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#1
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keel bolt torque
Hi,
can anyone advise me on the roughly correct torque setting for tightening the nuts on my keelbolts? The studs are 20mm (thats about 13/16") in 316L plus one at 12mm(about 1/2") The keel is 2 tonnes of lead if that makes any difference. I'd hate at this stage (five long and bloody years) to over or undertighten the bolts. Thanks Pete |
#2
posted to rec.boats.building
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keel bolt torque
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#4
posted to rec.boats.building
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keel bolt torque
On Wed, 14 Jan 2009 18:44:54 -0600, cavelamb
wrote: wrote: On Wed, 14 Jan 2009 21:13:59 +0100, wrote: Hi, can anyone advise me on the roughly correct torque setting for tightening the nuts on my keelbolts? The studs are 20mm (thats about 13/16") in 316L plus one at 12mm(about 1/2") The keel is 2 tonnes of lead if that makes any difference. I'd hate at this stage (five long and bloody years) to over or undertighten the bolts. Thanks Pete 1/2 inch = 80 pounds 3/4 inch = 250 pounds 1 inch = 350 pounds These figures above are for DRY hardware. Being stainless, it's highly advisable to apply some lanacote or grease to avoid galling. Lubrication means reduce the torque figures above by 10% Is that inch pounds or foot pounds??? Sorry. Foot Pounds |
#5
posted to rec.boats.building
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keel bolt torque
On Wed, 14 Jan 2009 18:44:54 -0600, cavelamb
wrote: wrote: On Wed, 14 Jan 2009 21:13:59 +0100, wrote: Hi, can anyone advise me on the roughly correct torque setting for tightening the nuts on my keelbolts? The studs are 20mm (thats about 13/16") in 316L plus one at 12mm(about 1/2") The keel is 2 tonnes of lead if that makes any difference. I'd hate at this stage (five long and bloody years) to over or undertighten the bolts. Thanks Pete 1/2 inch = 80 pounds 3/4 inch = 250 pounds 1 inch = 350 pounds These figures above are for DRY hardware. Being stainless, it's highly advisable to apply some lanacote or grease to avoid galling. Lubrication means reduce the torque figures above by 10% Is that inch pounds or foot pounds??? From Engineer's Handbook http://www.engineershandbook.com/Tables/torque3.htm I get the following values for 316 Stainless (assumed course thread) 20 mm = 13/16" 3/4"-10TPI = 1582 "lbs 7/8"-9TPI - 2430 "lbs interpolating 13/16" would be approximately 2006"lbs = 167 'lbs 12 mm = 1/2" 1/2"-13TPI = 542"lbs = 45'lbs From experience: Most common stainless alloys aren't very strong and tightening to levels recommended for some steel bolts will frequently result in stretched bolts. for metric steel bolts: 12mm 5D (71,160 psi med. carbon steel) = 34'lbs 8G (113,800 psi med. carbon steel) = 54'lbs 12K (170,674 psi Med. Carbon) = 86'lbs 22mm as above 182, 284, 464 ft. lbs. Cheers, Bruce (bruceinbangkokatgmaildotcom) |
#6
posted to rec.boats.building
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keel bolt torque
Be very careful here because you have not stated the material under bolt
compression. Depending on whether the material is wood, fiberglass, steel or aluminum and the washer diameter or cap size used to distribute the compression load, the answer could be quite different. The torque values or stretch limits stated by others reflect the maximum elongation force aacceptable by the bolt material without permanent bolt deformation and do not consider potential crush limitations of the compression sandwich, which could be much less. Steve wrote in message ... Hi, can anyone advise me on the roughly correct torque setting for tightening the nuts on my keelbolts? The studs are 20mm (thats about 13/16") in 316L plus one at 12mm(about 1/2") The keel is 2 tonnes of lead if that makes any difference. I'd hate at this stage (five long and bloody years) to over or undertighten the bolts. Thanks Pete |
#7
posted to rec.boats.building
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keel bolt torque
On Thu, 15 Jan 2009 07:30:19 +0100, "Steve Lusardi"
wrote: Be very careful here because you have not stated the material under bolt compression. Depending on whether the material is wood, fiberglass, steel or aluminum and the washer diameter or cap size used to distribute the compression load, the answer could be quite different. The torque values or stretch limits stated by others reflect the maximum elongation force aacceptable by the bolt material without permanent bolt deformation and do not consider potential crush limitations of the compression sandwich, which could be much less. Steve The figures I cited are from C&C. I have seen others from manufacturers of fiberglass sailboats with stainless steel bolts and bolt on keels and they are all very similar to this. |
#8
posted to rec.boats.building
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keel bolt torque
On Thu, 15 Jan 2009 07:30:19 +0100, "Steve Lusardi"
