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October 17

Some vehicle-related questions

In recent months, I have become interested in personal watercraft and other recreational vehicles. I’ve been doing a lot of reading about these things and I’ve found one or two areas which confuse me. I am aiming to get these matters clarified in order to ensure I have the right information necessary to make an informed decision about acquiring for myself something of this sort. I would appreciate it if you could take a look at look at these things for me.

The first point of confusion for me would appear to be pricing. My understanding of this is rather poor, and I’m making a lot of assumptions based on the prices of cars and motorcycles. What I am confused by is how high the price tags are for things such as 2-seater aeroplanes and rigid inflatable boats. The planes seem on the surface to be not that much heavier or more powerful than an average motor car, yet they have six digit prices. The boats seem to be as expensive as a family car despite being considerably lighter and less mechanically complex. Why are the prices so high, and why isn’t anyone offering these types of vehicle at a lower price? What is it about the planes that stops them from being made as cheap as a 1.5 tonne automobile? And, what is it about the RIBs that makes them have 5 digit prices despite being made of rubber and not metal?

The other thing that I’m not quite sure about is the fact that battery electric technology still hasn’t completely taken over yet as far as recreational vehicles are concerned. In particular, even in light of climate change and respiratory concerns, gasoline powered go-karts and boats are still quite common. While I understand that price and battery size are important issues at the moment, I still would have thought that the technology would be a no-brainer for such small vehicles. Why would anyone risk damaging their lungs by using a petrol go-kart on an indoor tracks? Wouldn’t that be as bad as smoking? And, why haven’t batteries completely replaced fossil fuels for vehicles, such as small boats, jet skis, motorcycles, quad bikes, and snowmobiles? Why do people still support climate-destroying engines when battery-electric alternatives are possible with today’s technology? This is especially strange, when it would be easy to do battery swaps to deal with charging times.

I hope I can have some light shed on these mysteries. Then, I can make a more informed choice and be less confused. Thank you. Pablothepenguin (talk) 21:12, 17 October 2024 (UTC)[reply]

Price: There are several major factors in the cost of producing a factory-made vehicle (or any other manufactured item).

One is the cost of designing it, including the (often considerable) costs of demonstrating to the relevant regulating bodies that it will be (and continues to be) safe. This is a fixed cost, the same if you then go on to make one hundred or one million of the vehicle.

A second is the cost of making the factory that will make the vehicle. This is also largely fixed.

A third is the labour costs of paying the people who make the vehicle, manage the factory, etc. This generally increases with time (because wages usually increase), and obviously has a lower bound.

A fourth is the cost of the materials and components. This is variable, because the more you make the bigger discount you will be able to negotiate on bulk purchase, but it has a lower bound.

(There are other costs, such as marketing, after-sales service and spares manufacture, etc., but let's ignore those for the moment.)

The first two costs have to be recovered by spreading them over the price of all the vehicles sold, over and above the third and fourth which are inherent in producing each vehicle. This means that the more vehicles that are sold, the less that each individual vehicle's price will have to cover those upfront costs (which may have been paid for by investment or borrowing, which generate dividend or interest costs that also have to be covered).

'Average motor cars' are typically made (often in already-established factories that can easily switch to new designs) and sold in hundreds of thousands per model, so the first two costs are spread very thinly.

Vehicles such as recreational aeroplanes and boats are sold in much smaller numbers, so the upfront costs to be recovered are much higher per individual vehicle.

This is a very crude and non-comprehensive outline, based on my experience of working in both retail and manufacturing environments. No doubt an expert can give a far better one. I have some thoughts on battery power, but I'll leave that for others. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 03:45, 18 October 2024 (UTC)[reply]

Today's popular consumer cars are manufactured in assembly lines in a continuous process using highly automated processes. At the rate in which they are produced, the automation results in considerable savings on the production costs. The rate of production of 2-seater aeroplanes or rigid inflatable boats of any brand is far lower, not justifying a comparable investment in automation. --Lambiam 05:27, 18 October 2024 (UTC)[reply]

Another factor is that aircraft manufacture and component parts are subject to a far stricter regime of quality control. [1] Alansplodge (talk) 09:36, 18 October 2024 (UTC)[reply]

Does anyone know why 60 year old Cessna aeroplanes are still super expensive. Surely oldness = cheapness, right? Pablothepenguin (talk) 11:36, 18 October 2024 (UTC)[reply]

Also, can anyone explain why a rubber boat comes in at a five figure price? Why can’t such things be cheaper than metal vehicles? Pablothepenguin (talk) 11:39, 18 October 2024 (UTC)[reply]

I note that a Rigid inflatable boat is not inflatable except for the sides. I too am somewhat puzzled by the steep price. Leaving material costs out of it, there are some mysterious market forces at work. Old leisure boats, typically small cabin cruisers, are frequently abandoned and left to rot, yet those offered for resale are typically in relatively good condition and still offered at relatively high prices. I suppose the main cause of the high price is that people looking to buy boats have money, and want good quality. On the positive side, this means there is no RIB market for lemons. Card Zero (talk) 14:27, 18 October 2024 (UTC)[reply]

Any/one know anything about the aforementioned 60-year-old planes or RIBs? Pablothepenguin (talk) 19:51, 18 October 2024 (UTC)[reply]

Size of production run has already been covered.

