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Microwaves to dry boat hulls
Say you want to drive the moisture out of gelcoat. I've used a heat
gun to do it and was surprised at how much water came out. So, what would a high power microwave unit do? Water absorbs the microwaves much better than the polyester so it would get hot and come out. This would avoid the months of waiting for a hull to dry if you are repairing blisters (a real scam as blisters are not a real problem). |
Microwaves to dry boat hulls
Probably would work well, but I know of no way to do this safely. You would be irradiating the world.
Steve "Frogwatch" wrote in message ... Say you want to drive the moisture out of gelcoat. I've used a heat gun to do it and was surprised at how much water came out. So, what would a high power microwave unit do? Water absorbs the microwaves much better than the polyester so it would get hot and come out. This would avoid the months of waiting for a hull to dry if you are repairing blisters (a real scam as blisters are not a real problem). |
Microwaves to dry boat hulls
On Wed, 24 Mar 2010 20:20:45 -0700 (PDT), Frogwatch
wrote: Say you want to drive the moisture out of gelcoat. I've used a heat gun to do it and was surprised at how much water came out. So, what would a high power microwave unit do? Water absorbs the microwaves much better than the polyester so it would get hot and come out. This would avoid the months of waiting for a hull to dry if you are repairing blisters (a real scam as blisters are not a real problem). Some years ago I read, in one of the boating magazines, about a guy that had invented an innovative method of drying a hull. He removed the door from a micro-wave oven and bypassed the "door-open" safety switch. Placed the oven face down on the deck and turned on the power. I never read anything more about the method and have visions of him heating the saturated deck core to the point that steam was generated and the resultant upheaval. Water when heated turns to steam and I can assure you that the steam will come out :-) Cheers, Bruce |
Microwaves to dry boat hulls
On Mar 25, 7:58*am, wrote:
On Wed, 24 Mar 2010 20:20:45 -0700 (PDT), Frogwatch wrote: Say you want to drive the moisture out of gelcoat. *I've used a heat gun to do it and was surprised at how much water came out. So, what would a high power microwave unit do? *Water absorbs the microwaves much better than the polyester so it would get hot and come out. *This would avoid the months of waiting for a hull to dry if you are repairing blisters (a real scam as blisters are not a real problem). "some" blisters are not a problem. Who said anything about being safe? Seriously, you could put an absorber on the far side to stop the waves or even a metal plate (thin foil) to reflect em back to be more efficient. |
Microwaves to dry boat hulls
Bruce writes:
On Wed, 24 Mar 2010 20:20:45 -0700 (PDT), Frogwatch wrote: Say you want to drive the moisture out of gelcoat. I've used a heat gun to do it and was surprised at how much water came out. So, what would a high power microwave unit do? Water absorbs the microwaves much better than the polyester so it would get hot and come out. This would avoid the months of waiting for a hull to dry if you are repairing blisters (a real scam as blisters are not a real problem). Some years ago I read, in one of the boating magazines, about a guy that had invented an innovative method of drying a hull. He removed the door from a micro-wave oven and bypassed the "door-open" safety switch. Placed the oven face down on the deck and turned on the power. Innovative and dangerous. I never read anything more about the method and have visions of him heating the saturated deck core to the point that steam was generated and the resultant upheaval. Water when heated turns to steam and I can assure you that the steam will come out :-) Heat the laminate + water quick enough and you create blisters. This is one of the quality assurance tests of printed circuit boards. Too much moisture (which is much, much less than found in any boat laminate) or poor laminating quality (still much better than you hand layup boat laminate) will cause blisters. OK, that test involves much higher temperatures than what you are likely to subject your laminates to. Bear in mind that high temperatures degrade laminates. Why not try the kind of equipment used to dry out buildings that got drenched one way or another? It may not be as innovative but also much less likely to damage your boat or indeed yourself. /Martin |
Microwaves to dry boat hulls
On Thu, 25 Mar 2010 11:04:49 -0400, I am Tosk
