How do you measure the draught of a boat?.........

[ditchcrawler]

1 hour ago, Mike the Boilerman said:

 

If you cill a full length boat by 1", there will be about half a tonne of downward force on the cill I reckon. 

 

But I'm not sure. It might be 1/4 tonne. 

 

 

It will be enough to stop you driving it off

[Wanderer Vagabond]

3 hours ago, Mike the Boilerman said:

 

If you cill a full length boat by 1", there will be about half a tonne of downward force on the cill I reckon. 

 

But I'm not sure. It might be 1/4 tonne. 

 

 

How have you calculated this?  As a thought experiment, if you put a 12 inch solid steel roller across underneath a narrowboat on a hard standing (don't try this at home folks ), with judicious adjustment, in theory you should be able to find a balance point somewhere between the bow and stern (probably closer to the stern given the weight of the engine) which would have both bow and stern off the ground (yes I appreciate that in the real world the stresses involved would probably fracture some welds, hence the 'thought experiment'). Once you've found the balance point you could then quite easily lift up the bow or stern by three inches or so, not because you are super strong, but simply because, by lifting, you've upset the equilibrium. You don't have to have half a tonne of lift to do this. This equilibrium point still exists whether the boat is on a roller or in the water, so my suggestion is that the actual draught of a boat is the depth at the equilibrium point rather than just at the deepest point (skeg) since the boat will pivot around this point.

 

I may have completely got hold of the wrong end of the stick, but if so can someone explain how?

Edited June 5, 2019 by Wanderer Vagabond

[Tacet]

22 minutes ago, Wanderer Vagabond said:

How have you calculated this?  As a thought experiment, if you put a 12 inch solid steel roller across underneath a narrowboat on a hard standing (don't try this at home folks ), with judicious adjustment, in theory you should be able to find a balance point somewhere between the bow and stern (probably closer to the stern given the weight of the engine) which would have both bow and stern off the ground (yes I appreciate that in the real world the stresses involved would probably fracture some welds, hence the 'thought experiment'). Once you've found the balance point you could then quite easily lift up the bow or stern by three inches or so, not because you are super strong, but simply because, by lifting, you've upset the equilibrium. You don't have to have half a tonne of lift to do this. This equilibrium point still exists whether the boat is on a roller or in the water, so my suggestion is that the actual draught of a boat is the depth at the equilibrium point rather than just at the deepest point (skeg) since the boat will pivot around this point.

 

I may have completely got hold of the wrong end of the stick, but if so can someone explain how?

With a see-saw (or your hypothetical boat balanced on a roller) the centre of gravity is higher than the rotation point but essentially it is balanced with (over a limited arc) only a limited weight going over centre from one end of the travel to the other.   Hence each kid can push the see saw up with ease - and you might be able to shift the boat. 

 

But in the water, the boat does not see-saw about a single point.  It is correct that as you lift (or cill) the stern, the bow will descend and eventually sink.   However, the weight will not be transferred from one end to the other in full; it's quite complex.

 

As a further thought experiment, put your hand between the cill/underwater obstruction and the underside of the boat - and you will feel some significant, if hypothetical pain quite quickly.  Or, if you really want to try an experiment.  get in a shallow canal and try lifting the back end by, say 6 inches.  If it was nicely balanced at mid length, it will take no effort as the bow drops by the same.  You could even change the propeller with your other hand.

[peterboat]

Having seen boats moved around at Jonnys  sometimes they only have one roller under them at some points and yes they seesaw around, when boats are in water to an extent they still do it

1 hour ago, Wanderer Vagabond said:

How have you calculated this?  As a thought experiment, if you put a 12 inch solid steel roller across underneath a narrowboat on a hard standing (don't try this at home folks ), with judicious adjustment, in theory you should be able to find a balance point somewhere between the bow and stern (probably closer to the stern given the weight of the engine) which would have both bow and stern off the ground (yes I appreciate that in the real world the stresses involved would probably fracture some welds, hence the 'thought experiment'). Once you've found the balance point you could then quite easily lift up the bow or stern by three inches or so, not because you are super strong, but simply because, by lifting, you've upset the equilibrium. You don't have to have half a tonne of lift to do this. This equilibrium point still exists whether the boat is on a roller or in the water, so my suggestion is that the actual draught of a boat is the depth at the equilibrium point rather than just at the deepest point (skeg) since the boat will pivot around this point.

