Electric vehicles compared to normal

@swirlieI have often wondered how EVs can be practicable for many residents in continental nations.

A lot of the pro-EV publicity in the UK was based only local use, stating "most journeys total under x miles a week". I forget the usual values of x, but it was really only commuting and shopping.

Although probably correct for some people, it ignored that very many people with cars do travel much further than that, especially at weekends, for "domestic, social and pleasure" purposes, as the insurers have it.

It also ignored that by no means all motorists could recharge a battery-electric car at home so are dependent on public chargers.

So what became called "range anxiety" developed:

"I want to drive to ::::: nearly two hundred miles away. Will I find suitable charging-stations compatible with my car, with pay systems I can use, are even in working order; and how much earlier will I need start to account for possible queues at them?"

Although the fear has lessened as the cars' ranges and number of chargers have increased, it is still relevant - and that in a country physically far smaller and far more densely populated than the USA or Canada. Also with much milder weather generally, though you'd not want to risk your car coming to a halt in the middle of Highland Scotland or the Yorkshire Moors on a cold Winter night.

I have long thought EVs would not really be very practical in continent-size nations, especially those with few towns far apart away from the major cities, unless very many public chargers are installed at least along the main and secondary routes..

It would of course depend on the individual.

An EV might be feasible if you live in a heavily-populated area with plenty of public facilities, you can park and charge your car on your own house drive, and you never drive more than a few tens of miles from home.

Live far out in a rural village with no public transport, or you sometimes need or wish to travel some hundreds of miles for any reason, especially in a very large region subject to severe Winter weather, and I still cannot see an EV being practical.

.....

ME? I live in a fairly densely-populated region. I cannot have an electric car. I cannot afford one. I have nowhere to charge it at home. I can and do use buses for local journeys, but my life entails occasional, much longer journeys by car, sometimes with round-trips of 600 miles and more.

@ArishMell
I've done a lot of research on EV's for cars because I was trying to apply the same EV application to the nautical marine industry which is where my expertise lies in my real world.

According to technical data supplied by Tesla, where all testing and potential range is based on for battery serviceability alone, is between 30 degrees North Latitude and 40 degrees North Latitude, anywhere in the world.

In Europe for reference, 40*N is well-south of France and 50*N is in the vicinity of Toronto Canada and London England.

If you operate an EV in winter that is north of 40*N, expect a 1% decrease in range for every degree below the freezing mark it is outside. 25 degrees below freezing equals a 25% reduction in range for a fully charged EV battery.

For every degree of outside air temperature above 25C or 80*F, expect a 1% decrease in an EV's battery to come to a full charge when placed on a fast charger, due to overheating issues which automatically restrict the amount of charge that a charging unit will put into a battery that's being charged.

This means, at an outside air temperature of 100*F, an EV battery can only be brought to an 80% charge instead of 100% charge. Your resultant range is now decreased by that same 20%, which means your range is based on 80% of max advertised range, not 100% of max advertised range.

Therefore, unless you intend to operate your EV within those two latitude references of 30N and 40N, none of the predicted range potentials actually apply to your vehicle! On a brand new, fully charged battery, your car will typically achieve 20 to 25% less range if it's very cold outside or if it is very hot.

That is why any Tesla's you see running around anywhere in North America will almost always have their car windows open and the air conditioning turned off, just to extend the range of the vehicle in hot weather.

@swirlie Thank you for that - very interesting information.

I knew EVs are not happy in cold conditions but had not previously seen the figures.

I doubt any vehicles of any type really meet their manufacturers' test claims but battery-powered ones seem worse in that respect.

I have not heard of anyone claiming serious range problems due to the air temperature in Britain, at least not in the Southerly half, as our climate is generally milder than that in Canada. Instead I have encountered anecdotes about owners not daring to use the heating in cold weather because that is an extra drain on the battery. The opposite of the American motorists in their hot Summers!