wrote: In article , says... On Wed, 24 Mar 2010 20:20:45 -0700 (PDT), Frogwatch wrote: Say you want to drive the moisture out of gelcoat. I've used a heat gun to do it and was surprised at how much water came out. So, what would a high power microwave unit do? Water absorbs the microwaves much better than the polyester so it would get hot and come out. This would avoid the months of waiting for a hull to dry if you are repairing blisters (a real scam as blisters are not a real problem). Some years ago I read, in one of the boating magazines, about a guy that had invented an innovative method of drying a hull. He removed the door from a micro-wave oven and bypassed the "door-open" safety switch. Placed the oven face down on the deck and turned on the power. I never read anything more about the method and have visions of him heating the saturated deck core to the point that steam was generated and the resultant upheaval. Water when heated turns to steam and I can assure you that the steam will come out :-) Cheers, Bruce Won't vacuum boil out water vapor? Scotty Well, yes I suppose that you are correct in that a decrease in pressure results in water vaporizing at a lower temperature, however suspect that the evaporated vapor has far less energy then water vapor that is produced by heating. At least it is difficult to put a pot of water out in the sun and power a steam engine with it :-) I suspect that the O.P. was trying to devise a method to laminate layers and get a chemical bond between layers. In practice no one who works in the trade seems to consider this a problem. The worry about laminating epoxy structures is always amine blush and cleaning it prior to laminating the next layer. There are epoxies that do not produce blush but I have never seen them used in actual practice. I suspect it is a matter of cost. It would be interesting to see some testing of laminated structures produced by continuous laminating, I.e., not letting the epoxy set up between layers, and the same structure produced by waiting until each lamination hardened and then sanding with coarse paper before applying the next layer. Cheers, Bruce |
Microwaves to dry boat hulls
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Microwaves to dry boat hulls
Frogwatch wrote:
Say you want to drive the moisture out of gelcoat. I've used a heat gun to do it and was surprised at how much water came out. So, what would a high power microwave unit do? Water absorbs the microwaves much better than the polyester so it would get hot and come out. This would avoid the months of waiting for a hull to dry if you are repairing blisters (a real scam as blisters are not a real problem). A few years ago there was a system developed in Europe that used a combination of heat and vacuum to dry out laminates. I see it is now available in the USA. Take a look at: http://www.hotvac.com/testimonial/default.aspx Brian C |
Microwaves to dry boat hulls
I do not think Microwave heating to eliminate moisture in fiberglass is practical. The oven in a microwave unit is a reflective
cavity. You would have to have a reflective chamber the size of the boat and a several megawatts of RF to be effective. There would be dead spots and spots of excessive heating, just like in a microwave oven. Even if you would do this, you would still have to provide a means of absorbing the moisture generated in the chamber's air. (Basic gas laws and equilibrium apply) There are more practical ways of achieving this. It is important to understand the problem in order to find a solution. No construction material lasts forever. They each have their disadvantages and advantages and a finite life. The failure mode of all fiber based plastics are UV driven disintegration and osmosis. Osmosis is the wicking effect all fibers have when exposed to a liquid, which causes hydraulic delamination at the weakest bond. Although FG is not waterproof, it is not readily permeable either and there is your dilemma. Once moisture has invaded the material, it is next to impossible to get it all out.Even though fiberglass boat construction has been around since the 50's, there are not many boats still around that old. The cost of FG hull maintenance is only exceeded by wood. All other materials have a better TCO (total cost of ownership). I'm sure that statement will generate some flames, but it is observable and self evident, Steve. |
Microwaves to dry boat hulls
On Fri, 26 Mar 2010 10:51:31 +0100, "Steve Lusardi"
wrote: I do not think Microwave heating to eliminate moisture in fiberglass is practical. The oven in a microwave unit is a reflective cavity. You would have to have a reflective chamber the size of the boat and a several megawatts of RF to be effective. There would be dead spots and spots of excessive heating, just like in a microwave oven. Even if you would do this, you would still have to provide a means of absorbing the moisture generated in the chamber's air. (Basic gas laws and equilibrium apply) There are more practical ways of achieving this. It is important to understand the problem in order to find a solution. No construction material lasts forever. They each have their disadvantages and advantages and a finite life. The failure mode of all fiber based plastics are UV driven disintegration and osmosis. Osmosis is the wicking effect all fibers have when exposed to a liquid, which causes hydraulic delamination at the weakest bond. Although FG is not waterproof, it is not readily permeable either and there is your dilemma. Once moisture has invaded the material, it is next to