 

I may have completely got hold of the wrong end of the stick, but if so can someone explain how?

 

20 minutes ago, Tacet said:

With a see-saw (or your hypothetical boat balanced on a roller) the centre of gravity is higher than the rotation point but essentially it is balanced with (over a limited arc) only a limited weight going over centre from one end of the travel to the other.   Hence each kid can push the see saw up with ease - and you might be able to shift the boat. 

 

But in the water, the boat does not see-saw about a single point.  It is correct that as you lift (or cill) the stern, the bow will descend and eventually sink.   However, the weight will not be transferred from one end to the other in full; it's quite complex.

 

As a further thought experiment, put your hand between the cill/underwater obstruction and the underside of the boat - and you will feel some significant, if hypothetical pain quite quickly.  Or, if you really want to try an experiment.  get in a shallow canal and try lifting the back end by, say 6 inches.  If it was nicely balanced at mid length, it will take no effort as the bow drops by the same.  You could even change the propeller with your other hand.

I have seen the exol pride with it bow on the bottom and its stern in the air as it uses water to ballast itelf they had to cut a mattress off the prop so yes they wil seesaw if enough leverage is applied

[Tacet]

9 minutes ago, peterboat said:

Having seen boats moved around at Jonnys  sometimes they only have one roller under them at some points and yes they seesaw around, when boats are in water to an extent they still do it

 

I have seen the exol pride with it bow on the bottom and its stern in the air as it uses water to ballast itelf they had to cut a mattress off the prop so yes they wil seesaw if enough leverage is applied

Yes - there is a tendency for the bow to rise as more weight is added to the stern.  But it is not a simple, balanced rotation like a see-saw or wheel.  If it were, the boat would move from horizontal to vertical when a sparrow landed on the bow.     

[Wanderer Vagabond]

1 hour ago, Tacet said:

With a see-saw (or your hypothetical boat balanced on a roller) the centre of gravity is higher than the rotation point but essentially it is balanced with (over a limited arc) only a limited weight going over centre from one end of the travel to the other.   Hence each kid can push the see saw up with ease - and you might be able to shift the boat. 

 

But in the water, the boat does not see-saw about a single point.  It is correct that as you lift (or cill) the stern, the bow will descend and eventually sink.   However, the weight will not be transferred from one end to the other in full; it's quite complex.

 

As a further thought experiment, put your hand between the cill/underwater obstruction and the underside of the boat - and you will feel some significant, if hypothetical pain quite quickly.  Or, if you really want to try an experiment.  get in a shallow canal and try lifting the back end by, say 6 inches.  If it was nicely balanced at mid length, it will take no effort as the bow drops by the same.  You could even change the propeller with your other hand.

I'm not sure that I was suggesting any transfer of weight, it was more to do with the balance equilibrium. I seem to recall being in the Chester staircase locks and catching my bow button under one of the crossmembers of one of the top gates (not my fault, someone had opened the paddles too quickly dragging the boat forwards) I realised that there was a problem when the bow stopped rising and the rudder started to get higher out of the water. I do understand that there is complexity to it as the further you try to push the bows down into the water the greater will be the supporting force from the water which is why it takes more and more weight being put onto a boat to cause it to lie deeper and deeper in the water.

 

Trapping my hand between bottom of the boat  and a cill is more to do with momentum than anything else; on the hypothetical roller on the hardstanding, although I'd be able to upset the equilibrium easily, but if I put my hand between the bottom of the boat and the ground, only a small momentum on an 18 ton boat would be more than enough to either break most of the bones in my hand or sever it completely if the boat hit the ground. 

 

I suppose what I'm trying to figure out with the draught question, is what is the minimum depth of water needed to stop the ground supporting the boat thereby transferring the support to the water? Although my skeg is 2'8" below the waterline, if I'm in 2'7" of water the weight of the boat is not being supported on the skeg, the vast majority of it is being supported by the water so it is technically afloat. What would be the minimum depth of water for that to happen?  I'm guessing somewhere around the draught at this hypothetical balance point, which would explain why the CRT bod at Standedge Tunnel used his gauge along the side of the boat about 10 -12 from the stern rather than trying to measure how deep the boat was at the skeg.

Edited June 5, 2019 by Wanderer Vagabond

[ditchcrawler]

6 hours ago, Mike the Boilerman said:

 

If you cill a full length boat by 1", there will be about half a tonne of downward force on the cill I reckon. 

