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Is my Spring in the Air - or my prop not supported? Answered

I have been reading on this site about the problems associated with building and using a vehicle for road use that runs on a clock-work basis. The square cube law problem re the spring and also the problems created by the gyro forces of the flywheel. What I want to ask is: Would it be possible to have a spring or series of springs big enough that could drive a generator to charge a bank of batteries that would then power a narrowboat on the inland waterways and potentially rivers of the UK. There is a company that supplies engines and batteries and their paraphernalia suggests it is possible to get 2 hours of battery propulsion from one hour of diesel use - http://www.betamarine.co.uk/inland/Beta_Hybrid/inland_hybrid.html. So, if the engine was removed could it be possible to use some kind of clockwork spring-thing instead of the engine big enough to charge batteries that would then power the boat. I am thinking that winding the spring would be done but either a very geared down bicycle or some kind of geared down lever crank with ratchet or even a transportable friendly donkey...I appreciate that fitness and maintaining it would be important to wind up the spring by pedalling the bike, cranking the lever or chatting to the donkey to keep it friendly. How big would the spring need to be and how long would it take to wind it up by bicycle, crank or donkey. Keen to know what the real problems would/could be...am thinking it might be possible to use a series of springs so they do not have to be so very big and therefore could overcome the square cube law problem and how many would be needed to charge the bank of batteries to then turn the prop.


Dang!  I was looking for a quote on the typical energy density, or the related value, specific energy, of a clockwork type mainspring.  Surprisingly Wikipedia failed me.  At the time of this writing, I found no mention of mainsprings here:
or here:
or here:

But via Google I did find a paper on some newfangled mechanical springs made from carbon nanotube (CNT) yarn,
and here's the quote:

Defect-free groupings of CNTs stretched in tension with a density of up to 7.7*106 kJ/m3 or 5*103 kJ/kg, more than three orders of magnitude higher than the energy density of traditional springs made of steel, and a factor of 5 greater than the energy density of lithium-ion batteries.

The emphasis on the words "three orders of magnitude" is mine.  I don't know if you're familiar with language like that.  One order of magnitude means ten times, and three orders of magnitude is one thousand times.  So that's kind of a big deal.

Assuming that quote is believable,  I can make a table like so:

energy storagespecific energy (megajoules/liter)
gasoline(petrol) 36 MJ/L
CNT superstrong mainspring 7.7 MJ/L
lithium ion battery 1.5 MJ/L
ordinary steel mainspring 0.0077 MJ/L

Note that it is necessary to include the efficiency of your energy conversions.  For example, that number for gasoline looks really good, but a typical internal combustion engine (ICE) is only going to be about 20% efficient at converting chemical energy into mechanical. I mean compared to a battery driving an electric motor, which might give as high as 80% chemical into mechanical.  That means you would need about only 6 times the volume in Li-ion batteries compared to gasoline, not 24 times, which is the number you get if you just divide 36 MJ/L by 1.5 MJ/L.

I can do the math for an ordinary steel mainspring too.  I think I can safely assume it would have about the same (good) 80% efficiency as a battery powered boat, the only difference being it only has about 1/200th the specific energy, and that will be about (1/200)*(1/6) = (1/1200), when compared to gasoline. 

So um... there's your answer... approximately.  If the gasoline powered boat has a 10 liter tank, then a comparable steel-mainspring powered boat needs about 12 000 liters of steel-mainspring.  Or you could just use 10 liters of  mainspring, with a range of (1/1200) that of the gasoline powered boat.

BTW, that carbon nanotube yarn is whole different animal.  That stuff, if it were ever actualized, erm... made real.  Then I think a mainspring could power your boat, and give you performance comparable to that of the gasoline powered boat. 

Although I am not sure what happens when that super-thin, super-strong, nano-spring slips its bearings and unwinds itself explosively. 

I am guessing it would slice the boat into ribbons, and the same for anyone unfortunate enough to be in the boat when that happens. Of course that's just speculation on my part.  I'm just saying, that nano-tech is weird stuff.

