Mark Wallace's Black Skiff

Sunday, June 11, 2017

Laying In a Waterline

You’ve built your boat, but now you want to lay in a waterline so that you can:

  1. Know where the bottom paint and the topside paint meet and/or
  2. Know where the fiberglass sheathing on the bottom stops and/or
  3. Know where to paint a boot-top of contrasting color (or boat-striping-tape). Note: I’ve used this West Marine tape and it has held up for three seasons with no peeling or discoloring… highly recommended (I have no connection with West Marine.)

First Step: Determine waterline END locations

Using the waterline marked on the plans for the boat, mark with a pencil about 1” to 2” inches (25 to 50mm) above (toward the sheer line) where the plans specify.


Put the boat into shallow water, load it (with people, sand bags, etc.) as you will normally be paddling, rowing, sailing, motoring and mark at the bow and stern about 1” to 2” inches above water level.

Second Step: Mark proposed waterline

See this Tips From a Shipwright video. The video shows the technique I used on my Ross Lillistone Flint. As shown in the video, use a tight string between the two horizontal supports, marking the waterline with either a pencil or short pieces of masking tape. You can do this by yourself, no help is needed. This technique is useful if the boat is NOT level, either fore and aft, or side to side.

Horizontal Stick at the Stern for Laying in a Waterline...

...and at the Bow.

A variation of this technique, which requires two people, is to set up the horizontal sticks as above. One person is the ‘marker’ (using pencil or short pieces of tape) and the other person stays at least one boat length away and sights across the two sticks, telling the ‘marker’ where to mark the waterline. I used this technique on an earlier boat I had with my wife as the ‘marker’. Worked well.
Another technique is to use a laser level such as this, (if you already have one!) . This can also be done by yourself.

You can level the boat (so that the bow and stern marks you did in the first step are level) by using a long clear plastic tube filled with water taped to the bow and stern and then moving the boat so that the water level in both ends are at the marks you placed in Step 1. Once the boat is set up ‘level’, take one end of the tube (making sure you don’t spill any water from the tube), walk around the hull, marking  every 6” the proposed waterline.

If the floor under the boat is level and flat (mine isn’t) and you have ‘leveled’ the boat as in the paragraph above, then just use a stick held vertically on the floor to mark the proposed waterline.

Third Step: Mark the full waterline

Using the guide pencil marks (or pieces of tape), lay in a continuous strip of masking tape around the hull. The ‘keel’ side of this tape will be the edge of the bottom paint and fiberglass cloth (if used).

When I glassed the bottom of Lillistone Flint, I laid in the waterline using blue painter’s tape. I then taped newspaper sheets to this ‘waterline tape’ in order to prevent any epoxy from dribbling onto the topsides. When I epoxied the cloth to the bottom, I overlapped the tape by a half inch (12mm) or so.

I then spread about four layers of epoxy on the cloth (sanding between each layer) until the weave was totally filled (each mixed with graphite powder). Epoxy dripped down over the tape and newspapers. When it had all thoroughly dried, I was able to lift the waterline tape, flex it up and down a couple of times, and the epoxied cloth broke off cleanly at the edge of the tape. There was no need to cut the cloth with a knife.

After the hull was painted, I used the West Marine Boot Top Tape, slightly overlapping the top edge of the fiberglass cloth.

Let us know of any other techniques you have used to lay in a waterline.

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