How wide is a canal?

[Guest]

Is squat always a BAD THING?

 

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

 

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!

 

From my perspective from hull hydrodynamics then yes, squat is always a bad thing because it consumes energy and reduces efficiency - but riding the bow wave and surfing over humps does sound like a whole load of fun!

 

By the sounds of it the odds are stacked very well against me - maybe my best chance would be to start the event at the aforementioned venue, it could level the playing field...

[RLWP]

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.

 

Actually, they do exactly that. You create a theory, devise an experiment and use the real world to prove or disprove your theory

 

I'm going to go back and ask you something again. What is your experience of canal boats please? I notice you have taken your location from your profile which from memory isn't the UK

 

Richard

[Guest]

You are correct, I am not UK based. I have minimal experience on UK canals, although we've transited the Suez a number of times but the Panama only the once to date.

 

Our forum colleague and good friend Jan however has huge experience, and he shares my faith in formula - does that make him correct and me wrong?

Edited March 7, 2016 by dpaws

[RLWP]

You are correct, I am not UK based. I have minimal experience on UK canals, although we've transited the Suez a number of times but the Panama only the once to date.

 

I'm wondering how you can properly come up with the right criteria for modelling something you have no experience of

 

Richard

[Guest]

 

I'm wondering how you can properly come up with the right criteria for modelling something you have no experience of

 

Richard

 

I consult people with huge experience of relevant test conditions.

 

Here "as an example of a direct comparison" we have people considering two boats of 55' and 71'6" LOA respectively to be indistinguishable, furthermore basing their opinions on this assumption.

Edited March 7, 2016 by dpaws

[RLWP]

 

I consult people with huge experience of relevant test conditions.

 

Here "as an example of a direct comparison" people consider two boats of 55' and 71'6" LOA respectively to be indistinguishable, furthermore basing their opinions on this assumption.

 

Yet you reject people with experience of the boats you are modelling in favour of people who can manipulate computer models. You are putting your faith in the computer model but don't want to put in the real world factors that will give a reasonable answer

 

Richard

[Guest]

Not at all Richard, but you have to sort the wheat from the chaff. Misinformation and unrealistic comparisons are not the sources of raw data that I wish to back with my personal investment.

[RLWP]

In which case, like it or not, Tony is dealing in wheat not chaff.

 

I'd happily make some guesses as to what might be included in a computer model, Tony will tell your exactly what he has experienced making a difference. Take that and use it to form theories to produce models that confirm Tony's observations. Then you know you have a valuable tool to do the rest of your hull optimisation. Given a choice between my guesses and Tony's facts you'd be a fool to choose guesswork

 

If you'd like to do some study on your own, get a copy of this:

 

 

http://www.amazon.co.uk/Boaters-Boating-Christopher-Norton-Deuchar/dp/0953151204/ref=asap_bc?ie=UTF8

 

Chris also has experience of handling boats and has written down his observations for others to read and try for themselves. I have tried some of Chris's theories and found them to work on our boat

 

Richard

Edited March 7, 2016 by RLWP

[Guest]

Thank you - that looks to be a useful source of reference that had escaped me - it's now on order, should make the night watch at anchorage pass far quicker!

[hughc]

dpaws you have obviously misread my post. I was not, as you must be aware, directly comparing boats of different lengths. The scientific method relies on observation followed by the determination of a theory which can be tested by experiment. You appear to have missed out step one. Regards, HughC.

[Guest]

dpaws you have obviously misread my post. I was not, as you must be aware, directly comparing boats of different lengths. The scientific method relies on observation followed by the determination of a theory which can be tested by experiment. You appear to have missed out step one. Regards, HughC.

 

Well I must have Hugh, because of my reaction to the post.

 

You said that the squat on the finer and shorter Avon boat was significantly greater than on the larger buffer Banstead.

 

You supported TD's comment that the squat calculation formulae are completely wrong and irrelevant to

canals. "Tony Dunkley is, as one would expect, absolutely correct... "

 

You then subsequently contradict that by supporting the formula by observing "Our fine lined modern tug has the same problem; the shallower the water the greater the squat"

 

The comment about the two boats in comparison supports it too. The shorter boat has a higher Cb despite it's finer lines than the longer working boat. The squat formula supports this, it uses Cb as a factor. The length is more important in the Cb determination than the curves in the hull.

 

The thing that confused me was your support for TD who was against the formula, when your two examples both confirm the same formula previously rejected. That puts you in conflict with TD...

Edited March 7, 2016 by dpaws

[Tony Dunkley]

 

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.

 

 

Is that remarkable, and completely incorrect, statement something else that you and your professor have worked out ? In contrast with your ideas and theories, everything I've said, or any opinion on offer, has it's origins in first hand, practical experience of the subject in hand

 

There were some hints and clues for you in my Post #211, and other members have provided you with some more, but despite knowing even less about me, and how I was earning a living 50 plus years ago, than you do about English canals, you consider that half-arsed theories are more credible than first hand experience of operating and working the different types of boats mentioned when time was money, and something over which a boat's carrying, operating and handling characteristics had considerable influence.