Wow what a total answer - in fact I am consumed by your answer, I've read it so many times - there's lots of language I am not familiar with but i understand your explanations up to a point...thanks for the way you've got your head right into every aspect. My donkey has just left i think he knows he's out of a job...like an earlier answer I have to now go and read up on not just the reality of the maths you've alerted me to but also the concept nanotube and from what little I know I think it would slice the boat and all its occupants into small pieces if it went twang ...I did read something about an enlarged spring someone had made for a bicycle doing considerable damage to both bike wheel and the riders calf muscle when it broke its anchor and unwound at a pace. Also on wiki read quite a lot about injuries from mere tiny wrist-watch springs back at the beginning of the 20th century before they put the spring into a barrel. I like the weird stuff despite its potential slicing abilities.

So for hypothetical reasons you want to know how to do the math to figure out how to make a clockwork engine. While i don't know much of anything about the math behind it all i do know how to effectively use a google search. So here are some links that will put you in the right direction.


I'm sure there would be a lot more needed to work everything out but i wouldn't even know where to start. Hope that helps.

It totally helps thanks...I guess like any question it raises more questions for me anyway and i see I have a lot of reading to do. I thought maybe springs had come a long way and with modern materials might have made them more efficient....ultimately whether or not its very efficient compared with an engine I wanted to know if the batteries could be charged another way and wondered whether a spring could work. Thank you for your time and patience with this. I will read more.

I can design a charging system the can supply a city with electricity for 24 hours and only has to run for one hour.

But the kicker is that it has to be a really small "city" and a really huge motor and battery set.

The key to any system is finding a way to utilize the highest percentage of the energy and sizing all the parts to fit.  And it seems that every conversion wastes some amount of that energy.

The amount of work involved and the energy lost from one bit to the next makes this highly inefficient.

First of all the engine provides a good amount of torque and RPMs to get the generator spinning fast enough to charge the batteries. To match this you would need a rather large and long running spring that would take a good bit of energy to get coiled up. If you could find a good enough spring that could run a generator for an hour then you could get 2 hours of use out of it. But it could take you 4 to 8 hours of very hard and fast peddling to get that spring wound up. In the end probably not worth all the effort. Might as well make it a paddle boat.

cut out the middle men...? you mean cut out the men in the middle...? you mean snip around the outside edges of the figures without dresses commonly referred to as men and remove them completely...? why didn't i think of that...cut out the middle men - its genius...

Try this. English may not be your first language:

You may also want to look up "cumulative efficiency losses".

lol, Try this: are we talking the same English:

I may indeed want to look up "cumulative efficiency losses". Original post was a question not an assertion ... is this one of those sites where people just come to pose then. I get 20 words from you thus far and none go anywhere near attempting to answer my question - the rest well that's just a pose i think.

You got an excellent response from MPilchFamily. He pointed out quite well that motors are much better than human beings at delivering the kind of sustained output you need to drive a generator to charge batteries.

He also pointed out that doing multiple stages of energy conversion is quite inefficient, and therefore that your proposal is a very poor engineering design. He used a common English expression to summaries that statement, which instead of responding to you chose to ridicule.

In summary, you did get an excellent attempt address your problem. Just because you didn't like the answer doesn't mean there wasn't one.

I agreed with MPilchFamily that he was probably correct and it wouldn't work etc however went on to point out that I wasn't looking to compete with the engine just asking (whether or not it was or wasn't efficient) if it would work. I don't get what your point is...'common English expression' what's that got to do with the price of bread (oh there's another one)... is it that in your mighty opinion I got a good answer and should be quiet now ask no further questions, clarify no further pursue the subject no more. If so why comment at all and what was the meaning of +1 ...blah de blah de blah and why bother with it. It's meaningless and totally unhelpful.

If you intended that I should be quiet now why didn't you say that in the first place then I could have just ignored you (that's coming soon) as pretty much everything else you've said save 'You may also want to look up cumulative efficiency losses' - which has been an interesting read thus far has been a complete waste of words, time and whilst we're on the subject energy too.

I find you exceptionally patronizing, your comments unnecessary. However if you have knowledge in the area I'd like to read about it if not - go and find someone else to patronize of protect or whatever it is you do to inflate your own ego...I asked a question I got an answer but wanted more, don't try and stifle that in anyone ever would be my advice to you.

