If I were contemplating such a task I'd remove the tape after each coat of paint's been sanded 90%. Once tape's been pulled, go back over the hard edges very carefully with fresh sandpaper to break down that hard edge just a tad. Wipe down with water-dampened paper towel, then re-tape once surface has dried thorougly.

When you add next applications of tape I'd try to place them each about 1/32" outside previous placement so that the next and later coats of paint taper off a bit instead of forming a hard, deep nearly right-angle edge that could be prone to chipping later on.

Trying to pull masking tape off after three coats of polyurethane have been applied over it will be difficult and tedious unless you take a very sharp knife & carefully score along the tape edge to weaken the paint layers a bit. Otherwise I think both the tape will be tricky to remove cleanly and you may find the paint chipping away from the hard edge too.

Another approach is to triple tape the line before you apply the fist coat of paint.  When done painting the first coat, pull off the tape then wet sand when the paint dries.  Repeat for second and third coats.  This was the technique advocated by the makers of the bottom paint that I used on my skiff and it resulted in a good crisp line.  Not sure if it is easier than the sequence spclark suggests or not.  I have done it both ways and I am unsure.

Whatever you do, use the Fine Line tape that CLC sells.  It is much better than the blue or green stuff that you buy at box stores.

Another tip is that if you end up with a ragged line, it is easy to cover with 1/4" pin stripe available at any auto store.

   thank you for this tip

Denis

I'm a fan of the triple tape method. Only the first-applied, last-used layer needs to be Fineline, and needs to be applied with fussy accuracy. Getting a fair curve along the shear either accentuates the clean lines of the boat, or makes the boat look wavy. It's worth sighting the line from low angles, creeping along the shear, looking at the tape edge forwards and backwards, and carefully adjusting anything that isn't right. I only want to do that once, so the next two tape layers lap over the hero piece by an extra sixteenth each, and are just painter's blue tape, put on much more quickly.