The engine size may appear to be similar for cars compared to boats or aeroplanes, but there's one difference. Car engines only run at maximum power for a few seconds a time when accelerating or a few minutes when climbing a steep hill at high speed – but most steep roads are to sinuous for high speeds. So car engines are only designed to run at peak power for a short time. Engines of boats and aeroplanes run close to peak power almost all the time. Worse, they have to be more reliable. If a car engine breaks down, you simply coast to a stop; if the same happens in an aeroplane, you have to find a suitable landing spot very nearby or you crash. The engines of racing cars do run at full power all the time; maybe you've noticed how often one breaks down during a race.

As for making them battery-electric, some are. Slow recreational boats have been electric for decades. The sporty ones however need such a high power-to-mass ratio that battery power would only last a very short time, maybe half an hour. For an aeroplane, half an hour is about the limit now and it won't be sporty at all. Go-karts can certainly be made battery-electric or on overhead power (think bumper cars), but some users seem to like the noise and smell. Battery swapping could work, but battery designs must then be standardised and demand high enough, or charged batteries will be waiting for ages before a user comes to pick them up. PiusImpavidus (talk) 09:48, 18 October 2024 (UTC)[reply]

And yet an electric car can last for over 200 miles. Explain that? Pablothepenguin (talk) 11:43, 18 October 2024 (UTC)[reply]

Bearing in mind that said cars are much heavier, maybe 2 tonnes, than any boat or go-kart, therefore they take a lot more energy to move and still too 200 miles on a full charge. Explain that? Pablothepenguin (talk) 11:47, 18 October 2024 (UTC)[reply]

First, an electric car may carry several hundred kilogrammes of batteries. It's a significant fraction of the loaded vehicle weight and you can't increase that fraction much on other vehicles. And for vehicles lighter compared to the person using it, you'll get less battery compared to loaded weight, therefore less battery compared to energy use (weight is often a decent proxy for energy use), therefore less range. Electric cars only get their decent range at that speed by being heavy compared to their payload (which in turn makes them inefficient).

Second, a car on a motorway only uses about 10 kW of power, something like 50 watts per kilogramme of battery you can put in. The engine is more powerful, but you rarely use it at full power. Our article on Jet Skis mentions that the 2017 model has a 120 kW engine and weighs 250 kg; maybe you could put a 50 kg battery in one of those. As it actually runs close to full power most of the time, that's 2400 watts per kilogramme of battery. The battery will be drained in five minutes. PiusImpavidus (talk) 18:07, 18 October 2024 (UTC)[reply]

[Edit conflict] Much of that weight is the battery itself, and a car does not have to either float, or remain airborne. As yet, battery technology has not yet been developed to routinely combine very large energy storage and low weight, safely: storing a large amount of energy in a small space is always a potential bomb or conflagration. Cutting-edge experimentation (for example in the form of Formula E racing cars and MotoE bikes) is ongoing, and has shown rapid progress year by year. As for why various recreational vehicles in electric form have not caught on – it boils down to lack of public demand; manufacturers would offer such vehicles if there was sufficient demand to make them profitable. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 18:23, 18 October 2024 (UTC)[reply]

I still don’t understand why a 250kg vehicle needs a more “powerful” engine than a 2 tonne vehicle. It just doesn’t make sense to me. Could someone explain the physics behind this? Surely there is no doubt to the fact that 2 tonnes takes 8 times as much energy to move as only 250 kg? So why the discrepancy? I mean, if we have the technology to power a 2 tonne vehicle for 200 miles, then why can’t we do the same with a vehicle one eighth of the weight? I struggle to understand the physics of this and it’s messing with my head.

Also, why are people not faking climate change more seriously? Shouldn’t they prioritise cutting gasoline out of their lives as soon as possible? Pablothepenguin (talk) 19:41, 18 October 2024 (UTC)[reply]

Heh. Faking seriously? That's an unfortunate typo. But anyway a jet ski, or a RIB for that matter, is for zooming around, bouncing giddily over the waves. It not only has to go fast, it has to go fast in water, overcoming friction by planing. "To plane, especially to initiate planing, the power-to-weight ratio must be high". This kind of hedonism is not typically associated with environmentalism, although I see an image of an electric jet ski, or "electric personal watercraft", positioned opposite Electric_boat#Efficiency. It has an external link and looks suspiciously like an advert, you may want to check that out before I get round to removing it as promotional. Card Zero (talk) 20:46, 18 October 2024 (UTC)[reply]

I still don’t understand the physics here. You still can’t deny the fact that a 2 tonne vehicle requires eight times as much energy to move as a 250kg vehicle. So, why the big difference in engine power? Surely it is impossible to deny what you can physically see with these numbers. If we can get a 2 tonne vehicle to travel 200 miles on battery power, then what is stopping us from doing the same with a 250kg vehicle? It should only require one eighth of the energy. Pablothepenguin (talk) 00:59, 19 October 2024 (UTC)[reply]

