the keel is conservative, being only 50" deep from the fair body, and the root is 13' long and 10" wide. A more extreme fin would have required more depth to get sufficient area and righting moment.

A coupe of builders that quoted suggested a steel fabrication bolted to the fair body with lead at the bottom. But I didn't like the idea of steel in salt water, and that would leave no sump. A keel stub is easily molded when you are working with a male plug (much more difficult to do properly in a female mold). It is about 1 1/8" thick solid vacuum bagged uni glass and epoxy extending out into the hull fair body and then tapering into the skins and core. All of the glass overlaps are on the bottom of the stub with is about 2 1/2" thick. Into this the keel floors where bonded and tabbed, they are a 3" foam sandwich with heavy skins capped with carbon fiber.

The 10,500 lb lead casting is only 28" tall, CG is 14.5" down from the top-of-lead line. Due to wall thicknesses and the space required for nuts and backing, they can be spaced only 2" off center, or about 7 inches from the opposite side, taken to be the fulcrum. At 90 deg heel then, the bolts have to resist 152,000 in-lbs moment (1G case). Running the ABS calculations ( a very antiquated scantling rule at this point) we needed only eight SS or bronze bolts 9/16 in diameter. That is 4 per side but the ABS gives you credit for the ones on the leeward side even though they don't do anything until the windward ones break. The NA specified eight 7/8 SS bolts, plus a 3/4 in the middle forward and aft for grounding type loads. 316 SS has a 0.2% yield point of about 35,000 psi minimum, as it stretches it hardens so the ultimate can be 80,000 psi but at that point they have stretched maybe 20% which I would certainly consider failed. However many NAs take 80,000 psi as the strength. At the yield point, those 4 windward bolts would resist 433,000 in-lbs moment, about a 2.8x safety factor over gravity alone. At the ultimate tensile approximately double that, but the keel would be seriously loose and wobbling. What I ended up installing was twelve, 7/8 inch K500 Monel bolts (six per side) plus another pair closer together aft as the sump narrows, and a 3/4 forward and aft at the ends (16 total). The material for the bolts cost about $3000 dollars as I recall, they are fixed with Nitronic 60 nuts at about $60 each over substantial K400 Monel backing plates. Money well spent - the material/lb costs were after all, less than the average cost of the boat/lb. K500 Monel is almost impervious to chloride corrosion and the test certification suppled with the rods from which the bolts were made showed a 105,000 psi 0.2% yield point and 130,000 psi ultimate tensile. At the yield point, the 6 windward bolts doing the work will resist 1,948,000 in-lbs, well over 12x safety factor (at ultimate about 16x). That is not counting the other 10 bolts as contributing anything (which they probably don't).

No one knew what the effect of bending these into "J"s would be, so we threaded both ends, bolted monel cross pieces on them (and also ran a partial thread deep in the lead) all of which was embedded in the casting by Mars.

I have seen several (of what I would consider) engineering errors even in this ordinary type of installation: calculating strength based on ABS rules, using ultimate instead of yield strengths, using nominal bolt diameter instead of minor thread diameter, arranging the bolts in a curve along the perimeter instead of in a line. An example is the 40.7: if we believe the internet postings (always reliable ), there is a line of bolts down the CL with two pair offset near the middle. That forces 2 bolts to do all the work of resisting heel until they break.

If I had opted for a more extreme fin, I probably would have either built a fabricated stub from metal with a wide flange to bolt to the hull, and mold a matching recess in the hull for fairing; or molded a socket in the hull deep enough to react the bending moment over enough distance to get the material stresses down to a conservative level. Either of these methods would work in a production boat. The socket is easy to mold in a female mold (far easier than a stub) as is a recess for a flange. Neither is particularly expensive. After my trip to the Bahamas, if I were keeping the boat on the east coast I might have opted for a retracting keel. That does use up some interior space though.

Keel bolt preparation at Mars for Anomaly

Keel is pretty conservative