How wide is a canal?

[Guest]

 

I really wish I could understand that, Dals. It sound so true, but I'm not sure where. The only word I knew was 'washout'!

 

Is it related to scrumpy cider? Only I've felt that way on many mornings....

[RLWP]

 

I really wish I could understand that, Dals. It sound so true, but I'm not sure where. The only word I knew was 'washout'!

 

And I bet we both misunderstood it

 

Richard

[Loafer]

 

And I bet we both misunderstood it

 

Richard

 

I'm thinking it may be the way that the angle of attack reduces toward the tip, to prevent all sorts of radius-related rotational snags.

[Dalslandia]

 

I really wish I could understand that, Dals. It sound so true, but I'm not sure where. The only word I knew was 'washout'!

 

just some mix of plane airplane talk and propeller head talk, it washout those that don't fly and/or don't make propellers, but it is all there, just sort out the mud from the water, and it will be clear as ...

Edited March 6, 2016 by Dalslandia

[RLWP]

 

I'm thinking it may be the way that the angle of attack reduces toward the tip, to prevent all sorts of radius-related rotational snags.

 

Probably...

 

This Shepherd Neame is nice stuff

 

Richard

 

hic

[Dalslandia]

More serious.

 

If a wing or propeller blade, have the leading edge (LE) bent down, a little, the reduced angle delay stall or cavitating. to much and stall/cavitating will accure on the underside. at some angles. To much bend and the upper side curvature will produce large under pressure and cavitate.

 

If the trailing edge (TE) is bent down, like a cupped propeller, it increase pitch, and the forward part from the cup of the blade can have less angle and still make the same thrust, the result is less cavitating.

 

if the TE is bent up, the thrust or lift, become less and the rest of the blade need to be angled more to make the same thrust. more cavitating in the forward part.

 

In reverse the cupped will be less efficient, the S curved airfoil will be just as good as in forward gear.

but the period we are in reverse gear is very small compered to forward.

 

A propeller with narrower tips will make more of the thrust halfway between hub and tip, and less of the tip area will be effected by the drag making tip vortex and cavitating

Edited March 7, 2016 by Dalslandia

[Loafer]

More serious.

 

If a wing or propeller blade, have the leading edge (LE) bent down, a little, the reduced angle delay stall or cavitating. to much and stall/cavitating will accure on the underside. at some angles.

 

If the trailing edge (TE) is bent down, like a cupped propeller, it increase pitch, and the forward part from the cup of the blade can have less angle and still make the same thrust, the result is less cavitating.

 

if the TE is bent up, the thrust or lift, become less and the rest of the blade need to be angled more to make the same thrust. more cavitating in the forward part.

 

In reverse the cupped will be less efficient, the S curved airfoil will be just as good as in forward gear.

but the period we are in reverse gear is very small compered to forward.

 

A propeller with narrower tips will make more of the thrust halfway between hub and tip, and less of the tip area will be effected by the drag making tip vortex and cavitating

 

What's a 'cup'? I'm almost with you, apart from that.

 

Also, I am completely in awe of your understanding in technical English Language. Greenie for that alone.

 

(I am genuinely trying to understand your propeller theory, with my having been flying aircraft that had turboprop engines, with constant rpm, variable pitch arrangements.

[Dalslandia]

 

What's a 'cup'? I'm almost with you, apart from that.

 

Also, I am completely in awe of your understanding in technical English Language. Greenie for that alone.

 

(I am genuinely trying to understand your propeller theory, with my having been flying aircraft that had turboprop engines, with constant rpm, variable pitch arrangements.

 

http://www.mercuryracing.com/prop-school-part-4-blade-cup/

 

http://atljsoft.com/html_help/propeller%20geometry.htm

​

Edited March 7, 2016 by Dalslandia

[Loafer]

 

http://www.mercuryracing.com/prop-school-part-4-blade-cup/

 

http://atljsoft.com/html_help/propeller%20geometry.htm

​

 

OK i get that. Is it a bit like the underside of a glider's wing, i.e. a concave surface on the underside?

[colinwilks]

............

 

Do you know, I'd love to see a lock challenge, time trail style - problem is I guess it'd use up too much water - but it would be fun - I'd put some money on Roger Fuller - who would you back? ........

