Saturday, December 31, 2011
We are building a spar factory for this job and the more rote each task becomes the better we like it. The painstaking and really fun part is setting the routines up and seeing them work. In this factory the production run is relatively short so there is still some handwork and still the possibility of messing things up through human error. We have not yet brought on the automaton robot zombie boat builders or the next generation of software to replace them so we do have to be careful through each phase of this job
All of the spars we are building in this run will be of eight-stave birds mouth construction. We begin by cutting the staves to their widest dimension on the table saw then joining them with a slash scarf joint to make up the required length for each spar. The joints are roughed on a band saw then finished in a router jig and glued together on a bench
The staves are then clamped into a jig on the backboard of our spar bench. The taper is cut into them with a circular saw adapted to slide along that jig and smoothed with a router set up in a similar way. In this way each stave comes out exactly the same as the other seven that make up the spar. The position of the batten and its wedge clamps is changed for each spar. That position is determined by a little exercise in graphic geometry where we start with the diameter of each column and proceed to determine how wide each facet of an octagon must be to encompass that diameter. Remember how many times we protested the uselessness of geometry in high school? I loved geometry.
So far the staves are scarphed together, birds mouthed and tapered just as in any hollow wood spar of this type. Silent Maid 's spars will be lined with carbon fiber cloth and rod vacuum bagged to the inside face of each stave. In this way a very stiff spar of a smaller diameter, wall thickness and weight can be built. In this case the carbon is in the form of a woven layer, a 1/4" rod set in a groove down the middle of the stave, and a layer of unidirectional cloth. In effect the wood is now a matrix for the carbon fiber which is doing the real work. All of this depends on a good bond between the carbon and wood as well as keeping the amount of epoxy to a minimum, hence the use use of a vacuum bag.
After the carbon the first layer that is not part of the finished spar is the release fabric. This soaks up excess epoxy and can be peeled off the finished composite easily. Then a layer of plastic to keep the glue out of the breather fabric. The breather allows to vacuum pumps to pull evenly on the entire bag. There are two pumps one for each half of the bag. The air is drawn out through nylon tubing with the ends sealed and small hole drilled in it. The tubes are taped to a batten and care is taken to keep the tubes in contact with the breather fabric over the length of the spar.
The first step is to set up a group of staves so they are perfectly straight inside the vacuum bag. We joined plywood panels with strips of wood hot glued to their top face then hot glued spacers to that base to hold the staves in place. The simple jigs pictured to the right were used to align the staves. After the alignment was complete the staves were lifted and a sheet of thin plastic placed over the ply and spacers kept the staves from being glued to the set up. All faces of the stave that are not to be covered with carbon are sealed with packing tape to make the epoxy cleanup as easy as possible.
The Workshop has a large compressor so two Venturi type pumps are used to draw a vacuum. They draw this 40' long bag to 9 lbs of pressure per square inch and the compressor is up to the task of maintaining this pressure overnight. A close inspection for leaks is the last step in the process. These usually occur where the hoses enter the bag or where there are folds in the bag. Since everything is sucked into the bag these are easily plugged with mastic
There is something very cool about using the atmosphere for a clamp.
The finished staves are bundled and held in place with hose clamps so the fits can be checked and plugs for the ends fashioned. More geometry and handwork. Once this is done they can be glued. That is a bit of a gooey juggling act as the bundle of staves tends to fall apart until they are all together and at least one hose clamp is on. One of the basic tenets of boatbuilding is, Never ever cut a piece of wood to its exact length until you absolutely have to. I am sure Noah chiseled this into a tablet and it will be found someday. Because our staves are long we can tack them together with dry wall screws in the very ends. The drywall screw holes will be removed when it is essential that the spar be cut to length. Once the glue is set the spar can be 16 sided with a power plane and roughly rounded with a spar plane to prepare it for the lathe.
The information needed to establish deck camber was all available on the lofting so cutting out the beams and carlins was not a problem. Of course they were all left long and fitted to the actual boat. With the beams in work could begin on the assortment of reinforcement and blocking needed to support various elements of the rig and to provide backing for the deck hardware. Work could also begin on the numerous plywood knees that would turn the deck hull connection into a box beam running the length of the boat. These knees are also part of the
cabinet work that will give the boat a great deal of storage space.
As much as possible the deck structure is designed to belp the boat resist torsional strains. A shallow beamy boat with a large rig and a crew sitting out will want to twist. One of the original Silent Maid's owners tells a story of sailing her in an ocean race between Manasquan and Cape May. Driving to weather and coming up on a mark his wife decided to use the head. Because of the boat's twisting she was not able to open the door to exit the head, the only solution was to tack the boat. Her doting husband refused to do so until he reached the mark which was still some ways off. I believe the marriage survived, no indication was given as to the Maid's placement in the race. We mean to build a boat that does not present such domestic conundrums.
Getting around the inside of a bare boat hull is like walking around in a big salad bowl, everything tends to slide to the center. In the center of the hull all of those carefully wrought floor timbers become the work of an evil genius with a thing for sprained ankles. The first priorities are to make the boat easy to get in and out of and to provide flat places to walk as we move about the boat. First a couple planks are temporarily fastened to the tops of the floor timbers then the cockpit sole beams are fitted to provide the base for a work platform. As soon as possible a 14" bandsaw is moved into the boat to reduce the number of trips in and out of the boat as the interior progresses.
Physically the most demanding thing about making boats may be these innumerable trips in and out of that salad bowl. The staircase is worth every penny espescially on a project of Silent Maid's size. As we move along any number of stationary tools will be set up in our shop within a shop to reduce the need to clamber in and out of the boat. Before starting on the deck structure the ceiling and cabin sole will be finished. The ceiling in Silent Maid was an aesthetic feature of boats of her style and era more than a structural one. It is thin, 3/8" and only found in the living space. We did overlap the cockpit so it would help stiffen that part of the boat but it does end short of the mast
To define the interior space of the cabin half of the previously fabricated beams are set up on posts clamped to the carlins. One berth has been mocked up so a person can sit or lie on it; most of the other components are being defined with bits of wood and string tacked together with drywall screws. This is the last chance to get everything right and every option is being mapped out and carefully considered. It is looking like the Maid will have four berths, a galley and enclosed head. The boat just isn't big enough for a dedicated inside navigation station, a berth would have to be sacrificed and that is too high a price to pay. There will be a nav station below but the table on the centerboard case will have to serve for studying charts and instruments can go on the forward face of the head bulkhead. The primary navigation will take place outside on the motor box forward of the helm.
The cockpit and the area beneath the side decks outboard of the staving will be utilized for a cooler with a cold plate on starboard and for the head's vacuum pump on port. The tanks and batteries will be beneath the cockpit sole. The galley will be just inside the companionway on starboard and the enclosed head just inside the doors on port.
Silent Maid's systems will be fairly complete with a vacuum flush head, and washbasin a galley with a basin, two burner stove and refrigeration. There will be a 30 horsepower deisel to turn a large alternator and battery storage necessary to run all this and three winches. As much of this as possible is placed in the cockpit area so the living spaces are free for storage and living.
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.
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.