User talk:Don Huseman

keel bolts
Keel bolts are used to hold on the keel of a sail boat. The keel has two functions. The first is to act as a wing to make the boat go to weather, or up wind. The second function of the keel is to act a counter ballance wieght to prevent the boat from falling over when the wind blows on the sail. To resist this force on the sail keel bolts bolt the keel to the bottom of the boat. The force that the keel has to resist is not only the healing force of the boat but the G forces that the boat gets when it is dropped of a wave or other movments that a keel faces in a heavy sea. The modern formula for keel bolts is Center of gravity of the keel depth times the weight of the keel = tensil strength of the bolt materialx the area of the bolt x the distance of the center line divided by the bolts only on one side of the keel. All center bolts are included in this formula. If you have a simple keel bolt pattern of four bolts at 4" of center line. The tensil strength is 60,000 psi. The bolts are 1" dia. The bottom of the thread is .750"  The  square area is .44. Take .44x 60,000 = 26493 lbs. use 2 bolts x 4=8 8x26493= 211950 holding strength.  If you have a keel with the center of gravity at 50" down and the keel weights 4239 pounds the you have a ballance of the keel bolts and the bending force of the keel. It is not practle to have that much force concentrated in two parts of the hull so there would be about 6 more bolts.

Keel bolt material All keel bolts are subject to rusting. All keel bolts are subject to galvanic action. If you have keel bolts going through oak timbers then they are subject to acids that will eat the bolts. With these basic fact in mind we can start talking about the type of keel bolts. The first choice are Iron Keel Bolts. Iron keel bolts rust a little and then they stop rusting. The still rust but at a slow rate. Old iron bolts resist tanic acid that is caused by oak keel bolts. The main problem is that Iron bolts are not strong. Bronz bolts are an excelent choice. They are strong don't rust and last for a very long time. The only problem is they are more expensive than the other materails. The three hundred series of stainless steel is very good. 304 and 316 type stainles steel are good. 316 is the best and most modern keel bolts are made out of 316. There has been some problems with 304 and it is not used any more. The cost of 316 is a bit more but because of the great coorosion resitance to salt water it is the best of the stainless steel. Galvanized steel is used and it works well for about 10 years or longer untile the galvanizing were of and then you have rusting problems. There are a lot of boats that were built in the 70ies and they are now having problems with their galvanized bolts rusting through to failure. That is 35 years old not so bad. The only problem is the fiberglass boats seem to be lasting a lot longer so the keel bolts will have to be replace, or sistered in. A replacemt bolt that is put in next to the galvanized bolt. Lead Or Iron Keels Iron keels are more common out of the united states. They are very strong and are easy to attach to the bottom of the bolt. The disadvantage is they are less dence and there for have to be bigger to give the amount of wrighting force. They also rust. Lead is the ideal material because the racing rules say that you can't use any thing dencer than lead. It is easy to cast and with the correct keel bolt material will last for ever. It has a the ability to bend if you hit something under water. Saves the hull. Depending on the loading on the keel there differnt type of structures in the lead keel. On ordiary boats threaded 316 stainless is cast into the keel. The end of the bolt is bent into a j shape. The depth of the bolt should be about 12" down. On high loading keels a stainless structure is cast into the lead. The keel bolts are made out of much stronger materials like Nitronic 50 about 125000 psi. There are more stronger materials like the most strongest MP35N. This has a 350,000 psi Many of the keels are bulbs on long fins. The fins are 15ft long with 45,000 lbs of lead on the bottom. The fins are very short for and aft and are not very thick. The material of choice is 4130 forged to give it 200,000 psi . These arn't bolts but they are part of the modern Keel. Electrosis of differn't materials If you put a stainless steel nut on a steel bolt in salt water you will have the stainless attack the steel bolt and distroy it in three years. If you put stainless steel bolts in a cast Iron keel you can have a galvanic action between the iron keel and the stainless bolt. The stainless can win. The threads of the iron keel can be eaten up. You must watch out for the differents in the nobility of the metals you put togeather in salt water.