Maximum weight for boat on the London canal network

[k_lj]

Hello, I hope someone can help

At what point would a boat be too heavy for the London canal network. I'm interested in buying a boat that is LOA 18.20m, Beam 3.50m, Draught 1.00m, Air draught 2.00m. I have just been advised that the estimated weight is around 80 Tonnes. I hadn't expected this however it is an iron constructed hull with poured concrete ballast (previously a working water tanker). I'm wondering how this works with water displacement. I can't find any information about the actual depth of the canals however  the maximum draught permitted for a boat on the Regents Canal seems to be 3ft 10", Grand Union 3ft 8", Lee navigation 4ft 2". 
Thank you in advance!

 

[hider]

You will be glad of the concrete ballast after you have worn the iron off the bottom dragging it long shallow canals.

 

At 1m draught you will do lots of dragging on the rubble and rubbish on the bottom of practically all the canals.

s

[David Mack]

Its not 80 tonnes. A rectangular flat bottommed brick 18.2m x 3.5m x 1.0m would displace 63.7 tonnes, and your weight will be much less due to curvature in the hull.

The Lower GU, Regents and Lee are regularly used by working narrowboats with a draught of around 0.9m. If your boat has some hull curvature, the 1m depth will only apply at the keel and probably towards the rear of the boat, so you should generally be fine, although inevitably you are more likely to touch the bottom in any shallow spots or where there are sunken obstructions (ranging from shopping trolleys to brick rubble).

 

[MtB]

Have you actually done much boating in London? Or any boating at all? 

 

Water depths on websites are mostly fiction. And taking a such behemoth of a boat into London isn't likely to endear you to other boaters unless you have taken a permanent home mooring for it.

 

 

[Tony Brooks]

and you may find that the cabin shape together with the beam will prevent it passing through arched canal bridges where a much taller narrowboat will pass.

 

Personally, I would take any CaRT stated depth on canals with a very large pinch of salt, especially for a wide beam that may totally span the channel made by narrowboats.

[MtB]

14 minutes ago, k_lj said:

At what point would a boat be too heavy for the London canal network.

 

This is an odd question to be asking. The weight of the water displaced by the boat floating is the same as weight of the boat, so the net weight being supported by the canal bed remains the same whatever weight a boat might be.

 

So no there is no formal 'weight limit' as such. Just that the heavier a boat is, the bigger it will be and the bigger it is, the less likely it is to physically fit in the canal and get past other boats etc.

[k_lj]

17 minutes ago, MtB said:

Have you actually done much boating in London? Or any boating at all? 

 

Water depths on websites are mostly fiction. And taking a such behemoth of a boat into London isn't likely to endear you to other boaters unless you have taken a permanent home mooring for it.

 

 

 

16 minutes ago, Tony Brooks said:

and you may find that the cabin shape together with the beam will prevent it passing through arched canal bridges where a much taller narrowboat will pass.

 

Personally, I would take any CaRT stated depth on canals with a very large pinch of salt, especially for a wide beam that may totally span the channel made by narrowboats.

Thank you for the head's up Tony!

10 minutes ago, MtB said:

 

This is an odd question to be asking. The weight of the water displaced by the boat floating is the same as weight of the boat, so the net weight being supported by the canal bed remains the same whatever weight a boat might be.

 

So no there is no formal 'weight limit' as such. Just that the heavier a boat is, the bigger it will be and the bigger it is, the less likely it is to physically fit in the canal and get past other boats etc.

Hmm.. I've had conflicting advice on another thread from an experienced boater.

19 minutes ago, MtB said:

Have you actually done much boating in London? Or any boating at all? 

 

Water depths on websites are mostly fiction. And taking a such behemoth of a boat into London isn't likely to endear you to other boaters unless you have taken a permanent home mooring for it.

 

 

 Only a little.. though I've recently cruised a 60  X 12 ft dutch barge east to west all the way across London and back encountering no problem.. We all have to start somewhere right? 

 

[MtB]

3 hours ago, k_lj said:

Hmm.. I've had conflicting advice on another thread from an experienced boater.

 

In which case s/he is wrong, or they didn't explain it properly to you. I think Archimedes explains it better than me. Can you explain in what way you think the weight of a boat might somehow affect the structure of canal it is floating in, please? Or have I perhaps misunderstood your question?

 

 

3 hours ago, k_lj said:

Only a little.. though I've recently cruised a 60  X 12 ft dutch barge east to west all the way across London and back encountering no problem.. We all have to start somewhere right? 

