h a l f b a k e r yYou could have thought of that.
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Maybe they ought to produce 100kW, but I'm pretty sure they
won't - that'd be 500W per passenger, which is out by a factor
of way. |
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Yeah you're probably looking at about 8kW at the prop, if everyone is motivated (but an average cross section of society). |
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I'm on a ferry carrying up to 1500 passengers (and cars / lorries) across the channel. We use 20,000kW of power to go at 20 knots (about 25mph). Even by your calculations that means we still have 19,250kW to find. It uses a lot of energy to push water out the way! For small river crossings where you don't have to worry about waves, and you are happy to go slow, then human power is baked in the form of rowing boats (some big enough to carry horses and carts etc). Good Morning. |
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Yes, car ferry - Big lumps of steel weighing tons. You're talking about many hundreds of tons extra. It's not going to be like that. The Channel goes woosh. I would consider a less wooshy place, maybe, presumably not the Solent, but how about the Swale or the Humber? What i want to know is, how much energy is used up by the water.
The other thought i just had is: what if there was a way of harnessing the power of the vehicle engines, maybe by putting them on treadmills? It would suffocate everyone, but that could be avoided by sticking hoses in the exhaust pipes. Then you get a reduced fare because you partly pay with your own fuel. |
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Good morning, by the way. |
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Oh and, checking the link, oddly i had one of my recurring dreams about NYC last night, so there you go. |
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True enough - that's why I added the note about having cars & lorries. I imagine that our engines are a lot more efficient than running everyone's car onboard, and since we burn heavy fuel oil it's an awful lot cheaper than petrol or diesel. |
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I've done some looking up on smaller boats - the one I've linked to is a 150 pax boat that looks a bit more heavy duty than you want. It has 460 bhp which I think is 343 kW to do a max speed of 10.8 knots. As far as I remember, to double the speed you multiply the power by 8 so using your figures you should be able to do a respectable 7 knots ish. Using Texticle's figures the speed is rather lower at 3 knots. Good for crossing a narrow river, but I suspect there would be lots of power losses to get the power out of lots of people and down to the propellor. It also could be hard work when the ferry is only half full. Vote changed to a neutral because the idea is more practical than I first thought, but I think a rowing boat is probably more practical |
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<obligatory> Add peddalling chickens for more thrrrrrrrrrust </ob> |
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[bigsleep], yes, and i make that sort of calculation about PCs too. OK, so the engines are more efficient. In that case, why not do it the other way round? Brake the ferry by transferring the momentum into flywheels in the vehicles, or, if they're electric, into a dynamo and recharge the batteries with it. |
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Nice idea, It is just possible to get some energy out of a ship by ' braking' - effectively let the propellors free-wheel. On a diesel electric ship, this will put electricity back onto the board, very useful in brown-outs - where you have lost one or more - but not all of the generators. The problem is this doesn't slow you down quickly enough, or under control, as you then can't steer properly. Generally to stop a ship you need to use more power by putting the engines astern. Perhaps your ideas would work on a floating bridge - a type of cross river ferry guided by chains? |
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I can see it wouldn't be well-controlled. I'm now thinking about a paddle-steamer type arrangement with a number of rotors parallel to the direction of the ship. For braking, first one slows, then the next, until they've all stopped. As each one slows, it transfers energy to a dynamo, and you get controlled deceleration which also generates electricity for whatever purpose. |
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I haven't checked the links yet, but will do so now. |
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