impossible to get it all out.Even though fiberglass boat construction has been around since the 50's, there are not many boats still around that old. The cost of FG hull maintenance is only exceeded by wood. All other materials have a better TCO (total cost of ownership). I'm sure that statement will generate some flames, but it is observable and self evident, Steve. I'm sure that you are correct regarding the micro-wave method of drying a hull as in the article, I read, the writer sounded as though he had discovered sex and was going to start a company to bring his innovative methods to the multitudes. Certainly he stated that he had dried his own deck, or parts of his deck, but I never read another word about his company of anyone else using salvaged micro-wave ovens to dry boats. There also was an article, in Practical Boat Owner, about one of the their staff who had purchased what was apparently one of the first fiberglass yachts ever built commercial in the U.K. For whatever reason the owner, or perhaps the surveyor, cut cores out of the hull and had them tested. The cores tested at 90-something percent of the calculated original strength of the hull material. There was no mention of the boat's history or how much time it had spent in the water, and in England many boats are hauled out for part of each year, so the testing was hardly a comprehensive study but, as the magazine wrote, it did show that fiberglass did not deteriorate greatly with age. Regarding the cost of wooden boats, there was another article in the same magazine written by a bloke who was something of a pundit regarding wooden boats. He had a "Channel Cutter" that had been built in 1800-something, and after years and years had sold it. Apparently there was a great hue and cry, he was a traitor to the traditional boat world, and on and on.. His article was in justification of his decision. He simply described, in detail, the trials, tribulations, and costs of owning a wooden boat of great age. It was an eye opener as the boat had required substantial repairs nearly every year since he had owned it. Port garboard replaced, four ribs replaced, portions of the deck relayed, recaulked hull, etc. What most people don't realize when they see a wooden boat that when they were built their life was usually expected to be about 10 years and many of them were only afloat for a few years - read the history of the tea clippers. I once knew Chester Carter who's family had built boats on Miscongus Bay, in Maine for generations. He told me that the conventional Maine built work boat, oak timbers, cedar planking, fastened with galvanize boat nails, would last about ten years and then needed refastening and might last another five or six years after that. He was well aware of fiberglass construction and didn't think much of it - not because it was fiberglass but because it was lighter then wood and bounced around a lot. He used to say things like "well, you should try pulling pots in one of those things, jumping around like a rabbit". Cheers, Bruce |
Microwaves to dry boat hulls
Bruce writes:
For whatever reason the owner, or perhaps the surveyor, cut cores out of the hull and had them tested. The cores tested at 90-something percent of the calculated original strength of the hull material. I find it highly unlikely they could calculate the original strength with a 10% inaccuracy. The materials used were not characterized that well and the variation in the lamination process is much bigger. I have been told by a senior structural engineering consultant that the uncertainty in fatigue life for the materials we know best-- structural steels -- is roughly 6%. Composites, even aerospace qualities, are much, much harder to get good data on. There was no mention of the boat's history or how much time it had spent in the water, and in England many boats are hauled out for part of each year, so the testing was hardly a comprehensive study but, as the magazine wrote, it did show that fiberglass did not deteriorate greatly with age. This is pure nonsense. Fiberglass laminates have limited fatigue life as do all materials. This boat has lived a pampered life relative to its scantlings. /Martin http://hem.bredband.net/b262106/ |
Microwaves to dry boat hulls
If you want to make your wood boat last a long time, you must fasten
it with something that won't rust, you must keep it dry inside, but most of all you must wash it down morning and evening with salt water! Gordon course, you have to protect the bottom from the borers also. |
Microwaves to dry boat hulls
On Sat, 27 Mar 2010 10:07:40 +0100, (Martin
