Electric?

[IanD]

59 minutes ago, Jen-in-Wellies said:

The Thames used to have a tow path all the way along the navigable bits. Other rivers did too. It was how narrowboats got from London to Oxford. Reinstate that and remove anything that blocks the tow line, then you have a way to move an electric boat without flattening the batteries by a much more efficient towing tractor as a modern version of a horse on the path. On the Severn, a group of boats would be pulled by a tug. Have a tug for the river section with the ammonia power being proposed for coastal freight. Lots of ways of doing things, mostly worked out and regularly used a century, or two ago.

 

You put all your 250W or so in to moving the boat when bow hauling it from the bank side. With a propeller in water, a lot of the power is wasted thrashing the water around. It is why canals were built with tow paths for a horse (740 ish Watts max), rather than have the horse on the boat with a tread wheel to turn a paddle wheel, or prop.

Jen

You might be misunderstanding how force and energy works, especially for horses and people. So long as you can provide enough static pull force to not be dragged backwards, you can always move forwards slowly even dragging something heavy (like a boat against a current, or a *very*heavy boat in still water), the power/energy needed is OK because you're moving slowly (power=force*speed). The "power ratings" for horses (and people) are based on long-term outputs at a speed and against a force which is best for the animal, when Watt defined the horsepower (746W nowadays) it was for a horse pulling something like a plough or a cart, the sustained human limit of a few hundred watts is usually for something like a cyclist thrashing away at 120rpm.

 

https://en.wikipedia.org/wiki/Human_power

 

Both animals can generate much bigger forces at slow speeds (but with lower power output), which is why they can pull heavy boats (or ones against a current) slowly. Unlike a propeller, sustaining this force doesn't really take much energy for animals -- imagine a boat moving at 3mph against a 3mph current, this would need 4bhp/3kW from an engine just to stay still, but a man or a horse can hold the boat in place with a tiny fraction of this power consumption. Indeed, a stake knocked into the ground can do it with no power at all...

 

Nothing to do with a propeller thrashing the water around as such, a well-matched prop has typical efficiency of 70% or so which is not bad -- it means your idealised horse needs a 1.4bhp engine to match it in still water. So if there's no current a horse doesn't have a huge advantage over a prop (about 40%) , but against a current this rises rapidly as explained above, because the horse only sees the forwards speed of the boat against the ground (e.g. 1mph) but the engine sees this plus the speed of the current (e.g. 3mph) -- in this case you'd need more than 5bhp from the engine to equal one horse.

 

Exactly the same applies if you have a tractor on the bank (not a tug in the water), this sees the same advantage as the horse (and no propeller power loss). So if towing against a current this is way better than an onboard engine, even in still water it only needs to have 70% of the power. It's one reason why they experimented with tractors (and even miniature trains) to pull boats in the early 1900s, but the practicalities didn't work, and anyway power was cheap with the new-fangled engines.

Edited October 13, 2020 by IanD

[dmr]

56 minutes ago, peterboat said:

And yet dumb barges traveled up and down the Trent using mud weights no engine power at all, that is a fact. The answer is of course they were proper boaters that knew you dont fight the tide or current you let it do the work,

Also the 100 ton fully laden barges used to travel around with 20 hp listers again up and down the Trent how did they do that?

The working pair with an 18Hp engine is often quoted, but they did not go unaided up rivers with any flow, even proper boats with proper engines, proper propellers and driven by proper boaters can not defy the laws of physics. 18Hp will work in most conditions but even that is too much for current battery technology to sustain for long periods.

 

The experienced boatman able to "read the water" is also often quoted and it's true that boaters with no river knowledge will sometimes not choose the best route, but there is just no way of avoiding much of the flow, especially on narrower rivers like the Kennet.

 

We have about 35Hp available and on several occasions have used every last bit of it.

 

Electric will work for some boaters, a home mooring and short days out like you, but not for CC'ing and rivers. Maybe some types of boating (like mine) will just have to go.

 

.................Dave

[dmr]

11 minutes ago, IanD said:

 

Both animals can generate much bigger forces at slow speeds (but with lower power output), which is why they can pull heavy boats (or ones against a current) slowly. Unlike a propeller, sustaining this force doesn't really take much energy for animals -- imagine a boat moving at 3mph against a 3mph current, this would need 4bhp/3kW from an engine just to stay still, but a man or a horse can hold the boat in place with a tiny fraction of this power consumption. Indeed, a stake knocked into the ground can do it with no power at all...

 

 

I disagree.