 

I've ordered a trolling valve on the PRM to help out when locking solo...

Good morning,

 

I think you might find the annual BCN Challenge fits the bill. It's over the w/e of 28th/29th May this year.

 

See http://www.bcnsociety.co.uk/

 

Whom would I back? Well when your boat is afloat come back to me for a wager on the BCN Challenge, say all the Batham's you can drink in one session, losing crew pays?

 

Mmmm, trolling valve. I've often thought this forum could use one of those to differentiate the sardonic from the sarcastic to the down right rude!

[Tony Dunkley]

 

squat graph.jpg

 

Cb is the block co-efficient, the finer the boat hull, the lower the Cb and thus less squat.

 

~ wrong

 

 

If you've got a boat that is less fine than my design or the quoted designs of the wooden boats from the turn of the century then this squat will be more,

~ wrong again

 

The above quotes from you may be what happens in theory, and in the minds of you and your professor, but in practice it's the complete opposite of what happens, or more precisely what used to happen, with real narrowboats on real canals.

As you are already aware, carrying/working boats built and operated by different companies all varied considerably in hull form and back when all the different types [ ex. FMC, ex. GUCCCo., and the BW Admiral motors] were still at work together on the same canals at the same time it was possible to make practical, in-service comparisons between them based on how well they performed at work doing what they were designed and built for.

When comparing the merits of different types of narrowboat in the real world, there was only one thing taken into consideration, and that was ~ which sort of motor will get you round a pound better and faster than anything else ? ~ and the answer was that, empty or loaded on most canals, and with comparable engines and sterngear, the boats with what you call " finer" hull shapes [lower Cb value] invariably came off worst, with Woolwich or Northwich motors markedly better than FMC motors except on rivers or exceptionally deep lengths of canal, and the ugly, bluff ended 'Admirals' leaving everything else for dead on the shallower and smaller canals, but very soon left behind by everything else as the depth and size of the canal varied and increased.

What better way of comparing the efficiency [encompassing such as all the different sorts of hull resistance as well as 'sguat'] of different hull shapes and designs could there be ? All your theories, graphs and calculations are utterly meaningless and completely wrong.

Edited March 7, 2016 by Tony Dunkley

[Dalslandia]

 

OK i get that. Is it a bit like the underside of a glider's wing, i.e. a concave surface on the underside?

 

Right, it gives more camber, rear camber, rear load, that lessen the forward load and cavitating. If compeering a cupped propeller and Axiom, think 15m class with flapped wing, negativ flap is Axiom, positive flap is Cupped. If we satt negative flap the wing need more alpha to make same lift, (or increase speed)

[Guest]

 

 

All your theories, graphs and calculations are utterly meaningless and completely wrong.

 

I really don't have the motivation, please, direct your concerns to Dr C Barrass here bryan_barrass@hotmail.com - although I'm not sure that he'll agree with you either.

 

He is one of the world's experts regarding squat - but I'm not so convinced that he will have heard about your work in this field of hydrodynamics.

 

Some say the earth is round too, such heathens...

Edited March 7, 2016 by dpaws

[RLWP]

 

I really don't have the motivation, please, direct your concerns to Dr C Barrass here bryan_barrass@hotmail.com - although I'm not sure that he'll agree with you either.

 

He is one of the world's experts regarding squat - but I'm not so convinced that he will have heard about your work in this field of hydrodynamics.

 

Some say the earth is round too, such heathens...

 

Except you are ignoring Tony's real world experience of handling boats.

 

You can construct a model to simulate what a boat is doing on a canal but in doing so you have to make a lot of assumptions and simplifications. That's what modelling is - a means to get an answer. What Tony is telling you (in his own inimitable way) is that all attempts in the past to do this have failed because the assumptions and simplifications made are ignoring factors that make a large difference to the performance of the boat.

 

Richard

[Guest]

There are so many variables, as members have taken lengths to point out - so, prove it. Model the different hulls in scale, produce test data and I'll happily have a look at the data. Other than that thank you, but no, I'm not interested.

