Frame end progress

Work has stopped on scarfing the frame ends. We have installed the laminated ends which were completed, but now we have no more glue.
The only glue I know of that is really satisfactory is the Aerodux-500, and yet that seems not to be available. As of Tuesday afternoon, the distributor in California admitted that he did not have it in hand.
We sought alternatives. We made up sets of laminations using epoxy, Weldwood resorcinol clamped lightly,and Weldwood clamped tightly. We then broke them using a weight suspended below a fork lift. We also broke a sample of the Aerodux which had been cut off of frame scarfs.
The Weldwood failed completely. The glue itself split apart, indicating its cohesion failed rather than its adhesion to the oak slats. DAP system engineers promised an investigation, if we would send them our lamination and glue batch.
The epoxy was very strong; the glue sucessfully adhered, until the slats themselves split apart. We would use epoxy, except for the folklore we have heard, which says that West system epoxy does not adhere to oak.
The Aerodux scrap also broke by wood fiber failure, rather than by failure of adhesion or cohesion. In view of the poor reputation that epoxy has with oak, I am planning to wait for the Aerodux.
Work therefore has begun on reinstalling the rudder. Fitting it in place, using the replacement shaft, showed that we need a little more trimming on the dutchman at the top of the stern post, and I am doing that. When that fits, we will install the bottom bearing.
Roger is shaping the false keel timber, using his favorite adze. It should be done quickly.
We discussed the false keel liner. Its failure was due to delignification of the wood next to the bronze liner, and excessive wear at the bottom opening for the centerboard. The bronze liner was not reusable, and a replica would have been awkward and unsatisfactory to install. Instead, the present plan is to line the false keel with G-10 FRP, and install a UMHWP (ultra-high molecular weight polyethyline) replaceable wear insert on both sides of the bottom opening, to carry the side load of the centerboard. We will attach the G-10 with West System G-Flex, which is designed for gluing plastic to wet wood. The UMHWP, formed into a 1" by 2" bar, will be attached behind the bronze worm shield with wood screws. All the parts have been ordered.

Frames update

Four new laminated frame ends have been built, and number 29 has been installed. (pictures coming) Each frame end is scarfed to the upper frame and the half-lapped scarf is secured with a bronze strap. A bronze flat head machine screw goes through the doubled layer of planking, the frame and the strap, secured by a bronze washer and a heavy nut. The end of the bolt is cut to size and punched to secure it.
The same scarfing procedure has been followed for the forward frames, numbers 13, 15, 17 and 19, except that the shape of these frame ends is straight enough so they can be shaped from ordinary planks, instead of multi-ply laminations.
In summary, the status is that all the floors from 24 to 12 are now fitted in place; those from 29 to 23 are fitted, but are being temporarily removed, one or two at a time, for ease in installing the frames. The odd frame ends are being installed first; 13, 15, 17, and 29 are done.
We are now held up because of a shortage of glue. Snediker recommended that the frame ends be laminated using Aerodux-500. Apparently, though, the only US supplier is in California and not too responsive. At any rate, we have used up T&S's supply and are awaiting more.

First lamination

Today, we finally started building the most difficult of the frame ends. These are for the ten split frames around the centerboard, and they reach deep into the bilge, around a moderately tight curve.
Snediker decided that they would be build out of 16 eighth-inch slats, about two inches wide, laminated around a curved plywood mold. The slats are of knot-free quarter-sawn oak, about forty-two inches long, which is four inches longer than necessary. We plan that the frames will come out with one flat side, so that the other side can be planed easily and the bevel can be cut into the concave side to match the curve of the planking.
They are laminated using Aerodux-500 resorcinol adhesive which claims to be water- and weather-proof. Its technical specifications are excellent; it passes boiling and strength tests for use with exterior and underwater structural oak timbers.
Snediker made two inside molds out of four layers of half-inch plywood, cut to the curves of the frame templates. He drilled one-and-a-half inch holes into the center of the jigs to hold the heads of bar clamps and screwed a sixteenth-inch steel strap around the outside to help with clamping. Two frame ends can be laminated on each jig at one time.
He intends to recut each jig after using it twice. The first jig will be used for frames 29 and 28, the second for 27 and 26, then the first jig will be recut for frames 25 and 24, and the second for frames 23 and 22.
I can't help too much with the planning, but I became the apprentice cutting the slats from kiln-dried oak planks. When it came time for the glue, both of us were up to our elbows in mixing and applying.
We were able to assemble four frames in an afternoon. We used about ten liquid ounces of glue per frame; this averages out to 175 gm/square meter.

