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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 05-15-2006
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Waterline

I am just about ready to paint my boat, but I need to take off the old waterline completly. My intention is to prime the hull then mark where the waterline should be (not where it is now, I am raising it up about 4"), tape off the waterline, then paint the hull, putting the waterline on as a last step. My question is: How do I mark the waterline on the hull and keep it straight?
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Old 05-15-2006
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The waterline is really something that does not change on a boat. It is where the designer planned on having the boat lie to the water when fully loaded. Sounds like you are making a new boot top stripe.

You can try one of the inexpensive laser line projectors that are a available at Sears or from Black and Decker. You need to mount it on a stable platform, something like a sturdy step ladder would do, and then tape it in place. Make sure that the height of the laser projector is at the same height as the the line on the hull. Once you have the line shining on the hull, use a high quality painters tape to mark your line.
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Old 05-15-2006
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Typically, lasers are used for scribing new lines parallel to waterlines. However, using this technique requires the boat to be perfectly level on keel blocks and boat stands to start with - not always an easy task.

If your present boot stripe (or bottom paint line) is parallel with the water level, but you simply want to raise it 4", mark the new line using inexpensive, 4" masking tape. Then make a new run of 2" blue tape above the 4" tape, remove the 4" tape and you have a new mark for the bottom paint.

Another method is to run the point of a large compass along the present waterline, marking the new line 4" above with the parallel pencil point end. Use the penciled mark as a guide for laying a line of masking tape.

Of course, the consistency of new lines marked using either of these techniques, will be off level by wide variations in hull curvature. To compensate, a small hand level held horizontally with the old line, may be utilized in conjunction with a compass. This takes steady eye-hand co-ordination, but is effective.

A third method, and probably the most accurate next to using lasers, is by using an adjustable 90 degree machinist's square with a built-in bubble level. By sliding the square's base along the length of the steel rule, to compensate for hull curvature, while keeping the base level with the old line, a new parallel line is traced at a consistently gauged vertical distance above.
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Last edited by TrueBlue; 05-15-2006 at 10:37 AM.
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Old 05-15-2006
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If you are raising thewaterline because the boat is heavily loaded and riding lower...a trick I saw was to put talcum powder in water in the haulout slip and the talc would leave a line on the new actual waterline which then could be used to scribe the lines for the new paint.
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Old 05-15-2006
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I am rasing the waterline, as the existing line was originally placed too low. Secondly, I want to put a boot stripe on that will not in continuous contact with the water. I have had problems with the original bootstripe, peeling each year.
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Old 05-15-2006
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The most difficult part of a project like this is to keep the line visually the same width from stem to stern. As the angle of the topsides relative to the water tapers in, the line must get wider to have the same visual width from a distance. This is most apparent at the stern overhangs where the run of the hull can be very flat, a two inch bootstripe could be 12" wide under the counter, but appear to be 2" wide (high) when viewed from a distance.
Using lasers seems the trick, but the laser base must be in the same plane as the boat in all directions, not an easy thing to ascertain.
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Old 05-15-2006
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The laser level method should work, but if you are outside in bright sunlight you will need a level with a bright enough laser to be seen on the hull surface. You will need to level the boat using the jackstands and lase level so that the existing waterline is level both fore and aft and port and starboard. Then make a mark where you want the new waterline to be, take a reference measurement at that point to the ground/floor. When you are ready to mark the new waterline/bootstripe re-establish your reference mark on the hull using the measurement you recorded and then use the level to mark the line around the hull.

If your boat is on a smooth, hard, flat surface you can dispense with any kind of level. In this case you can adjust the jackstands so that the existing waterline is equidistant from the surface. Record this measurement from waterline to surface. Then when you are ready to mark the new waterline add the 4 inches to the previous measurement and mark the new waterline. This is most easily done with a T-square whose vertical member equals the new distance from surface to waterline.
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Old 05-16-2006
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Fill a clear plastic tube with colored water. The tube could be 3/8th inch diameter, and a bit longer than your boat. This tube then becomes a long flexible level. Attach one end of the tube just above your desired new level. As you raise and lower the free end, the colored water will move up and down at the attached end. Work your way around the hull carrying the free end of the tube. Set the level to the mark at the attached end (you may need a second person to let you when the colored water is on the mark), and mark the level of water at the free end on the hull at regular intervals. Then join the dots. You can repeat this process a second time to get the width of line you desire. Your boat must be level to start with. This process will cost you a couple of bucks and an hour's work.
Cheers, Jim
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