Electric?

[Flyboy]

Ford electric cars being recalled due to fires when charging.   https://www.autocar.co.uk/car-news/new-cars/updated-ford-kuga-phev-deliveries-halted-due-battery-fires

[cuthound]

11 hours ago, Jen-in-Wellies said:

We are in the early adopter phase at the moment.. Expensive if you want a commercial system as you are paying their development costs. Cheaper if you have good engineering skills, or know someone who does. No charging network on the waterways, so only suits certain cruising patterns. Unless this is you, then it is worth waiting a few years and benefit from all the early adopters hard work.

 

A bit like buying a CD player in the mid 80's. Very expensive and only a few people had one and would play you Vivaldi's Four Seasons on their stereo when you visited as that was all there was available. A few years later they were cheap as chips and everyone had one and all albums were available in the format. Continuing the analogy, now CD players are landfill and people buy vinyl and turntables, so in the future, perhaps people will rip out their batteries and electric motors and install diesels 'cause they reckon the sound is warmer?

 

Jen

 

Nah, in the future people will go even further back in time for their nostalgia trip and tow boats with horses. ?

 

Their emissions will be a bit different and be highly collectable by gardeners.

[cuthound]

10 hours ago, nicknorman said:

All of which ignores the fact that an all electric boat is only one solution to the problem of eliminating fossil fuel usage by 2050. What about hydrogen power? Make the hydrogen using renewable energy, deliver it in tankers to boatyards, fill up your boat’s hydrogen tank and off you go for a couple of weeks. With weight of the pressure tank not being much of an issue for boats, and the probability of a high speed accident rupturing the tanks almost zero, it seems to me that boats are an ideal vessel (pun intended) for hydrogen power.

 

And they could modify existing engines to run on hydrogen more cheaply than getting a fuel cell. ?

 

BMW have been running a fleet of hydrogen powered cars for years.

[dmr]

1 hour ago, IanD said:

The force is the same in both cases, it's what it takes to pull the boat through the water at 4mph (which is why I deliberately didn't put a number in, because it's higher than the force to pull it at 3mph).

 

The speed/power difference is exactly what you said, 4x higher power (ignoring propeller losses) for the propeller compared to the tractor.

 

Maybe you can see how to explain this to dmr, I keep trying but failing? ?

 

A couple of beers and I can certainly see your argument, and logically I can see that you must be correct, but I can still write a little equation that proves the opposite, I think maybe a cider might sort it out.

 

Work done = force x distance

so if the waterflow imposes a force on the boat the work required to move it a distance depends only on that force and the distance moved....no mention of water speed.

I struggled with this until the second beer.

You must be correct because if the boat is not moving over the land (like going up through Newbury in the winter) then no work is done, but the boat is obviously using a load of power just to stand still. So for the equations of motion and energy to work I need to include a static loss or power to standstill.

 

Its a bit like running on a treadmill.....more beer

[Murflynn]

1 minute ago, dmr said:

 

 

Work done = force x distance

 

easier to say power required = force x speed. 

speed is always relative to something.

it is false to assume the speed is necessarily relative to the static ground and not the moving water.

in this case the speed of the tractor (and therefore the boat) is relative to the medium in which the resistance to the force is generated - the water.

 

a more abstract analysis will tell you that you don't get owt for nowt.  you can't pull the boat with less effort just because you are on the towpath.

[Alan de Enfield]

4 minutes ago, Murflynn said:

................. easier to say power required = force x speed. 

 

There can be quite a difference between 'speed thru the water' and 'speed over the ground'.

T'other day I was doing 6 mph thru the water but only achieving 1mph over the ground, I turned around and was doing 11mph over the ground and 6mph thru the water.

[dmr]

4 minutes ago, Murflynn said:

easier to say power required = force x speed. 

speed is always relative to something.

it is false to assume the speed is necessarily relative to the static ground and not the moving water.

in this case the speed of the tractor (and therefore the boat) is relative to the medium in which the resistance to the force is generated - the water.

 

a more abstract analysis will tell you that you don't get owt for nowt.  you can't pull the boat with less effort just because you are on the towpath.

Well that's exactly what I said, but IanD says otherwise and he has (almost) convinced me, you can pull a boat with less "effort" (power or energy) if its done from the towpath, but not with less force, and energy is what its all about. It does feel like out for nowt, and I am still thinking that through, so even with a 100% efficient prop there must be excess energy going into the water, but how is that more when providing power from the prop than the tractor????

This is no good, its only 9 and Ive already almost hit the daily beer quota.