 

Yes we do, and good that you've steered one already. Had you not, I'd suggest you might be better off starting with a narrow boat. 

 

[Paul C]

MtB I think you're the one who has misunderstood or doesn't understand properly. Weight is a function of size, and size certainly can affect the canal (structures) for example if it scrapes the clay puddling away, or hits a bridge, or the edge(s). Its a bit odd expressing the size dimensions as weight but that's all.

[ditchcrawler]

8 minutes ago, MtB said:

 

In which case s/he is wrong, or they didn't explain it properly to you. I think Archimedes explains it better than me. Can you explain in what way you think the weight of a boat might somehow affect the structure of canal it is floating in, please? Or have I perhaps misunderstood your question?

 

 

Maybe it was me when I said it would be fun with a boat with a draft of a meter on the canals when in the other thread he said his 60 footer weighed 80 tons 

[MtB]

1 minute ago, Paul C said:

MtB I think you're the one who has misunderstood or doesn't understand properly. Weight is a function of size, and size certainly can affect the canal (structures) for example if it scrapes the clay puddling away, or hits a bridge, or the edge(s). Its a bit odd expressing the size dimensions as weight but that's all.

 

Yes I agree the physical size of a boat matters, but I hold that weight doesn't. Except in the way you suggest, that size is a derivative of wieght, to a degree. 

[dmr]

5 minutes ago, MtB said:

 

In which case s/he is wrong, or they didn't explain it properly to you. I think Archimedes explains it better than me. Can you explain in what way you think the weight of a boat might somehow affect the structure of canal it is floating in, please? Or have I perhaps misunderstood your question?

 

 

 

Yes we do, and good that you've steered one already. Had you not, I'd suggest you might be better off starting with a narrow boat. 

 

 

I think this is all my fault, in the other thread I pointed out that if the boat really is 80 tonne then its going to be too deep for the canal so now we are confusing draft and weight, even though they are closely linked by that Archimedes bloke.

I did a very very quick mental estimare based on the approximation that a 70 foot narrowboat goes down an inch per ton, and came up wit a four foot draft.

I suspect the ops boat is not 80 tonne but as its a tanker of some sort? it just might be extra deep, though the 80 tonne figure might be fully loaded in which case it might be a pig to handle when empty.  A photo and more details would be a good idea in case the op buys a very unsuitable boat.

[bizzard]

If it goes aground and gets fast  stuck, good escape can be executed by owning an enormously powerful generator. The object of this is to whack hundreds of amps into the boats batteries, ''remove cell tops first'' so that they boil with fury and gas off lots of lifting force hydrogen, this hydrogen once held in captivity by shutting off all doors windows and othe apertures should raise the boat a little, ''like the Hindenburg;; and so unstick it enabling you to resume your voyage.

[MtB]

1 minute ago, dmr said:

A photo and more details would be a good idea in case the op buys a very unsuitable boat.

 

Given that I think I read it has poured concrete ballast, I think the jury on that won't be out for long! 

 

[ditchcrawler]

1 minute ago, MtB said:

 

Given that I think I read it has poured concrete ballast, I think the jury on that won't be out for long! 

 

Last week we met a chap who had was refitting a Narrowboat with poured concrete ballast, He was trying to remove it, in the one bay where he had succeeded the steel was like new, far better than the to forward bays that were not ballasted and just painted.  

[IanD]

13 minutes ago, bizzard said:

If it goes aground and gets fast  stuck, good escape can be executed by owning an enormously powerful generator. The object of this is to whack hundreds of amps into the boats batteries, ''remove cell tops first'' so that they boil with fury and gas off lots of lifting force hydrogen, this hydrogen once held in captivity by shutting off all doors windows and othe apertures should raise the boat a little, ''like the Hindenburg;; and so unstick it enabling you to resume your voyage.

And if you smoke while doing that, you'll be lifted much higher than the boat and won't have to worry about the draft any more... 🙂

[MtB]

34 minutes ago, ditchcrawler said:

Last week we met a chap who had was refitting a Narrowboat with poured concrete ballast, He was trying to remove it, in the one bay where he had succeeded the steel was like new, far better than the to forward bays that were not ballasted and just painted.  

 

Did he just lift it out like it was paving slabs? 

 

 

[GUMPY]

4 hours ago, k_lj said:

I'm interested in buying a boat that is LOA 18.20m, Beam 3.50m, Draught 1.00m, Air draught 2.00m.

