The point is, you don't have to ever
climb onto the belt before lowering the chain. All you really need to do is
to stay the hell away from the belt (apart from flipping the switch when you first get to the island) until you escape from the vault with Meche. At that point you get to the crane from dry land. Then, you move to the other side of the island and lower the chain. If you flipped the switch at the belt first thing, then when you lower the chain it will be pulled along the entire length of the belt. When Manny climbs down to the belt, he simply walks on top of the chain and is unaffected by the belt.
Just remember that before doing anything else at the island that you go to the belt and flip the switch. Then stay away from the belt until the PLOT
brings you to it.
This problem is caused by the speed of the computer. If you're processor is, say, a 700 MHz PIII or slower, the belt isn't much of a problem (though you need a bit of 'twitch' to get off the belt the closer you get to 700 MHz). Above 700 MHz it gets impossible. There's no frame limiting going on (as in the case of the wine-cellar elevator after the patch is installed).
The trouble with giving you a saved game is the order of certain tasks at the island isn't fixed. You can raise the LaMancha
before or after freeing Meche.