How wide is a canal?

[Guest]

We know the lock dimensions, but in general, how wide are our canals?

 

There's a lot of variation I am sure, but could we say for example 40% are 12 meters wide, 50% are 18 metres wide etc - really, I've no idea of the numbers! Depth too? generally 3.5ft to 5ft in the centre channel?

 

I ask because a naval architect has kindly offered to estimate the squat on a hull design, and to do it he also needs to know dimensions of the waterways...

 

Much obliged

 

 

[Dalslandia]

Interesting question.

[matty40s]

Is the squat a new term for a london based boat hull with a tent on it??

[David Mack]

You can measure the widths of he canals you boat on on Google Earth. Depth varies quite a lot, but I would guess around 1.2m in the middle over a width of say 3m, then sloping up to anything between 0 and 0.6m depth at the sides, and a little deeper at some designated moorings.

[Loafer]

Brindley's original spec, for the T&M, included the ability for 2 x 3' draft boats passing each other, IIRC. That'd mean 15' across before it starts to shallow.

[Guest]

Well, I'd guessed at 13m because I used to fish with poles, and they were 13m for the UK canals, lose the metre that hangs over your leg and that's 12m out in front of you, onto the far ledge... 3m seems a bit of a squeeze... is that big beautiful aquaduct in Wales that I can't pronounce about 3m across the channel?

[Paul C]

The Middlewich branch of the SU is a narrow canal, and is 32' wide in the piled sections, although there is an amount of variation here. That should give a reasonable starting point.

[Guest]

Thanks Paul, that's starting point - top of your head, % of canals that are narrow, in length, out of the whole system, just ball park?

[Paul C]

If you Google around, there's a handy map of the UK canal network, with colour codes for broad and narrow ones. That would save me guessing.

[Tony Dunkley]

Leaving aside that calculating 'squat' for a canal boat is completely pointless, the width of any canal is irrelevant and meaningless for the purposes of your squat calculation, . . . cross sectional area below water level is the only influencing factor.

[Keeping Up]

IIRC the Grand Union Canal was specified to be 45ft wide.

 

I am struggling to remember the width of the "deep" section in the middle; I think it was 22ft6in, which was originally that width to allow to 7ft narrowboats to pass easily, but which led them to experiment with a coulple of wide boats (such as "Progress" on the basis that a wide boat and a narrow boat would just be able to pass each other even if they were fully loaded, and that there would only be a small number of wide boats so the chances were that one of them would be only lightly loaded if they ever they passed each other.

 

There was of course in theory no reason why a boat would ever need to come to either bank, except at a wharf etc (nobody moored overnight anywhere except the recognised places) therefore threre was not much depth at either edge.

[Guest]

Leaving aside that calculating 'squat' for a canal boat is completely pointless, the width of any canal is irrelevant and meaningless for the purposes of your squat calculation, . . . cross sectional area below water level is the only influencing factor.

 

Thanks for your thoughts Tony, though it's strange that this chap would ask me for such variables if they weren't relevant. Especially that he's one of the world's leading Professors in the subject...

 

Recent research papers include those concerning ship squats for the QE2 and QM2.

 

Of course the boundary position is important! A canal can be considered as a confined channel (different line to open conditions, that's a hint...)

 

Edited February 23, 2016 by dpaws

[Guest]

IIRC the Grand Union Canal was specified to be 45ft wide.

 

I am struggling to remember the width of the "deep" section in the middle; I think it was 22ft6in, which was originally that width to allow to 7ft narrowboats to pass easily, but which led them to experiment with a coulple of wide boats (such as "Progress" on the basis that a wide boat and a narrow boat would just be able to pass each other even if they were fully loaded, and that there would only be a small number of wide boats so the chances were that one of them would be only lightly loaded if they ever they passed each other.

 

There was of course in theory no reason why a boat would ever need to come to either bank, except at a wharf etc (nobody moored overnight anywhere except the recognised places) therefore threre was not much depth at either edge.

 

Great job - that's broad and narrow sorted, close enough! That centre section sounds about right, again from fishing days - thanks all

[Tam & Di]

Has your professor any experience of cruising on UK canals? What sort of boat are you designing where squat is going to be a significant factor when cruising at up to 4mph? I don't think you can get the QE2 or QM2 onto UK canals, and their characteristics have little relevance to a canal boat on a shallow muddy ditch.

 

Tam

Edited February 23, 2016 by Tam & Di

[Tony Dunkley]

 

Thanks for your thoughts Tony, though it's strange that this chap would ask me for such variables if they weren't relevant. Especially that he's one of the world's leading Professors in the subject...

