Forming compound curves in heavy aluminum plate

This is going to sound silly but it works.
I needed to bend a 1/2 inch plate for Door. We made mold out of Concrete and drove my diesel pickup truck over plate a few times to bend it. Used propane torch to make it stay bent.

 

Lyle,

It seems we have a similar design philosophy. I'm now in the process of working on the weight and balance aspects of my design however, and as it turns out I backed off the hull thickness to 3/8" (9.5 mm) because of weight. Given Lazeyjack's comments, and yours, I am not too "broken up" about this, as I suspect he is right about the difficulty involved using half-inch plate, and you are right about the consequences of both . . . and the 3/8" plate should still give me a very rugged hull.

And in the meantime my wife has been giving me grief about the time involved in building a boat and has been searching the web for one to buy instead . . . with absolutely no luck at all! Very rarely is hull thickness even mentioned in the advertisements she shows me, and in one case a 3/16" hull was bragged about as "well above the accepted norm," making me really wonder about boats built to the "norm." On another aluminum boat she found you could see ridges from the frames like the ribs on a starving horse . . . which made me seriously wonder how thin that one was. Hull thickness was not mentioned, of course, but I bet it is nice and light for racing. Even so-called "expedition" boats all seem way too fragile to me. Of course, the folks who buy these boats have probably never actually been to sea in a storm, so they have no idea of the forces involved when things really kick up.

I too have dreamed of some machine to quickly produce compound curves in plate. Mydauphin suggests a concrete form and pressure in the post after yours, and this will certainly work for a limited number of items. Taking a similar approach, there is hydroforming as well. With hydroforming you could make your concrete mold and put it in a massive frame with a flat plate of the material you want to form cut to fit in a mating piece with a rubber layer just above it into which water is pumped at high pressure. Lots of industrial items are made with hydroforming and it works extremely well . . . but you need a separate mold for every part. This actually might not be so bad given how cheap concrete is, but in my own case with roughly 900 square feet of hull and imagining a hydroforming press of, say, 9 square feet . . . yikes! One hundred molds to make and mess with. Along these same lines I have also thought it would be possible to make a variable-shaped mold with a "bed" of hexagonal rods with spacers to get the desired curvature. Each rod could be domed with a slight curvature, and when the flat material was pressed into it you would end up with an array of "dimples" where the metal was pressed against the rods. Or, each rod could have a pivotable flat attachment. Such a bed of rods would also make a fine curvature gauge if provision was made to lock the rods in place. All of which just gets too complicated for a one-off effort. Another possible way to go is explosive forming, which works well, but may upset the neighbors.

I'm very interested in your approach to this problem, Lyle, so keep in touch! It's nice to know that I'm not the only crazy dude who wants a sturdy hull. Maybe this feeling comes from early experiences on a WWII aircraft carrier with 18" of steel armor. The bow of that boat was split in a storm once when I was aboard, but then it was only an inch and a half thick up there. Armor steel, of course. Ripped in two by a nice, soft, watery wave. Another mere wave took off all the catwalking forward for about 200 feet, and removed the ship's bell in the same move. It sure taught me some respect!

BillyDoc

 

Hull thickness... H'm ...I did not think about it when you said it. I have a professionally designed and built Aluminum 70' Motor yacht and only part of hull that 1/2" thick is transom and motor mounts. Both of these are straight. Hull is a combination of 5/16 and 3/8. There are a lot of weld braces and internal structure. Remember the hull skin is just that. Aluminum is very strong. I bought my boat after a hurricane threw it on its side against the rocks. The dents incur where no more than 3 inches deep. They where local and where repaired by welding a new piece over it.

I would spend my times and money - not on thickness but design, actual quality of metal and anti-corrosion treatments of hull.

 

BillyDoc; have u finished your project ,have pics and can i contact u thru e-mail, thank you k.

 

Korvello,

By all means contact me about anything. My project is still in the design phase, however, I'm just starting to do a structural analysis of the rig which I hope to begin today. I still have several "details" to work out on the hull as well, and get weights for, but most of the major stuff is done . . . if I don't have to go back over this %@#^*@ "design spiral" AGAIN. Assuming that works out I'll go over the basic hydrostatics again and if that works out as well I at least "believe" that I have a viable design to begin making hardware for. My first job, however, will be building a building to build the boat in. I've ordered a quonset style steel building which I plan to basically use as a roof on some heavy concrete stem walls to build in, and I just heard yesterday that they will ship it on the 20th. That felt like real progress! This is definitely a long-term project.

No pictures, but I do have drawings up here if you're curious: http://poiesisresearch.com/lieserl.php. I haven't updated this page for a while now and the design has evolved, but I expect to do another update sometime this week.

BillyDoc

 

thank you BD; i'm in the process of designing my aluminum cat and do not intend to build till maybe next year ,got caught in other things ,my curiosity is because having read some of your posts we have a similar building approach of making it strong first and everything else is secondary...i was curious on your choice of aluminum and from what supplier and also about your welding ,are you going to TIG the whole thing and like you i intend to make my boat rotate on an axxis to be able to weld easier and on the flat.....maybe if it will be ok with you even visit your shop to learn a little or maybe even give you a hand ......k

 

BD; also looked at your renderings and they look good ;who made them and with what software? thank you k

 

Hi Korvello,

Glad you like the renderings, they're from Rhino but using a screen-capture program to actually grab them. I used Delftship to do the hull, then moved it to Rhino with RhinoMarine to do the rest. Rhino is turning into a very nice program, by the way (version 4). Everything actually works almost all of the time, unlike a good number of other programs I have tried. Delftship is excellent as well, and the Freeship version is also quite good, or downright superb if you factor in the cost!

