Underthinking Back to the Future 2

Tonight I watched Back to the Future 2, and I noticed a few things that appear to defy logic. Now I won't discuss the various time travel paradoxes that arise, for example, if Biff goes back in time to give himself the sports almanac then gets the Doc commited sometime prior to 1985, then the time machine won't be invented therefore Biff wouldn't be able to go back in time to give himself the sports almanac. But if you are interested in these things they are summarised nicely here

Anyway how hard could time travel be? Two Slackers from California managed to manipulate it succesfully

No what I am concerned about are more simple and often overlooked inconsistencies in this movie.

1/. Why do they leave Jennifer in the Alley?

When they first arrive in the future Doc, puts Jennifer to sleep because she is asking far too many questions, so this is a valid movie to save the explaining. However when they arrive Marty has to complete his mission of saying no to Griff, and Doc needs to run and errand in the DeLoren, we find out later this is to pick up Einstein his dog. My question is why did they have to remove Jennifer in the first place, her and Marty fitting in the DeLoren easily, why could Doc not leave her in the front seat when he went to pick up his dog?

A safe place to leave a comatose teenage girl.

And let's be honest the act of leaving Jennifer in the alleyway, set the whole movie in motion, if she had been in the car the whole time, then they could have left straight away making it impossible for Biff to disrupt the space-time continuium

"We can't have you sitting beside a woman can we Einstein?"

2/ Hoverboards and water are incompatible?

Now for start, let's presume that the hoverboard is possible (Incidentally here is a commercial about purchasing one). I imagine how it works is some sort of resistance with the ground, a downforce that allows the board to hover. The benefit of  this design of wheels, is the lack of friction meaning you gain a lot more momentum for less energy.
The problem I have is the claim hoverboards don't work on water unless you have power. If you note in the photo below, Marty doesn't sink when he is above the water. He just can't gain forward momentum.

By the way those shoes have Power laces! Awesome

I don't understand this, when Marty is pushing himself along on the road is foot isn't touching the ground, he seems to be just wafting it through the air, to gain the forward momentum.
Given there is enough resistance to keep the board a float above water, why does Marty's pushing no longer work above water?

He is pushing enough to cause a wave? But not to move.

3/ How exactly do the flying cars work?

In 2015, we are all going to have flying cars, sweet! That's only like 4 years away. But how do the flying cars in this movie work?

This is what a flying car looks like

Note in the above picture the car has wings allowing for the appropriate lift required for the car to fly, while this garners us flight, it also means that the lanes for just normal driving would need to be widened 3 fold to accomadate the wingspan. But that is not how the flying cars work in the Back to the Future universe.

Note the lack of wings

So no wings, also note no rotors, so the flight is not achieved through helicopter methods either. Hang on a minute you say, they have hover boards can't they just make the cars hover too?
Well yes, they could make the cars hover a foot off the ground, maybe a couple of meters but the downforce required to get the car 200 metres into the air would be so powerful it would make walking around under flying car a health hazard.

Rush Hour is a killer in 2015

Also they have flying cars, why is the speed limit the same? We notice when Marty and Doc go back in time, they are passing the other flying cars as they reach the required 88 mph. Surely there is room to increase the speed limit in the sky, there would appear to be a lot more freedom to avoid accidents, now you can move in 3 dimensions.

Although this would now make more sense.

4/ How does Biff know how to operate the time machine?

Let's just ignore the fact that Marty decided to just wander off from the time machine, their ONLY means of returning home, with both doors wide open. Forget Biff, Marty was lucky some street hood didn't just drive off in the car.

If the doors look like this, the Delorean is NOT secure.

Biff knew what he was looking at though, so knew it was worth stealing. So he hopes into the car, and takes off back to the past to give himself the sports almanac. Wait what, Biff a 70 year old man at this time, just hops into a time machine and immediately figures out how to travel back in time.

Just your standard time circuit right

I mean admittedly Doc had labelled the circuits using his 1980's label maker, so most lay people should be able to figure out which buttons to press to set the destination time. Note most lay people, not all people. As previously mentioned Biff is a 70 year old man, have you seen old people with technology ? (I have discussed this before here)

"Oh S*** the pictures they are moving"

Also from what I can gather Biff has washed cars his entire life, and doesn't appear to run a business, he just washes the cars, so probably not the most educated of people.

It's not rocket science

So this uneducated 70 year old man just climbed into a time machine,and worked out he needed to set the time circuits to his desired date, he also worked out he needed to get the car to 88 mph to go back in time. Maybe he just got that fast by driving normally you say. Have you see old people drive?

"Hang on to your bonnet Mavis, I am taking this thing to 20 mph"

5/ How did Doc not notice Biff's cane under the pedals?

Okay lastly after Biff returns to the future we see his cane break in the car, and the handle falls under the pedals of the Delorean. That's right the pedals, where you put your feet when you drive the car, not in the boot or under the seat where you keep your used fast food wrappers, and assorted CD's. Under the PEDALS!, so presumably Doc would have stood on it, as soon as he entered the car. Its not like it is inconspicuious its a Golden fist! 

"It took you 8 hours to find this?"