Boot Top/Copper Coat/Top Sides Boundary?

[D'eau!]

only if the boat is level fore and aft and side to side. And on a boat what is level? On many boats, on which the moulds are made by eye, they are not even symmetrical.

Remember the boat is curved, move the height of the laser up and the line will bend down amidships and visa versa. The laser can help, just put the line on by eye, not slavishly level and use with caution.

Even then you have the problem that if you follow the laser as accurately as you can in small sections, the tape line will bob up and down.

The best way to mark the waterline is to use quality tape, (3M blue is best) stick it on at the stern, pull it tight right to the bow about 2m off and move to the bow to put it onto the boat in 1 clean action.

Eye it up, if it looks right it is. If is doesn't do it again.

Powerboats are harder. The tape line gives reference points only at each chine, the gaps between need to be done individually using the reference points. It often takes me many attempts to get the bows of a powerboat to look right. A bent line here looks straight, and looking right is right........

I'll let you know how this works out (using the laser). I had the boatyard level my boat when they moved it in its cradle, and some time over the next few weeks I'll be painting on the boot top. I agree that it's best not to have the line horizontal for the entire length of the yacht, with a slight upturn at the bow improving the look enormously, but the laser will help mark-out the majority of the line.

From sailnet.com "Pulling on a true boot-top line with "fine line" masking tape is an art that requires patience. If the old boot-top line is visible, this is a good start—if not, the hull will need to be marked at intervals of about three feet where the new line is to go. If the hull is leveled, this can be accomplished with a water-tube level, a transit, or a laser level. Be aware that most boot tops, to look right in the water, are wider near the bow and stern than amidships—that is, they are straight on the bottom and flared upward at the bow and stern. This is especially important on a fine-lined boat such as a Friendship, because a boot top the same width for the length of the boat will provide the optical illusion of being "hogged," or wider amidships—very unbecoming."