Why nuking the fridge and not riding the sub?

My opinion is the "nuke the fridge" scene wasn´t even that bad. Mutt vine-swinging like Tarzan, catching up to speeding vehicles was infinitely more dumb. I think the reason it gets singled out is because the entire movie was bad so the fans had to nitpick something but you could literally take your pick at the amount of dumb scenes in the movie. Raiders is all around a great movie, so the sub part gets a pass.

I think riding the sub is barely mentioned because it's not an important detail. They don't SHOW Indy hanging on the submerging sub or have a scene of him looking around in a panic when it starts to dive. You see Indy on top waving triumphantly to the crew of Katanga's ship, then the scene cuts to the action inside the U-boat. We don't see Indy again until he suddenly appears in the port. You're meant to conveniently ignore what happens in between and I think if you're not watching too critically, it's quite easy to do just that.

The nuke scene, on the other hand, draws attention to itself because it shows every detail of Indy jumping in the fridge and being subjected to a nuclear explosion. It's impossible to ignore and I find it impossible to suspend disbelief enough to think the terrific acceleration and deceleration wouldn't cause instant death and break every bone in his body.

To me the riding the sub is just another cool/funny scene that flows well with the movie. After all, the Indy movies were based on the 1930's serials where every week the audience was left with a cliffhanger/ impossible escape to live another day.

So yeah, riding the sub flowed well in Raiders so what's wrong with nuke the fridge in KOTCS? Well, aside from Harrison Ford actually doing a damn good job reintroducing his Indy character THE WHOLE MOVIE IS HORRIBLE..and having prairie dogs and monkeys and flying cars for kiddie audiences is either lazy or just an admission by the movie makers that even after 29 years to develop a plot or script they threw up their hands and admitted "we got NOTHING"

GOD!

My guess is the sub would conserve battery by being on the surface.

You just have to wave your hand and dismiss reality in this scene. There's no way Indy could have done it in reality. This is a Type VII U-boat (or a mockup of the upper half -- same one used in the movie "Das Boot" BTW). WWII submarines like the German Type VII U-boat were submersibles rather than true submarines. They spent most of their time on the surface running on their diesel engines and keeping the batteries fully charged, and only submerged for relatively brief periods. With the boat on the surface, the conning tower would have been manned, and Indy would have been spotted. If the sub had submerged (which it really has no reason to do unless it's attacked or about to attack another ship), it wouldn't stay at periscope depth so Indy could hold on and keep his head above water; it would have gone deeper and he would have drowned unless he let go.

There's no way to square it with reality, so you just have to let it go and not allow it to spoil your enjoyment of the movie.

As others have said, the better movie gets more of a pass for this sort of thing. Also the fridge scene was way more in your face ridiculous, while Indy's journey on the sub happens off screen, so the highly implausible semantics of it never even occurred to most people.

The way they are presented helps. One leaves it up to the imagination. The other leaves nothing to the imagination and relies on CGI to absurdly show the same fridge Indy gets in flying through the air from a nuclear bomb going off, ridiculously overtaking the truck of Russians on its way while they get wiped out by the blast, then landing and bouncing around and having Indiana Jones fall out of it unscathed to a CGI prairie dog, or whatever that thing is. It's a series of unbelievable events all rolled into one. However unbelievable Indy riding on the submarine might have been it's made more believable than what we see in Skull by comparison.