I have purchased and intend to use a 1 1/2" vinyl tape as a waterline mark. After applying Blue Painters tape to prepare for bottom finish I realize this is going to be difficult if not impossible without some form of a trick, such as heat, etc.. Any suggestions would be appreciated.
You'll need some heat to get it off in a few years, but not to put it on now. Use a ruler, a pencil and maybe a level to draw a few small marks on the gelcoat to help keep the tape straight and level, then pull out maybe 2 or 3 feet of tape at a time and try to place it on the boat at the pencil marks. The better vinyl tapes for this purpose have a backing which you've got to pull off as you work down the side of the boat. Trying to do less than 1 foot or more than about 30 inches at a time will tend to look a little ragged.
I'm in the process of re-doing mine also. I have removed the old bootstipe and have been taking a lot of oxidation off the sides. Before I completely obliterated the old line, I took some cheap vinyl dollar store tape and followed the ghost lines where I removed the old tape. It went on well and will preserve the line for the new bootstripe tape. If you do not have a visible line, it is going to be tough - not just to keep it straight, but to follow the water line!
I agree with the previous post, make a touch every 12" or so and smooth it out before applying too much pressure.
Lay the tape on over a nice layer of dish washing soap suds, and then squeezy out the water.
This allows the tape to move around a bit till it's right where you like it. Used it at the sign company this way.
skip.