I never said anything about a common English expression, that was someone else. I used the expression "Cut out the middle man" to emphasize mplichfamily's point about the inefficiency. i.e. Cut out the middle man and just drive the boat with the motor or donkey directly. Your responses about cutting out paper, and then about some non existent joke, and again now about the price of bread are, puzzling, to say the least and come across as dismissive and arrogant.
I also never asked you to stop asking questions or be quite, just think about them a little more. A simple google search will tell you how to calculate the work from a spring. If you want a better understanding of how to apply that to your question then that's great.
+1 is the short hand way people on this site show agreement. I simply posted to show that I too agreed with what mplichfamily said and then summarized with a commonly used expression. This is not useless as it shows that more than one person supports someones take on the problem without having to retype what they said.
Once again I did not say anything about looking up cumulative efficiency losses, that was someone else.

Now one more time lets try to get back on topic: At 2 knots, assuming 2 hours of cranking and 30 min of battery, you get an effective speed of .4 knots. At those speeds you might be better off just drifting and wouldn't be able to get back up stream. From some of your posts I get the feeling this is more about getting the boat of the grid and a smaller carbon footprint than anything else, which is fine. With that in mind you might want to consider upstream pollutions like how terrible the manufacturing of batteries is for the earth and the extra food required by you or your donkey to crank the spring for 2 hours. The extra food requires more trips to the shops and requires more farm machinery and factories to run.
How long each day will the boat be running? I suspect that solar panels could do the job if it doesn't run all day and you have enough panels. This doesn't get rid of the battery pollution but it could be more efficient and getting rid of all pollutants in this day and age is barely possible.

Ok well ducking all the 'we are here to help kind of patronizing stuff’ (because I don't feel helped by you especially) you've given me in your answer let me start with this. I apologise if I have offended you but I don't understand why your answer whatever abbreviations it used was in the least bit helpful save to you and something that I find (in your words) dismissive and arrogant especially to new people who come to this site thinking they might find knowledgeable people here who can answer their questions in an informing way however simple, rudimentary, basic those questions may appear to be to you. It seems from some of the other answers that there's a nodding clique here all in agreement but not clarifying to me the physics that I am asking about.

If I may use your ‘Now one more time let’s try to get back on topic’ (rather condescending approach):

Drifting is not an option, 15 tons of barge drifting is a danger especially to canoeists, fishermen and others including bathers who use the canals and moves away from the question I am asking.

Canals don't have streams the water is stagnant between locks save one canal in the UK which is a dead-end and therefore one comes back down it anyway should one venture up it in the first place.

I could have the donkey drag it but I need electricity for other things too like lighting, music, telly, pumps to pump out the water from washing/shower/bilge etc (Barge floor pan in below waterline). For the next part re: your footprint issue etc I do consider these things but unlike fuel for household electricity /cars etc my carbon footprint whilst living on a barge is considerably less than your average household. The company that does the latest batteries for boat use speak of many recyclable components of the modern secondary cell batteries that they produce and how much then this saves on planetary pollution as opposed to burning oil for example.
The donkey idea. Well I can see that feeding him/her might be an issue as cycling (don't use a car) to the foodery for the wee chap and carrying back enough food so I don't have to go the next day might be difficult though the canals do run through a lot of farms and this might then make it feasible up to a point but then I included cycling to charge batteries or wind springs if springs were likely to be of any feasible use...but cut out the middle man as u say and maybe cycle to charge the batteries. It would be hard to peddle and reach/maintain 2 knots for a 15 ton barge and also steer etc as well.

Currently I use about 1.5 litres of diesel per hour for a period of no more than 5 hours per day (usually less) this includes the diesel fired heating system and averages out overall to about 6 - 8 litres of diesel every day I cruise - I don’t cruise everyday or run the engine every day but still have enough electricity for my needs. I have currently one solar panel which is pretty hopeless if I am honest and also the sun especially this time of year is off on its own holiday and nowhere in sight, also its snowing at the moment.

So, moving back to my motivation for the original question, living on a barge with minimum requirements for heating, cycling a lot when shopping is needed all I was doing was speculating about how and if I could get away without a diesel engine and if so what would I put in its place. I have to accept that whatever I use it's never going to be as efficient as the diesel engine and its battery charging capability or the newer electric/diesel hybrids (links in original question). But given I have the boat and already have the batteries then I further consider how to save on my carbon footprint.

I don't know if you're able to see it but your answer is very full of condescending assumptions about what it is I should/should not consider assuming that I haven't considered them from the start.