 

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

[peterboat]

7 minutes ago, dmr said:

Well that's exactly what I said, but IanD says otherwise and he has (almost) convinced me, you can pull a boat with less "effort" (power or energy) if its done from the towpath, but not with less force, and energy is what its all about. It does feel like out for nowt, and I am still thinking that through, so even with a 100% efficient prop there must be excess energy going into the water, but how is that more when providing power from the prop than the tractor????

This is no good, its only 9 and Ive already almost hit the daily beer quota.

 

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

And we haven't even talked about putting ecofans on the stern pushing hot air................??

[dmr]

8 minutes ago, peterboat said:

And we haven't even talked about putting ecofans on the stern pushing hot air................??

or an electric motor more than 100% efficient, efficiency has increased steadily over the years so it must happen soon.

 

so, when the boat is pushed upstream by its own engine rather than pulled by a tractor where does the extra energy go??? I am gonna have a sleepless night with this.

 

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

[peterboat]

14 minutes ago, dmr said:

or an electric motor more than 100% efficient, efficiency has increased steadily over the years so it must happen soon.

 

so, when the boat is pushed upstream by its own engine rather than pulled by a tractor where does the extra energy go??? I am gonna have a sleepless night with this.

 

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

Have another beer. 

Electric motor using super conductors are very efficient 

[IanD]

OK, here are the equations:

 

Force*distance=energy

Energy/time=power

Force*distance/time=power

Distance/time=speed

Force*speed=power

 

Speed here is how fast the thing doing the pushing (or pulling) is moving relative to whatever it's pushing (or pulling) against.

 

Ignoring the exact units, take a force of 1 unit to pull (or push) the boat, which is travelling at 1mph (land speed) upstream against a 3mph current.

 

The tractor is pushing against the ground so for it speed is 1mph, so power is 1 unit.

 

The propellor is pushing against the water so for it speed is 4mph, so power is 4 units.

 

It might seem magic, but it's physics really ?

Edited October 13, 2020 by IanD

[dmr]

3 minutes ago, IanD said:

OK, here are the equations:

 

Force*distance=energy

Energy/time=power

Force*distance/time=power

Distance/time=speed

Force*speed=power

 

Ignoring the exact units, take a force of 1 unit to pull (or push) the boat, which is travelling at 1mph (land speed) upstream against a 3mph current.

 

The tractor is pushing against the ground so for it speed is 1mph, so power is 1 unit.

 

The propellor is pushing against the water so for it speed is 4mph, so power is 4 units.

 

It might seem magic, but it's physics really ?

Yeah, i'm good with physics and equations like this, i'm an engineer.

I like going to extremes because that tests things out, I also like conservation of energy as that's a good test too.

I can see that you are correct (I think) but am struggling to resolve a couple of things.

If driving the boat by its prop rather than pulling it by a tractor uses four times more power (energy) then where does that extra energy go to? In both cases the boat is moving through the water at the same speed so any energy moved to the water by various hydrodynamic effects will be the same, so where does all that extra energy go?????

 

From a conservation of energy standpoint I have a nagging doubt that your 4 times factor is wrong and the only energy or power gain is due to the relatively low efficiency of a prop???? but the concept of the boat using a lot of power to stand still (over land) is a convincing argument in your favour.

 

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

 

[nicknorman]

8 hours ago, dmr said:

Yeah, i'm good with physics and equations like this, i'm an engineer.

I like going to extremes because that tests things out, I also like conservation of energy as that's a good test too.

I can see that you are correct (I think) but am struggling to resolve a couple of things.

If driving the boat by its prop rather than pulling it by a tractor uses four times more power (energy) then where does that extra energy go to? In both cases the boat is moving through the water at the same speed so any energy moved to the water by various hydrodynamic effects will be the same, so where does all that extra energy go?????

 

From a conservation of energy standpoint I have a nagging doubt that your 4 times factor is wrong and the only energy or power gain is due to the relatively low efficiency of a prop???? but the concept of the boat using a lot of power to stand still (over land) is a convincing argument in your favour.

 

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

 

The extra energy, arising from having to push against something already moving away from you (the water) as opposed to something unmoving (the towpath) is converted to kinetic energy of the water being pushed back, wave energy in the wake, rotational energy in various vortices and some heat arising from friction and viscosity at the prop/water interface. Of course the energy eventually ends up as heat, the various motions of the water subsiding due to friction and viscosity.

 

Oh another analogy. Carrying your shopping basket up the Shopping Mall stairs requires much less energy than achieving the same thing by walking (or running) up the adjacent down-going escalator.

