Spelljammer explained

So I didn't explain a spell jammer ship well, so here is some basic information.

A spell jammer ship can traverse into other planes of existence if the pilot has access to the plane shift spell and a object from another material plane, like Exandria.

But if the pilot wants to go to another plane like the Fallout universe the pilot will have to navigate the Astral Sea blind and try and locate the various "doors" to the desired universe.

The Astral Sea is the gap between dimensions where thoughts and dreams have actual power where if a person have enough intellect or willpower thy will entire beings into existence. But sentient minds do not always have good dreams so the sea is filled with as just many nightmares as it is good ones.

[Examples of monsters and creatures]

Ship details

A Ship has two different movement speeds in atmospheric and vacuum. For example the HMS Prince while in atmosphere can go about 30 miles an hour while flying or at sea, while in a vacuum or in the Astral plane it can go 100 million miles in 24 hours.

So the HMS Black Prince once out of Atmosphere it could travel to Mars in about half a day, also to enter the Astral Plane the pilots has to be at least 500 million miles away from any celestial body.

Then when in the Astral sea to head to Exandria (where Percy is) where it can take days of travel to locate a "door" into Exandria.

I hope this explains everything better and I recommend to watch some YouTube videos about spell jammers.