Not far off the size of Parglena. LOA 18.7m Beam 3.50m Draught 0.91m AD 1.98m with the wheelhouse down.

Weight on the crane was 37ton so way lower than whoever calculated yours.

Had no problems on the Thames, the GU through London or the Lea and Stort. It did get a bit more difficult the further north I went on the GU,  we moored at Berko. 

The only caveat is that this was over 12 years ago so it may be shallower now.

Personally I would run away from poured concrete ballast unless I had seen the hull before it was done.

 

[bizzard]

26 minutes ago, IanD said:

And if you smoke while doing that, you'll be lifted much higher than the boat and won't have to worry about the draft any more... 🙂

If smoking caused an explosion the extra heat developed would help a lot with raising the boat like a hot air balloon.

[zenataomm]

I'd come at this from a different angle and comment that the boat becomes "too heavy" or "unsuitable" at the point where: -
You can't find a suitable sized gap to tie up in.

Can't get near enough to a water point to fill your water.
Find it very difficult to get against the bank without grounding feet away.
Irritate others when you double moor against them because you're so *&##$% big and block out all their light.
Move so slowly because of your unwieldly size that there's always a queue behind you trying to get past.
Get involved in so much evasive action because you shock so many others on blind bends.
Need every nano inch of a winding hole, and still take ages to turn.
Experience resentment from fellow boaters as your one boat needs as much room as 4 others.

And then there's the really negative experiences that will drive your soul from your body in short time.
 

[ditchcrawler]

53 minutes ago, MtB said:

 

Did he just lift it out like it was paving slabs? 

 

 

No he will be spending days with a Kango , he had only done the first bay when we were there 

55 minutes ago, GUMPY said:

 

The only caveat is that this was over 12 years ago so it may be shallower now.

Personally I would run away from poured concrete ballast unless I had seen the hull before it was done.

 

 

And I remember you saying to me "did you see that wide beam on your way" I think it was big blue.

[dmr]

2 hours ago, bizzard said:

If it goes aground and gets fast  stuck, good escape can be executed by owning an enormously powerful generator. The object of this is to whack hundreds of amps into the boats batteries, ''remove cell tops first'' so that they boil with fury and gas off lots of lifting force hydrogen, this hydrogen once held in captivity by shutting off all doors windows and othe apertures should raise the boat a little, ''like the Hindenburg;; and so unstick it enabling you to resume your voyage.

 

The op is likely new to boating, I think your advice should come with a serious eccentric humour warning 😀

[GUMPY]

9 hours ago, ditchcrawler said:

And I remember you saying to me "did you see that wide beam on your way" I think it was big blue.

That was 70x14 and rarely moved. There are wide beams and there are barges.🤔

[k_lj]

11 hours ago, dmr said:

 

I think this is all my fault, in the other thread I pointed out that if the boat really is 80 tonne then its going to be too deep for the canal so now we are confusing draft and weight, even though they are closely linked by that Archimedes bloke.

I did a very very quick mental estimare based on the approximation that a 70 foot narrowboat goes down an inch per ton, and came up wit a four foot draft.

I suspect the ops boat is not 80 tonne but as its a tanker of some sort? it just might be extra deep, though the 80 tonne figure might be fully loaded in which case it might be a pig to handle when empty.  A photo and more details would be a good idea in case the op buys a very unsuitable boat.

 

Thank you dmr. Yes, that is what I was referring to. As you said on the other thread "The weight of a boat relates directly to how deep it sits in the water and if the 80 is correct this boat will be deep. Most canals are good for three feet, maybe a little more. 80 tonnes will be well over 4 feet deep."

 

I was trying to get other perspectives on to what degree this tonnage would cause the boat to lower in the water. I thought that was clear but perhaps not! 

 

For whoever it was that asked.. I gave the dimensions as I understand that the surface area of an object determines the amount of water it displaces and therefore it's buoyancy.

 

Anyways.. Thanks again. Over and out! 🙂

[Jen-in-Wellies]

8 minutes ago, k_lj said:

For whoever it was that asked.. I gave the dimensions as I understand that the surface area of an object determines the amount of water it displaces and therefore it's buoyancy.

The boats all up weight will displace the same weight of water. How deep in the water it sits is determined by the volume of the hull below the water line. Too small a hull for the weight and the boat will sink! That nice Mr Archimedes worked it all out in his bath tub. A rubber duck had co-authorship of the scientific paper he wrote.