Amount of labor involved---Fiberglass vs. welded aluminum?

[SEASWIRL PAUL]

I was recently stunned at the amount of time it took to weld up simple rocket launchers and T-tops. I talked at length with a gentleman who built his own welded aluminum boat and he said it took many, many hours. I thought that welding was fairly quick. He seemed to imply that it was a long tedius job.

If someone were to compare the time involved in manufacturing a welded aluminum hull vs. a glass hull of the same size which would take more manhours to build?

Man this stretch of below freezing is goin on 3 weeks!!!

You guys in temperate climates got it made! Except that your dock don't cost $550.00 for the whole season like mine.


Paul

[jav]

Unlike welding steel, where even average welds are stronger than the base material, welding aluminum is much harder. Even perfect welds are weaker than the base material and to get the best welds, you need a TIG or really good MIG as well as special shielding gasses and good technique. It's a slower process than steel welding and becoming quite expensive for materials.

On the other hand, IMHO, glass construction is only easier and cheaper than aluminum IF you have a mold, which is a huge expense. Other than that, cold mold glass construction doesn't seem any less time consuming or cheaper than aluminum.

[Bullshipper]

jav - 2/9/2007 8:23 AM

Unlike welding steel, where even average welds are stronger than the base material, welding aluminum is much harder. Even perfect welds are weaker than the base material and to get the best welds, you need a TIG or really good MIG as well as special shielding gasses and good technique. It's a slower process than steel welding and becoming quite expensive for materials.

On the other hand, IMHO, glass construction is only easier and cheaper than aluminum IF you have a mold, which is a huge expense. Other than that, cold mold glass construction doesn't seem any less time consuming or cheaper than aluminum.

Fiberglass is less labor intensive and you use a less qualified laborer than a certified welder. In other words welding is about 1.5 x as expensive on a mono hull w/o a cabin, and about 3x as expensive using welders to build a CC catamaran, even with time saving CNC cutting techniques.

But I would really disagree with this post, after studying this question in the past pretty extensively.

New square wave pulse mig machines will weld up to 12 feet per minute on aluminum pipe. Boat work goes slower, but 3 fpm is considered typical and the austrailians will weld both sides of the seam simualtaneously to reduce distortion and prep work.

Aluminum welds add strength if done correctly but the material has to be scarfed or brushed to provide a new unoxidised soot free surface just before the weld is applied. TIG welding with hand held rods can be used for any for any application, but very very very slow for butt, seam and lap welds.

Molds have not been necessary for decades unless you are going to produce a large number of units and most custom builders will simply go to a cold molding glass or epoxy process to build their boats and plugs.

And finally one should consider the climate where they live as the FG boat will be more comfortable than AL where it is very hot and cold IMO. But aluminum is the way to go for longer life and commercial applications, so you get what you pay for.

[SEASWIRL PAUL]

Can someone describe the "Cold molding" process for me and how you don't need an expensive mold to build a boat that way? Much appreciated as I am curious.

[Bullshipper]

West Epoxy systems has great literature on the layups if you want the nitty gritty,
but basically you seal and fasten the ends of the wood with adhesive prior to setting screws to hold, then back out the screws, saturate all surfaces with resin or epoxy and lay around 4 layers of wet cloth prior to applying the finish outer coat.

Here is a current thread showing some of the carpentry in progress.

http://www.thehulltruth.com/forums/t...ts=45#M1391485

[jav]

Bullshipper,

perhaps my information is dated but the last reports I read suggested that regardless of welding procees, joint type, prep, filler or sheilding gas, the HAZ of the aluminum around the weld and the weld itself, would have a lower yeild point and tensile strength compared to original base alloy (which I presume to be 5052 in a marine environment). I'm aware there were ways to age or re-heat treat in some cases but that this wasn't normally done as matter of course in marine weld applications. I'd be interested to learn more if aluminum weld strengths have improved and would appreciate any more info you might have as this is something I would like to do having done some cold mold work, TIG and MIG aluminum work. I did not find the cold mold FRP work easier, cheaper or faster but thats just me.

[Codfisher]

Bullshipper - 2/9/2007 8:56 AM

And finally one should consider the climate where they live as the FG boat will be more comfortable than AL where it is very hot and cold IMO.

Aluminum hulls are no hotter than the temperature of the water in which they rest.

[Bullshipper]

Codfisher - 2/9/2007 10:38 AM

Aluminum hulls are no hotter than the temperature of the water in which they rest.

