How do i mark the waterline on a new boat

[kaimusailing]

When I got my catamaran project, the waterline was already painted onto the hulls, but the many modifications they had made ended up with the waterline being way out. Also the counters and soles were not level when the boat was launched. Later I did the bottom paint aligning with the water marks on the hull. Items still roll on down the countertops. Can't fix that.

[David M]

With the boat in the water and the boat at its proper displacement, trim and a zero degree list, make up a float with a grease pen, Sharpee or use tape to mark a set distance above the actual waterline. I have done this and it came out perfect. I used tape every couple of feet. Then you obviously have to haul out right away and paint.

[Cheechako]

You will find that the even harder part (than where the line is located vertically) is getting it to look proper when on the water.... as the hull changes shape, the line needs to change also to look right. One of those twirling laser devices used by contractors would be a good way to do it......

[Cavalier]

Originally Posted by Cheechako

You will find that the even harder part (than where the line is located vertically) is getting it to look proper when on the water.... as the hull changes shape, the line needs to change also to look right. One of those twirling laser devices used by contractors would be a good way to do it......

It would! One extra essential detail though.. You need to ensure that the laser's emission plane is level with the dots on the hull, otherwise the 'straight line' projected will differ in contour across the hull compared to the waterline.

[Cheechako]

yeah,,... it's a mind scramble for sure. I made the waterline boot disappear with bottom paint on one boat and spent days and many discussions with yard staff how to get it back! I think you are saying that the boat needs to be level... as it would sit on the water, and then the laser level needs to be calibrated to that... right? The other thing is, if you are having a stripe above the bottom paint, that stripe gets wider on the hull, the more the hull turns "in" due to hull shape!

[Reefmagnet]

I did mine with a cheap laser level/tripod purchased via Ebay. I had totally lost the original waterline for the boat bar a few reference points because of lowering the original line and the associated fairing and painting. The boat also wasn't sitting level fore and aft. Had to do it at night because the spinning laser couldn't be seen in daylight. I marked the waterline at the bow and each side of the stern. As Cavalier said, the key to using the laser is that it has to be set level to this line where the laser intersects at a point perpendicular to the hull (otherwise it can trace along the wrong contour - think of tracing across, say, a basket ball!). Other then that it can follow any angle as it sweeps across the hull. I did find it a bit fiddly to set up at the three points (each side and stern), and keeping out of the way of the laser beam when scribing the line is a little bit frustrating also.

On a side note, I also used the same laser in conjunction with a simple jig to align the engine beds to the stern tube when reconverting back to an inboard as it also has a non rotating beam in addition to the rotating one.

[resilientg]

Hey Everyone,

thanks for your input, i figured out a waterline level that I'm fairly happy with. Did it the easy way and picked two points along the hull that appeared level to my beady little eye, then measured my draft of it, then cross referenced back to the floor level, and what do you know the water line that i estimated is parallel to the floor level inside the boat.

That should be good enough for me to paint the initial water line, and i will paint a little below any way, that way once i'm in the water i can find somewhere to tie up let her settle on the keel in a low tide and adjust the waterline as need be and by that time i should have a good idea of where the true water line is.

thanks once again

Matthew

[HopCar]

I recently helped a friend of mine build a strip planked canoe. As the planking came together in the center of the bottom, we needed a very accurate center line to cut on. I suggested a laser and it worked great. Laser can be very handy when ever you need a straight line.