 

If my boat was in a river flowing at 10mph I could not hold it on a rope, the required force would be huge. There is a big difference between a man or horse holding a boat and a boat firmly tied up. A tractor without brakes would use a lot of power holding a boat steady (and burn out its clutch ?).

Power is force times speed, but that speed is speed over the land so the power required will be the same regardless of whether it is applied by a horse on the land or a propeller on the boat. The speed of the water changes the force that is required.   

but I could be wrong.

 

..................Dave

[peterboat]

1 hour ago, Jen-in-Wellies said:

The Thames used to have a tow path all the way along the navigable bits. Other rivers did too. It was how narrowboats got from London to Oxford. Reinstate that and remove anything that blocks the tow line, then you have a way to move an electric boat without flattening the batteries by a much more efficient towing tractor as a modern version of a horse on the path. On the Severn, a group of boats would be pulled by a tug. Have a tug for the river section with the ammonia power being proposed for coastal freight. Lots of ways of doing things, mostly worked out and regularly used a century, or two ago.

 

You put all your 250W or so in to moving the boat when bow hauling it from the bank side. With a propeller in water, a lot of the power is wasted thrashing the water around. It is why canals were built with tow paths for a horse (740 ish Watts max), rather than have the horse on the boat with a tread wheel to turn a paddle wheel, or prop.

Jen

I am getting ready for a mod on boat with props and gearing which will slow prop down but increase it in size, bigger props are more efficient so fingers crossed that it works 

[Murflynn]

25 minutes ago, dmr said:

I disagree.

 

If my boat was in a river flowing at 10mph I could not hold it on a rope, the required force would be huge. There is a big difference between a man or horse holding a boat and a boat firmly tied up. A tractor without brakes would use a lot of power holding a boat steady (and burn out its clutch ?).

Power is force times speed, but that speed is speed over the land so the power required will be the same regardless of whether it is applied by a horse on the land or a propeller on the boat. The speed of the water changes the force that is required.   

but I could be wrong.

 

..................Dave

you're not wrong.  

as far as the tension in the towrope is concerned, pulling a boat at 4mph in a canal will be exactly the same as holding a boat stationary on a river where the current is 4mph. 

the power required in each case is the same (unless the rope is anchored in the first case).  

engine power is determined by a 'brake test' where the power is transmitted from a drum attached to the output shaft to a belt passing around the drum that provides friction resistance to the engine.  the tension in the belt is measured along with the circumferential speed of the drum - as stated before power = force x speed. 

so in the stationary case an engine would be required to hold the towing rope in tension around a drum (i.e. in balance and not anchored)..

 

as you say, the tractor would burn out its clutch, which is the equivalent of the rope around the drum.

 

 

Edited October 13, 2020 by Murflynn

[Jen-in-Wellies]

 

50 minutes ago, IanD said:

Exactly the same applies if you have a tractor on the bank (not a tug in the water), this sees the same advantage as the horse (and no propeller power loss). So if towing against a current this is way better than an onboard engine, even in still water it only needs to have 70% of the power. It's one reason why they experimented with tractors (and even miniature trains) to pull boats in the early 1900s, but the practicalities didn't work, and anyway power was cheap with the new-fangled engines.

It may be that in the future it could go the other way. We have more efficient and smaller batteries and motors now. Diesel fuel and its cheap energy dense power may be taxed and legislated to the point that the balance shifts.

Edited October 13, 2020 by Jen-in-Wellies

[dmr]

11 minutes ago, peterboat said:

I am getting ready for a mod on boat with props and gearing which will slow prop down but increase it in size, bigger props are more efficient so fingers crossed that it works 

I have looked at some figures for prop efficiency and the gain with a bigger prop is significant, if you have space then fit one.

More generally the trouble is that bigger props need a deeper boat and these use more power to push them along, especially when they get close to the bottom.

 

................Dave

[IanD]

33 minutes ago, dmr said:

I have looked at some figures for prop efficiency and the gain with a bigger prop is significant, if you have space then fit one.

More generally the trouble is that bigger props need a deeper boat and these use more power to push them along, especially when they get close to the bottom.

 

................Dave

There is a gain but it's not that big. A typical prop is 70%, a bigger really well-matched one can be 80%, a smaller one can be 60%. Enough to make a difference, but not a game-changer.

Edited October 13, 2020 by IanD

[IanD]

41 minutes ago, dmr said:

I disagree.

