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steel hulls?
On Sun, 9 Mar 2008 07:43:23 -0400, "Roger Long"
wrote: Aluminum is not theoretically as strong but aluminum boats tend to deform and stay watertight in accidents where steel will fracture. For equal weight Al and steel are equal in strength. Considering weldability and panal stiffness aluminum is better because it is thicker. Note that the alloys used for boatbuilding are not the strongest available in either material. In the case of aluminum, the usual alloys do not need paint, Every fifty year old al boat I know has been out in the weather without paint and no sign of corrosion. Most aluminum commercial boats, for example Alaskan fishing boats are left unpainted in salt water and don't corrode. My 22 foot cuddy is bare Al, and I wouldn't consider any other material. You are correct about the fact that steel will tear in cases where aluminum will just get a big dent. Think shipping container. 10 000 a year get washed off the boxboats, Casady |
steel hulls? adding armor to FG hulls
Red wrote:
OTOH if you're thinking of an object piercing the hull like an ice pick, having the Kevlar layer on the outside might not make much difference. In any event, having it on the outside is better than nothing. Fresh Breezes- Doug King ------ Actually I was just pondering this as there are frequent stories about the various partially submerged objects such as shipping containers sinking boats. Since I am getting closer to buying a boat, I wondered if there wasn't something that could be done to at least reasonably increase protection from said objects. I realize you aren't going to make it bullet proof, but any amount of improvement without too much tradeoff in weight, etc, may be worth it. Peace of mind sort of thing. Thanks. Red Had a friend that put in many, many thousands of miles with at least 7 round trips between New Zealand and Victoria BC. In that time he hit one container and one sleeping whale. This was in a homebuilt 33' steel cutter. Both hits in the South Pacific. The container left a good dent in the bow and the whale bent the rudder. I guess what I'm trying to say is the chances of hitting something large enough to cause serious damage is very slight and then probably wouldn't be catastropic G |
steel hulls? adding armor to FG hulls
On Mon, 10 Mar 2008 22:27:50 -0500, Red wrote:
OTOH if you're thinking of an object piercing the hull like an ice pick, having the Kevlar layer on the outside might not make much difference. In any event, having it on the outside is better than nothing. Fresh Breezes- Doug King ------ Actually I was just pondering this as there are frequent stories about the various partially submerged objects such as shipping containers sinking boats. Since I am getting closer to buying a boat, I wondered if there wasn't something that could be done to at least reasonably increase protection from said objects. I realize you aren't going to make it bullet proof, but any amount of improvement without too much tradeoff in weight, etc, may be worth it. Peace of mind sort of thing. Thanks. Red Perhaps the first thing wold be to research the subject to determine how many fiberglass/steel/aluminum/wooden yachts are sunk annually. Once the frequency is determined it should be easy to assess the appropriate action. as an example, airplanes crash nearly every year but few passengers carry a parachute as part of their carry-on luggage... Bruce-in-Bangkok (correct email address for reply) |
steel hulls? adding armor to FG hulls
On Tue, 11 Mar 2008 04:43:42 +0000, Gordon wrote:
Red wrote: OTOH if you're thinking of an object piercing the hull like an ice pick, having the Kevlar layer on the outside might not make much difference. In any event, having it on the outside is better than nothing. Fresh Breezes- Doug King ------ Actually I was just pondering this as there are frequent stories about the various partially submerged objects such as shipping containers sinking boats. Since I am getting closer to buying a boat, I wondered if there wasn't something that could be done to at least reasonably increase protection from said objects. I realize you aren't going to make it bullet proof, but any amount of improvement without too much tradeoff in weight, etc, may be worth it. Peace of mind sort of thing. Thanks. Red Had a friend that put in many, many thousands of miles with at least 7 round trips between New Zealand and Victoria BC. In that time he hit one container and one sleeping whale. This was in a homebuilt 33' steel cutter. Both hits in the South Pacific. The container left a good dent in the bow and the whale bent the rudder. I guess what I'm trying to say is the chances of hitting something large enough to cause serious damage is very slight and then probably wouldn't be catastropic G That is somewhere around 45,000 N.M. so if he hit two objects in that distance it averages one object every 22,000 miles. How many people will cruise that distance in their whole life. Bruce-in-Bangkok (correct email address for reply) |
