How wide is a canal?

[Guest]

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.

 

Found it : The water runs through an iron trough that measures 11ft 10ins wide and 5ft 3ins deep

[Jerra]

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

Amazing I don't remember anything near a foot each side when we last crossed. Looks can be deceptive I suppose it seemed much nearer than a foot to 18 inches each side of the narrow boat.

 

Surely the channel refers to the "navigable" part. You wouldn't refer to part of the canal which was too shallow for a boat to float in as the channel would you?

 

The cast iron trough is possibly 10 feet.

[Guest]

 

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.

 

No, I meant, how much more ballast would you need inside your hull to increase the draft by 3"?

 

Does an aeroplane fly because the air has been lowered?

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.

 

I think dimples, like a golf ball should help.... About 9% fuel savings over 48 months for the slippy paint, in case you were curious...

 

 

(Apologies, really screwed up that edit!)

Edited February 23, 2016 by dpaws

[nicknorman]

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.[/size]1977 - Ph.D. in Naval Architecture. [/size]1967 - M.Sc. in Naval Architecture. [/size]1963 - B.Sc.(Honours) in Naval Architecture.[/size]1959 - HNC (two endorsements) in Naval Architecture. [/size]1958 - HNC in Naval Architecture. [/size]1955 - ONC in Naval Architecture.[/size]

 

The point is that it is a question much the same as "how long is a piece of string". There is no answer. You can pick a nominal value but it won't really have much bearing on reality as the reality on many canals changes every few metres. It is not even feasible to come up with an average figure without surveying every mile of every canal and navigable river, of which I think there are around 2500. Edited February 23, 2016 by nicknorman

[David Mack]

Amazing I don't remember anything near a foot each side when we last crossed. Looks can be deceptive I suppose it seemed much nearer than a foot to 18 inches each side of the narrow boat.

 

Surely the channel refers to the "navigable" part. You wouldn't refer to part of the canal which was too shallow for a boat to float in as the channel would you?

 

The cast iron trough is possibly 10 feet.

 

 

The water channel is the full width of the structure, but the towpath is built out over one side of the trough (not cantilevered, though, I think it has a series of vertical supports). The channel width at towpath level is not much more than 7 ft, so you won't have noticed a significant gap either side, but as far as water moving back past the boat is concerned, that has the full trough width including the bit under the towpath available, so that is the channel width for the purposes of the hydraulic calculations.

[Guest]

But I get that Nick, and he gets that, but we're playing with ball park numbers, they are interesting

 

How much of your power at the prop do you waste trying to pull the hull down into the water? 5%? 20%? Fancy a guess?

 

Is there anything you can do to minimise that effect?

 

If you take a snap shot of a moment then yes, you fix all of the variables for a calculation, but a % ish is enough to know if it's important or not - research papers suggest that it is, but no-one has published anything for canals yet, at least nothing that I can find, and I have looked, so I thought I'd ask.

 

Given the two general categories of wide and narrow canals, that might yield two estimates,

 

and that's two more than anyone else has been able to suggest,

 

including all of the boat builders that I've asked - including some of the best ones...

Edited February 23, 2016 by dpaws

[Dalslandia]

dpaws, if you are thinking of propeller calculations, you are right, drag isn't the same in the canal as in open water, shallow water is said to be less then 10 times the draft, shallow and narrow doesent make it easier. we know two things, the boat is slower, the water speed is higher then boat speed, it takes more power to push the boat forward, but how much? good thing if anyone can have a real answer, even between thumb and indexfinger is better then nothing, those that sell propellers in hundreds to NB get a feeling what it takes in size, by try and error.

 

We do see that power demand is very low for canal speed, but those calculations is for open water, and it is indicated that it takes some more.

1 - 1.5 litre/h is said to be normal (with some alternator load that is a big % of it) so 4 - 5 HP from engine.

when calculations say 1,5 -3,5 HP for 3-4 MPH in open see

[Hairy Animal]

Some decades ago now I had experience of just this effect when we took the wide beam Bruce Trust boat, Rachel, out for a week. I think it might have been on the summit level of the K & A where it must have been a bit shallow, certainly not particularly narrow, where we could only achieve about 2 mph, no matter how much throttle I used. The more thrust I gave it, the lower the boat would get in the water and the more resistance it got from the water needing to move faster to get under the boat. It was curious that 2 mph was the absolute limit for that boat on that stretch of canal, irrespective of throttle setting. At no point were we actually hitting the bottom, but were presumably getting close.