Why you seem to think you're being so very reasonable with your answers is completely beyond me but then I'm just a guy living on a barge with a partner and a dog, listening to the wind howl outside and the rain lash musing about springs and other means of battery charging that could possibly overcome the need for a diesel engine.
I came to this site because of looking on Google and was directed to a question someone else had posted about building a clockwork car. A lot of the issues against seemed to be about the weight of the springs, the power output re: friction and hill climbing, the square cube law and steering with a huge inboard flywheel. It just got me thinking that accurate steering on a barge is not so essential and takes place over a long distance, hill climbing/road surface etc doesn’t come into it, and size/weight isn’t such a great issue.

I expect what would be important to know is revs and time required to charge the batteries so they can be effective in propelling the boat, lighting, pumps etc. How much time it would take to charge the batteries, how much cycling/cadence rate would be required to render a decent charge. If I can get that info I’ll leave the donkey with a friend.

"Cut out the middle man" is a viable summery of what mplichfamily said. As is KISS (Keep it Simple, Stupid). Here's a question, why would even want to use such an inefficient system, particularly when it involves using at least two other, more efficient, systems in inefficient ways (just use a direct drive motor, have the donkey just drag the boat).
If you don't have the technical and mathematical expertise to answer the questions you have then you really have no grounds with which to dismiss the many and varied responses telling you this is not a feasible plan.
When you almost immediately resort to cheap sarcasm and insulting the community you insure that you are going to get fewer and fewer cordial responses. You came to us and we like helping people, but only when they want to be helped. If you are looking for people to always agree with you and tell you your ideas are great this is the wrong place (unless they really are great). Also if you look at a sample of other questions here you will see that just throwing basic google questions at us (Spring work output, etc) doesn't yield a lot of responses. The answer to pretty much every question starting with "Where can I find ..." is "Google".

Now back to the boat. How fast will this boat travel when running on the batteries?

Thanks for your reply. The trouble I see with a constant drive such as a paddle boat would be that it would need continuous peddling (though I understand the joke). It would require a lot of energy to wind up the spring to match the efficiency of the engine but that was not the intention of the question - it is not my intention to try and match the engines efficiency of 1 hrs diesel to two hours electric. All I want to know is; is it feasible, what sort and/or size of spring would I require, if a series of springs would be affective in overcoming the square cube law, what measurement of torque and rpm output would be required to charge the batteries. If I could get 30 mins of battery power sufficient to drive the boat against two hours of winding - I would deem it to be successful as fuel costs would be minimal - why would it need fast peddling, surely winding is winding and I think if it didn't use any diesel, petrol and other such planet destructive fuels then in the end the effort would be very much worth it.

You would be lucky to get 30 min of battery life out of multiple runs of a given spring. Not to mention the hours of effort needed to rewind the spring each time. Another aspect you may not have considered is the amount of additional clockwork needed to wind the spring and make use of the power. The whole system may be too big for your application.

I'm with you on this...I would be lucky i think. I mean if it was a good idea everyone would be doing it. The question was born of another post on this site about springs and road vehicles and I was then just thinking of the battery power on a boat, the reduced friction, constant gravity etc as opposed to hills, undulations and the like on roads and also I am about to buy a narrowboat. As I am sure you will know in olden times they used horses to drag barges...I was thinking i could have a donkey that via a contraption could wind up my spring for me...yes i would have to feed said Donkey and transport it with me but I think I could do that but it could drag a rope that could wind up my spring...if it was worth winding up that is. Any ideas where i can get any figures on output of spring etc or calculation to work out said output?

From a process perspective look at it like this:
You could cut the storage and just drive a propeller.
For storage, use a generator and battery. Springs are no good use to you for this.


I suppose i could spend a few days or weeks perhaps in the sunshine assuming i could find some using solar panels to charge my batteries and then get a couple of hours propulsion. I was trying to think of a way to add to my ability to charge my storage cells; wind power will give me something, solar panels will add to this and then something else - the spring idea was just a thought but the energy to re-wind would be prohibitive in efficiency terms - i suppose I could just cycle hard for a few hours to charge the batteries. It would probably not be efficient in the way we think of efficiency but then moving a 20 ton vehicle about the Inland Water Ways at 2 knots isn't the most efficient lifestyle/pastime anyway but wouldn't cost much if anything after initial purchase.