 

But I'm not sure. It might be 1/4 tonne. 

 

 

It will be enough to stop you driving it off

Last year on the SU I stopped above a lock and gave a hand to work the lock , the result was the pound above dropped very slightly and the bow of the boat grounded on something very hard, It took 3 of us to get the bow off that obstruction. All you theorising is great, if it works follow my suggestion and cill the boat. by your calculation you should be able to safely drop it by 6" and still get off.

[mykaskin]

On 05/06/2019 at 12:18, bizzard said:

Years ago this happened to the QE2. It was doing cruises to the Carribee's out of New York when it had had engine trouble in the Carribee's. So on its way back to New York it sped up to make up lost time. Whilst passing over a shallowish bit off the east coast it dragged its bottom and damaged its sterngear. The ship always passed that way but at moderate speed, but the extra speed lowered the ship by about 5 meters or so.  You'd have thought the crew would have realised this. Why I don't don't trust cruise ships.

Squat as they call it on ships is a relatively new phenomenon to the captains and pilots of such vessels. They don't understand close water interactions like canal folk do. It is sometimes used to get under low bridges believe it or not! 

[howardang]

45 minutes ago, mykaskin said:

Squat as they call it on ships is a relatively new phenomenon to the captains and pilots of such vessels. They don't understand close water interactions like canal folk do. It is sometimes used to get under low bridges believe it or not! 

That's an interesting couple of assertions, Mike. I would certainly disagree with your generalisation that Ships Masters and Pilots don't understand close water interactions "like canal folk do". I can certainly remember the subjects being part of the syllabus at Nautical College when I first went to sea many years ago, and subsequently  when being examined for various certificates. Pilots are also particularly well  aware of the issues caused by such effects on a daily basis - especially on rivers such as the Humber which I think you know well -  and when manoeuvring in confined waters in docks and harbours. The Royal Navy too has been well aware of ship interaction, especially when undertaking refuelling at sea from a ship close alongside - RAS.  These effects are well known and have been for many years, - I have been aware of them since 1959 for example and I am certainly not alone. I joined this forum in 2004 and over the years the subject of squat has been raised by me and others on one or two occasions.  

 

However,  what often causes calamities such as groundings and so on is more to do with taking risks, and cutting corners. In other words, human error, something which is not confined to sea going ships! 

 

Howard

[Richard10002]

1 hour ago, mykaskin said:

Squat as they call it on ships is a relatively new phenomenon to the captains and pilots of such vessels. They don't understand close water interactions like canal folk do. It is sometimes used to get under low bridges believe it or not! 

I reached the dizzy heights of 3rd Officer with Blue Star Line in 1984, and part of the training included being aware of squat. One would assume that those who had reached the position of captain, or pilot, would have even more experience and knowledge than I had.

 

What do you mean by “relatively new”? I’d say “we” have been well aware of it for at least half a century, probably more.

[mykaskin]

34 minutes ago, Richard10002 said:

I reached the dizzy heights of 3rd Officer with Blue Star Line in 1984, and part of the training included being aware of squat. One would assume that those who had reached the position of captain, or pilot, would have even more experience and knowledge than I had.

 

What do you mean by “relatively new”? I’d say “we” have been well aware of it for at least half a century, probably more.

From what I gather from comments on the 'net about incidents where these effects were a factor - it seems that the masters weren't aware of it - especially in confined waters - the ship squats more in a confined channel, and other effects like getting sucked towards the bank if you get to close to it seem to evade even regular users of such waters.

 

ps. Canal boaters have been aware of it for over a century!
 

 

 

Edited June 6, 2019 by mykaskin

[howardang]

What that video clip shows is what I was saying. It was bad ship handling, not lack of awareness.  

 

Howard

 

 

 

 

[mykaskin]

Well indeed, and not knowing the full details I can't say how much was down to handling or awareness. I think while it might be taught, it's only people who deal with it on a constant basis (like that found on confined waters like the Humber and Trent) that tend to deal with the effects on a regular enough basis to be able to expect them, and deal with them without even thinking. Knowing something doesn't always mean you can deal with it when it happens.

 

Victoria is always in a state of sucking herself up the bank on most canals. Even on the Aire and Calder you could see the water dropping at the bank side a little!

