You might fix something to hang from the sky with that set of spells. The question is, will that truely benefit you? The ship would be affixed to a certain place in the air by those ropes, I don't think the 'anchor points' are made movable, at least I don't see that in the description. I might be wrong but it does make me wonder a little. Creative idea I wont argue that, just curious to hear others comments.
Anyway, it might be useful in some cases but I don't think its the key to having a ship flying around.
It is implied as there is only mention of the rope is lifted veritcally, thus if the bottom moved the point about it verically would move. I also think because the spell was cast on the rope ... not enchanting an area to attract ropes, or an area to attract a specific rope. It is cast on the rope.
But there are additional complications .. the strange part about extradimentional beings to me is a little silly - would love the idea of the gm dropping that a portal you can create as a low level mage which opens into a dimention of creatures hungry to pull ropes... but only ropes ? ... really. Treating it as a "rope trick" from an effect point I think could work... but it does have addtional issues that doesnt solve the problem on their own.
For a ship to be viable it has to be able to vary how much these things as a whole effect the ship, and be able to turn them off and on at will.
So its more likely there has to be a cerntal point or plague or something that can enable you to command these ropes to dance for the ship or not... and they can't be simply attacked to the deck - but more likely linked to other ropes and each other indirectly in a system of pulley's which would be like a "loom" in a deck below - that mainly balance loads when different ones are being turned on or off at will.
So even if the storyteller was ok with it you would need 6-8 of them... all linked with a elaborate pulley and rope system
that takes up the better part of some level on the ship.
So probably 20 000 gp or more on that network of under-deck ropework, perhaps the same for a plaque that can turn individual ones off and on easily.
So realistically (assuming my rope trick view is acceptable).
12500 gp x however many sets of 8 tonnes you want to lift
? gp for a plaque to control them
? for silk-rope linked-loom for distribution their individual tensions.
? For re-rigging or creating a new ship that uses this strange under-deck rigging methodology.
This doesn't help with forward locomotion though, but i thought would be one way to have literal flight feasible.