 

If my boat was in a river flowing at 10mph I could not hold it on a rope, the required force would be huge. There is a big difference between a man or horse holding a boat and a boat firmly tied up. A tractor without brakes would use a lot of power holding a boat steady (and burn out its clutch ?).

Power is force times speed, but that speed is speed over the land so the power required will be the same regardless of whether it is applied by a horse on the land or a propeller on the boat. The speed of the water changes the force that is required.   

but I could be wrong.

 

..................Dave

You're taking it to extremes, there are always obviously two limits (force and power) and both have to be met. A tractor with brakes wouldn't use any power. A tractor in a low enough gear with the clutch let out could pull (slowly) any boat that didn't drag it backwards if the gearing was low enough -- remember "Give me a long enough lever and I will move the world"?

 

You are wrong about power; for pulling from land it's (force*speed over land) which can be as slow as you want, for a propeller its (force*(speed over land + water speed)) which can be many times higher. It's why you can see a boat at full throttle (lots of power) going absolutely nowhere upstream against the current.

16 minutes ago, Murflynn said:

you're not wrong.  

as far as the tension in the towrope is concerned, pulling a boat at 4mph in a canal will be exactly the same as holding a boat stationary on a river where the current is 4mph. 

the power required in each case is the same (unless the rope is anchored in the first case).  

engine power is determined by a 'brake test' where the power is transmitted from a drum attached to the output shaft to a belt passing around the drum that provides friction resistance to the engine.  the tension in the belt is measured along with the circumferential speed of the drum - as stated before power = force x speed. 

so in the stationary case an engine would be required to hold the towing rope in tension around a drum (i.e. in balance and not anchored)..

 

as you say, the tractor would burn out its clutch, which is the equivalent of the rope around the drum.

 

 

He is wrong, see my other reply -- use a low gear, not a clutch.

Edited October 13, 2020 by IanD

[nicknorman]

2 hours ago, IanD said:

 

No, it's that none of them make sense from an energy efficiency point of view -- generating/storing/using hydrogen starting from fossil fuel is less efficient than burning it in a diesel engine (at least 2x worse than using batteries), and all the alternatives are even worse.

Agreed, but my proposal was to use renewables to create the hydrogen, not fossil fuel.

[IanD]

22 minutes ago, Jen-in-Wellies said:

 

It may be that in the future it could go the other way. We have more efficient and smaller batteries and motors now. Diesel fuel and its cheap energy dense power may be taxed and legislated to the point that the balance shifts.

Absolutely, it's starting to happen with cars and will (very likely) happen with boats on inland waterways where recharging is possible (if not cheap to install). But it's likely to stay as (electric) power on boats not tractors/trains pulling them for exactly the same reasons this didn't work last time it was tried, it's just too inconvenient on a spread-out network.

2 minutes ago, nicknorman said:

Agreed, but my proposal was to use renewables to create the hydrogen, not fossil fuel.

So use the renewables to recharge batteries, then the same amount of renewables can propel 2x - 3x as many boats (or cars). Power isn't free now and never will be until we get working nuclear fusion... ?

 

(right now the total efficiency for the entire energy delivery system using hydrogen and fuel cells is about 3x worse than batteries; if we assume lots more development and better systems, thermodynamics says the ratio might come down to about 2x at best)

Edited October 13, 2020 by IanD

[Murflynn]

13 minutes ago, IanD said:

He is wrong, see my other reply -- use a low gear, not a clutch.

no. 

you are assuming the boat can be kept moving. 

dmr specifically said 'holding the boat steady'. 

in order for a gearbox to achieve that it would require a reduction ratio of infinity : 1 (which is possible with an automatic gearbox on a car, but is not possible in conventional terms).

[Jen-in-Wellies]

15 minutes ago, IanD said:

Absolutely, it's starting to happen with cars and will (very likely) happen with boats on inland waterways where recharging is possible (if not cheap to install). But it's likely to stay as (electric) power on boats not tractors/trains pulling them for exactly the same reasons this didn't work last time it was tried, it's just too inconvenient on a spread-out network.

What also killed off towing last time, both horse and tractor, was that it took two people to run one boat. One steering and one in charge of the horse, or steering the tractor. Instead, two people could run a motor and butty. Nearly double your cargo capacity for the same pay. It is what kept many UK narrow canals in use long enough for them to survive in to a time when people had enough leisure time and cash to have boats for pleasure. Going back to towing would make single handing impossible, unless the tow gadget is smart enough to drive itself, but with a crew doing the journey for fun, two people to one boat isn't a problem.

