Canopus and Sculptor

[MtB]

2 minutes ago, dpaws said:

It's not a square blade, but the blades are quite "fat" (apologies, can't place the photo at present).

 

Terminology alert...

A 'square' blade is one where the pitch = the diameter and considered a bad Thing. Ideally any blade should have pitch significantly less than the diam. Yours is close to being nominally 'square'. 

Once you get 'over-square' the turbine effect (where the prop grabs a cylinder of water its own diameter and just spins it) tends to become marked and tiresome.

[Guest]

5 minutes ago, Mike the Boilerman said:

 

Terminology alert...

A 'square' blade is one where the pitch = the diameter and considered a bad Thing. Ideally any blade should have pitch significantly less than the diam. Yours is close to being nominally 'square'. 

Once you get 'over-square' the turbine effect (where the prop grabs a cylinder of water its own diameter and just spins it) tends to become marked and tiresome.

Thanks Mike, hadn't come across that before - I was off in the land of square cut-off tips! 

[David Mack]

3 minutes ago, dpaws said:

Thanks Mike, hadn't come across that before - I was off in the land of square cut-off tips! 

Axiomland! 

[MtB]

4 minutes ago, dpaws said:

Thanks Mike, hadn't come across that before - I was off in the land of square cut-off tips! 

 

At least you don't have one of them Axiom abominations, heaven forbid!!

[Guest]

Well, Canopus has had an Axiom before... and to be fair.... by all accounts it worked better than the one I have fitted at present! 

The previous owner swapped it out to fit this one, this one's spec fitted against best advice. I understand what he was trying to do now, increasing pitch to increase stopping power, but unfortunately, like me, had not understood the square blade / turbine effect issue. It seems that slowing down has been a recurring issue, regardless of prop fitted, only this prop made it a whole lot worse, not better...

 

[Guest]

"Turbine" effect / square prop question - why doesn't the same happen going forward?

Is it because the prop is so close to the deadwood that somehow the deadwood is preventing the cylinder of water from rotating around with the prop?

Jan... ?

Edited March 17, 2017 by dpaws

[GUMPY]

From memory the Blackstone box has separate brake bands for reverse. These are prone to slippage would give exactly the effect you describe. As in good on forward crap in reverse. 

Check with steamraiser as he knows them well.

[Dalslandia]

My first thought was that the propeller have some cup but that is not common on low speed propellers, if the gearbox slip there will be no prop walk, atleast not more then stopping Power.

[MtB]

On 17/03/2017 at 19:50, dpaws said:

"Turbine" effect / square prop question - why doesn't the same happen going forward?

Is it because the prop is so close to the deadwood that somehow the deadwood is preventing the cylinder of water from rotating around with the prop?

Jan... ?

 

I don't know, but it's an annoyingly valid question. 

I'm tending towards the opinion your reverse brake band is goosed, as recently suggested by Loddon above.

[Dalslandia]

I would say it is because the airfoil is cambered to work good in FW. and not at all in reverse it stall out a lot easier going backward (the propeller)

I don't understand why someone don't make a propeller with airfoils that is equal good in both directions. with some nosecamber at both the LE and TE

Edited March 17, 2017 by Dalslandia

[Guest]

12 minutes ago, Dalslandia said:

I don't understand why someone don't make a propeller with airfoils that is equal good in both directions. with some nosecamber at both the LE and TE

Are you referring to the Axiom prop? Equal in both directions....

[Guest]

1 hour ago, Loddon said:

From memory the Blackstone box has separate brake bands for reverse. These are prone to slippage would give exactly the effect you describe. As in good on forward crap in reverse. 

Check with steamraiser as he knows them well.

Very interesting Julian, thanks - of course, I don't know how much prop walk to expect as everything's new to me... there's a fair mass of prop spinning...

It would explain in part the generic poor reverse performance. The previous owner was an experienced mariner but not a vintage gearbox box hands dirty sorta chap so neither he or I would be aware of a brake band slipping...

My apologies all, the present prop is a FOUR blade, not a three...

Edited March 17, 2017 by dpaws

[MtB]

I'd say there is no way that blade is the 50% DAR I think you mentioned earlier. I'd say more like 85%!

Make me wonder what diameter and pitch it actually is, too...

[Guest]

 

6 minutes ago, Mike the Boilerman said:

I'd say there is no way that blade is the 50% DAR I think you mentioned earlier. I'd say more like 85%!

Make me wonder what diameter and pitch it actually is, too...

Yes, sorry Mike, I had found a picture of the original three blade 24" prop that was around 50% DAR. I don't have the pitch details for the original I'm afraid.

The prop chap who supplied the four blade quoted the 26" / 24.5" spec.

