Tuesday, June 10, 2008

Marking the Waterlines

I spent most of yesterday morning setting up a water level and marking the waterlines on both hulls. This is a project I wanted to get done while in the fairing process, as the hull surfaces below the waterline will be covered with a thicker anti-fouling paint and therefore to not have to be sanded to perfection like the topsides that will be painted a high gloss.

A simple, jury-rigged water level is the most accurate means of establishing a true waterline on a boat hull. I bought 35 feet of clear plastic tubing with and I.D. of 3/8." Total cost: 8 dollars and change. This is better than an expensive laser level that can't "see" through the hulls. A water level allows you to mark all sides of the hulls all the way around in one set up. Wharram's plans for the Tiki 26 include a sheet with waterline measurements, showing the height of the bow and the height of the stern (both at the sheer) above the waterline. These measurements are vertical distances above the water, however, and cannot be measured on the hull. Since my hulls are currently upside down, what I had to do is establish an arbitrary waterline at a level within the range I could hoist or lower them with slings. I marked this line on a clean piece of wood taped to one of my shed support posts, as shown below. I then marked the distance from the waterline to the bow and to the stern by measuring vertically from the arbitrary waterline mark. Since the hulls were upside down, this meant measure down from the line - 31 5/8" for the bow, and 25 3/4" for the stern. I then adjusted this for the maximum load waterline by subtracting 3 inches from these numbers.

The water level consists of nothing more than a bucket of water and the clear hose. The bucket is filled, then lifted up with the hose on the ground and one end secured inside the bucket below the waterline. The hose is filled by starting a siphon until the water flows freely from the open end. Then the open end is picked up and held higher than the bucket to prevent air bubbles in the line. The water level is now operational, and the water in the hose will match the waterline in the bucket.

I started by taping the hose to the side of my marked pole. Then I lowered the bucket until the water level in the hose matched exactly the mark for the bow. The open end of the hose was then moved to the first hull, and using my webbing slings I lifted the bow until it matched the waterline in the hose, and of course, the marked line on the pole. This was repeated for the stern, adjusting the bucket to the mark for the stern. It took a couple of back and forth operations to get the hull exact, bow and stern, then I leveled it athwartships by crawling under it with a spirit level and blocking it in position with scrap wood. With the bow and stern now the correct height above true waterline, I then readjusted the bucket until the waterline in it matched the marked waterline on my pole. When this was done, all I had to do was take the free end of the hose to the hull and make marks all the way around both sides about every foot or so. The marks were then connected by carefully pulling a line of masking tape through them. I masked above the marks, so I could paint a swath of dark gray primer above the actual waterline, then remove the tape and still be able to see it clearly.

In the first photo below, the bucket is set at the height of the waterline and the clear hose standing vertically against the hull in the background is being used to transfer the marks (already painted in this photo).

Here's a view from the bow showing the port hull with waterline marked with primer. You can also see the side of the starboard hull to the left. The other hull in the top right of the photo is a 19-foot woodstrip canoe I built years ago and have no where else to store. It's somewhat in the way, but hopefully it won't be long before I'm pulling the Tiki 26 hulls out in the open for assembly with the beams.

Another view of the starboard hull shows the straight waterline, with gray primer above. This line is 3 inches high to accommodate a fully loaded boat. Waterlines are always optically deceiving viewed like this and do not usually look straight when the boat is upside down. But using a water level is fool proof and the boat will sit on it lines when launched if the numbers given in James Wharram's plans are correct.

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