Saturday, December 31, 2011

Upright











From the moment the decision was made to build Silent Maid's hull upside down we started thinking about how we were going to flip her upright when the time came. Several ideas were considered including bringing in a crane at $1500 a day and constructing a large plywood wheels to turn her with. Both of these seemed too labor intensive. The crane involved moving the boat out of the shop and back in; the wheel would have to be built. Often we start out with complicated ideas then move towards simplifying them. We decided to use a pair of gantry cranes we already had to do the job.

The cranes had come to us from the Sandbagger program and were each rated at 4,000 lbs. We knew the Maid's displacement to be 13,000 lbs and we also knew we have yet to build half of that. Also we could flip her over without lifting her clear of the floor. Still a boat hull is an awkward thing to grab and flip so we built a quick and dirty scale model of the boat and crane to figure out our lifting system. With two straps chokered to the hull we found the model would lift easily and safely to vertical then the aft strap would slip off the transom and the boat would fall in a most dramatic way. We needed to rig double chokers so the second strap would grip the boat after the first let loose at the vertical point. We also needed to put restraining lines on the straps to prevent them from sliding fore or aft. We also saw that the cranes were just high enough to do the job and that each needed to be fitted with a trolley to keep the pick point directly over the weight at all times.
With a clear picture of the physics involved we set about building the minimalist net we would use to maintain control of the boat. We borrowed straps from Olympia and bought a trolley for the crane that still needed one. It took a morning to get everything set and just a couple hours to do the actual turn. We moved very deliberately through the process. There is a little adrenalin flowing during jobs like this and pays to use it to slow down and focus. Any minor glitches need to be carefully considered, we only get to do this once. The only change from the model was to use come alongs to shift the trolleys across the crane as the vertical point was reached and to use a small electric winch
to slide the port side across the floor. Packing blankets were between the hull and floor to save our precious varnish job.




All went smoothly and there was enough time left in the day to level the boat and get the mold out of her so we could clearly see how large a container we had yet to fill with joinery







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