 

As for the potential gearbox issue I guess I'll find out soon enough by default - unfortunately everything will change, so it will be a fresh start - and no doubt with some fresh niggles to begin with...

Edited March 17, 2017 by dpaws

[MtB]

Have you bought the Redshaw samofa then???!!

One way of checking for slip is to buy a engine timing strobe. Mark the flywheel and the propshaft, and measure the speed of both whilst in astern.

Do you have a 1:1 transmission or is it 2:1 reduction? If the latter then that blade isn't quite so insane  

[Guest]

9 minutes ago, Mike the Boilerman said:

Have you bought the Redshaw samofa then???!!

One way of checking for slip is to buy a engine timing strobe. Mark the flywheel and the propshaft, and measure the speed of both whilst in astern.

Do you have a 1:1 transmission or is it 2:1 reduction? If the latter then that blade isn't quite so insane  

Well spotted indeed - and they've mated it with a PRM500, not an easy task by all accounts with a fair bit of machining involved for the adaptor plate. There's a thermostart fitted too as I understand from a Dutch friend that they can be a bitch to start when it turns really cold. The extra flywheel groves are for the 5kW AC generator.

2:1 for the Blackstone - I'll mention the bands and the strobe to check it before it comes out, good thinking!!

[MtB]

On 17/03/2017 at 23:31, dpaws said:

Well spotted indeed - and they've mated it with a PRM500, not an easy task by all accounts with a fair bit of machining involved for the adaptor plate. There's a thermostart fitted too as I understand from a Dutch friend that they can be a bitch to start when it turns really cold. The extra flywheel groves are for the 5kW AC generator.

2:1 for the Blackstone - I'll mention the bands and the strobe to check it before it comes out, good thinking!!

 

You're too kind. But thinking tends to get one into trouble sometimes so is best avoided in my experience...

Another way is a £3 ebay bicycle speedo/computer, and a couple of little neodymium magnets on the flywheel and propshaft.

[Guest]

 

6 minutes ago, Mike the Boilerman said:

But thinking tends to get one into trouble sometimes so is best avoided in my experience...

You do have a point.... 

Is "Samantha" still part of your plans Mike? If I recall you have an original 2:1 gearbox with yours?

[MtB]

On 17/03/2017 at 23:49, dpaws said:

 

You do have a point.... 

Is "Samantha" still part of your plans Mike? If I recall you have an original 2:1 gearbox with yours?

 

I still have her on a trailer in my garden. No boat to put her in though. And yes, the real original gearbox (but no electric start).

[Guest]

Finger's crossed a hull comes up - at least you know where there's a spare mechanical box in the UK, should the need arise

I hadn't realised that Lincoln Keels used the JP3M, a better suited craft for the power available. Spoke with the owner this morning, 

"She has a 2:1 reduction box (mechanical). Originally it was a 3 bladed 28" prop of unknown pitch. It now has a 26" 4 blade prop of 17" or 18" pitch. Forwards isn't too bad, stopping is interesting and there is a reasonable amount of prop walk."

He seems content with the power on hand, but is also considering an extra cylinder when  the time comes for Thames stretches etc.

I credited the forum (thanks again Lodden) for the bands slipping possibility idea that I mentioned in response, just in case...

http://misterton.squarespace.com/

Edited March 18, 2017 by dpaws

[davidg]

On ‎3‎/‎17‎/‎2017 at 18:12, dpaws said:

The prop could be way too fine, but then that doesn't tie in with the complete lack of reversing bite...

5 gets you 10 it's slipping in stern gear. You can adjust it by taking the top off the box and winding down the adjusting screw a little bit. Don't overdo it or the stud will rip out of the bottom half of the gearbox casing (don't ask...)

[GRLMK38]

I have read this with interest but it seems to stop in mid-flow back in March 2017.  Have all the changes now been made to Canopus (rudder, prop, engine etc.) and has it resolved all of the issues reported by the OP?

 

[MtB]

1 minute ago, GRLMK38 said:

I have read this with interest but it seems to stop in mid-flow back in March 2017.  Have all the changes now been made to Canopus (rudder, prop, engine etc.) and has it resolved all of the issues reported by the OP?

 

 

I suspect not as Canopus was still moored on Roger Farrington's wharf last time I passed, not long before xmas!

[matty40s]

The boat is currently being worked on in Braunston. Everything was delayed due to Roger Farringdons illness and was restarted again in the Autumn. The back cabin has been reconfigured and a new engine dropped in. 

[MtB]

Just now, matty40s said:

The boat is currently being worked on in Braunston. Everything was delayed due to Roger Farringdons illness and was restarted again in the Autumn. The back cabin has been reconfigured and a new engine dropped in. 

 

Really??

Last I heard was DPaws had bought a vintage Samofa like mine, restored by Tony Redshaw.