If there's no friction, then any tiny force F will move them both the same distance. If we want them to cover the same distance in the same time, a = F/m, so yes, it takes 8 times more. But you should pay attention to the missing f (friction), of which there are many kinds. The watercraft needs more power because it pushes through water. Outboard_motor#Portable says that a 15hp motor (about equivalent to four 50cc scooters) can only move a small dinghy at less than 10 mph. Card Zero (talk) 03:14, 19 October 2024 (UTC)[reply]

There's quite a big difference between land vehicles and water vehicles. At low speed, a land vehicle mostly suffers from rolling resistance and friction in the drivetrain. This is more or less proportional to weight and independent of speed. A boat mostly suffers from skin drag and wave-making resistance, increasing more or less linearly with speed. As the resistance of the boat has no constant term, it's at low speed much less than that of a land vehicle. That's why freight ships are so efficient.

At high speed this changes. For land vehicles, air drag becomes dominant, roughly increasing with the square of velocity. The speed where this becomes dominant depends on the vehicle, maybe 20 km/h for a bicycle and 70 km/h for some cars. For a boat, the critical point is the hull speed, which depends on the size of the boat. For a kayak it's around 8 km/h, for a big container ship 80 km/h. Once you reach the hull speed, drag increases enormously. For a planing hull it's not as bad as for a displacement hull, but it's still bad. That's why fast boats are such an inefficient way of moving things around. Jet Skis and rigid inflatable boats are designed to work well above their (rather low, because they're small) hull speed, so their drag is huge.

For aeroplanes, drag is proportional to weight and practically independent of speed. If you want to go faster, you go higher, keeping lift and drag constant. The lower density of the air compensates for the higher speed in the drag equation. PiusImpavidus (talk) 11:06, 19 October 2024 (UTC)[reply]

Ok, that seems reasonable. Now I want to know more about my first question. For instance, why is a 60 year old plane still expensive? Also, how do price drops work in the first place?

Also, why are petrol go-karts still a thing? Can’t we get rid of them and use batteries instead? Pablothepenguin (talk) 17:33, 19 October 2024 (UTC)[reply]

Especially in the US, many people believe that climate change is either a hoax or a natural phenomenon unrelated to human-caused greenhouse gas emissions. Apart from that, the price is an issue. I think gasoline-powered go-karts are substantially cheaper than electric ones. The go-karts rented in competitive racing events organized by commercial go-kart track operators need all to be the same type, so switching to an all-electric fleet is a very costly proposition. Also, gas-powered karts produce a more satisfying vroom-vroom noise (satisfying to the driver). --Lambiam 06:37, 20 October 2024 (UTC)[reply]

On aircraft pricing, this source [2] lists pre-owned aircraft for less than $100,000. However, I would hate to be flying in one and need repairs ... DOR (ex-HK) (talk) 20:43, 19 October 2024 (UTC)[reply]

That still sounds like a lot. Why are 60 year old planes still that expensive? I’ve seen brand new cars that cost less than that? Pablothepenguin (talk) 21:26, 19 October 2024 (UTC)[reply]

Because (a) they're rare, and (b) old things have appeal beyond their utility – see for example Antique.

With reference to your earlier queries, see Electric boat. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 05:24, 20 October 2024 (UTC)[reply]

Regarding the planes, a 60 year old aircraft isn't that old overall. For example, components like the engine need to be overhauled/rebuild/replaced regularly (every 2000 hours). Every component that is replaced needs to be certified, which also drives up the cost. This ties in with the earlier mentions: if your car engine fails, you call for a tow truck, if your plane fails, your family calls for an obituary.

An earlier post mentioned that aircraft engines always run at full power, but this is not necessarily true. they need a lot of power for take-off, to get enough speed for the wings to work. After that, engine power can be a lot less.

for boats, they live in a lot more corrosive environment and need proper maintenance to keep working (usually way more than road vehicles), driving up the price. Regarding the engine power, realize that the resistance is based on a friction factor times the density. Apart from that, the free surface drag is a major component, which scales with the root of the length of the craft (see Froude number). Small displacement hull ships are very inefficient.

Regarding the batteries, the power density of a battery is an order of magnitude smaller than that of gasoline. I can drive 600 km on my 35 liter tank, but an electrical version has a battery of ~200kg, and reaches only 200km Rmvandijk (talk) 10:45, 29 October 2024 (UTC)[reply]

It's basic economics: supply and demand, whatever the market will bear. If you offer an object for 1,000 dollars and nobody buys it, you can either keep it or reduce the price until it sells. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:42, 20 October 2024 (UTC)[reply]

To return to the electric aircraft question, Wikipedia has (of course) an article called electric aircraft. Most commercially available examples are motor gliders, such as the Lange Antares and Pipistrel Taurus, although a few are proper light aircraft, the Pipistrel Velis Electro for example. A number of passenger aircraft are in the pipeline, the 10-seat Scylax E10 being perhaps the nearest to actual service. Alansplodge (talk) 13:43, 21 October 2024 (UTC)[reply]