Bring your boat to Mexico and we will see if you are "more comfortable" walking barefoot on the decks, leaning up agasinst your console, or sitting on the foredeck as you are in a fiberglass hull.

I also like to tinker with my boat on its trailer, and its just too hot here to wear jeans and tennis shoes to protect my skin when the boat is not in the water.

I like Al, but in extremely cold and hot climates, it is colder and hotter to the touch than glass.

[Bullshipper]

jav - 2/9/2007 10:22 AM

Bullshipper,

perhaps my information is dated but the last reports I read suggested that regardless of welding procees, joint type, prep, filler or sheilding gas, the HAZ of the aluminum around the weld and the weld itself, would have a lower yeild point and tensile strength compared to original base alloy (which I presume to be 5052 in a marine environment). I'm aware there were ways to age or re-heat treat in some cases but that this wasn't normally done as matter of course in marine weld applications. I'd be interested to learn more if aluminum weld strengths have improved and would appreciate any more info you might have as this is something I would like to do having done some cold mold work, TIG and MIG aluminum work. I did not find the cold mold FRP work easier, cheaper or faster but thats just me.

You would be better to research technical reports published by Miller for current equipment and production rates and Ansii reports on destructive testing if you doubt my conclusions. Beyond that, plate aluminum boats are as strong as they have to be to last for years of hard commercial service in real life applications.

As previously indicated, cats and mono welding vary greatly in the amount of feet you have to weld. On my 24' AL cat design, I have to weld over 1600 feet to complete this job where on a Pacific 23, I would guess its closer to 400, so I suggest that FG is the way to go with the cat due to the time and hourly rate of each worker. Plus it is hard to keep your material drops under 25% when using $4 a lb 5086 and 6011, and the equivelent area in glass or would and epoxy cost you less than 1/3 of the former.

Comparing the 2 hulls, produced with Mexican labor, the 24' unrigged cat hull will run you $24K to produce at cost in Aluminum and the same hull, weighing 37% more in glass costs $12.2K. I would add about $15K and $5K to these labor and material numbers if you plan to do this in the states.

If you plan to do this yourself, the bare cut alumunum is $15K for 3500 lbs gross, 2457 lb net weight after cutting+ rod, gas, electrical, abrasives and tools.

But again, the waste and welding labor are far less on a mono fabrication making designs like the Pacific, state of the art IMO.

[Codfisher]

Bullshipper - 2/9/2007 11:31 AM


I like Al, but in extremely cold and hot climates, it is colder and hotter to the touch than glass.

Laws of physics must change south of the border I guess

[Codfisher]

Laws of physics must change south of the border I guess

[petersr2]

I guess they are different in Texas as well. When I was a kid I had a 16ft MonArk alum boat. The bottom might have been cool enough, but the seats would burn the skin right off your as, through a bathing suit.

[dingbat]

Codfisher - 2/9/2007 12:10 PM


Laws of physics must change south of the border I guess

Radiant heat transfer is just much more effective than that of conduction.
The sun introduces energy into the aluminum at a higher rate via radiant heat than can be transferred from the aluminum to the water via conduction. Net result, aluminum hotter than water.

[Codfisher]

Better rip all those aluminum bleachers out of those southern football stadiums and replace them with glass then.

[Bullshipper]

Not trying to get in a global warming war over this, but there is a difference in comfort on parts that are not in direct contact with water.

[petersr2]

Those bleachers are very hot as well when you first sit on them.

[jav]

bullshipper,

I'm very familiar with Millers newest machines (extremely impressive) however, I have not found anything at Miller to support your assertion regarding welded aluminum being stronger than the parent alloy. If you know of any, I'd like to read them. I did find a recent paper that supports what I said in my original post at Lincoln from 2/07 - here is the link and an exerpt:

http://www.lincolnelectric.com/knowl...comistakes.asp



"Why Isn’t the Weld as Strong as the Original Base Metal?

A designer of steel structures generally assumes that a weld is as strong as the parent material, and the welding engineer who is responsible for fabricating the structure expects to make a weld which is as strong as the steel being used. It would be tempting to assume that the situation is the same when designing and fabricating aluminum structures, but it isn’t. In most cases, a weld in an aluminum alloy is weaker, often to a significant degree, than the alloy being welded.