 

When you observe an effect then there must be a reason for that effect, and it must be possible to explain that effect mathematically. If all of these theories and formulae are rubbish then please, propose alternatives based on these experiences.

 

I hear the talk, (oh Gawd I hear the incessant nay slaying), I'm waiting for the evidence, the same as on previous posts....

 

Let's have some evidence eh?

[Guest]

Good morning,

 

I think you might find the annual BCN Challenge fits the bill. It's over the w/e of 28th/29th May this year.

 

See http://www.bcnsociety.co.uk/

 

Whom would I back? Well when your boat is afloat come back to me for a wager on the BCN Challenge, say all the Batham's you can drink in one session, losing crew pays?

 

Mmmm, trolling valve. I've often thought this forum could use one of those to differentiate the sardonic from the sarcastic to the down right rude!

 

Not sure about the Batemans, but a decent cider and I'd be happy to... once i've sussed my electric booster motors...

 

I've no doubt that the boat will kick ass, I'm not so sure about the general knowledge questions on UK canal history... are we allowed to ask the audience?

[ChimneyChain]

God I'm surprised you got any one helping you with an attitude like you've got.

 

Darren

[cuthound]

The problem lies, not with the modelling of various hull forms, but with modelling the canal itself.

 

This will vary on depth, width, and solidity of the bottom, even in a small stretch of canal, and that's without modelling the plastic bags, bits of old rope, bicycles and shopping trolleys!

 

You are putting way too much faith in academics, trust me. The last company I worked with bought into a green energy idea from a Danish university, involing running stirling engines on the gas produced by burning wood chip, to produce a small amount of electrical energy and a lot of hot water.

 

The real engineering problems resulting from things not included in the original model, broke both the Danish university offshoot company and the company I worked for.

[X Alan W]

 

I have every confidence of his abilities to resolve the physics for the canals... the prestigious projects illustrate his standing amongst current naval architects. The Polish Marine research paper regarding squat suggests that, as a resistance to forward motion, it's far more significant than the hull form itself in shallow muddy ditches.

 

What to do with the value he suggests? Well many things, I would hope, for example, prop calcs are based on hull resistance alone, could be a bit of an oversight maybe?

 

One of the UK's leading prop manufacturers certainly agreed with my thinking, "one of only a handful of boaters to understand in his 20 years of experience on the canals" - which I took as a sweet compliment.

I have no doubt your guy is great with the theory, but all the calculus will not be of much use when you are sat on a load of bridge coping stones/shopping trolleys & general canal crud I would guess my canal theory would be If it's floating moving "Yipee" if it's stuck " Oh Bu***r" whats the best/easiest way to get it free Happens more often the deeper the draft.

[Guest]

 

Except you are ignoring Tony's real world experience of handling boats.

 

You can construct a model to simulate what a boat is doing on a canal but in doing so you have to make a lot of assumptions and simplifications. That's what modelling is - a means to get an answer. What Tony is telling you (in his own inimitable way) is that all attempts in the past to do this have failed because the assumptions and simplifications made are ignoring factors that make a large difference to the performance of the boat.

 

Richard

 

No, I disagree - Tony hasn't handled all of these boats on a comparable stretch of water in repeatable conditions, will all other things equal apart from the hull form, and in particular the Cb. Obviously I would expect a difference in performance between the hull forms, but there will be something responsible for this difference in performance, and it should be possible to explain why, even if it's only an educated guess.

 

The difference will not be down to the Cb value of the hull. The bigger the hull, the more water it needs to push out of the way. Try it in the bath, more your hand through the water, feel the resistance. Put on many pairs of gloves to make your hand bigger and try the same again. The only way the later would provide less resistance is if the fingers of the glove were opened.

 

In this case would it therefore be correct to summise that the larger glove offers less resistance without stating the relative conditions?

 

Open the window of the car when your driving, hold a clenched fist in the airstream and then open your fingers and offer your palm to the airflow - which condition causes your arm to dislocate?

 

The propulsive efficiency of larger propellors increases in deeper water, and when the props themselves are deeper in the water. For this reason I can accept that a loaded Woolwich would have a better performance than a canoe with an egg whisk, but the difference is not down to squat and Cb arguments.

