greater.

 

Reducing the gap will also make it more likely that something will get stuck. between the bats and the counter.

 

In an ideal world you are looking for a gap of at least 10% of prop diameter.

 

If you are happy with the existing blade It might be worth getting a prop repair company to sort it.  Crowthers would  have been handy....  Maybe someone can suggest a suitable fixer.  Norris are a long way sarf.  Not sure where Clements (Crowthers reccomend) are.

 

N

 

 

Does prop walk relate to clearance?

and does reduced clearance significantly increase the risk of something getting jammed? I read somewhere that the recomended clearance was based on the typical size of bits of wood found floating in the canal 😀 and that has probably changed with time?

Are cavitation and other noise issues a likely problem?

 

6 minutes ago, IanD said:

 

Since you're diameter limited, a 4-blade prop might be a better choice, but this would mean shelling out for a new one...

 

I suspect we think too much about using the engine power and getting maximum speed, but for most boaters much of the time getting a good low speed at tickover is probably more important for pleasant boating.  The 3LW is a big engine.

[Maudesmaster]

I got the prop from Jonathan at Norris and had it re worked there as I will probably do again I just wondered if having a smaller gap would stop stuff getting trapped and damaging  the blades 

also 1 thought if I go longer blades I can have less pitch  I dunno just wondering 

I wish they were still in Isleworth as easier to get to without a car 

With the damage slightly less speed but when reversing boat goes a lot more to the port side 

luckily I had built in a bow thruster when ordered the shell 

1 hour ago, dmr said:

I suspect a 3LW could handle something much bigger than a 21x21, but with only 24" of space going any bigger than 21" might give problems, but chances are it would be ok.

A new 22" inch prop will cost a bit but if you have the money it would be nice to try it.

I assume it could be reworked down to 21 if it doesn't work out?

Are you happy with your current tickover speed and maximum speed?

 

You must have hit something big and hard to do the damage. I suppose a bigger prop very slightly increases the risk of it happening again, but its such a rare event its probably not worth worrying.

Max is ok tickover very slow almost stops but gets a bit of Patricroft smog with low revs so tent to up em a bit just yell sorry Gardner on min steerage 

 

[MtB]

1 hour ago, dmr said:

I suspect we think too much about using the engine power and getting maximum speed, but for most boaters much of the time getting a good low speed at tickover is probably more important for pleasant boating.  The 3LW is a big engine.

 

I had a 21 x 19 on the Kelvin K1 after a lot of experimentation. That was on a 1:1 final drive ratio and as you no doubt remember, it was fairly over-propped. I have a similar sized blade on the Gleniffer, also with 1:1 final drive ratio. Works well.

 

Given the OP's concern about clearances, rather than get a bigger diameter blade it might be an idea to experiment with final drive ratios. Its probably a PRM D260 on the 3LW and I think there are a variety of ratio gears available for the D260.

 

 

[magnetman]

Might it be worth dropping the skeg a little as a way to prevent debris getting caught between the prop and the skeg if this is a concern? 

 

Won't help with the uxter plate clearance but gravity suggests heavy items on the canal bed are more likely to get caught below than above the propeller. 

 

 

 

 

A dropped skeg can of course cause other problems. 

[MtB]

10 minutes ago, magnetman said:

A dropped skeg can of course cause other problems. 

 

 

Here's mine:

 

 

 

 

Not just a dropped skeg but the stern tube moved down a bit too.

 

A work of art, done by Brinklow.

 

 

Edited November 12, 2023 by MtB

[magnetman]

Plasma cutters are cool toys. 

 

 

I had a dropped skeg on one of my narrow boats. It used to be odd under bridges with random motorbikes under the water as it lifted the starn up very odd sensation. 

 

Also a nightmare if a pound went low and it got wedged in the canal bed. 

 

 

[MtB]

2 minutes ago, magnetman said:

Plasma cutters are cool toys. 

 

 

I had a dropped skeg on one of my narrow boats. It used to be odd under bridges with random motorbikes under the water as it lifted the starn up very odd sensation. 

 

Also a nightmare if a pound went low and it got wedged in the canal bed. 

 

 

 

Had to flush myself out of quite a few locks on the southern Oxford a couple of years ago

 

 

[Maudesmaster]

11 hours ago, MtB said:

 

I had a 21 x 19 on the Kelvin K1 after a lot of experimentation. That was on a 1:1 final drive ratio and as you no doubt remember, it was fairly over-propped. I have a similar sized blade on the Gleniffer, also with 1:1 final drive ratio. Works well.

 

Given the OP's concern about clearances, rather than get a bigger diameter blade it might be an idea to experiment with final drive ratios. Its probably a PRM D260 on the 3LW and I think there are a variety of ratio gears available for the D260.

