Saturday, May 31, 2008


Still working on the pond, but also made some progress on the boat.

Beginning to plank the first float half was an exciting step. I reread the plans, reviewed several other builder blogs and developed a plan. (Note: in checking the battens for 'fairness' I found a very flexible metal ruler, placed perpendicular, could show you if there was a batten that was an out layer).

As seems to be the tendency, I planned to place the foam and then fill between with bog. I decided to place the keel first, then scribe the planks to fit. A 'two footed' device helped with this. The deck flange would be last.

Starting in the middle helps get things going as the angles and bending get more severe near the ends. I would cut to shape with a utility knife.

I quickly learned that I developed the best shape by thermoforming each plank. No stress or tension became my motto. Maybe because of the flexibility of my battens, forcing a plank of 500 weight CoreCell would deform them slightly, which then 'flattened' the shape of the hull. It's easy to shape the foam by using a heat gun while flexing it by hand. Constant motion equals no scorching and no sharp angles. The foam expands with heating, so start on the 'outside' to begin forming the curve, then inside, then outside a second time. At three minutes you have to be careful not to flex too hard as it starts to give. Hold in place quickly to get near perfect fit.

I rechecked the keel fit and beveled the join with a small palm micro-planer. Especially near the ends where a compound or twisting action develops, the plank-to-plank join can be adjusted top or bottom with a couple of swipes with the hand planer. Instead of making a groove for the bog after attaching the foam, I ran it though a table router with a dove-tail bit. The curve never presented a problem with several feather boards to hold it in place.

In the end I stopped using my long clamping bars. The clamps are flat -- there is very little of the hull that is flat. As you get towards the ends, the foam twists with changing angles, and bending fore-aft and athwart ships.

It's the fore-aft bending that argues for narrower planks, especially with the decreased holding power of the screws with the thinner 3/8 foam. Once satisfied with the shaping, I pre-drilled holes in the battens from the top and pre-placed screw from the underside. A light-weight lithium-ion driver with clutch is the tool to get. Push from the top, drill from the bottom. A 'spinner' has no holding power in the foam, so set the clutch low to start.

I learned to run my hand along to check for smooth transitions.

A very pleasing shape. I cut the deck side to length and slipped the deck flange mold in place.

I placed the foam filler along the deck edge with bog and screws through the deck flange mold (the deck is not 90 degrees to the side of the hull as it bows out slightly). This keeps the deck flange oriented correctly, and the gap bellow will need to be filled with bog and given a smooth radius to ease glassing later.

I spent some time deciding what to use to fill the grooves. Using premixed fillet and fairing materials was something I had already decided. The instructions are: "use low density, it only needs to be stronger than the foam." System Three replied about QuickFair: "You can use QF for this but you must SAND before coating with itself or anything else."

The grooves were filled with System Three Quickfair in a zip-lock bag. This was easy, quick, and made for no voids.

Being efficient with glass usage can be difficult. It seems that the farther you can look ahead, the better you can plan. I am not cutting my own tape, so long thin sections are difficult to use. For this situation it seemed that I could save by going across, parallel with the foam.

I used the 'poor man's vacuum' technique, working from bow to stern, one section at a time.

Order of events:

Pre-wet ahead one section of tape at deck flange. My tape has a thin matte backing, which makes it easy to work with as it holds its shape/size, but it takes longer to wet (and will also add weight).

Wet foam. No point in having a dry interface where it is a mechanical bond. Concerns about the glass floating or excess resin are minimized by the VB technique. (I would like to look at the foam under a microscope after thermoforming. The surface is made up of little open cells and filling these with resin would seem to significantly increase the surface area of the bond with the glass [obviously happens maximally with VB'ing]. I wonder if heating the surface with a heat gun smoothes or reduces this interface in any significant way? You can see subtle changes as you do it.)

Lay out tape, then piece of glass, and second layers where called for. Subsequent sections require overlap. Wet, moving excess resin towards next area.

I placed peel ply as a final layer.

(I wore a simple paper mask as I found that when mixing the resin, occasionally small bubbles would float in the air -- don't want to breath those! The resin has low volatility, so with adequate airflow I haven't worried about the fumes.)

Begin placing plastic, width dependent on curves. I found 2-3 per 50 inch section. The plastic should be covered with some extra resin so that there is no resistance to the flexible squeegee. Position with light dragging strokes to remove air bubbles.

The plastic I used had many creases from packaging folds that initially concerned me. It seemed that they could be removed, only to reappear. This later proved to not be a problem (see below).

To remove the excess resin and 'micro' bubbles, using more force and pulling towards yourself with the squeegee's edge seemed effective.

I worked from the center towards the deck flange and keel, placing excess resin on the plastic. Since the resin has to be removed, not having the plastic too long is helpful. This resin usually had some micro bubbles so I did not move it forward onto the next section of glass.

Making sure that you have resin to remove answers the question, 'is it too dry?' Interestingly, after a little experience you can tell too little, too much, or just right by listening to the sound of the squeegee.

One key was making sure that the plastic sections had a minimum 3 inch overlap that had enough resin between them to act as a seal.

The keel was a little more challenging than the deck edge. Don't let the excess resin just glob up on the foam edge. Remove it, using paper towel if necessary. The plywood deck flange mold acts as an extension to seal the edge, but you don't have this on the keel side. I went back several times as the resin gelled to make sure it hadn't lifted off along the keel. This prevented any problems.

I cut the excess cloth and plastic off the keel easily with a knife while still green. Then removed the plastic after cure. The plastic leaves a shiny finish and some imprinted creases as well.

I removed the PP in the area of the future BH's and strengthening stringer, leaving some to allow easy, clean removal of the VB tape.

I'll take a close-up next time, but what I discovered is that the crease imprints were excess resin that was pulled on top of the PP (by the "poor man's" vacuum effect as the plastic fought to regain its fold), so they pulled off when the PP was removed (before this I had been wondering if I would repeat this technique or search for expensive, creaseless plastic like my rolled VB material . . . not a worry, it seems.)

I VB'd the stringer and extra scheduled glass layers. (Note: initially I measured from the deck flange, not the form -- look close before placing.)

No final picture, I guess. I next cut out the BH's, backfilled the access opening, and worked on a gig to ensure proper placement.