Sunday, November 15, 2009

Planking the hull












Planking the hull has been fairly straightforward. First, I had to assemble my new band saw and learn to properly adjust and check it. That proved a bit more difficult than expected since it was shipped to me minus a screw (which took a while to discover) needed for proper tensioning. I also needed to choose which wood to use. Surprisingly, I found a local source in Colorado for cypress at moderate cost. I resawed the boards into a 3" by 3/16" cross-section. Most boards have some kind of curve to them; so, I had to be careful to mark and maintain a straight line when laying them out on the curved hull surface. Then it was simply a case of coating each board and the underlying hull plywood with epoxy and temporarily stapling them in place with minimum mess. I used a bit of excess to make sure that they were thoroughly wetted and bonded which then required that I sand the entire hull to remove blebs and discontinuities.

Saturday, August 29, 2009

initial hull sheathing













Once all the frames and the anterior keel are mounted and aligned on the strongback, the entire framework was then faired so that panels would lay flat instead of merely touching one edge of each frame. This provides more panel support and more bonding/nailing surface. Once faired, rosin paper patterns were made for each proposed panel of the hull sheathing. I was planning to make thin ply patterns but found that stiff paper was accurate enough in this case.

I had to decide the order of panel placement and the position of junctions between panels. I wanted to place the panels which required the most bending first, and I wanted to join separate panels in places where hull curvature was at a minimum. On my previous boat I scarfed all the panels together before placement, but found that handling an 18+' long, narrow panel wet with epoxy resin, precisely placing it, and getting it securely fastened in place quickly was a difficult task. Fortunately, this hull has convenient panel juncture points where either a butt plate could be placed or a nearby frame could back an in-place scarf joint.

Those plywood panels which required significant bending, the bottom forefoot and stern side tumblehome, were submerged in a shallow basin of water for several hours and then quickly clamped on all edges into place of the frame and left to dry for a couple days. The panels were then removed, trimmed for a more exact fit, and bonded into place. As more panels were placed with adjoining edges, clamps could no longer be used on all edges. For these locations I used a nail gun with a 3/4" or 1" 18-gauge nail and scrap 1/4" ply placed under the head to facilitate later removal.

At this point, the entire hull is sheathed, and we can begin to see the full shape of the hull. I now want to cover the entire hull with a second layer; 6 mm. just isn't enough thickness for me. Sure, I could used multiple layers of resin and cloth, but that stuff is heavy and expensive. The strength-to-weight ratio for wood is excellent, so I will add about 4 mm. of thin wood planks; sand it as needed, and finish with a layer of resin and cloth. I've had to research band saws and blades to get the right setup for "resawing", cutting a normal plank into 3-5 mm. thicknesses. The band saw I bought was missing an important set screw, and I was unable to properly adjust it until I figured out that the mechanism was not functioning properly. Looks like it is now properly set, and producing thin planks is my next task. I have picked cypress wood for the planks- available, relatively cheap, fairly light, and rot resistant.

Wednesday, May 13, 2009

The Design Becomes a Reality












I have already posted on the design of this boat, so I will skip that subject other than to mention that my initial "plan' consists of tables of computed offsets in an X,Y,Z three-dimensional framework. I am having computer issues with importing photos, so they will get posted a little later.

1. First job was to convert those dimensions into full-size patterns for all the frames and the curved keel forefoot. I used stiff rosin paper for the patterns, the largest pattern is about 36" by 68". The offsets only define the outline of each part; thus, each frame was then drawn as a series of boards with joining angles and gussets. A horizontal reference line was drawn at the same level for each frame; this was used to align them all vertically when mounted on the strongback. The centerline can be used to align them horizontally.

2. With full-size patterns it is relatively easy to build the actual frames, all 14 of them. An outboard engine is to be contained in a semi-well which intersects with three frames, so those internal details had to be included in the frame designs.

3. A strongback was built with vertical support posts attached at each frame position. The frames were sequentially clamped in place using a laser beam to align them. Then longitudinal components, starting with the keel, were bonded in place. I really was anxious to get the engine well fit and bonded in place. Being integrated with the deck, hull bottom, transom, and three frames and structurally important to transmit the power of the engine, its fit was critical.