Edited October 14, 2020 by nicknorman

[Murflynn]

9 hours ago, IanD said:

OK, here are the equations:

 

Force*distance=energy

Energy/time=power

Force*distance/time=power

Distance/time=speed

Force*speed=power

 

Speed here is how fast the thing doing the pushing (or pulling) is moving relative to whatever it's pushing (or pulling) against.

 

Ignoring the exact units, take a force of 1 unit to pull (or push) the boat, which is travelling at 1mph (land speed) upstream against a 3mph current.

 

The tractor is pushing against the ground so for it speed is 1mph, so power is 1 unit.

 

The propellor is pushing against the water so for it speed is 4mph, so power is 4 units.

 

It might seem magic, but it's physics really ?

no it ain't - it's fairy-tale analysis.

[IanD]

9 minutes ago, nicknorman said:

The extra energy, arising from having to push against something already moving away from you (the water) as opposed to something unmoving (the towpath) is converted to kinetic energy of the water being pushed back, wave energy in the wake, rotational energy in various vortices and some heat arising from friction and viscosity at the prop/water interface. Of course the energy eventually ends up as heat, the various motions of the water subsiding due to friction and viscosity.

 

Oh another analogy. Carrying your shopping basket up the Shopping Mall stairs requires much less energy than achieving the same thing by walking (or running) up the adjacent down-going escalator.

Funnily enough the escalator analogy is exactly what I was going to use next -- walking up stairs at 1mph compared to up an escalator descending at 3mph, you climb 4x as many steps so your legs do 4x as much work -- the truth of this should be familiar to anyone (not me!) who's ever used a stair-climbing exercise machine...

Edited October 14, 2020 by IanD

[Murflynn]

1 hour ago, IanD said:

Funnily enough the escalator analogy is exactly what I was going to use next -- walking up stairs at 1mph compared to up an escalator descending at 3mph, you climb 4x as many steps so your legs do 4x as much work -- the truth of this should be familiar to anyone (not me!) who's ever used a stair-climbing exercise machine...

 

 

a simpler example - if you exercise on a walking machine the work/energy is expended while you are actually stationary, but your speed is measured relative to the moving belt.

[dmr]

1 hour ago, nicknorman said:

The extra energy, arising from having to push against something already moving away from you (the water) as opposed to something unmoving (the towpath) is converted to kinetic energy of the water being pushed back, wave energy in the wake, rotational energy in various vortices and some heat arising from friction and viscosity at the prop/water interface. Of course the energy eventually ends up as heat, the various motions of the water subsiding due to friction and viscosity.

 

Oh another analogy. Carrying your shopping basket up the Shopping Mall stairs requires much less energy than achieving the same thing by walking (or running) up the adjacent down-going escalator.

I am now happy that a pull from the land is more efficient but am struggling with the conservation of energy thing. All the wake and vortices stuff (from the boat) will be identical in both cases because the boat is moving through the water at the same speed, so the only difference is what goes on at the prop-water interface. In the real world a prop moves a lot of water backwards which takes a lot of energy, but using an extreme case and energy conservation concept as a test, what would happen if we had a 100% efficient prop (zero slip)???      The excess energy must go into the water...but how?

 

With a zero slip prop (infinitely big?) the boat would move through the water  at a speed dictated only by prop speed and pitch, there would be no jet of water and all the energy would go into the wake etc.

 

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

[Mike Todd]

14 hours ago, nicknorman said:

I have to agree with Ian on this one - sorry! The force required to push the boat is the same regardless of whether the force is applied by the prop or by the tractor, but due to the current the speed at which the force is applied is much higher for the prop than for the tractor, hence the tractor requires much less power than the prop, even disregarding the relative efficiencies.

 

Using the helicopter analogy, a helicopter requires a LOT more power to hover out of ground effect, than it does in forward flight at modest speed. Bear in mind that aircraft including helicopters remain aloft by pushing (accelerating) air down. So in the hover, the helicopter is pushing down on air that has already been pushed down - ie it is in a column of already descending air. Whereas the helicopter in forward flight is constantly encountering new air that is not already moving downwards fast, it therefore requires a lot less power to accelerate the air downwards to generate the lift.

If this (or what I think you are saying) were true then the towing tanks used to test ship hull forms would be a waste of time! They use, effectively, a tractor to pull the model through the tank water and measure the force as a means of measuring the ship resistance.