 

You're by no means the first theory peddling know-all to come along with weird ideas about canalboat design, and you probably won't be the last, but I think you're in with a fair chance of adding to the list of some of the more notable balls-ups of more recent times, one of the most recent and spectacular of which originated from a reputable Naval Architect who designed some new-build boats for a gravel carrying contract on the southern Grand Union. The boats were utterly useless, and were comprehensively outdone in operation, by a 1950's built Leeds and Liverpool shortboat and a newly built copy of a big Northwich.

[hughc]

ammodels.co.nr

[Paul C]

The theories and the science (hydrodynamics) behind them are absolutely 100% robust, I have no bother with that and I think you'd be a fool to say they were wrong. After all, they're derived from the laws of physics.

 

HOWEVER its their applicability to a canal boat on a canal, which is the issue here. Basically, I still don't know what you're trying to achieve or why. And if you're trying to improve something, I don't think you've even quantified the baseline your trying to better adequately. Until we know exactly what you're trying to achieve, then I'd say you've not applied the theory to the practical considerations of the issue at hand. This means that no matter how good the theory is, its somewhere between irrelevant and vaguely useful.

[Guest]

I recognise the risk of failure, but I also recognise the potential reward.

 

Canals have changed and are now shallower than before when the traditional designs were conceived. This change means that squat as an energy consuming phenomena has a greater relevance today than it had back in the 30's.

 

If I commissioned a heritage replica for a new build then it would be less suited to the water that it's going to spend it's life in. But, if we're going to modify an original hull by ANY dimension then we step into the unknown as far as it's new shape will handle and how it will perform - I think we can agree so far, at least up to this point.

 

Now I can follow two paths, as the builder to do what he things would be best, or I can get lost in theory etc.

 

So, logically, I initially took the easier route and started to ask A list builders as to how they'd adapt a traditional design, with particular attention to hull squat. I didn't get the answers form the people who I'd hope could answer them, and with hindsight, that's maybe a fair result, because a gifted metal fabricator, as all of the A listers are, are not obliged to understand the mechanical principal of squat.

 

I have therefore decided to learn a little about it myself, so that I can understand how you would go about optimising a narrowboat hull from the perspective of minimising squat - I need to modify it anyway to have a shallower draft, so I may as well make these modifications as beneficial as possible.

 

I can then support a fabricator and guide him accordingly, and the final hull would be net result of some useful theory and some invaluable experience.

 

An obvious example would be the knowledge that a simple shallow V in the base plate will lower squat and save me fuel, because the Cb will be less etc etc

Edited March 7, 2016 by dpaws

[hughc]

Add trim tabs to the rearward portion of the swim. Adjust the size and angle of these until the squat disappears. Two small ones on Wyrd lift the back end by about 1/2" at normal cruising speed, about 3mph I guess. Consider thin film hydrodynamics because the skin drag which IIRC varies as the square of the difference between the water flow and the hull speed is a vital factor. If the equations don't drop out add more terms until they do. HughC.

[Paul C]

 

If I commissioned a heritage replica for a new build then it would be less suited to the water that it's going to spend it's life in. But, if we're going to modify an original hull by ANY dimension then we step into the unknown as far as it's new shape will handle and how it will perform - I think we can agree so far, at least up to this point.

 

 

Complete bollocks - there's 30,000+ boats on the canal system, and old ones plus their "heritage replica" sisters are a small fraction of that. There's plenty of empirical evidence on hull shapes and variations of draft, evidence that the hull designer/builder knows and uses to influence their hull designs. Its not rocket science to see that as boats have changed from being working boats (where their cargo carrying capacity would have been an important factor) to leisure boats (no such importance to their tonnage) their draft has reduced. And the draft, prop size, engine choice and gearbox ratio are all inter-related anyway. As far as hull shape goes, its so weighted towards 1) fitting in the lock and 2) providing good accommodation space against hull efficiency in moving at speed, that any improvement in efficiency is going to massively affect its interior space (IMHO). For example, even a shallow V hull vs flat bottomed, causes much complication in interior fitout.

 

Looking back at the previous pages, you seem to have settled on using a figure of 4mph to base a lot of your assumptions on. The simple fact is, canal boats don't go this speed on canals! There's a lot of reasons why. Re-evaluate your assumptions based on 2.5mph and I reckon the importance of squat will be pretty much negligible. By all means do the sums...but show your workings out...

[Tony Dunkley]

The theories and the science (hydrodynamics) behind them are absolutely 100% robust, I have no bother with that and I think you'd be a fool to say they were wrong. After all, they're derived from the laws of physics.

 

HOWEVER its their applicability to a canal boat on a canal, which is the issue here. Basically, I still don't know what you're trying to achieve or why. And if you're trying to improve something, I don't think you've even quantified the baseline your trying to better adequately. Until we know exactly what you're trying to achieve, then I'd say you've not applied the theory to the practical considerations of the issue at hand. This means that no matter how good the theory is, its somewhere between irrelevant and vaguely useful.

