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#1
posted to rec.boats.building
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A2, A4, 316 steel keellbolt nuts? Help!
Hi,
well I'm just getting around to casting and fitting my lead keel, and I'm using 316 steel bolts ( I know some people disagree but if its good enough for Van der Stadt its good enough for me!) So I have ordered the rod and will have a thread cut for the bit that sticks into the boat, but now my suppliers are offering me A2 nuts to fit the thread and hold it to the hull. Does this sound good enough? Should they be A4- or do I have to get nuts made from 316 steel too? What is the differnce between A2, A4 and 316 anyway? Hoping someone can clear a little confusion here. Pete |
#2
posted to rec.boats.building
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A2, A4, 316 steel keellbolt nuts? Help!
I would go with stainless. Think about it. The nuts and washers will be in
the bilge and exposed to rain water, sea water, gray water, and all the other gunk that ends up down there. You can get them from McMaster. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com "pete" wrote in message ... Hi, well I'm just getting around to casting and fitting my lead keel, and I'm using 316 steel bolts ( I know some people disagree but if its good enough for Van der Stadt its good enough for me!) So I have ordered the rod and will have a thread cut for the bit that sticks into the boat, but now my suppliers are offering me A2 nuts to fit the thread and hold it to the hull. Does this sound good enough? Should they be A4- or do I have to get nuts made from 316 steel too? What is the differnce between A2, A4 and 316 anyway? Hoping someone can clear a little confusion here. Pete |
#3
posted to rec.boats.building
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A2, A4, 316 steel keellbolt nuts? Help!
pete writes:
Hi, well I'm just getting around to casting and fitting my lead keel, and I'm using 316 steel bolts ( I know some people disagree but if its good enough for Van der Stadt its good enough for me!) So I have ordered the rod and will have a thread cut for the bit that sticks into the boat, but now my suppliers are offering me A2 nuts to fit the thread and hold it to the hull. Does this sound good enough? Should they be A4- or do I have to get nuts made from 316 steel too? What is the differnce between A2, A4 and 316 anyway? Hoping someone can clear a little confusion here. Pete A2 and A4 are designations I am used to see here in Sweden. A4 is the stuff you want on a boat if you want to avoid rust. It is also very strong. A2 is not quite as stainless. If the difference is merely about looks or if there is more to it I don't know. I have to look it up. 316 is an American designation I think. How it relates to A2 and A4 I don't know. There are conversion tables that should tell you. -- Martin Schöön "Problems worthy of attack show their worth by hitting back." Piet Hein |
#4
posted to rec.boats.building
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A2, A4, 316 steel keellbolt nuts? Help!
Martin Sch??n wrote:
:A2 and A4 are designations I am used to see here in Sweden. :A4 is the stuff you want on a boat if you want to avoid rust. :It is also very strong. A2 is not quite as stainless. If the :difference is merely about looks or if there is more to it I don't :know. I have to look it up. :316 is an American designation I think. How it relates to A2 and A4 :I don't know. There are conversion tables that should tell you. A2 is 304 -- 18% chromium, 10% nickel. A4 is 316, 18% chromium, 10% nickel, 2% molybdenum. |
#5
posted to rec.boats.building
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A2, A4, 316 steel keellbolt nuts? Help!
Pete,
The DIN designation A2 is about the same as AISI 304 and DIN A4 is equivalent to AISI 316. There are also variants 316 L (2% Molybdenum) and 316 TI (Titanium). Both A4 and 316 have superior anti corrosion properties over A2 and 304. The 316 variants have even better anti corrosion properties and are primarily directed at the chemical industry. Type 304 / A2 are used in fresh water environments and A4 / 316 in salt water. As far as strength, all stainless bolts have less strength than a Grade 8 high strength bolt, but slightly better than a Grade 5. Most stainless fasteners are made from 8-18. This variant has the corrosion resistance of A2/304, but has superior strength. In application, stainless bolts used in threaded stainless holes(nuts) have a high tendency to gall and seize under load. Try not to do this. If the threat of corrosion is significant, use a different alloy nut than the bolt, never use 304 with 304 or 316 with 316 and always use an anti-seize grease. Understanding the corrosion failure mode of stainless is very important as well, before deciding on its use. Stainless steel relies on absorbing free oxygen on its exposed surface not to corrode. If a stainless bolt is exposed to stagnant water AND is subject to even the slightest working motion where the surface is rubbed, the surface oxygen will be removed. The surface will then attempt to re-absorb free oxygen from its environment. As long as its environment has free oxygen, its corrosion resistance will continue. However, if the environment now has a depleted supply of free oxygen, then crevice corrosion starts and it is very rapid. So the gamble is the bolt never gets wet or is continually flushed with new water or the bolt never moves after installation. In the case of keel bolts, your odds are not good for a favorable environment. Remember "Drum" in the Solent in the '80s or the British gentleman in the BOAC off the coast of Australia in the '90s. These are the ones we hear about. It's very difficult to report a failure when you're dead and the boat is sunk. I love stainless, but not for keel bolts, Van der Stadt or otherwise. Think wrought iron, manganese Bronze or even Silicon Bronze, but not stainless. Steve |
#6
posted to rec.boats.building
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A2, A4, 316 steel keellbolt nuts? Help!