Schöön) wrote: Bruce writes: For whatever reason the owner, or perhaps the surveyor, cut cores out of the hull and had them tested. The cores tested at 90-something percent of the calculated original strength of the hull material. I find it highly unlikely they could calculate the original strength with a 10% inaccuracy. The materials used were not characterized that well and the variation in the lamination process is much bigger. I have been told by a senior structural engineering consultant that the uncertainty in fatigue life for the materials we know best-- structural steels -- is roughly 6%. Composites, even aerospace qualities, are much, much harder to get good data on. I am not sure whether they had sufficient data to do accurate strength calculations although I had a book written back in he very early days of fiberglass boat building by someone who was described as an expert, that did list tensile strengths for various boat building materials and certainly there would have been tests made before publishing such a table. Having said that, certainly there is a variance in strength of a fiberglass structure that varies with all kind of things - chemical makeup of the actual resin used, hardener/catalysis mix, amount of glass and resin in the structure and so on. I assume that why they said calculated strength. There was no mention of the boat's history or how much time it had spent in the water, and in England many boats are hauled out for part of each year, so the testing was hardly a comprehensive study but, as the magazine wrote, it did show that fiberglass did not deteriorate greatly with age. This is pure nonsense. Fiberglass laminates have limited fatigue life as do all materials. I didn't say that it didn't deteriorate with age, I said it didn't deteriorate GREATLY with age. This boat has lived a pampered life relative to its scantlings. /Martin http://hem.bredband.net/b262106/ Cheers, Bruce |
Microwaves to dry boat hulls
Bruce writes:
On Sat, 27 Mar 2010 10:07:40 +0100, (Martin Schöön) wrote: Bruce writes: For whatever reason the owner, or perhaps the surveyor, cut cores out of the hull and had them tested. The cores tested at 90-something percent of the calculated original strength of the hull material. I find it highly unlikely they could calculate the original strength with a 10% inaccuracy. The materials used were not characterized that well and the variation in the lamination process is much bigger. I have been told by a senior structural engineering consultant that the uncertainty in fatigue life for the materials we know best-- structural steels -- is roughly 6%. Composites, even aerospace qualities, are much, much harder to get good data on. I am not sure whether they had sufficient data to do accurate strength calculations although I had a book written back in he very early days of fiberglass boat building by someone who was described as an expert, that did list tensile strengths for various boat building materials and certainly there would have been tests made before publishing such a table. And the accuracy was stated as? All material data I come across at work is within +/- something. It is hugely important to make sure material data used for engineering calculations are for the stuff coming out of production and not from some lab. Material data should be for relevant ambient conditions, temperature, humidity or whatever applies for the intended application. The use of a new family of high strength steels in ship building in the early 1908s is a grueling case story. Ships and life were lost because fatigue life in the corrosive real world was so much worse than in the lab. Earlier steel qualities had not been affected by environment in the same way. Having said that, certainly there is a variance in strength of a fiberglass structure that varies with all kind of things - chemical makeup of the actual resin used, hardener/catalysis mix, amount of glass and resin in the structure and so on. I assume that why they said calculated strength. And I say that stating that the laminate still had 90 % of its calculated strength is nonsense since the errors in calculation and measurements stack up to far more than 10 %. There was no mention of the boat's history or how much time it had spent in the water, and in England many boats are hauled out for part of each year, so the testing was hardly a comprehensive study but, as the magazine wrote, it did show that fiberglass did not deteriorate greatly with age. This is pure nonsense. Fiberglass laminates have limited fatigue life as do all materials. I didn't say that it didn't deteriorate with age, I said it didn't deteriorate GREATLY with age. Which is what my statement below was all about. This boat has lived a pampered life relative to its scantlings. Leave the thing resting in a cool, dry place away from harmful UV radiation etc and it will last a long time. Hard everyday use will see it break down in a few years. That is at least what happen to the boats used for daily transports by the population of the Gothenburg archipelago. Three years is what they expect glassfibre boats to last. These are boats designed and built for recreational use. /Martin |
Microwaves to dry boat hulls
On Sun, 28 Mar 2010 12:43:51 +0200, (Martin