Non-Heat-Treatable Alloys


Figure 2

Alloys in this category (i.e., 1XXX, 3XXX, 4XXX, and 5XXX families) are produced by a cold working process: rolling, drawing, etc. After the cold working process, the alloy is given the designation of an F temper (as-fabricated). Alloys are then often given a subsequent annealing heat treatment, after which they are classified as an O temper (annealed). Many alloys are sold in this condition. Thus the correct designation for a plate of 5083 which was annealed after rolling is 5083 – O. One of the attractive properties of these alloys is that they can be significantly increased in strength if they are cold worked after annealing. Figure 2 shows what happens to several alloys with varying amounts of cold work. For example, alloy 5086 rises in yield strength from approximately 18 ksi (125 MPa) to 40 ksi (275 MPa) and is now said to be strain-hardened. A complete designation for this alloy would be 5056-H36. The H temper designation can be somewhat complicated, since it is used to designate a number of processing variables. However, the last digit designates the level of cold working in the alloy, with 9 denoting the highest.


Figure 3

A common mistake in designing welded structures using non-heat-treatable alloys is to look down a list of properties, disregard the O temper material, and choose an alloy of the highest temper because it is significantly stronger. This would seem to make sense, but it often doesn’t, because the heat of welding acts as a local annealing operation, significantly weakening the heat affected zone (HAZ) of the weld. If one plots the yield or tensile stress versus distance from the weld, a curve such as that seen in Figure 3 is obtained. If the design is based on the strain hardened properties, the allowable design stress will usually be above the actual yield point of the HAZ. Although it may seem counter-intuitive, the fact is this: No matter what temper one starts with, the properties in the HAZ will be those of the O temper annealed material due to the welding operation. Therefore, the design must be based on the annealed properties, not on the strain-hardened properties. Because of this, it usually doesn’t make sense to buy the more expensive strain hardened tempers for welded fabrications. One should design with and specify the alloy in the O temper and up-gauge as necessary.

An obvious question is whether anything can be done to restore material properties after welding a strain-hardened material. Unfortunately, the answer is almost always no. The only way to harden these materials is through mechanical deformation, and this is almost never practical for welded structures. "

I'm always up for learning... please let me know if you still find disagreement and can point me to better answer.

[Chaps]

The aluminum yards that are welding boats for security & DOD are using 5183 mig wire which provides the 40,000 psi where specs require.

Speedwise also agree that the new micro processor controlled machines like the Lincoln Power Mig 350 pulse have alum boats going together very fast, particularly production craft with good jigging and computer cut parts.

Rocket launchers and t-tops are often tig welded which is quite slow but provides the pretty welds however the new mig welders are getting close to achieving tig visuals if they have a pulse-on-pulse feature.

[Bullshipper]

Here is an example by Stephen Pollard that points out that the weld strength depends primarily on the type of Aluminum, although he does conclude that there is up to a 10% loss of material strength in the 5086H within one inch of the welded area, and I concede that this could be the case if using older technology.

6000
Primarily produced for marine applications, 6061-T6 has good resitance to corrosion, but will not yield high weld strength. Heat affected areas can reduce strength up to 80%.

5000 series
5052-H32 is a popular formable sheet common used for small boats due to considerable savings over the 5086-H116. It is very ductile and retains good strength in the welded condition.

5086-H116 As indicated by the H temper designation, this is a strain hardened series, not a heat treated alloy, and because of this, will retain its high strength and not fully anneal when heated by welding. The heat affect zone is generally considered within one inch of the weld bead. The material can potentially become partially annealed if there is excessive heat in this zone, but even in this condition the resulting heat loss is no more than 10 percent, and this is the primary reason that the US Navy specifies 5086 exclusively .

Mig square wave pulse welders came on the scene after this book was published in 1993. The sole purpose of this technology is prevent excessive heat and burn through using old fashioned Tig and Mig welders because Aluminum does not visably turn red like steel, to warn the operator.

Pulsing high bursts of energy specifically on the tip of the rod produces a puddle faster increasing production speed and greatly reduces the heat going to the metal. This signifigantly reduces the amount of time, temperature and anneal to the parent alloy while adding overall thickness to the joint.

[kerno]

As a machinist (and definitely not a welder as much as I've tried), I learned a lot form this group of posts. I am very familiar with the alloys mentioned, both heat treatable and cold worked. I have always felt that the HAZ went back to nearly the O condition and am pleased to hear that 5086 does not loose all its cold woked properties. Designing a welder with a microprocessor to minimize the annealing is outstanding. Now if I could just buy 5086 in all the shapes and sizes that 6061 comes in.....