Edited June 6, 2019 by mykaskin

[howardang]

I think you underestimate how frequently even large ships may have to manoeuvre in shallow and/or confined waters. I can assure you it is much more frequent than you may think. As I said earlier pilots are aware of these issues on a daily basis, and ship masters at the beginning and end of each voyage which these days can be often be very frequent indeed!

 

Everything is relative and a confined channel for a large vessel can be just as problematical as a narrow, shallow for Victoria, believe me!

 

Howard

 

 

 

[roland elsdon]

I got mecca which drew2’9’’up from trevor to llangollen simply by climbing off. In gear with me on the back ( a hefty 59 kilos) she wouldnt go, hit the concrete. However tying the tiller straight and in gear at idle  walking alongside she crawled up there  eventuality. 

Current boat had to be dragged through battesford by a nice man with a bus engine. We saw the top of the prop when we landed on the sandebar. Not helped by this boat dropping 2’’ the minute it goes forward.

normal response to a grounding go into neutral and wait a bit.

[howardang]

1 hour ago, mykaskin said:

Well indeed, and not knowing the full details I can't say how much was down to handling or awareness. I think while it might be taught, it's only people who deal with it on a constant basis (like that found on confined waters like the Humber and Trent) that tend to deal with the effects on a regular enough basis to be able to expect them, and deal with them without even thinking. Knowing something doesn't always mean you can deal with it when it happens.

 

Victoria is always in a state of sucking herself up the bank on most canals. Even on the Aire and Calder you could see the water dropping at the bank side a little!

Mike, and further to our discussion re ship handling and training if you haven't seen this before you may like to see what is available in addition to the more traditional teaching methods and these courses are supplemented by mandatory simulator training. The video  gives a flavour of some aspects of modern day ship handling training. The one in the UK - Warsash - is one of a number of such facilities around the world. You may have come across a similar one which is in France - Port Revel.

I hope you find it interesting.

 

Howard

 

 

 

 

 

[Wanderer Vagabond]

1 hour ago, roland elsdon said:

I got mecca which drew2’9’’up from trevor to llangollen simply by climbing off. In gear with me on the back ( a hefty 59 kilos) she wouldnt go, hit the concrete. However tying the tiller straight and in gear at idle  walking alongside she crawled up there  eventuality. 

Current boat had to be dragged through battesford by a nice man with a bus engine. We saw the top of the prop when we landed on the sandebar. Not helped by this boat dropping 2’’ the minute it goes forward.

normal response to a grounding go into neutral and wait a bit.

If being on the stern made the difference you suggest (I'm not disagreeing) would the boat have gone quicker had you then jumped onto the bows with your 59 Kilo weight since it seems logical that if the bow goes down, the stern goes up.

 

Our skeg is 2'8" according to my measurement but we managed to keep going from Trevor to Llangollen on a gentle tick-over (particularly through the narrow bits). This was significantly different to a Canaltime boat coming through the same bit on which the girl was thrashing the engine and I could seriously have crawled on my hands and knees faster than they were going. Having used Canaltime boats in the past, they are quite shallow draughted and it shouldn't have been any sort of a problem going up to Llangollen in one of them.

 

Coming back is obviously easier because you've got the current behind you.

[CaptAWOL]

On 04/06/2019 at 22:53, Wanderer Vagabond said:

The see-saw effect I was thinking of was more like I experienced on the Kennet & Avon, I think it was approaching Burghfield road bridge, when the stern of the boat lifted up as I went over a sand bar at normal cruising speed (first year on the boat, frightened the life out of me?). The bow had passed over the sand bar but when the stern hit it we rode up and over it with the stern lifting and the bow going down.

That is actually the same effect, as you pass over a shallow patch at speed the restriction of water, like a block effect slows the boat down, the stern wave catches up lifting the stern. 

[Wanderer Vagabond]

9 minutes ago, CaptAWOL said:

That is actually the same effect, as you pass over a shallow patch at speed the restriction of water, like a block effect slows the boat down, the stern wave catches up lifting the stern. 

It sort of re-iterates what I was questioning, that my draught isn't necessarily the deepest point of the boat (skeg) since, like the bow, it can go up and down.

[Chris Williams]

2 hours ago, roland elsdon said:

normal response to a grounding go into neutral and wait a bit.

Working 'Jaguar', we met 'Caldy' in a particularly shallow bit of the Oxford.  Caldy's steerer indicated to me to cut the engine, and he did likewise.  The boats then passed each other quite easily, just by walking them.  Not by pulling water from under us both with the engines.