Schöön) wrote: Bruce writes: On Sat, 27 Mar 2010 10:07:40 +0100, (Martin Schöön) wrote: Bruce writes: For whatever reason the owner, or perhaps the surveyor, cut cores out of the hull and had them tested. The cores tested at 90-something percent of the calculated original strength of the hull material. I find it highly unlikely they could calculate the original strength with a 10% inaccuracy. The materials used were not characterized that well and the variation in the lamination process is much bigger. I have been told by a senior structural engineering consultant that the uncertainty in fatigue life for the materials we know best-- structural steels -- is roughly 6%. Composites, even aerospace qualities, are much, much harder to get good data on. I am not sure whether they had sufficient data to do accurate strength calculations although I had a book written back in he very early days of fiberglass boat building by someone who was described as an expert, that did list tensile strengths for various boat building materials and certainly there would have been tests made before publishing such a table. And the accuracy was stated as? All material data I come across at work is within +/- something. It is hugely important to make sure material data used for engineering calculations are for the stuff coming out of production and not from some lab. Material data should be for relevant ambient conditions, temperature, humidity or whatever applies for the intended application. It is? Here is a section of a specification sheet: "The standard requirements for ASTM A516 physical and chemical characteristics are given in the tables below." Mechanical Properties: A516 Grade 60 A 516 Grade 65 A16 Grade 70 Tensile Strength (ksi) 60-80 65-85 70-90 Tensile Strength (MPa) 415-550 450-585 485-620 Yield Strength (ksi) 32 35 38 Yield Strength (MPa) 220 240 260 Elongation in 200mm (%) 21 19 17 Elongation in 50mm (%) 25 23 21 Max Thickness (mm) 205 205 205 The supplier is Oakley Steel, " a specialist steel supplier focusing in boiler and chrome moly steel plates. We stock pressure vessel quality plate in ASME and ASTM grades principally for use in the oil and gas industry." Hard to find a mention any tolerance, any +/-. The use of a new family of high strength steels in ship building in the early 1908s is a grueling case story. Ships and life were lost because fatigue life in the corrosive real world was so much worse than in the lab. Earlier steel qualities had not been affected by environment in the same way. This is news" Nearly all uses of new materials,or use of materials in a new way, has resulted in failure. Not always catastrophic failure but some problem. The first iron bridges were built with cast iron - they fell down. The de Havilland Comet, the first commercial jet airliner, used to explode in flight. Pressurization caused the fuselage to flex, the aluminum cracked and the side blew out. I have sent quite a number of coupons for testing and processed quite a few materials certificates, furnished by steel makers, and I have never seen a tolerance, never; "Tensile strength 50,000 psi +/- 10%". Every materials certificate or test coupon has listed only the results of the test as "tensile strength 50,000 psi" without a tolerance. Having said that, certainly there is a variance in strength of a fiberglass structure that varies with all kind of things - chemical makeup of the actual resin used, hardener/catalysis mix, amount of glass and resin in the structure and so on. I assume that why they said calculated strength. And I say that stating that the laminate still had 90 % of its calculated strength is nonsense since the errors in calculation and measurements stack up to far more than 10 %. There was no mention of the boat's history or how much time it had spent in the water, and in England many boats are hauled out for part of each year, so the testing was hardly a comprehensive study but, as the magazine wrote, it did show that fiberglass did not deteriorate greatly with age. This is pure nonsense. Fiberglass laminates have limited fatigue life as do all materials. I didn't say that it didn't deteriorate with age, I said it didn't deteriorate GREATLY with age. Which is what my statement below was all about. This boat has lived a pampered life relative to its scantlings. Leave the thing resting in a cool, dry place away from harmful UV radiation etc and it will last a long time. Hard everyday use will see it break down in a few years. That is at least what happen to the boats used for daily transports by the population of the Gothenburg archipelago. Three years is what they expect glassfibre boats to last. These are boats designed and built for recreational use. /Martin Cheers, Bruce |
Microwaves to dry boat hulls
On Fri, 26 Mar 2010 10:51:31 +0100, "Steve Lusardi"
wrote: All other materials have a better TCO (total cost of ownership). I'm sure that statement will generate some flames, but it is observable and self evident So which is cheapest, steel or aluminum ? We are seeing a lot of steel sailboats from Europe with semi-hard chines down here in the Caribbean. Some are showing rust streaks but most seem to be holding up fairly well. |
Microwaves to dry boat hulls
On Mon, 29 Mar 2010 17:15:54 -0400, Wayne.B