steel hulls? adding armor to FG hulls
" wrote:
Amen. But, having been tangentially involved in a completely disastrous attempt to bond Kevlar (tm) fabric to PVC foam with epoxy I strongly advise getting advise from the fabric provider before bonding. A Method that worked very well with both epoxy and polyester with stitched glass didn't fly with Kevlar (literally as the structure was a wing for an ultra-lite). I wonder why. Incompatible binder in the cloth? One issue with both carbon fiber & aramids (you're right, Kevlar is a trademarked brand name) is that the cloth is much lighter than conventional fiberglass... duh, that's a big reason to use it... but it also means that the cloth tends to float up out of the resin. The best way to bond it is to vacuum bag it, or use pre-preg, but it can be laid up like conventional FG once you know to not pour on more resin when it looks dry. Or you can use thickening/bonding agents mixed into the resin, that holds it in place better anyway. I used peel ply, with no vacuum bagging, over a carbon fiber & Kevlar lay-up with very good results. .... And, yeah, you're right, the stuff goes all fuzzy if you look at it funny and it kills scissors. Carbon is less of a pain to work with but you can't use it to armor existing hulls. It would help add compression srength as an outside layer. I dunno if it would help with impact resistance. The yield curve for carbon fiber (also called graphite) is almost straight, the stuff tends to fracture and people think of it as brittle. Of course, it takes about 10x more force than steel can withstand, but we're so used to seeing stuff bend before it breaks that it's counterintuitive that material which *doesn't bend* and suddenly snaps is really strong. And it also doesn't lend itself to "soft failure" modes. DSK |
steel hulls?
(Richard Casady) wrote:
For equal weight Al and steel are equal in strength. The "rule of thumb" I recall is that aluminum is half as strong as steel, and 1/3 the weight of steel. For equally strong structures, aluminum will be about 25% lighter than steel. DSK |
steel hulls? adding armor to FG hulls
Gordon wrote:
Had a friend that put in many, many thousands of miles with at least 7 round trips between New Zealand and Victoria BC. In that time he hit one container and one sleeping whale. This was in a homebuilt 33' steel cutter. Both hits in the South Pacific. I wonder what time frame this was? I think shipping losses of containers is much higher in the late 1990s ~early 2000s although they say it's tapering off now. I also wonder what happened to the whale. The container left a good dent in the bow and the whale bent the rudder. I guess what I'm trying to say is the chances of hitting something large enough to cause serious damage is very slight and then probably wouldn't be catastropic In a steel boat ;) Bruce in Bangkok wrote: That is somewhere around 45,000 N.M. so if he hit two objects in that distance it averages one object every 22,000 miles. How many people will cruise that distance in their whole life. Lots and lots and lots. Not so many do that many open-sea miles. But look at the odds another way... if you had a revolver with 1,000 chambers, and "only" one chamber had a live round.... would you spin the chamber, put it to your head, and pull the trigger? Just for fun? If the odds are low, but consequences very serious, then it's worth a little work and study to avoid that BANG. Of course, YMMV DSK |
steel hulls? adding armor to FG hulls
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steel hulls? adding armor to FG hulls
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steel hulls? adding armor to FG hulls
"Bruce in Bangkok" wrote in message ... That is somewhere around 45,000 N.M. so if he hit two objects in that distance it averages one object every 22,000 miles. How many people will cruise that distance in their whole life. Certainly not you, sir! Pretty hard to get that kind of mileage under your keel sitting at the Bangkok dock. Wilbur Hubbard |
steel hulls? adding armor to FG hulls
On Mar 11, 2:45 am, wrote:
" wrote: Amen. But, having been tangentially involved in a completely disastrous attempt to bond Kevlar (tm) fabric to PVC foam with epoxy I strongly advise getting advise from the fabric provider before bonding. ... I wonder why. Incompatible binder in the cloth? One issue with both carbon fiber & aramids (you're right, Kevlar is a trademarked brand name) is that the cloth is much lighter than conventional fiberglass... duh, that's a big reason to use it... but it also means that the cloth tends to float up out of the resin. ... Good points. Kevlar has been used with great success. I can only speculate on the reasons for the failure. I was in the shop where it happened re-building my dagger boards and the wing was going together on the other side of a hull of a big cat that was also building. So, I didn't see every detail. They were building it using Kelsall's KSS system with Kevlar twill, epoxy and pvc. They bonded one face