 

6 minutes ago, Murflynn said:

no. 

you are assuming the boat can be kept moving. 

dmr specifically said 'holding the boat steady'. 

in order for a gearbox to achieve that it would require a reduction ratio of infinity : 1 (which is possible with an automatic gearbox on a car, but is not possible in conventional terms).

Or stick the handbrake on.In which case, you are limited by the weight and tyre friction of the tow vehicle to avoid being dragged in to the water. Splash!

Edited October 13, 2020 by Jen-in-Wellies

[IanD]

22 minutes ago, Murflynn said:

no. 

you are assuming the boat can be kept moving. 

dmr specifically said 'holding the boat steady'. 

in order for a gearbox to achieve that it would require a reduction ratio of infinity : 1 (which is possible with an automatic gearbox on a car, but is not possible in conventional terms).

So put the brake on, like Jen said.

 

Given (for example) a windlass with enough step-down gearing anchored into concrete, I could hold a thousand-ton ship and move it (*very* slowly) forwards against any current. Or a heavy enough tractor with a low enough bottom gear could do the same, even with a tiny engine. Doing the same thing using the propeller would take hundreds of horsepower.

 

You're both missing the point about the different speeds for something pulling from shore (tractor) and in the water (propeller) when there's a current, go and write out the equations if you don't believe me. Newton was right ?

Edited October 13, 2020 by IanD

[Jen-in-Wellies]

18 minutes ago, IanD said:

Newton was right ?

Clever bloke Newton

[mrsmelly]

17 hours ago, TheBiscuits said:

 

Thanks Ian. You saved me the effort of typing, and you were pretty much word for word what I wanted to say.

 

Peter is an electric boat evangelist, and good for him.  I'd quite like one, but need to know for sure I can move it tomorrow ...

As with cars. As a for instance. I went to Cornwall last week. One tank of petrol and to a remote site. I asked if they had leccy charging points for cars. No we dont said the owner maybe in the future who knows. So no problem the next day I spent 3 minutes at one of the thousands of petrol stations and that was that for a few days. until lectric cars can come even anywhere near as useable for the millions then they will remain a pipe dream as now.

[dmr]

6 minutes ago, IanD said:

You're taking it to extremes, there are always obviously two limits (force and power) and both have to be met. A tractor with brakes wouldn't use any power. A tractor in a low enough gear with the clutch let out could pull (slowly) any boat that didn't drag it backwards if the gearing was low enough -- remember "Give me a long enough lever and I will move the world"?

 

You are wrong about power; for pulling from land it's (force*speed over land) which can be as slow as you want, for a propeller its (force*(speed over land + water speed)) which can be many times higher. It's why you can see a boat at full throttle (lots of power) going absolutely nowhere upstream against the current.

He is wrong, see my other reply -- use a low gear, not a clutch.

Extremes are a good way of testing that the assumptions, logic, and maths are correct.

I was using the static tractor and clutch as a sort of "intuitive visualisation" and the power = force x speed as the maths.

I think Murflynn explains it well. Think of a dumb barge getting towed by either a tug or a tractor, its the tension in the rope that matters, not the type of pulling device.

The only advantage of a bank side tractor (quite a big advantage) is that the losses in the tyres or tracks will be much less than the losses in a prop, which as you say can be huge if a prop is only 60% efficient.

 

..............Dave

[IanD]

2 minutes ago, dmr said:

Extremes are a good way of testing that the assumptions, logic, and maths are correct.

I was using the static tractor and clutch as a sort of "intuitive visualisation" and the power = force x speed as the maths.

I think Murflynn explains it well. Think of a dumb barge getting towed by either a tug or a tractor, its the tension in the rope that matters, not the type of pulling device.

The only advantage of a bank side tractor (quite a big advantage) is that the losses in the tyres or tracks will be much less than the losses in a prop, which as you say can be huge if a prop is only 60% efficient.

 

..............Dave

No, no, and a thousand times no...

 

Let's say you have a given force in the rope pulling the boat, the tractor is moving at 1mph and the current at 3mph. The engine power needed by the tractor is force*1mph (because power=force*speed), in whatever units you want to work, because the tractor is pushing against the grounds and it's moving over it at 1mph. The engine power needed by the propeller is force*4mph, because the propeller is pushing against the water and it's moving past it at 4mph and the force needed to pull the boat is the same. So the boat engine needs 4x the power of the tractor engine.

 

I don't see how much more clearly can I explain this, it's basic definitions of force and work and power.