Yesterday, I narrowly avoided what I now believe would have been an engineering disaster. I had planned to repair the frame ends by replacing them with parts machined from phenolic plastic sheet. Yesterday morning, I awoke with a vague worry about its strength in applications subject to shock and vibration while under tension; I undertook a brief experiment to allay my fears.
Introduction:
Oak has been used in marine construction since before America was founded. The scantlings of modern ships and the intuition of boatwrights are based on their experience with its properties; the plans for RUNE specified that its ribs be built of oak steamed and bent into shape.
Since the second World War, plastics have been applied to diverse engineering situations. Phenolic resin is reinforced with cloth, formed into sheets under pressure and heat, and available for easy machining with woodworking tools. Its strength is measured with standardized tests, and its properties are predictable. The tensile strength cited in the literature is comparable to that of oak, and because it does not have a favored grain orientation, heavy phenolic sheet should be ideal for making the curved shapes of RUNE's frames.
On the other hand, its thermoset resin seems stiff, and I worried that it might be too brittle for the varying loads applied to a boat hull. Oak can respond to cyclic and impact stresses without catastrophic failure; is the same true of phenolic sheet?
Therefore the null hypothesis is that parts made of phenolic resin sheets are comparable in strength and fracture toughness to oak.
Procedure:
I cut the same shapes in oak and phenolic. The shapes resembled the cross-section of an I-beam, with 2 inch by 4 inch rectangles at the top and bottom, connected by a 6-inch stick, with a cross-section 3/4 inch square. The three zones blended into each other with fillets of 1.5 inch radius.
I drilled two 5/16-inch holes in the top and bottom rectangles to connect them to chains. The chains were shackled to nylon straps and the linked arrangement was used with a fork lift to raise a large oak timber an inch or two above the ground.
After the timber was raised and lowered, I drilled a one-eighth inch hole through the square section, and raised it again. While the timber was being held by the test shape, I tapped sharply on the side of the piece, aiming for the side of the central stick near the eighth-inch hole. I then lowered the timber and drilled another hole in the same plane.
I repeated the cycle of drilling, raising, and rapping until the piece broke.
Results:
I first tested the phenolic piece. I drilled a first hole front to back at the mid-line of the stick. I then drilled side to side above the first hole. Third, I drilled a second hole, front to back about an eighth inch away from the first, and parallel to it. After the third hole, the phenolic ruptured abruptly, in the plane of the two parallel holes.
I then tested the oak piece. I raised and lowered the timber, drilling first front to back at the middle plane, then side to side above it, then I returned to the middle plane. I drilled four parallel holes at the mid-plane, and then two side to side holes through the same plane, before the oak splintered and parted.
Discussion:
The mass of the timber, sized 13 inches by 15.5 inches by 147 inches, was calculated to be about 802 lb using a density of 46.8 lbf per cubic foot. If the tensile strength of the phenolic were 6000 psi, it should be able to lift a load of 3375 pounds at its full cross section. A wide range of strengths are reported for oak, but it should also be able to lift the entire timber at its full cross section.
Calculating the effective cross sectional area is difficult for holes that are not co-planar. In this discussion I calculate the cross sectional area by assuming that the fibers do not adhere to each other at all, perpendicular to the tensile stress. The area is calculated by projecting all the holes to a single plane perpendicular to the pull.
The cross section of the phenolic test piece after three holes were subtracted was 0.312 square inches. Since the sample broke when the area decreased to that point, the maximum tensile strength for the phenolic sample would be 2570 pounds-force per square inch.
The equivalent calculation for the oak test piece yields a cross-section of 0.094 square inches, from which a maximum strength of 8560 lbf/sq. in may be inferred.
Conclusion
Considering the uncertainties in the testing method, it can be concluded that the tensile strength of phenolic laminate, when subjected to impacts, is about a third that of oak. Since the design of this boat is predicated upon the characteristics of its wood frames, it would be unnecessarily risky to substitute the phenolic sheet.
Without having repeated the tests, I cannot infer the accuracy of these measurements.
Acknowledgements:
All the sample preparation and forklift operation was done by Roger Hambidge; I received significant suggestions for safe operating procedures from Wade and Joel, and the debate with Dave Snediker focused my thoughts on the need for this test.

Centerboard trunk waiting for frames

The present status is:

• The two centerboard clamps have been made and fitted.
• The notches for the clamps are done, and the holes for the wooden trunk have been bored in all the parts.
• The trunk itself has now been removed and the clamps replaced by temporary stiffeners to allow easy replacement of the frame ends next to it.
• We have received a huge piece of linen phenolic to use for the frame ends.