 

"simplifications made are ignoring factors that make a large difference to the performance of the boat"

 

I totally agree, and one of those factors is called squat.

 

The Admiral Class boats performed better in shallower waters only serves to prove the point, the hull was smaller, it produced less squat.

 

The bigger the water the less the influence of squat.

 

The large traditional hulls have poor squat performance, but that's irrelevant in larger and/or deeper waters as the UKC is larger and the compounding effects of a confined channel are considerably reduced.

 

Remember, formulae are born when explanations are sought for real world observations, and real world data is considered when deriving formulae. People don't sit in an office and randomly invent a formula which they they go out into the real world to try and prove.

Edited March 7, 2016 by dpaws

[hughc]

Tony Dunkley is, as one would expect, absolutely correct. In the 'real' canal world the results are exactly opposite to the theoretical calculations. As an example of a direct comparison, which dpaws seems to think TD's explanation lacks : I have many times taken a very fine lined motor the Avon along the Erewash canal and as a direct comparison a GUCC motor , Banstead, along the same water. The squat on Avon was significantly greater and although the draught on both was similar the Avon was much more difficult to steer than Banstead. Our fine lined modern tug has the same problem; the shallower the water the greater the squat. Regards, HughC.

[Guest]

Our fine lined modern tug has the same problem; the shallower the water the greater the squat. Regards, HughC.

 

Yes, thank you - that observation corresponds perfectly to the published graph, which has been rejected as being incorrect...

 

I suspect that your observations may relate to the relative speed of the two vessels, the squat has a squared relationship with velocity, so speed variation has a huge influence. Without comparable hull speed data then the observations are open to misinterpretation, just as the "gloved hand" observation can be misinterpreted without the additional information declaring that the fingers were spread at the time of the observation.

 

"draught on both was similar the Avon was much more difficult to steer than Banstead"

 

The draft aft at the counter stern maybe, but what was the trim of the two vessels - was Banstead fully loaded i.e. at even keel? What was the forward draft of both vessels?

 

How do you steer a skateboard and how do you pivot a skateboard? Sit a hull on her arse with her bow in the air and she's highly manoeuvrable, she will have a lower Cb in a trimmed condition than a finer hull at even keel.

 

Naturally the squat will be less in the trimmed condition because the average draft will be less.

 

Do you have a link for the nb Avon, I'd like to understand the boat that you've mentioned.

Edited March 7, 2016 by dpaws

[colinwilks]

Is squat always a BAD THING?

 

I may be being unfair to you, but this seems to be your premise.

 

A real world example of where (I think) squat helped rather than hindered: Until CaRT dredged it last year and cleared the related silt trap there was an infamous scour at Wightwick Mill, just south of Compton on the Staffs & Worcester. Most leisure boats would pass over it with no bother, but we were on a loaded pair, down by the head and drawing well over 3' at the stern. The scour stopped us but we were able to back off. After a bit of thought we decided to untie the butty and allow the motor to take a run at it, winding right off and taking it out of gear just before we reached the scour. Result, the following wave, which I guess contains the water displaced by the squat, caught the boat up and carried it majestically right over the obstruction. Of course if our ploy had not worked we'd have been like Noah perched on the top of Mount Ararat, but it did and we weren't.

 

The same technique is handy when approaching suspect bridge holes (ie all of them) as it helps avoid the piles of bricks that seem to congregate there as well as reducing the risk of picking up the a selection of tee shirts, saris and fishermen's keep nets on the prop.

 

Regarding our wager, I know the Great Western at the top of the 21 stocks a variety of ciders, some of which don't make you go blind immediately, so I'm sure we'll find a suitable venue for settlement!

[hughc]

There is a photograph of the Avon on dock in the AM Models web site. As to trim both were trimmed as near as practically possible to level. the modern hull has a three foot draught over its whole 55' length. Regards HughC.

[Guest]

There is a photograph of the Avon on dock in the AM Models web site. As to trim both were trimmed as near as practically possible to level. the modern hull has a three foot draught over its whole 55' length. Regards HughC.

 

Thanks Hugh - I assume that Banstead is still 71'6"?

 

Google has failed me - do you have a link to the photo? Cheers

Edited March 7, 2016 by dpaws