Another lesson from an old boy.

[mykaskin]

14 hours ago, Chris Williams said:

Working 'Jaguar', we met 'Caldy' in a particularly shallow bit of the Oxford.  Caldy's steerer indicated to me to cut the engine, and he did likewise.  The boats then passed each other quite easily, just by walking them.  Not by pulling water from under us both with the engines.

Another lesson from an old boy.

I nearly always slack off when passing boats, so good to know it was common practice. A pity that others don't, it drags the butty around as they pass, pulling it forward, so I often put the power on again just as they are passing to try and counter act it.

 

15 hours ago, howardang said:

Mike, and further to our discussion re ship handling and training if you haven't seen this before you may like to see what is available in addition to the more traditional teaching methods and these courses are supplemented by mandatory simulator training. The video  gives a flavour of some aspects of modern day ship handling training. The one in the UK - Warsash - is one of a number of such facilities around the world. You may have come across a similar one which is in France - Port Revel.

I hope you find it interesting.

 

Howard

 

I've seen the Port Revel stuff, not seen this one I don't think. I've always dreamed of sizing these up to narrow boat sort of dimensions then you could have some fun on the canals with them too - though the bigger ones are probably not far off. However when you think the power to weight ratio would be less then a fully loaded Victoria with the JP barely turning...

 

Mike

[howardang]

1 hour ago, mykaskin said:

 

 

I've seen the Port Revel stuff, not seen this one I don't think. I've always dreamed of sizing these up to narrow boat sort of dimensions then you could have some fun on the canals with them too - though the bigger ones are probably not far off. However when you think the power to weight ratio would be less then a fully loaded Victoria with the JP barely turning...

 

Mike

The Warsash facility is only a few years old and replaces the previous one which was near Southampton at Marchwood. I have visited both and they are a superb addition to the more traditional methods of training, although quite expensive. This is a scale model of a 300,000m tonne tanker at Port Revel.  Myself and a colleague were there in around 1989 and this is us preparing to enter a narrow channel simulating a section of the Suez Canal. The transit  was entertaining to say the least but very realistic when demonstrating bank effect and other narrow channel interactions etc. The model length is approximately the same as an average narrow boat. The scale handling is quite authentic to full size using electric propulsion, however, it is much slower to respond to engine and engine orders than an average narrowboat which is very much overpowered by comparison. It is also more susceptible to wind and like the real thing, you have to plan any manoeuvres a long way ahead 

 

Howard

 

 

[Mike Todd]

17 hours ago, Chris Williams said:

Working 'Jaguar', we met 'Caldy' in a particularly shallow bit of the Oxford.  Caldy's steerer indicated to me to cut the engine, and he did likewise.  The boats then passed each other quite easily, just by walking them.  Not by pulling water from under us both with the engines.

Another lesson from an old boy.

I may well have recalled this here before (in which case I apologise to those who remember) but Jack Monk told me with some delight that in the days when working and leisure boats shared the canals, it was not uncommon for one of the latter to attempt to overtake uninvited. The working boatman would simply stand on the stern smiling sweetly as he, invisibly, wound up the engine speed as the overtaker came alongside and then watched in some amusement as the cruiser steerer could not wok out why they were stuck alongside!

[Naughty Cal]

On 06/06/2019 at 13:09, mykaskin said:

Squat as they call it on ships is a relatively new phenomenon to the captains and pilots of such vessels. They don't understand close water interactions like canal folk do. It is sometimes used to get under low bridges believe it or not! 

The Potter Heigham bridge pilot uses this to his advantage.

 

Takes a good run up with the hire boats and they squat into the water. Gives him a good few inches extra clearance.

[Chris Williams]

3 hours ago, Mike Todd said:

I may well have recalled this here before (in which case I apologise to those who remember) but Jack Monk told me with some delight that in the days when working and leisure boats shared the canals, it was not uncommon for one of the latter to attempt to overtake uninvited. The working boatman would simply stand on the stern smiling sweetly as he, invisibly, wound up the engine speed as the overtaker came alongside and then watched in some amusement as the cruiser steerer could not wok out why they were stuck alongside!

Did this on the Trent, 1975, some guy in a big plastic cruiser tried to overtake Jaguar, on the wrong side, of course, in a lock cut.  He got as far as my bow-wave.  Huge hole in the water as both boats sucked it away.