wrote: Be very careful here because you have not stated the material under bolt compression. Depending on whether the material is wood, fiberglass, steel or aluminum and the washer diameter or cap size used to distribute the compression load, the answer could be quite different. The torque values or stretch limits stated by others reflect the maximum elongation force aacceptable by the bolt material without permanent bolt deformation and do not consider potential crush limitations of the compression sandwich, which could be much less. Steve Thanks Steve, the hulll at that point is 22mm mahogany strip planking with two heavy layers of fibreglass epoxied on each side;, bonded to that are 100mm oak beams to take the keel bolts, also fibregalssed in with epoxy. Over most , but not all, of these beams is a 60mm thick oak plate spreading the load from the mast over the first five floorbeams. Under the hull is an oak packer varying in thickness from about 20mm to about 40mm to take up the curve of the hull. So for most of the bolts, they are all going through around 200mm of oak and mahogany plus around 10mm of fibreglass and epoxy. Between the nuts and the oak are 8mm thick stainless plates about 60mm x 150mm wide, linking each pair of studs. I know that the oak I chose for this job is the hardest I had and therefore I don't think it will compress much. (Potentially famous last words here) Hope that helps, and thanks for all the replies, I'm pleased to get so much advice. Pete wrote in message .. . Hi, can anyone advise me on the roughly correct torque setting for tightening the nuts on my keelbolts? The studs are 20mm (thats about 13/16") in 316L plus one at 12mm(about 1/2") The keel is 2 tonnes of lead if that makes any difference. I'd hate at this stage (five long and bloody years) to over or undertighten the bolts. Thanks Pete |
#9
posted to rec.boats.building
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keel bolt torque
Pete,
Your ultimate goal is to tighted the nuts enough to get the studs into the safe stretch zone without causing permanent deformation of the studs, but as stated previously, this can often cause excessive compression of the sandwich. In your case the keel load bearing assembly appears more than adequate. The idea is to spread the bolt load over the largest area of low density material as possible with a high density plate (stainless). The only way to know if the plate is adequate is to use antiseize on the threads, place a dial indicator to monitor the compression of the sandwich and apply torque with a torque wrench. There will be some compression, it is unavoidable. You want to see a linear increase in torque relative to the rotation of the nut all the way to the stretch zone. If the torque increase curve starts to flatten with nut rotation and you still observe increasing compression on the sandwich, your stainless load spreading plate is too small. Do not over compress the sandwich. Build a larger load bearing plate and try again. Please remember that it is NOT OK to leave the studs under tightened, because the keel will work, causing even more looseness, leaks and potential catastrophic failure. You really need to get this right. Steve Pete wrote in message ... On Thu, 15 Jan 2009 07:30:19 +0100, "Steve Lusardi" wrote: Be very careful here because you have not stated the material under bolt compression. Depending on whether the material is wood, fiberglass, steel or aluminum and the washer diameter or cap size used to distribute the compression load, the answer could be quite different. The torque values or stretch limits stated by others reflect the maximum elongation force aacceptable by the bolt material without permanent bolt deformation and do not consider potential crush limitations of the compression sandwich, which could be much less. Steve Thanks Steve, the hulll at that point is 22mm mahogany strip planking with two heavy layers of fibreglass epoxied on each side;, bonded to that are 100mm oak beams to take the keel bolts, also fibregalssed in with epoxy. Over most , but not all, of these beams is a 60mm thick oak plate spreading the load from the mast over the first five floorbeams. Under the hull is an oak packer varying in thickness from about 20mm to about 40mm to take up the curve of the hull. So for most of the bolts, they are all going through around 200mm of oak and mahogany plus around 10mm of fibreglass and epoxy. Between the nuts and the oak are 8mm thick stainless plates about 60mm x 150mm wide, linking each pair of studs. I know that the oak I chose for this job is the hardest I had and therefore I don't think it will compress much. (Potentially famous last words here) Hope that helps, and thanks for all the replies, I'm pleased to get so much advice. Pete wrote in message . .. Hi, can anyone advise me on the roughly correct torque setting for tightening the nuts on my keelbolts? The studs are 20mm (thats about 13/16") in 316L plus one at 12mm(about 1/2") The keel is 2 tonnes of lead if that makes any difference. I'd hate at this stage (five long and bloody years) to over or undertighten the bolts. Thanks Pete |
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