 

 

It’s a PRM D500 as originally wanted Hydraulic Bow thruster 

[blackrose]

12 hours ago, Maudesmaster said:

I wish they were still in Isleworth as easier to get to without a car 

 

 

I didn't realise they'd moved from Isleworthless. They repitched my prop 10 years ago and did a top job.

[magnetman]

I like the place name. 

 

Yes they moved quite recently. 

 

I did hear of someone on the Thames potentially moving into this area of business. Not sure but I think it might have been Tom Jones boatyard at Romney lock Windsor. 

 

They do have rather a good machine shop there. 

 

It may have been somewhere else and I'm not sure if they do prop work. 

 

 

 

 

 

 

[MtB]

1 hour ago, Maudesmaster said:

It’s a PRM D500 as originally wanted Hydraulic Bow thruster 

 

Hmmm... I doubt that was ever a possibility. 

 

From the PRM site:

 

"To cater for the widest possible variety of boats the PRM500 is offered with a choice of reduction ratios,1.459:1, 1.935:1, 2.565:1 and 2.904:1."

 

Which reduction ratio is yours? 

 

 

[David Schweizer]

16 hours ago, Maudesmaster said:

Eventually ordered a Left hand 21”x 18 pitch Propeller 3 years ago  was ok but lacking thrust so had it remodelled to 21”x21 pitch 1 year ago worked fine but hectic on right hand bends until got used to the stern pushing to the right 

Now then I have a throw of 12” ie 24” between skeg and uxter plate 

Up on Leeds Liverpool just west of Wigan flight top lock picked up a big rock or something winding all three blade ends are like the top of an “r”

I am wondering if better to have 1” gap top and bottom and going for a 22” prop 

62’ with a Gardner 3LW 

not done anything about it yet as needed to descend the flight before it closed

 

 

Over the years I observed that boats with only a small distance between the prop and counter plate had a tendancy to get lumps of wood, and other extaneous materials, jammed between them. We had a 6" gap on Helvetia, and rarely caught anything between the prop and the counter plate, just a bit of banging and watch the wood float off behind us. I would suggest that a 1" gap could be asking for problems.

[Alan de Enfield]

9 minutes ago, David Schweizer said:

 

Over the years I observed that boats with only a small distance between the prop and counter plate had a tendancy to get lumps of wood, and other extaneous materials, jammed between them. We had a 6" gap on Helvetia, and rarely caught anything between the prop and the counter plate, just a bit of banging and watch the wood float off behind us. I would suggest that a 1" gap could be asking for problems.

 

There must be a point where the gap becomes so small (1" ?) that pieces of wood and extraneous materials just cannot get stuck, bounce off the prop and continue on their way.

[Maudesmaster]

3 hours ago, blackrose said:

 

I didn't realise they'd moved from Isleworthless. They repitched my prop 10 years ago and did a top job.

Yes great company did you walk through the workshop to the loo Amazing place like the TARDIS countless machines never seen the like of 

 

[Maudesmaster]

1 hour ago, Alan de Enfield said:

 

There must be a point where the gap becomes so small (1" ?) that pieces of wood and extraneous materials just cannot get stuck, bounce off the prop and continue on their way.

My way of thinking but dunno 

[David Schweizer]

2 hours ago, Alan de Enfield said:

 

There must be a point where the gap becomes so small (1" ?) that pieces of wood and extraneous materials just cannot get stuck, bounce off the prop and continue on their way.

 

Or get stuck solid and stop the engine. Something I have seen happen on a couple of occassions.

[IanD]

19 hours ago, dmr said:

 

Does prop walk relate to clearance?

and does reduced clearance significantly increase the risk of something getting jammed? I read somewhere that the recomended clearance was based on the typical size of bits of wood found floating in the canal 😀 and that has probably changed with time?

Are cavitation and other noise issues a likely problem?

 

I suspect we think too much about using the engine power and getting maximum speed, but for most boaters much of the time getting a good low speed at tickover is probably more important for pleasant boating.  The 3LW is a big engine.

 

Prop walk is caused by unequal water flow into the top (less) and bottom (more) of the prop, so it's worse if the prop is too close to the uxter plate.

 

The usual "10% of diameter" clearance is based on reducing prop noise, presumably for seagoing boats and ships where the engine is well silenced and buried deep inboard. Given the noise a lot of canal boat engines make, perhaps this isn't such a concern... 😉

 

On top of this, for a smaller prop than 20" it's also often recommended to have 2" minimum to reduce the chances of debris jamming the prop -- obviously this isn't a hard and fast limit, it's just based on experience.

Edited November 13, 2023 by IanD

[Maudesmaster]

34 minutes ago, David Schweizer said:

 

Or get stuck solid and stop the engine. Something I have seen happen on a couple of occassions.

Happened behind the poachers pocket on the gollie last year Knocked it out with my Maul Axe 

Just now, Maudesmaster said:

Happened behind the poachers pocket on the gollie last year Knocked it out with my Maul Axe 

Was a log 

[magnetman]

This can also bend the tailshaft.