on a flat table with a wet lay-up using modest vacuum to clamp it. Then they cut darts in the pvc, draped the part into mdf formers and hand laid the inner skin. That's sop for the KSS system and it generally works quite well. In this case, though, both the hand laid skin and the bagged skin could be peeled off the pvc (failing at the glue line). They did it all a second time on the assumption that the problem was a bad epoxy mix and it failed exactly the same way. Other parts that came off the same table using pvc from the same batch before, during and after were fine. I was using the same epoxy to build my boards and it was also being used in a couple of other projects around the shop and it was fine. It's possible that they could have contaminated the pvc skins (boat shops aren't exactly clean rooms). That's what the guy building the plane though. But both sides twice? I think that using twill rather than stitched cloth and bending the parts around very tight molds (the guy wanted to mold right around the leading edge for some reason) were contributing factors. But whatever the reason, the epoxy/Kevlar joint was the weak one and I think that is cause for concern or at least careful testing when using Kevlar. ... Carbon is less of a pain to work with but you can't use it to armor existing hulls. It would help add compression srength as an outside layer. I dunno if it would help with impact resistance. ... The usual argument against carbon reenforcement is that it is so stiff that it will fail before the glass takes any load. At which point it might be more sensible to just do away with the glass. Price and compatibility wise "S" glass might be a better option than either Kevlar or carbon. In a crash you want strong but flexible to absorb energy. -- Tom. |
steel hulls? adding armor to FG hulls
I am not an expert on bonding neither aramid nor carbon to existing FG
construction, so I cannot add anything there, but you need to think through the whole scenario. Adding protection aganst puncture is only one aspect of the required protection. Although my hull is steel and it has collision bulkheads both forward and aft, it also utilises watertight bulkheads as well, but even that is insufficient. You must consider the flotation attitude of the hull under flood conditions. If any part of the deck falls below the water surface, the boat will most likely be lost before the flooding can be controlled.. So keeping the boat deck parallel to the water is really important and in my case I have a rather fine entry forward and if flooding the forward compartment should occur the bow would sink well below the deck line. Adding adequate fixed flotation removes too much space, so my solution, for what it is worth, is to place a 2 ton hyperlon lift bag below the forward cabin sole that can be inflated in an emergency. Hopefully, this would buy enough time for the pumps and to effect a repair from the outside. Steve wrote in message ... On Mar 11, 2:45 am, wrote: " wrote: Amen. But, having been tangentially involved in a completely disastrous attempt to bond Kevlar (tm) fabric to PVC foam with epoxy I strongly advise getting advise from the fabric provider before bonding. ... I wonder why. Incompatible binder in the cloth? One issue with both carbon fiber & aramids (you're right, Kevlar is a trademarked brand name) is that the cloth is much lighter than conventional fiberglass... duh, that's a big reason to use it... but it also means that the cloth tends to float up out of the resin. ... Good points. Kevlar has been used with great success. I can only speculate on the reasons for the failure. I was in the shop where it happened re-building my dagger boards and the wing was going together on the other side of a hull of a big cat that was also building. So, I didn't see every detail. They were building it using Kelsall's KSS system with Kevlar twill, epoxy and pvc. They bonded one face on a flat table with a wet lay-up using modest vacuum to clamp it. Then they cut darts in the pvc, draped the part into mdf formers and hand laid the inner skin. That's sop for the KSS system and it generally works quite well. In this case, though, both the hand laid skin and the bagged skin could be peeled off the pvc (failing at the glue line). They did it all a second time on the assumption that the problem was a bad epoxy mix and it failed exactly the same way. Other parts that came off the same table using pvc from the same batch before, during and after were fine. I was using the same epoxy to build my boards and it was also being used in a couple of other projects around the shop and it was fine. It's possible that they could have contaminated the pvc skins (boat shops aren't exactly clean rooms). That's what the guy building the plane though. But both sides twice? I think that using twill rather than stitched cloth and bending the parts around very tight molds (the guy wanted to mold right around the leading edge for some reason) were contributing factors. But whatever the reason, the epoxy/Kevlar joint was the weak one and I think that is cause for concern or at least careful testing when using Kevlar. ... Carbon is less of a pain to work with but you can't use it to armor existing hulls. It would help add compression srength as an outside layer. I dunno if it would help with impact resistance. ... The usual argument against carbon reenforcement is that it is so stiff that it will fail before the glass takes any load. At which point it might be more sensible to just do away with the glass. Price and compatibility wise "S" glass might be a better option than either Kevlar or carbon. In a crash you want strong but flexible to absorb energy. -- Tom. |
