Waterline - SailNet Community
LinkBack Thread Tools
post #1 of 8 Old 05-15-2006 Thread Starter
Senior Member
Ronbye's Avatar
Join Date: Nov 2005
Posts: 134
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12

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?
Ronbye is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
post #2 of 8 Old 05-15-2006
Senior Member
Join Date: Feb 2003
Location: New England USA
Posts: 261
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 15
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.
Silmaril is offline  
Quote Quick Reply Share with Facebook
post #3 of 8 Old 05-15-2006
Señor Member
TrueBlue's Avatar
Join Date: Oct 2004
Location: Narragansett Bay
Posts: 4,858
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 15
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.

True Blue . . .
sold the Nauticat

Last edited by TrueBlue; 05-15-2006 at 10:37 AM.
TrueBlue is offline  
Quote Quick Reply Share with Facebook
post #4 of 8 Old 05-15-2006
camaraderie's Avatar
Join Date: May 2002
Location: East Coast
Posts: 13,877
Thanks: 0
Thanked 6 Times in 6 Posts
Rep Power: 17
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.
camaraderie is offline  
Quote Quick Reply Share with Facebook
post #5 of 8 Old 05-15-2006 Thread Starter
Senior Member
Ronbye's Avatar
Join Date: Nov 2005
Posts: 134
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
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.
Ronbye is offline  
Quote Quick Reply Share with Facebook
post #6 of 8 Old 05-15-2006
Just another Moderator
Faster's Avatar
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 18,771
Thanks: 141
Thanked 499 Times in 473 Posts
Rep Power: 10
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.
Faster is offline  
Quote Quick Reply Share with Facebook
post #7 of 8 Old 05-15-2006
Join Date: Mar 2006
Location: CA
Posts: 18
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
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.
paulthober is offline  
Quote Quick Reply Share with Facebook
post #8 of 8 Old 05-16-2006
Join Date: Oct 2004
Posts: 30
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
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
jimthom is offline  
Quote Quick Reply Share with Facebook

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Forum Replies Last Post
What can you tell from the numbers? brazilnut Boat Review and Purchase Forum 10 07-01-2009 04:09 PM
Waterline higher tjgault Gear & Maintenance 2 03-29-2005 03:43 PM
Confused about overhangs... msl Boat Review and Purchase Forum 15 09-23-2003 06:17 PM
What is the formula for hull speed? I can''t remember. duffer1960 General Discussion (sailing related) 3 05-08-2003 05:17 AM
LP below waterline? birdboat Gear & Maintenance 1 01-21-2003 02:22 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome