Spraying lines of gelcoat

This may seem easy to you guys, may have a few questions

Starting with an all white gelcoat boat for example,
If you wanted to spray gelcoat lines on the boat (after it's out of the mold),
Or even a large area of black gelcoat,
You would use the green 3m tape to seal the line, however that line will be raised from the rest of the gelcoat after getting the coverage you need to tune out the white.
What is the technique to flatten the line between the two colors?
Would I then need to spray white like a gradient after putting down the black to that line?

Hope that make sense...

 

My thought is that if you were to sand the line down with #400 it may not end up being a fine straight line as you remove gelcoat??

 

One method is to spray the color, pull the tape, then spray over the color and out from the color line several inches or more with the hull color.

Then sand it all down. You will sand through the white (just assuming white is the hull color, it could be anything.) over the color and this can leave a good line and no raised edge. The white will then blend into surrounding hull.

The problem is matching the hull color if this is being done on an older boat, color matching old gel coat can be difficult.

 

I used white and black as contrasting colors
So in that example, if I am hearing you correctly,
Don't tape the second application and just spray the hull color slightly over the line and more broadly off the line?
Usually the first coat of gelcoat on a contrasting color is faded/clear so I can see how sanding it will show through the new base...
Am I getting that right?

 

Current project which I am using the same color and lines of the original gelcoat so it is easy to keep the line, some of the spider cracks that cut across the colors I filled had to be filled in delicately with gel to keep the line, then I use the green tape to keep the line and finely sand over the line after
Just wondered how it would be done on if you wanted to add some color to a plain hull, you are right Im sure the color matching will be difficult

 

Why does it have to be gelcoat?
A good PU paint will be much less painful.

 

How so? wouldnt you still have a raise line and the be unable to sand from there?
I guess you might need to find an edge or shape of the boat to work with and spray that whole panel?

 

Part of it is my learning to spray and work with gelcoat as I have some molds I want to work on this year...
So everything I can use gelcoat for I am trying (I know some processes of gelcoat in a mold is different than dealing with the part after it comes out)

 

In general, you would spray the lines on the mold so the surface doesn't have ridges. After the fact you will have to accept a small difference in thickness.

 

As gonzo mentioned, not a concern with in-mold work, only post applied color schemes.

 

If its just lines use vinyl stickers, fast cheap easy long lasting.

 

Good point about the vinyl