I know small, battery-powered boats for inland waters have been around for some years now but it will be interesting to see how electric propulsion, (battery or fuel-cells?) develops for large sea-going ships.

@ArishMell
One of the many challenges for large sea-going ships is the salt-laden air which corrodes everything that isn't made of wood!

Battery power for a ship works well in theory, but in practice, we are dealing with electrical corrosion at each connection which cannot be sealed from the salt air.

Additionally, the battery itself must be sealed in it's own compartment that is both waterproof and air-proof, which means the battery cannot remain cool through traditional means of air-cooling. As soon as a non-traditional way of battery cooling is introduced, it must be accounted for in the current-draw from the battery which of course reduces the range of the vessel as it uses battery power to cool the battery itself.

Another problem with battery powered sea-going ships is the dead-weight of the battery which never decreases as the power is used from the battery, unlike traditional diesel fuel engines which consume the fuel from within the tank, making the vessel lighter with each gallon of petrol that is consumed.

It takes 20% of the total liquid fuel load of a diesel ship JUST to produced enough energy to carry the weight of the fuel on an ocean crossing. This means that 20% of the fuel that's carried will be burnt just to move the weight of the fuel alone across the ocean. The weight of the ship and it's cargo requires the rest of the fuel to move it across the ocean.

That said, as the ship uses up it's fuel load and becomes lighter and therefore requires less energy to move it near the end of it's ocean journey, the most amount of fuel is used at the beginning of the journey when the vessel is obviously the heaviest.

With this being taken into consideration, the vessel becomes cheaper and cheaper to operate as the fuel is burnt off. But with a battery powered vessel of course, none of this happens! The vessel weighs the same at the end of the journey as it weighed at the beginning, which means a lot of battery storage power is required from start to finish of a voyage just to move the dead-weight of the battery across the ocean!

@swirlie I see the problem there. What of fuel-cells instead?

@swirlie Thank you for all this - it's a fascinating subject!

I must admit I'm a bit surprised that screws and sails can work together because the screw has a fixed pitch and constant rpm. So would there be times when the sails are effectively trying to over-drive the ship? I don't know what would happen if so - I suppose something like a severe slip effect.

Going back all right: the first steam-ships in the 19C combined engine and sails, though initially they were paddle-steamers so how efficient that combination was, might be more questionable.

Odd - the site has marked your post as "Sensitive". I can't think why.

@ArishMell
Don't know why it's marked sensitive? It's a computer generated AI response anyway, so I don't worry about stuff like that.


Whether sails are causing forward motion to occur or an additional engine and screw were providing that same forward thrust in addition to the screws in question, the fixed pitch and constant speed rpm is not actually an issue.

The reason for this is because the overall effect would be like putting the ship in a fast moving river where the ship is moving along from the flow of the water itself, but then add a second component called 'forward thrust' from the ship's screws and you'd end up with the ship moving faster OVER the stationary river bed than the water itself is moving over that same river bed.

If the river is moving at 10 knots and the ship is moving under it's own power through the fast moving water at 5 knots, the speed the ship would be moving over the stationary river bed would therefore be 15 knots, assuming the ship was also moving in the direction of the water flow.

If the ship reversed direction in the river and faced a 10 knot current flow, but then moved through water at 5 knots under it's own power, the ship would actually be moving backwards at 5 knots. (5 minus 10 equals minus 5 knots over the river bed... minus means moving backwards).

Keep in mind that water of course is a medium which the forces of the ship is acting against from all directions. If you mounted a jet engine on the ship's deck to propel the ship forward in the water, anything else that adds forward momentum such as a pair of screws or sails, merely adds to the total forward thrust component that moves the ship forward.

A screw on an ocean ship only turns at between 20 and 60 rpm at the very most, in the range from normal cruise power to full thrust. That is why it is called a 'screw' and not a propeller.

The screw literally 'screws' itself through the water like a screw nail screws itself through a piece of wood, whereas a propeller 'propels' a vessel through the water by rapidly displacing water backwards from the propellor blades... Newton said, "for every action, there is an equal and opposite reaction". Actually, it was me who said that but I'll let that one go for now.