[Hairy Animal]

Presumably, the point of the original question is to find a worst case example? If so, I'd guess that one of the long, narrow and possibly, shallow, sections of narrow canal would do, for example, Fenny Compton Tunnel, or the narrows near Llangollen where there's a significant flow as well? I don't offhand know the dimensions of either section, maybe someone else does?

[RLWP]

 

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.

 

I think you are deliberately over simplifying this Tony. Our boat famously floats on a damp dishcloth as proved on the Rushall when we not only passed a grounded boat but towed it to the next lock

 

So, either the squat equation needs to differentiate based on the draft of the boat as the OPs design evolves, or include more predictable anti friction solutions

 

 

Richard

[Dalslandia]

Some decades ago now I had experience of just this effect when we took the wide beam Bruce Trust boat, Rachel, out for a week. I think it might have been on the summit level of the K & A where it must have been a bit shallow, certainly not particularly narrow, where we could only achieve about 2 mph, no matter how much throttle I used. The more thrust I gave it, the lower the boat would get in the water and the more resistance it got from the water needing to move faster to get under the boat. It was curious that 2 mph was the absolute limit for that boat on that stretch of canal, irrespective of throttle setting. At no point were we actually hitting the bottom, but were presumably getting close.

 

Nothing beats experience, I moved a other passenger boat then mine a few times, with a "Block" area close to the hole in the lock entrance, it was like trying to get the cork into a full bottle. down stream it helped to lett some water out of the lock to suck it in. (and fill some from above)

I don't remember how it was in the canal. the deep chines was not of help, Dalslandia that is V bottom is much better in the canal and locks.

[Neil Smith]

Reading this I wonder if CRT would have an idea of the ops question,may be worth an ask.

 

Neil

[RLWP]

Reading this I wonder if CRT would have an idea of the ops question,may be worth an ask.

 

Neil

 

They will have a minimum dredging profile. It will be a minimum profile and will have many exemptions - bridges for instance

 

Richard

[Keeping Up]

Some decades ago now I had experience of just this effect when we took the wide beam Bruce Trust boat, Rachel, out for a week. I think it might have been on the summit level of the K & A where it must have been a bit shallow, certainly not particularly narrow, where we could only achieve about 2 mph, no matter how much throttle I used. The more thrust I gave it, the lower the boat would get in the water and the more resistance it got from the water needing to move faster to get under the boat. It was curious that 2 mph was the absolute limit for that boat on that stretch of canal, irrespective of throttle setting. At no point were we actually hitting the bottom, but were presumably getting close.

Was the boat actually being lowered in the water or was the water level itself being lowered?

[Tony Dunkley]

 

I think you are deliberately over simplifying this Tony. Our boat famously floats on a damp dishcloth as proved on the Rushall when we not only passed a grounded boat but towed it to the next lock

 

So, either the squat equation needs to differentiate based on the draft of the boat as the OPs design evolves, or include more predictable anti friction solutions

 

 

Richard

 

That looks as though it could be the answer to all this Richard, . . . . a load of balls.

[Tony Brooks]

Was the boat actually being lowered in the water or was the water level itself being lowered?

 

That is my question and I noticed the graph given stated squat at the bow. I know my boat squats by the stern and if anything the bow lifts. The water mark on piling clearly shows the water level drops alongside the boat which I assume is caused by a combination of the boat pushing water in front of it (because the water can not get past the hull fast enough and the prop pumping water away from the back of the boat.

 

I also know what squat means in relation to vehicle suspension so am having difficulty visualising squat at the bow. I suspect only a few on here really know what the OP is on about and that like my opinion of the hybrid drive thread is just over complicating things. I wonder if the actual amount of fuel saved in the end will be measurable.

[valrene9600]

All seems a lot to get the hull designed. I'm just wondering will the next stage of design be to get the aerodynamics right. Will op be asking for wind direction and average force across the canal system. Will a full Pumpout tank alter the squat? For sure no one will be squatting till it's emptied.