steel hulls? adding armor to FG hulls
On Mar 11, 10:35 am, "Roger Long" wrote:
... There was a rash of rudder stock failures that had an outer layer of carbon fiber for stiffness. Turned out the plain fiberglass part of the stock was plenty strong enough. ... Funny you should mention that. The guy working just up the bench from me was building the rudders and stocks for the cat and he had built carbon/glass stocks which failed exactly as you describe. He was building the cat's stocks out of S-glass/epoxy around small foam cores (for forming). He'd also built successful carbon stocks (including the one on his own boat) but felt strongly that mixing materials in rudder stocks was a bad idea. He also thought that S-glass stocks were nearly as good as carbon because carbon had to be over-built to absorb shock loads that were not a problem for S-glass of the required stiffness. Carbon that's durable enough ends up being stiffer than needed. There's still an advantage but not nearly as much as you would guess just looking at the materials. Adding a bit of spring into a system that takes sudden loads can reduce the peak forces by a lot. As you say, the engineering gets complicated. Some materials suppliers will provide engineering help to builders and designers for surprisingly reasonable fees (even gratis for small stuff)... -- Tom. |
steel hulls? adding armor to FG hulls
Forgive me for replying to myself, but I wanted to add this from the
letters in the February "Yachting World". "A chairman of the Scottish branch of the Institution of Structural Engineers once famously defined engineering as: 'The art of modeling materials we do not wholly understand, into shapes we cannot precisely analyze so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance.'" -- Tom. |
steel hulls? adding armor to FG hulls
On Tue, 11 Mar 2008 11:48:14 -0400, "Wilbur Hubbard"
wrote: "Bruce in Bangkok" wrote in message .. . That is somewhere around 45,000 N.M. so if he hit two objects in that distance it averages one object every 22,000 miles. How many people will cruise that distance in their whole life. Certainly not you, sir! Pretty hard to get that kind of mileage under your keel sitting at the Bangkok dock. Wilbur Hubbard And also difficult sitting there with the yellow rubber duck in the bathtub. Bruce-in-Bangkok (correct email address for reply) |
steel hulls? adding armor to FG hulls
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steel hulls? adding armor to FG hulls
Roger Long wrote:
A single bolt under tension is about the simplest structure on the planet. The riveted "Titanic" with all those hand fitted parts, highly variable steel characteristics, joint strength depended on individual workmanship in riveting, and great flexibility, was arguably one of the most complex structures to analyse ever built. These quys trying to arrange for their "official" paper to come out at the same time as the History Channel show were basing their case on calculations used at the design stage of a ship to help proportion the steel sizes in the most effecient way and pointing to a slight difference in stress to strength ratio as "proof" that this guy who came from nowhere to appear on TV was wrong. The completely ignored the visual evidence in the steel debris, survivor testimony, and common sense. I really got some good laughs out of the whole affair. -- Roger Long Roger, Since you have studied this incident so long, has anyone ever considered the effect of the temperature of the water on the fracture strength of the steel uesd to build the hull? In his book "Structures: Or Why Things Don't Fall Down", J.E. Gordon analizes the changes in physical properties that the near freezing water would have had on the steels of teh day. Had the metals retained their ductility, the damage may have been limited to a single bay, and the ship survive. I couldn't turn up that piece of text on line, but a sample of the book may be seen at http://books.google.com http://books.google.com/books?id=oQB...t%22+fall+down I think you would enjoy it. Richard Lamb ^1 Structures: Or Why Things Don't Fall Down by J. E. Gordon J.E. Gordon’s book is a great read. Gordon strips engineering of its confusing technical terms, communicating its founding principles in accessible, witty prose. Amazing factoids and insights for the lay person abound in this book, alhought the technical details may a bit heavy for some. Witty - it will change the way you see the world |
