Painting Waterlines

How do you get a nice smooth transition between colors? When I use masking tape I always get a ridge and if I try to sand it, it ceases to be straight. Do I have to build it up with clear and then sand?

Don - use thin vinyl for tape, or the more expensive green masking tape (3M-about $7.00/roll U.S.) tape and a light paint build. Otherwise, yes - a couple of clear coats may be needed to blend the strip with the hull.

If you can use a dark color on alight hull, paint will also cover better than light over dark. Consider using tape and a permanent marker too !

Edit: Added link to a forum where one of my motocycle helemt paint jobs lives.

i have bee playing with that problem for a bit. and talking to a very old sailor. ( some of those old guys are pretty sharp) he told me to do this. I did it with my 3r. paint your hull and dont worry about the water line. and when the hull is done. flip it over onto the deck and make the start and end or the waterline.
then grab a laser level. and raise the hull up level on a flat board. When you start the water line. Mark the laser level and run it down the length of the hull to match the end point. if your bow waterline and your stern waterline meet. cover the line with 1 inch masking tape. and then use a sharpie to mark it. what you then do is cut the below tape away always check with the laser level. then paint it
when dry. then you just remove the tape and you got a straight waterline:zbeer:
hope this helps
it is easy to do the waterline on a IOM. what are you doing?

The trick there is that the hull has to be perpendicular to the plane of the lazer or you get a perfectly straight line that is skewed on the boat. As long as you get them square you are fine.

PS… don’t bump it… or you have to start over DOH !


It was the painting part I was concerned with, not the actual drawing of the waterline but thanks for the info.

I once saw on TV where they painted pinstripes on a small airplane. The secret, they said, is to peel off the masking tape while the paint is still wet.

The theory being if the tape is removed after the paint dries, it leaves behind a hard, sharp edge the thickness of the tape. That edge then needs to be sanded. If the tape is removed while the paint is still wet (but not runny), the edge will slump and round itself off, almost feathering itself into the base layer and eliminating the need for sanding.

I never tried it, but you could do a test piece to determine whether the results would be satisfactory.

Good luck.

Dick(or anyone else that produce good work), I need a little advice. I want to paint and then sand with 1500 and buff til glossy and fast:). I put on one coat of color and sanded. I went through the color almost immediately. So I did a quick sand with 320 and applied another coat. I’m thinking I should have 2 or 3 coats to give me enough to sand. I screwed up somehow and got some crap in/on the paint so now I have some little imperfections. What I need to know is do I keep on applying paint and let the 1500 sanding take care of the imperfections before buffing or do I have to let the paint dry for 24 hrs so I can sand it before applying the 2nd and/or 3rd coat.
Thanks Don

A little distraction from the show at Windpower:confused:

I kept on painting and it looks pretty good. I’ll let it sit for a day or so and then sand and buff.

Hey Don;

Two things:
One, try this tape:

Two, thickness of masking tape creates a ‘dam’ which paint piles up against.
Ways to counter that are to spray paint from direction where it crosses over edge of tape instead of spraying at it; or to use thinner tape like matte finish Scotch tape for the actual edge then fill remainder with masking tape.
Another thing is to check art supplies for something called Frisket Film. It comes in sheets from which strips may be cut to use like tape.

I feel like week old cat litter tonight so the following may not be the best organized.

Several light coats instead of one thick coat will help with paint pile-up against masking edge.

Your comment on clear brings to mind that after masking, clear may be used to seal tape edge before applying color coat.

How long to wait before sanding will depend on paint. Spray cans should say in the fine print on back. Gloss enamels may need a couple days or more. Check also if paint is suitable for wet sanding. Using wetted sandpaper helps keep it from clogging up with heated soft paint particles.

Find some car modelers and ask how they get those “showroom” body paint finishes.
There are special paint buffing products marketed to car modelers.

Okay, that’s all I’m good for tonight.

Check with your automotive parts store that stocks painting supplies. There is a special tape for this purpose and is plastic based and more flexible. They also handle the ultra fine grit sandpapers (2000 & 2500) and rubbing & glazing compounds to generate beautiful finishes. They should be able to give good guidance.


some tips.

First: you paint lighter colors then darker ones, so you need to use less paint.

Second. dilute the paint enought and use many light coats until the desired tone is achieved.

Third. Some say you should peel away the maskind tape while the paint still a little fresh. I have tryed with dry and fresh paint, but the most importatnt thing is to do it with extreme cae pelleng the maskig tape back over it self, not at 90 degrees from the painted surface, this way you reduce the risk of pelleng off the paint.

Fourth. You could wet sand ( 1000 - 1500) the surface eliminating any built -up and then use 3M polisher ( cream color) that produces a lot of shine and smooth the surfaces a lot. After that, if neccesary you could use some transparent laquer.

I used for some time polyurethane paints, but as i live in a cold and rainy zone, quickly I moved back to acrylic paints that dry faster near to a heat source.

To mark the waterlines i placed the hull invertedover the bench and add some pieces of wood at the transom until the heigh of the transom bottom ( remember up side down) it equal to the height of the bow bottom, so water line is parallel to the bench.
After that I place a pencil over wood pieces at the same level than waterlines and move from bow to transom alonside the hull.

Then you get the perfect waterline.

Hope this can help.


For nicely delineated line you must use a very thin tape that has no surface features such as that found on masking tape. Three M (3M) number 218 is such a tape. It is commonly known as Fine Line Tape. Available at auto paint supply houses. Costs a plenty but the roll is 60 yards long and you’ll have enough tape to last through about 90 Footys. Part number 06301. It comes in various widths like 1/8, 1/4 and so on. It is plastic of some sort, will tolerate some modest curvature without kinking. Pull the tape off before the paint is fully dry. This stuff is only five thousandths thick (0.005) so it will not leave much of a ridge. Do not stretch it when you apply to hull.

To get the location of the waterline in the technically correct place, try this. Put enough water in the bathtub or other vessel to float the boat. Have all the ballast, batteries, etc in place. Let the water surface settle, that is don’t make waves. Float some fine sawdust, talcum powder, or even black pepper on the water. The powdery stuff will adhere to the hull of the boat at the exact waterline. Remove boat from water, let it drip dry, apply tape a millimeter or so above or below the powder line.