 

Recent research papers include those concerning ship squats for the QE2 and QM2.

 

Of course the boundary position is important!

 

Your Professor would want the width, along with the depth and bottom profile for calculating the cross sectional area. Knowing the width and greatest depth alone would not be sufficient to do so.

Just out of curiosity, . . . what do you intend to do about the calculated squat after he comes up with a value for it on various different canals, and how will he incorporate a variable into the calculations to compensate for the difference in cross sectional profile between today's undredged canals and the original profile when they were dug ?

Edited February 23, 2016 by Tony Dunkley

[Tam & Di]

He'd also need to know the engine size, trim of the boat and proposed speed - a boat which has sufficient water to float in and being moved manually at extremely slow speed will have zero squa, where a boat with 12" of water beneath it and a powerful engine can sit itself on the bottom at maximum revs - but I still fail to see the relevance of performing the calculations.

Edited February 23, 2016 by Tam & Di

[Guest]

Has your professor any experience of cruising on UK canals? What sort of boat are you designing where squat is going to be a significant factor when cruising at up to 4mph? I don't think you can get the QE2 or QM2 onto UK canals, and their characteristics have little relevance to a canal boat on a shallow muddy ditch.

 

Tam

 

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.

[dor]

Why not ask for a few examples? For example, I reckon the back end of my boat will squat down about three inches at three knots in three foot of water. The width of the canal, as requested in your thread title, makes bugger all difference.

 

The width, depth and profile of British canals is so variable that I do wonder what your good professor is trying to achieve.

Edited February 23, 2016 by dor

[Guest]

Why do you think this chap would ask specifically for the width of the canal if it wasn't relevant to the question?

 

Qualifications:

 

1977 - FRINA and C.Eng.
1977 - Ph.D. in Naval Architecture.
1967 - M.Sc. in Naval Architecture.
1963 - B.Sc.(Honours) in Naval Architecture.
1959 - HNC (two endorsements) in Naval Architecture.
1958 - HNC in Naval Architecture.
1955 - ONC in Naval Architecture.

 

Edited February 23, 2016 by dpaws

[Jerra]

. is that big beautiful aquaduct in Wales that I can't pronounce about 3m across the channel?

It seems a shame nobody has given an answer to this. It is single file so not 3m I would guess at about 8 feet in old money.

[dor]

Qualifications:

 

1977 - FRINA and C.Eng.

1977 - Ph.D. in Naval Architecture.

1967 - M.Sc. in Naval Architecture.

1963 - B.Sc.(Honours) in Naval Architecture.

1959 - HNC (two endorsements) in Naval Architecture.

1958 - HNC in Naval Architecture.

1955 - ONC in Naval Architecture.

 

Now, why would he ask specifically for the canal width if it wasn't relevant? Strike you as a casual, joker of a man?

Using a black font on a dark blue background but I think you were asking a question about why he should want to know the width of the canal. I am sure many others here, as well as myself, would be interested to know why he would want to know the value of such a variable parameter.

[Guest]

Why not ask for a few examples? For example, I reckon the back end of my boat will squat down about three inches at three knots in three foot of water. The width of the canal, as requested in your thread title, makes bugger all difference.

 

The width, depth and profile of British canals is so variable that I do wonder what your good professor is trying to achieve.

 

How much force does it take to displace an extra 3" on your hull?

[dor]

It seems a shame nobody has given an answer to this. It is single file so not 3m I would guess at about 8 feet in old money.

The width of the channel is actually about 9 - 10ft as the 'towpath' is actually a platform cantilevered out over the channel.

[Tony Dunkley]

 

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.

 

If you really want to make a thorough and worthwhile job of this, you will need to include some calculations on the frictional resistance arising from the hull graunching it's way over all the junk that the cut's full up with in addition to all the mud.

To help in reducing the frictional resistance values caused by this, I would suggest some sort of non-stick, low friction coating, similar to that used on frying pans, being applied to the bottom of the boat before launching.

[dor]

 

How much force does it take to displace an extra 3" on your hull?

This I think reveals that perhaps you are not familiar with the hydrodynamics of your typical British narrowboat. Under way it is only the stern that will dip; the rest of the brick stays pretty much were it was. Much of the 'squat' comes from lowering of the surface, although deep-draughted boats are known to be put out of gear when going through shallow bridge holes to allow the skeg to lift a little. As for the amount of force, probably about one horsepower when under way.