steel hulls? adding armor to FG hulls
Roger Long wrote:
Another quote from the infamous Roger Long" "Good engineers understand that the numbers are only a guide to their judgement. Bad engineers believe them absolutely." -- Roger Long that's a keeper! |
steel hulls? adding armor to FG hulls
These quotes are so good I wanted to include them all (more below)
" wrote: Forgive me for replying to myself, but I wanted to add this from the letters in the February "Yachting World". "A chairman of the Scottish branch of the Institution of Structural Engineers once famously defined engineering as: 'The art of modeling materials we do not wholly understand, into shapes we cannot precisely analyze so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance.'" cavelamb himself wrote: Aircraft design is 90% educated guesses, worked out to four decimal places. "Roger Long" wrote: Another quote from the infamous Roger Long" "Good engineers understand that the numbers are only a guide to their judgement. Bad engineers believe them absolutely." "Roger Long" wrote: Wow. I wish I had heard that in time to include that in the Titanic programs My quote was, "Any idiot can make things strong enough. Engineering is the science of making them light enough to be affordable and functional in the real world. The designers of that ship were under enormous pressure to use the absolute minimum of steel they could get away with." Engineering is also different from research. Engineers have to figure out how to build something with the available standard practices of the day; or provide a practical & workable innovation to standard practice. It's very easy to say "why didn't you do it like this" (pointing to some exotic & extreme method which may not even be a success at the experimental stage). An official panel of the Society on Naval Architects and Marine Engineers recently sponsored a paper intended, I believe, to show that I was completely wrong so as to preserve their standing as the adults and professionals since I was getting my own TV show, two in fact. They claim that the ship broke from the bottom up instead of the top down. That's possible. Further down you say there is a lot of evidence it didn't happen that way, I'm curious. Wasn't there a RINA paper some years back on the same subject? Until 1985 the expert opinion was that the Titanic didn't break in half at all. I'm also curious if you've ever checked into the newsgroup "alt.history.ocean-liners.titanic" which is a bit slow these days but is still a major rivet-counter hangout. DSK |
steel hulls? adding armor to FG hulls
Roger Long wrote:
"cavelamb himself" wrote Since you have studied this incident so long, has anyone ever considered the effect of the temperature of the water on the fracture strength of the steel uesd to build the hull? Yes, and it certainly had a bearing on the details of the event but not the big picture. She might have broken at 15 - 16 degrees instead of 10 - 12 if it had been on a summer day. AH, yeah. :) Thos balmy summer days in the Norht Atlantic.. I think he probably meant considerably warmer waters. In his book "Structures: Or Why Things Don't Fall Down", J.E. Gordon analizes the changes in physical properties that the near freezing water would have had on the steels of teh day. Great book. I have read it although quite some time ago. Why does that no surprise me? -- Roger Long |
steel hulls? adding armor to FG hulls
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steel hulls? adding armor to FG hulls
"Roger Long" wrote in
: My work was pretty damn solid and I enjoy arguing about how complex the fuel system is on my boat more at this point in life. .....And we are honored to rag on you about it...(c; Any more ham radio history show up, by the way? Any more contact with ARRL or the others? Larry W4CSC |
steel hulls? adding armor to FG hulls
"Roger Long" wrote in
: "Larry" wrote Any more ham radio history show up, by the way? Any more contact with ARRL or the others? No, I'm sorry to say and I apologize for dropping the ball on further research and contact. I bit off way more boat projects than I can chew on this winter and chewing on anything began to become a big problem shortly after Christmas (you probably saw my post above) which has really sapped my energy. I hope to get back to finding out more about my Grandfather's early radio experiments but I'm now facing for paying for land storage and marina dock at the same time while not sailing i(really, really, bad thing!) if I don't get an heroic mount of work done in the next couple of months. And, I still feel like ****. -- Roger Long Ah, I see. I'm still really interested in his historic work. When you get back into it, at some point, please keep me informed. Thanks I still think he was one of the earliest hams I know of to go on the air, predating all the famous guys by years and years! Most interesting....(c; |
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