How do people recreate hull lines from ships?

I am planning to start a big project. I want to recreate 100% of the titanic both the inside and the outside. I have done this before but it wasn't a 100% accurate and i want to do that now.

I find that the hardest task of recreating the titanic are the beautiful curves of the hull. I've done quite a good job at recreating them before but it just bugs me that they aren't as accurate as they can be. Now finally the actual question:

How do people recreate perfect hull lines from ships like the titanic?

Is there some sort of program that calculates these lines?

What i did in the past was look up a schematic from the titanic hull lines. That's how I've recreated them before but these hull lines from these schematics have a lot of space in between and it's hard to fill up those spaces. It's even hard to accurately recreate those lines to begin with.