Anyway hope it all gets sorted and the OP can squat down next to the tiller and enjoy some boating. I just give thanks my only worry of late has been tail current.

[Tony Dunkley]

The only type of vessel that doesn't 'squat' to some extent or another in either shallow water [relative term] or a narrow and restricted channel [river or canal] is a hovercraft.

The severity of the squat experienced by any given vessel at any one time is governed by a combination of the depth of water, the extent of the channel restriction, and the speed of the vessel.

As there is only one of those three factors you can change, ie. the speed, then there is no point whatsoever in calculating values for the effects of the other two.

[Guest]

The only type of vessel that doesn't 'squat' to some extent or another in either shallow water [relative term] or a narrow and restricted channel [river or canal] is a hovercraft.

The severity of the squat experienced by any given vessel at any one time is governed by a combination of the depth of water, the extent of the channel restriction, and the speed of the vessel.

As there is only one of those three factors you can change, ie. the speed, then there is no point whatsoever in calculating values for the effects of the other two.

 

Why? The squat is an interaction between the channel (below and to the side) and the hull itself. A designer can change the hull, the shape of the hull and thus the interaction between the channel and the hull - the Cb no? So yes, you want to know the values...

 

From the squat perspective, is a flat bottom superior to V-bottom? Traditional aft swim, clone craft aft swim, XR&D "slipper stern" profile - which one would minimise the squat from that part of the hull profile? Spoon bow? Racked bow? Eco-bow?

[Guest]

All seems a lot to get the hull designed. I'm just wondering will the next stage of design be to get the aerodynamics right. Will op be asking for wind direction and average force across the canal system. Will a full Pumpout tank alter the squat? For sure no one will be squatting till it's emptied.

Anyway hope it all gets sorted and the OP can squat down next to the tiller and enjoy some boating. I just give thanks my only worry of late has been tail current.

 

Ahh the windage area... and then there's the spinnaker.. but I personally I prefer the unidirectional Flettner rotors...

 

 

If you adapted a car wash sensor mechanism maybe you could get them to retract automatically for low bridges...

 

 

Unfortunately yes, full pump-out will increase the squat, but we can calc through at half full - even a stopped clock is correct twice a day

Edited February 24, 2016 by dpaws

[Dalslandia]

dpaws, I think it is better to calculate with a half empty black water tank.

 

I think it is right to put up this question, if the answer is possitive, = that things can be made better, or = it doesen.t matter what we do, we still get an answer.

And all will be happy.

 

At least, it would be nice to have an finger direction (no not that finger) about drag increase relative open water. because, I don't know.

[Guest]

Presumably, the point of the original question is to find a worst case example? If so, I'd guess that one of the long, narrow and possibly, shallow, sections of narrow canal would do, for example, Fenny Compton Tunnel, or the narrows near Llangollen where there's a significant flow as well? I don't offhand know the dimensions of either section, maybe someone else does?

 

Many thanks for your recollections, you encountered the power and relevance of squat! I suspect your baseplate was very close to the bottom but the system found equilibrium at 2 knots

 

I'm not so much after worse case, but a rough estimate of generalised conditions. With enough examples we could illustrate the data in a graph and interpolate / extrapolate - but the value isn't so important, I want to know if the effect is sufficient to have an influence on the shape of the hull to minimise the effect.

 

We fine a the swims and there's an advantage to doing so - if you don't the boat will still swim, just not quite as well - you'd probably never notice, and the fish wouldn't care, but I'm curious - for me, if I'm going to ask a chap to cut and weld metal for me then I feel it's right that I can explain why I want that shape, what effect it has etc. etc.

 

Maybe we should fine the baseplate's profile in relation to the bottom to minimise the squat?

Edited February 24, 2016 by dpaws

[Guest]

dpaws, I think it is better to calculate with a half empty black water tank.

 

 

but black water tanks are never half empty, they're are either half full, or completely empty

[Dalslandia]

 

but black water tanks are never half empty, they're are either half full, or completely empty

 

what way is most positive? half full or half empty?

[Dalslandia]

Slide of topic, but meantime we are awaiting professors answer, but to keep us on track or close to the center of tha canal, or deepest part, other string length question, how long and tall is a "normal" NB rudder plate?

Edited February 24, 2016 by Dalslandia