The aluminum alloy I will be using is 5083 in the marine grades (H116 or H321) and I will be TIG welding the whole thing. There is a lot of controversy around TIGing a large structure such as a yacht . . . it's slower than MIG, it uses more power, and both of these factors result in more opportunity for heat distortion. On the other hand, TIG makes a better, stronger and neater, weld BECAUSE it uses more heat to melt the filler into the surround and can do so without uselessly piling up molten wire all over the place, and if you turn up the power it is almost as fast. Both have their advantages, obviously. I anticipate spending a LOT of time waiting for things to cool down so I can continue, though. You know: "Honey, I am working! I'm sitting here waiting for it to cool down so I can weld some more."

I still haven't sorted out a supplier for the metal yet, and this is complicated because I want to go the cutting file approach for a lot of the parts. Layout is a real art form in and of itself . . . and I would just as soon avoid it as much as I can.

BillyDoc

 

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Hi BillyDoc :............................................................................................................................................................. thank you for taking the time to write back. interesting you would TIG the all thing i love it ,that and using twice the tickness of plate it sure goes against most so called experts opinion; i'm with you, after examining guys like Dashew and what they call good enough or more than it's called for i intend to build with 3/8 minimun below water line , i have no intention of caring a kill switch with me just in case i hit something , so much for believing in what you have built,ridiculous. some will argue that the new mig welders can match a tig weld ,what do you think about it ? have you consider 5086 , the us navy apears to be sold on it and it's somewhat more maleable ,but then again 5083 have slightly better numbers and is the favorite of most guys down under and will probably be my choice because i dont intend to have no compound curves to speak off , i wish i could find 3/8 on coil that would make a nice hull with no vertical welds .what prices do you have for 5083 ? thank you k

 

Korvello,

I haven't bought any metal yet, so I can't comment on price. From what I've read, I expect something like $3 a pound . . . probably more now with our dollar dropping like a lead sinker in Missouri River water (too thick to drink, too thin to plow).

In my lonely opinion MIG will never compete with TIG for quality of weld, and TIG will never compete with MIG for speed and less problem with heat distortion. Everything's a compromise, you go with what's most important to you.

5086 is also good stuff, but I have a lot of respect for those folks in Oz who use 5083 and figure that they know something I don't, so 5083 it is for me!

BillyDoc

 

My 2 cents worth.

Having actually mostly built a hull - a few ideas...

I used small MIG to tack weld pieces quickly. Then a big mig to weld piece together, Then used Tig to finish welds and make pretty.
I have found it is easier to sandblast or grind piece then prime with zinc chromate, then grind off where I am going to weld later. Unfornately sometimes you dont do everything in one day and when you come back to it. Then you have to start by cleaning everything. I had to build y boat in the open and it was a pain.

Buy the best/most powerful welding equipment you can, it will make your life easier in the long run.

Find a good AL like Betsy at http://www.adimetal.com/
AL has double in price since I started 3 years ago, so has Stainless, Copper, etc...

I used 5086 for hull but used 5083 for firewalls and other part. Also used 6063 Extrusions for roof structure . In other AL is expensive, sometimes you can use other than marine AL for above waterline if you keep it painted.

Also first thing you do is paint bilge, it will save you alot of problems later.

To work on AL boat you need a nice clean area hopefully with a roof. I dont have one and it has cost many months of work.

 

Mydauphin,

Good advice! And worth every penny, and more. I bought a quonset style steel building to build in and it is scheduled to be shipped on the 20th of this month. I figure it will take me about three or four months to get foundations and everything ready and the building up on them and the ends filled in, and then I can get my shop moved in and get started in near perfect conditions. No worries about rain, or wind blowing my gas all over the place . . . and I can leave my tools scattered all over just like I like them.

As for a good welder, I had a pile of cash about 10 years ago and bought a Miller Synchrowave 350 LX to upgrade some cheapo equipment I had been using . . . and I could hardly believe the difference! Like the difference between night and day . . . I love this beast of a machine! Even a crappy welder like me can make an excellent weld with this baby.

BillyDoc

 

thank you guys priceless advise and input .....BillyDoc 3 to 4 months to build the shop ,sounds like a long time, are you doing it yourself?..... been a contractor buildings is more my expertise and a building like yours is a 2/3 week job up here, wish i could say the same about boat building but that's why i'm asking so manny questions ,always cheaper and faster than trial and error.​

 

Hi korvello,

Doing it myself in the middle of a 160 acre parcel of Florida forest with, so far, no electricity and lots of trees in the way. Plus working on stuff to try and make that basic essential, money. And I'll be 64 years old next month, which means I don't move like I used to!

I expect a lot of "Motrin Mornings" in my near future . . . but you gotta do what you gotta do. Making things even more interesting, I got in a little, well, disagreement, with the people who sold me the building. They had promised a 150 mph wind rating (it gets "breezy" here sometimes), and part of the deal was engineering drawings for the building on 5 foot stem walls. When it came time to deliver the drawings the first set had no stem walls, and the second set had no engineering for stem walls and was plainly marked that they would be designed by someone else, at which point I offered to cancel the order. That got me a third set, and this time it was "complete" but not exactly "elegant" as it requires 102 yards of concrete and a thick matrix of bent-up rebar. When they sent the last drawings they had fulfilled the contract, and I'm stuck with it now. Oh, well, I like rugged. But this is going to be a pure ***** to actually do. I ache just thinking about it.

BillyDoc

 

Now you got my interest..

How big a boat are you building? How big a building? I am also contractor in Florida. 102 yds of Concrete. One could build a fairly large building with that alone.