[peterboat]

36 minutes ago, mrsmelly said:

As with cars. As a for instance. I went to Cornwall last week. One tank of petrol and to a remote site. I asked if they had leccy charging points for cars. No we dont said the owner maybe in the future who knows. So no problem the next day I spent 3 minutes at one of the thousands of petrol stations and that was that for a few days. until lectric cars can come even anywhere near as useable for the millions then they will remain a pipe dream as now.

And yet more and more electric cars are being sold Tim and the benefits to companies and company car drivers will put them to the top of the list. Car makers arnt really interested in private car buyers we are the minority car leasing and companies are the real target.

If you have not been watching google etc lots of delivery companies are ordering electric vans wonder why that is?

[mrsmelly]

2 minutes ago, peterboat said:

And yet more and more electric cars are being sold Tim and the benefits to companies and company car drivers will put them to the top of the list. Car makers arnt really interested in private car buyers we are the minority car leasing and companies are the real target.

If you have not been watching google etc lots of delivery companies are ordering electric vans wonder why that is?

New vans are a drop in the ocean against the millions of fossil fueled cars on the road. Until everybody has access to charge them they will remain a pipe dream. The government will have to find a way to make them work for millions of working class low paid people that need cars to get to work and add to the economy. It would be political suicide for any party to force electric onto people unable to charge them. Millions live in flats or streets without space to charge. Of course there is always the " Hybrid " that are not realy electric cars. I think we all agree that fossil fuel will go but it will not be ended without infrastructure for leccy cars or some other fuel coming to the fore.

[dmr]

15 minutes ago, IanD said:

No, no, and a thousand times no...

 

Let's say you have a given force in the rope pulling the boat, the tractor is moving at 1mph and the current at 3mph. The engine power needed by the tractor is force*1mph (because power=force*speed), in whatever units you want to work, because the tractor is pushing against the grounds and it's moving over it at 1mph. The engine power needed by the propeller is force*4mph, because the propeller is pushing against the water and it's moving past it at 4mph and the force needed to pull the boat is the same. So the boat engine needs 4x the power of the tractor engine.

 

I don't see how much more clearly can I explain this, it's basic definitions of force and work and power.

OK this is maybe my last go because its time for an early evening beer.

 

Lets imagine the boat getting towed by a little helicopter flying just above the water, the only things that matter are speed and force. The force is the tension in the tow rope (and this depends on water speed). The speed that goes into "power = force times speed" must be speed over the land because the helicopter has no knowledge that it is flying over moving water????

We need Nick Norman now, this is his neck of the woods?

 

There are of course many second order effects relating to prop behavior at different water flow rates (slip)

 

.............Dave

[mrsmelly]

1 minute ago, dmr said:

OK this is maybe my last go because its time for an early evening beer.

 

Lets imagine the boat getting towed by a little helicopter flying just above the water, the only things that matter are speed and force. The force is the tension in the tow rope (and this depends on water speed). The speed that goes into "power = force times speed" must be speed over the land because the helicopter has no knowledge that it is flying over moving water????

We need Nick Norman now, this is his neck of the woods?

 

There are of course many second order effects relating to prop behavior at different water flow rates (slip)

 

.............Dave

Now yer talking sense 

[ditchcrawler]

19 hours ago, peterboat said:

10 hours without sun and on a good day I can have used no battery power at all. The issue for some is that they want to cruise all day every day and in the future they will need deep pockets to do it

I know plenty of boaters and few that cruise all day, most only do 3-5 hours in one stretch 

Surly until there are lots of electric  the charging point wont appear, just like cars with hybrid systems which will soon be replaced by all electric with more charging points popping up each month. 

[peterboat]

6 minutes ago, mrsmelly said:

New vans are a drop in the ocean against the millions of fossil fueled cars on the road. Until everybody has access to charge them they will remain a pipe dream. The government will have to find a way to make them work for millions of working class low paid people that need cars to get to work and add to the economy. It would be political suicide for any party to force electric onto people unable to charge them. Millions live in flats or streets without space to charge. Of course there is always the " Hybrid " that are not realy electric cars. I think we all agree that fossil fuel will go but it will not be ended without infrastructure for leccy cars or some other fuel coming to the fore.

Its happening Tim their is always the electric bus for you ?

[mrsmelly]

1 minute ago, peterboat said:

Its happening Tim their is always the electric bus for you ?

Bought misen a fab turbo petrol today in awesome condition with a full service history, faultless and for peanuts, Ill let you wealthy bods get ripped off for a few years yet b4 I blow money on leccy jobby