As a result, the boat moves FORWARD at the same rate of knots that water is being displaced BACKWARDS and away from the boat.

When 1 ton of force is expended backwards from the prop or screw, 1 ton of reactive force happens in the opposite direction.

A ship's screw does not propel, ..it screws!

A small vessel does not screw, it propels! A propeller of a small pleasure craft turns approximately 10,000 rpm at the prop, compared to 20 rpm of a screw on an ocean vessel.

The ONLY time that severe slip as you refer to it, would ever occur would be with a propellor on a small craft or vessel, but never with a screw on a ship.

What defines a propellor versus a screw is the rpm that each use to move the vessel in question, which is wholly dependent on the weight of the vessel floating in the water. Extremely heavy vessels are not built for speed, but are only built to move forward very slowly. Pleasure craft are built for speed, but are not built to pull heavy loads.

Severe slip of a propeller occurs when cavitation occurs behind the high-speed of a rotating propeller of a small vessel, which then leads to an area of 'vacuum' to form behind the prop itself which is immersed UNDER THE WATER where there is literally no water making contact with the propeller blades during those moments that cavitation is occurring.

This causes the prop blades to over-speed within a cavity of 'air/vacuum' that the prop created from the expansion of steam that forms which was caused by the friction of the prop blades operating within that cavity of steam with no water making contact with the blades to keep them cool, at which point the engine itself will typically 'over-speed' due to the sudden REDUCTION of resistance of the prop blades against it's medium of water as those blades spin inside that miniature vacuum that steam created behind the prop.

When cavitation occurs, the prop blades become overheated and steam will form within that area of cavitation, further increasing the temperature of the blades to the point where they either melt from the heat or they grossly deform to the point of being unrecognizable as a propeller.

This most typically happens with an aluminum propellor which is the standard on all pleasure craft which use propellers. To prevent this self-destruction of the propeller, a stainless steel prop is used instead which is extremely hard metal and will not deform from heat. In fact, it is almost impossible to cut stainless steel with a hacksaw and therefore cutting stainless steel requires specialized cutting equipment. Because stainless is so hard, the blades will not warp from overheating.

The vessels that use stainless steel props to PREVENT prop failure from occurring due to momentary cavitation, are waterski boats or high speed search and rescue vessels.

The only downside with using stainless props on any pleasure craft is the resultant damage to the engine and transmission that will result if that stainless prop should ever hit a rock while operating in shallow water.

The prop won't sacrificially bend and therefore displace the impact shock, nor will the stainless blades self-destruct to absorb the immediate impact.

Instead, that shock-impact will transfer itself upstream from the stainless prop (and rock) to the transmission and then to the engine itself, where somewhere alone the way that 'shock wave' will find a way to displace itself, which usually results in a broken crank shaft or a destroyed transmission which of course is attached to the engine.

An aluminum propeller therefore, acts as a sacrificial anode should the vessel come in contact with rocks in shallow water. The prop is destroyed, but during that momentary destruction of an aluminum prop, the shock-energy is immediately absorbed by the bending and breaking of the aluminum blades.

On an ocean vessel which uses 'screws', the same principle applies.

Because the ship is SO heavy, an aluminum screw would literally bend and deform all the blades as soon as the throttle was opened. This is because a ship's screw is typically 24 to 36 inches in diameter tip-to-tip on a 4-bladed screw which means there is a lot of leverage being imposed on those screw blades when the power is applied at the throttle(s).

For the same reason that stainless steel propellers are used on high speed props which pull heavy water skiers on a lake at high speed, is also the reason why an ocean vessel's screws are made of bronze!

Bronze is extremely hard like stainless steel and will not corrode in salt water and bronze is also a heavier, thus stronger metal than stainless steel. That is why bronze screws are used to move heavy loads at slow speed and stainless props are used to move heavy loads at high speeds.