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Selecting woods and materials

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Selecting Materials

Since the chine log method relies so heavily upon the chine logs to provide strength and structure, all the plywood is doing here is acting as a sort of waterproof, ultra stiff cardboard, particularly with the thinner variations. The thickness of the plywood is directly proportional to how much you believe this principle is true. Materials selection seems to be the most vexing for newcomers, so I’ll try to cover this in great detail.

Plywood Plywood comes in three usable thicknesses. From thickest to smallest, 3/8ths inch, 1/4 inch, and 5.2mm Luan. I recommend 1/4 inch since it’s more forgiving to the first time wood worker than 5.2mm Luan. 3/8ths inch is recommended for the hull bottom if you’re a bit large, or plan on taking more than two people along, but my boat uses 1/4 inch, along with several runners along the bottom to improve strength and avoid “oil canning”.

Plywood selection is fairly easy, since they come in big pallets at the local Lowes or Home Depot, feel free to get picky and select only the best three sheets out of a stack of 50. Plywood sheets vary tremendously in quality. If you can get your hands on Marine grade plywood, that’s great – it’s not that they use a special waterproof glue – all plywoods do – it’s that there aren’t any voids in the middle layers of the plywood. Occasionally there will be voids in the outer layers of plywood, such as knots, or cracks/seams that have been “smoothed over” with some sort of putty-like substance. These voids cause the plywood to be weaker than it otherwise would be, and occur on about 90% of the sheets that I’ve found. Since you intend for this boat to last you a year or more, it’s worth the extra 20 minutes to find the plywood you’re happy with.

Chine Logs If you don’t own a table saw, your options for chine logs drops significantly. Since you’re probably doing this on a budget, your selection of chine logs is drastically simplified. The shortest screw I could find at Lowes that came in quantities large enough for me to build a boat with was 1 and 3/4” screws. Luckily, Lowes sells 1x2”s and 2x2”s – which are in reality 3/4x1.5” and 1.5x1.5”. When using 1/4 plywood, this is just long enough of a screw to go completely through the plywood and chine log without sticking through the other side, so you don’t have to clip, file down, or remove the screws entirely at a later point.

I ended up selecting 1x2”s for the curved chine logs, as they’re thin enough that they’ll comfortably bend to meet the curve of the bottom, but wide enough to accept a 1 and 3/4” screw comfortably. These come in 8 foot lengths, and cost about $2 each.

The rest of the boat was finished with 2x2s, simply because you can drive a screw in to it at nearly any angle and not worry about it popping out the other side. They also come in 8 foot lengths, making life extremely easy for building boats of 8 ft in length.

The problem with purchasing pre cut chine logs is that they come from the mill seemingly pre-warped. At my local Lowes, the 1x2”s were haphazardly piled on top of one another with the result looking not entirely unlike a game of pick up sticks; the result of hundreds of other people picking through looking for a matched pair of unwarped lumber. Since the main structure of the boat comes from the chine logs, it’s crucial you use absolutely straight – or as straight as you can acquire – chine logs. 1x2s tend to warp in a bow shape, while 2x2s tend to twist like a twizzler. The bow shape is actually beneficial, since they’re already shaped like the bottom of your boat – less work for you. After laying them out on the ground, flip them on each side to determine which pieces have the slightest amount of warp to them. Many 2x2s tend to warp three quarters along their length. If you can find one with a slight twist in the middle, it should still be serviceable, since most likely you’ll be cutting it in half as reinforcement for your bulkheads or transoms – which are slightly less than four feet wide. Save the absolutely straightest lumber for your boat’s gunwales.

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This page was last modified on 18 April 2008, at 18:15.
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