 

In fact, he isn't getting the theory right either, as this remark from Post #236 demonstrates :~

" The shorter boat has a higher Cb despite it's finer lines than the longer working boat." . . . which with a little thought, and consideration of what Cb is, can be clearly seen to be the exact reverse of the reality.

 

The value for Cb [block Co-efficient] is the greater for the longer bluffer ended vessel in comparison with the shorter finer ended one.

Block Coefficient [Cb] is defined as ~ The ratio of the immersed volume of the hull to the product of the length, breadth and draught, ie., the circumscribing 'block'.

Edited March 7, 2016 by Tony Dunkley

[Guest]

I completely agree that everything is a compromise, when you optimise in one direction you inevitably compromise in another. That's why it's important to quantify these effects, and weight their importance.

 

The squat graph can at least provide some assistance when estimating the effect, and yes, the location locally will be an influence, the more boats moored up, the slower the cruise. The interior design does provide a satisfying logical puzzle, but with persistence a decent layout can be achieved even fine curves.

[RLWP]

I recognise the risk of failure, but I also recognise the potential reward.

 

I'm completely at a loss as to what the potential reward might be.

 

You will probably come up with a hull design that is very expensive to make and saves a very small fraction of a litre per hour. In other words, something radical with a very long payback time. In addition, it's unclear what the stability or practicality of such a hull will be

 

Richard

[Dalslandia]

An invisible green one for Paul,

One way to have a shallow v is to keep the floor where it is and ad a few inch in the middle of what is the base plate. draft will increase but it also make more room for a bigger prop. ( I am not talking about 30" D)

 

My self that never been on an English narrow canal, (but did visit a NB when they was here) would like to go one day, one week or one year on the English canals, when I don't have to work in the summer season.

 

I support dpaws in his search for how and why, to make a better boat if it is possible, thats what he seaks out, So we with more or less boating years under the sun and ambrella, should not stamp on him because he want to learn and see if it is possible to make it better, or something that fitts his idea of boat, many NB looks about the same, but there are hardly two that is the same, and that would have been booring if they was.

It might be so that his finding, point in the direction of a specific well proven design, but he and we don't know what make it better then other similar boats.

 

Nothing wrong with learning. by saying that "he is wrong it can't be any better then it is today", is not an answer, just an excuse, but if someone can say if you make the swim like this and the bow like this, it perform better because this vill happen! then he or she don't just get a green one but a bottle of single malt,

Adults that jump on other people when they try to learn or make something better is somewhat interesting in it self, but not for this forum.

Edited March 7, 2016 by Dalslandia

[Guest]

 

In fact, he isn't getting the theory right either, as this remark from Post #236 demonstrates :~

" The shorter boat has a higher Cb despite it's finer lines than the longer working boat." . . . which a little thought, and consideration of what Cb is, can be clearly seen to be the exact reverse of the reality.

 

The value for Cb [block Co-efficient] is the greater for the longer bluffer ended vessel in comparison with the shorter finer ended one.

Block Coefficient [Cb] is defined as ~ The ratio of the immersed volume of the hull to the product of the length, breadth and draught, ie., the circumscribing 'block'.

 

I do apologise, I wasn't concentrating (we have Port State inspection in progress) - thanks for picking that up.

 

The Froude number for the longer hull is lower. For given conditions, the higher the Froude number the greater the wave resistance. Your results may suggest that the squat influence on in these conditions was less influential than the forward wave resistance?

 

I don't dispute your evidence, I merely want to understand as to why it has occurred.

[dave moore]

I'm not surprised that you have had scant response from those you call A list builders. Most would be reluctant to alter their designs, their reputation is based on their product. Whilst boatbuilders are fabricators, few fabricators are boatbuilders....the few in the latter group have an eye for balance and proportion only found in top end boats.

 

Whilst Tony may have a somewhat acerbic approach in his posts here, his experience is hard won and based in the real world of canals, rivers and boats. I knew him in the 60s when he was commercial boating and I have much respect for his opinions. Others who have shared real world experiences are also worth listening to in my opinion.

 

Dave

[Guest]

It's a personality thing Dave, I switch off when people tell me that proven equations and renowned Professors are all wrong.

 

Factors may have a smaller or larger influence on proceedings than first imagined, that's fine, maybe to suggest that someone reconsiders the weighting of relative arguments is great advice, but what's correct is correct, I'm no Katharina...

 

Then, God be bless'd, it is the blessed sun:

But sun it is not, when you say it is not;
And the moon changes even as your mind.
What you will have it named, even that it is;
And so it shall be so for Katharina.

 

(Shakespeare, 1590)

[Paul C]

Is anyone actually saying the laws of physics are wrong on this occasion? Which reminds me, I've seen none of your calculations or workings out.