 

For example, see https://www.southampton.ac.uk/engineering/research/facilities/towing-tank.page

[nicknorman]

1 minute ago, dmr said:

I am now happy that a pull from the land is more efficient but am struggling with the conservation of energy thing. All the wake and vortices stuff (from the boat) will be identical in both cases because the boat is moving through the water at the same speed, so the only difference is what goes on at the prop-water interface. In the real world a prop moves a lot of water backwards which takes a lot of energy, but using an extreme case and energy conservation concept as a test, what would happen if we had a 100% efficient prop (zero slip)???      The excess energy must go into the water...but how?

 

With a zero slip prop (infinitely big?) the boat would move through the water  at a speed dictated only by prop speed and pitch, there would be no jet of water and all the energy would go into the wake etc.

 

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

No there is a big difference between the two cases. In the case of the prop, as I said the thrust is produced by pushing water backwards. Pushing the water backwards, (ie giving it kinetic energy relative to the rest of the water) to create the thrust is where the energy goes. In both cases the water has to flow around the boat, but only in the case of the prop is the water sent whizzing backwards relative to the general flow of the water.

[Midnight]

On 12/10/2020 at 22:11, wandering snail said:

No-one has picked up as yet on the absurdity of having to use a diesel gennie to keep it all going.

Nail on head!
I met a fella at Ripon last year boasting about his 'all electric' boat covered in solar panels. When asked how many hours travel he gets he answered about five - not even enough to get down to York from Ripon. So I asked what he did when the batteries run down and he said "start the generator to charge them".
All electric boat hmmmmm!

[nicknorman]

3 minutes ago, Mike Todd said:

If this (or what I think you are saying) were true then the towing tanks used to test ship hull forms would be a waste of time! They use, effectively, a tractor to pull the model through the tank water and measure the force as a means of measuring the ship resistance.

 

For example, see https://www.southampton.ac.uk/engineering/research/facilities/towing-tank.page

No, the tests are a valid way to measure the force, from which drag etc can be derived. You have to think in terms of what frame of reference you are using. For a ship, the frame of reference is the water. It makes no difference to drag whether the water happens to be moving at some velocity relative to some bit of the earth, or not. The only thing relevant is the speed of the ship through the water.

 

It is the different frames of reference used in the original example ie using a tractor (ground frame of reference) or a prop (water frame of reference) in water that moving relative to the land, that causes the confusion.

[dmr]

24 minutes ago, Mike Todd said:

If this (or what I think you are saying) were true then the towing tanks used to test ship hull forms would be a waste of time! They use, effectively, a tractor to pull the model through the tank water and measure the force as a means of measuring the ship resistance.

 

For example, see https://www.southampton.ac.uk/engineering/research/facilities/towing-tank.page

I think we all agree that the force is the same regardless of where it comes from, its the speed and hence energy that is different.  The towing tank is not accurate, among other things I don't think water resistance simply scales with model size, but the ship science people at Southampton have a lot of experience and know all the correction factors.

 

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

[dmr]

26 minutes ago, nicknorman said:

No there is a big difference between the two cases. In the case of the prop, as I said the thrust is produced by pushing water backwards. Pushing the water backwards, (ie giving it kinetic energy relative to the rest of the water) to create the thrust is where the energy goes. In both cases the water has to flow around the boat, but only in the case of the prop is the water sent whizzing backwards relative to the general flow of the water.

But I think (and I do mean think rather than know) that the plume of water is not an intrinsic part of prop operation, its a result of prop slip and hence inefficiency?

As props gets bigger they are more efficient because the slip is less. Question....is the plume just bigger and slower or is it actually less? I think its less.  In the extreme a very big prop would have zero slip so all the energy would go into moving the boat forwards rather than pushing the water backwards?

 

I suspect the answer is that zero slip is theoretically impossible because there will always be water resistance from a moving boat.

If I am correct then the energy saved by towing from the land is effectively the prop slip inefficiency.

 

I might have to phone a friend in a minute (who by coincidence has strong connections with that tank in Southampton).

 

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

[Alan de Enfield]

Being a boater of simple-brain it's all beyond me, but this pic shows us doing 6 mph into a 5mph current, about 1500rpm

 

The two central 'disturbances' are the props, the two outer 'disturbances' are the hull 'edges'

 

 

 

[IanD]

49 minutes ago, Midnight said:

Nail on head!
I met a fella at Ripon last year boasting about his 'all electric' boat covered in solar panels. When asked how many hours travel he gets he answered about five - not even enough to get down to York from Ripon. So I asked what he did when the batteries run down and he said "start the generator to charge them".
All electric boat hmmmmm!

Even downstream (Ripon to York)? Doesn't have big enough batteries then. Size matters... ?

 

(upstream I could understand, this is *very* power-hungry as discussed above)