I realized I could copy the Beneteau technical notice as a text file (absent photos) and thought that might be worth while. I regret the formating of the tables, below, isn't perfect, but should be understandable.
• Cast Iron keel use galvanized bolts - There are threaded sockets cast into the keel
• Lead keels use stainless steel nuts - There are threaded rods cast into the keel
You can use stainless steel bolts in a cast iron keel, but you should remove and inspect the threads for galvanic corrosion yearly.
A bolt only has to engage the threads 1½ times the diameter of the bolt to be effective. 90% of Beneteau Keel bolts are 3 inches or less in length.
Use a battery powered drill with a wire brush wheel. Clean the heads down to new metal. Tip: use a shop-vac to clean rust dust and flecks as you clean the heads.
Remove 1 bolt and inspect. At this point you should be able to make a determination if the bolt is structurally sound or needs to be replaced. A complete set of the bolts and washers can ordered from the Beneteau Spare Parts Department. We will need the Model and Type of keel on of your boat.
14mm bolt uses 22 mm socket
20mm bolt uses 1-3/16 socket
30mm bolt uses 1 7/16 socket
If you have water entering the boat through the bolt hole, replace the bolt and make future plans with your local boat yard to haul, separate and reinstall the keel.
If the head of the bolts are so degraded that the socket will not back it out, use a side grinder to grind two flat sides on the bolt. This should allow you to remove the bolt with a wrench. Worst case scenario: Remove boat from the water, grind the heads completely off and remove the keel from the hull. Then using the remaining shaft of the bolt, remove the bolts and reinstall the keel.
Coating the heads of the bolts with a rust preventative paint will prolong the life of the bolts. Tip: I have used Trailercoat from West Marine with success.
Do not use sealant on the bolt threads; only use sealant around the bolt heads to keep bilge water out of the bolt socket.
The keel to hull joint and exterior seam should be sealed with Marine Adhesive Sealant 4200.
Keel bolt Torque Specifications.
DACROMATISED STEEL BOLTS TYPE 8-8.
DIAMETER M14 M20 M24 M30
TORQUE in M.Kg - minimum 5 13 23 45
TORQUE in M.Kg - maximum 9 27 46 90
TORQUE in ft.lb - minimum 36 94 166 325
TORQUE in ft.lb - maximum 65 195 333 651
STAINLESS STEEL BOLTS TYPE A4-70 and A4-80
DIAMETER M14 M20 M24
TORQUE in M.Kg - minimum 5 16 28
TORQUE in M.Kg - maximum 11 32 55
TORQUE in ft.lb - minimum 36 116 203
TORQUE in ft.lb - maximum 80 231 398
STAINLESS STEEL BOLTS TYPE A4-55
DIAMETER M30 M36 M42
TORQUE in M.Kg - minimum 19 33 52
TORQUE in M.Kg - maximum 38 65 104
TORQUE in ft.lb - minimum 137 239 376
TORQUE in ft.lb - maximum 275 470 752
PS: Keel bolts can be replaced, one at a time, while the yacht remains in the water. And, when I replaced our keel bolts, I coated them with Petit RustLoc primer--several coats--to good effect.