Thanks for your replies, I did think that A4 was equivalent to 316
but was nver sure and am pleased some people confirmed it. Steve, thanks for your input, you did press this point on to me (and a few others I believe) before, and I hear what you are saying,, I am going to see if I can find suppliers of the alternatives, but how would this affect the size of the bolts? For example, for my keel, the architecht has specified 20mm diameter steel, need this be increased if using bronze? I do vividly remember Drum, plus a few others, the most recent being Hooligan V a few months ago in the UK with the loss of a crewman, but that, in fairness, was a case of the keel itself snapping in two at the point of entry into the "letterbox" slot in her hull. Ta very much, Pete On Mon, 7 May 2007 19:12:56 +0200, "Steve Lusardi" wrote: Pete, The DIN designation A2 is about the same as AISI 304 and DIN A4 is equivalent to AISI 316. There are also variants 316 L (2% Molybdenum) and 316 TI (Titanium). Both A4 and 316 have superior anti corrosion properties over A2 and 304. The 316 variants have even better anti corrosion properties and are primarily directed at the chemical industry. Type 304 / A2 are used in fresh water environments and A4 / 316 in salt water. As far as strength, all stainless bolts have less strength than a Grade 8 high strength bolt, but slightly better than a Grade 5. Most stainless fasteners are made from 8-18. This variant has the corrosion resistance of A2/304, but has superior strength. In application, stainless bolts used in threaded stainless holes(nuts) have a high tendency to gall and seize under load. Try not to do this. If the threat of corrosion is significant, use a different alloy nut than the bolt, never use 304 with 304 or 316 with 316 and always use an anti-seize grease. Understanding the corrosion failure mode of stainless is very important as well, before deciding on its use. Stainless steel relies on absorbing free oxygen on its exposed surface not to corrode. If a stainless bolt is exposed to stagnant water AND is subject to even the slightest working motion where the surface is rubbed, the surface oxygen will be removed. The surface will then attempt to re-absorb free oxygen from its environment. As long as its environment has free oxygen, its corrosion resistance will continue. However, if the environment now has a depleted supply of free oxygen, then crevice corrosion starts and it is very rapid. So the gamble is the bolt never gets wet or is continually flushed with new water or the bolt never moves after installation. In the case of keel bolts, your odds are not good for a favorable environment. Remember "Drum" in the Solent in the '80s or the British gentleman in the BOAC off the coast of Australia in the '90s. These are the ones we hear about. It's very difficult to report a failure when you're dead and the boat is sunk. I love stainless, but not for keel bolts, Van der Stadt or otherwise. Think wrought iron, manganese Bronze or even Silicon Bronze, but not stainless. Steve |
#7
posted to rec.boats.building
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A2, A4, 316 steel keellbolt nuts? Help!
Pete,
Out of all 3 alternatives, I would use wrought iron. There are iron plated ships still in service in excess of 100 years old. Bronze is OK if you do not have other metals in use below the waterline. Iron is non-homogeneous (it is not an alloy) (no internal batteries) and is the least reactive electrolytically. In all cases I would increase the rod size to 30mm and not worry about them forever. Use plenty, it's cheap insurance. Steve "pete" wrote in message ... Thanks for your replies, I did think that A4 was equivalent to 316 but was nver sure and am pleased some people confirmed it. Steve, thanks for your input, you did press this point on to me (and a few others I believe) before, and I hear what you are saying,, I am going to see if I can find suppliers of the alternatives, but how would this affect the size of the bolts? For example, for my keel, the architecht has specified 20mm diameter steel, need this be increased if using bronze? I do vividly remember Drum, plus a few others, the most recent being Hooligan V a few months ago in the UK with the loss of a crewman, but that, in fairness, was a case of the keel itself snapping in two at the point of entry into the "letterbox" slot in her hull. Ta very much, Pete On Mon, 7 May 2007 19:12:56 +0200, "Steve Lusardi" wrote: Pete, The DIN designation A2 is about the same as AISI 304 and DIN A4 is equivalent to AISI 316. There are also variants 316 L (2% Molybdenum) and 316 TI (Titanium). Both A4 and 316 have superior anti corrosion properties over A2 and 304. The 316 variants have even better anti corrosion properties and are primarily directed at the chemical industry. Type 304 / A2 are used in fresh water environments and A4 / 316 in salt water. As far as strength, all stainless bolts have less strength than a Grade 8 high strength bolt, but slightly better than a Grade 5. Most stainless fasteners are made from 8-18. This variant has the corrosion resistance of A2/304, but has superior strength. In application, stainless bolts used in threaded stainless holes(nuts) have a high tendency to gall and seize under load. Try not to do this. If the threat of corrosion is significant, use a different alloy nut than the bolt, never use 304 with 304 or 316 with 316 and always use an anti-seize grease. Understanding the corrosion failure mode of stainless is very important as well, before deciding on its use. Stainless steel relies on absorbing free oxygen on its exposed surface not to corrode. If a stainless bolt is exposed to stagnant water AND is subject to even the slightest working motion where the surface is rubbed, the surface oxygen will be removed. The surface will then attempt to re-absorb free oxygen from its environment. As long as its environment has free oxygen, its corrosion resistance will continue. However, if the environment now has a depleted supply of free oxygen, then crevice corrosion starts and it is very rapid. So the gamble is the bolt never gets wet or is continually flushed with new water or the bolt never moves after installation. In the case of keel bolts, your odds are not good for a favorable environment. Remember "Drum" in the Solent in the '80s or the British gentleman in the BOAC off the coast of Australia in the '90s. These are the ones we hear about. It's very difficult to report a failure when you're dead and the boat is sunk. I love stainless, but not for keel bolts, Van der Stadt or otherwise. Think wrought iron, manganese Bronze or even Silicon Bronze, but not stainless. Steve |
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