wrote: On Fri, 26 Mar 2010 10:51:31 +0100, "Steve Lusardi" wrote: All other materials have a better TCO (total cost of ownership). I'm sure that statement will generate some flames, but it is observable and self evident So which is cheapest, steel or aluminum ? We are seeing a lot of steel sailboats from Europe with semi-hard chines down here in the Caribbean. Some are showing rust streaks but most seem to be holding up fairly well. It depends a lot on how the vessel is built. A steel boat that used stainless everywhere there is chafe or wear - rail cap, all exposed bolt or pin holes bushed, stainless cleats and fairleads, any dissimilar metals insulated, no wood, teak decks, cockpit combings, etc., the electrical system totally insulated from the hull and an alert captain or crew that catches every scratch that appears will certainly not require much, if any, major maintenance for very long periods. On the other hand I know a chap that has a French built aluminum sloop. Electrical system insulated from the hull, anything that is in the water is either aluminum or some alloy that doesn't react with aluminum strongly. To the best of my knowledge the only major maintenance he has done in probably 20 years is to overhaul the main engine. You often see French built boats that are unpainted aluminum, except for the anti-fouling. They appear to have few problems. And finally you see the home built boats, built by amateurs, that seem to rust away in 10 years or sometimes less. I believe that you are a power boat man so have a look at Seahorse Yachts, the Diesel Ducks, I did a bit of work on one when it came through Thailand on its way to the U.S. Beautiful work. Cheers, Bruce (bruceinbangkokatgmaildotcom) |
Microwaves to dry boat hulls
Bruce writes:
On Sun, 28 Mar 2010 12:43:51 +0200, (Martin Schöön) wrote: snip And the accuracy was stated as? All material data I come across at work is within +/- something. It is hugely important to make sure material data used for engineering calculations are for the stuff coming out of production and not from some lab. Material data should be for relevant ambient conditions, temperature, humidity or whatever applies for the intended application. It is? Here is a section of a specification sheet: "The standard requirements for ASTM A516 physical and chemical characteristics are given in the tables below." Mechanical Properties: A516 Grade 60 A 516 Grade 65 A16 Grade 70 Tensile Strength (ksi) 60-80 65-85 70-90 Tensile Strength (MPa) 415-550 450-585 485-620 Yield Strength (ksi) 32 35 38 Yield Strength (MPa) 220 240 260 Elongation in 200mm (%) 21 19 17 Elongation in 50mm (%) 25 23 21 Max Thickness (mm) 205 205 205 The supplier is Oakley Steel, " a specialist steel supplier focusing in boiler and chrome moly steel plates. We stock pressure vessel quality plate in ASME and ASTM grades principally for use in the oil and gas industry." Hard to find a mention any tolerance, any +/-. No, in your example I find that right away for tensile strength. If you find it hard to get the information it is either because you use the wrong suppliers or because you are not important to them. Having written that I think I have to point out that published data sheets seldom are really helpful because the tolerances found there are cooked up by the sales department... you have to go to the next level in most cases. snip I have sent quite a number of coupons for testing and processed quite a few materials certificates, furnished by steel makers, and I have never seen a tolerance, never; "Tensile strength 50,000 psi +/- 10%". Every materials certificate or test coupon has listed only the results of the test as "tensile strength 50,000 psi" without a tolerance. If I got such an answer I would start looking for another tester. Someone who knows and acknowledges that test equipment and test procedures have limited accuracy. Several samples should be tested since all manufacturing processes have variations. Trying to insert some boating content: The other day I revisited a report on the structural modelling of a racing yacht. One chapter is dedicated to material testing. They manufactured laminate samples and had them tested at a test institute to get data for the modelling. The data they got came with a mean value and a standard deviation number. The standard deviation for the material parameters of those carbon pre-preg laminates were roughly 3%. (You see were my skepticism regarding that 90% figure comes from.) Back to my rant: It is *very* important to realize that real world materials and production are subjected to random variations and modern engineering must acknowledge that and take it into account. "If you haven't done a proper yield analysis you aren't done." Yield in this case is not yield as in yield strength, but you realized that for sure. http://en.wikipedia.org/wiki/Six_sigma http://en.wikipedia.org/wiki/Cpk_Index http://en.wikipedia.org/wiki/Statist...rocess_control http://en.wikipedia.org/wiki/Design_of_experiments http://en.wikipedia.org/wiki/W._Edwards_Deming /Martin (sorry for the late reply, it has been busy times. I have been studying the impact of mechanical tolerances on a proposed design, among other things.) |
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