Frameless steel hulls: Is there a lenght limit?

(Originally Posted by mydauphin )
"The only 60 feet frameless hull of anything I would go in would have to be piloted by Jesus Christ Personally. A frameless boat would have to be too heavy to be of any use, to have the basic strengths of a thinner hull with a basic skeleton."

What is the length limit of a frameless steel hull of a sailboat, if any ? The closed shell, formed by the welded steel plates, seems a quite sound structure to me. Shell structures need not be heavier than skeleton/skin structures, isn t it that so?

 

See my response in the original thread.

 

Thank you jehardiman,
So you say that a 60 ft LOA hull is out of this limit ? What is the biggest hull made by this method?

 

Frame does not take up space if done right. You need room for plumbing, air conditioning, electrical, insulation, fuel tanks, water tanks, bilge and making floors even. The only way to make a frameless work is make it completely round cylinder, but you still need a floor.

 

well maybe he good take a 6foot pipe, weld off the bottom, throw in a pile of lead and then he could float around like a a bottle half full of water

 

Boat made from old Milk truck

I saw, on the internet, a boat made from a old stainless steel milk container trailer. About 30' long, 8 foot beam. It looked kind of cramp, but he could close hatch and weather storm. I dont remember rest of story.

 

By what method? Homogenous shell? Lognitidunal stiffened panel? Double wall panel? Formed shell? Singlely developed shell? Double developed shell? Narrow panel? Wide panel?

Lots of options.

For a "real" sized "boat shaped" vessel; made of steel to an "appropriate" weight with "managable" costs and forming and no internal frames or transverse stiffening (including thawarts, floors, brackets, and decks), the length is less than 30 feet, more likely less than 20 given a flat floored shape.

PS, You really should take a mechanics of materials and a structural design course if you want to get into understanding the limits in designing vessel hulls. There is way too much "it depends" given the interplay between primary secondary and tertiary loading to be covered in a few posts on the web.

 

Thank you jehardiman,

I agree that "There is way too much "it depends", given the interplay between primary secondary and tertiary loading to be covered here". I have seem some pictures of frameless steel hull constructions that seemed interesting, although I don t know if they ever managed to float ...
This hull, for example, looks quite real, and a little bigger than 20 ft...
http://www.origamimagic.com

 

That hull has and will be getting transverse framing, indeed, you can see the chainfalls that are holding it in shape until the deck and cabin frames are put in even though the harpin is in place. Also notice the transverse chine brackets, chines will buckle/fold up without those. Scroll through the building pictures and you will see where the transverse brackets are added to give section strength to hold geometry during fold up and the stanchions added to tie the harpins to the bottom to prevent the hull from springing. All transverse framing, and that doesnt even include the transom and the floors to be added.

You really need a basic understanding of vessel structures. You are confusing forming methods (fold up) with the structure that is needed to be in place to support sea loads (brackets, floors, and frames). That is why i was very specific in the way i answered your question; i.e. NO transverse framing. There is no more magic here than there is making this boat.

http://personal.eunet.fi/pp/gsahv/skiff/skiff.htm

Cut the panels
Fit the transom
Fold up the panels
Fit the bottom, thwart and sheer clamps/harpin to hold shape.

 

but if that ss tank has baffles, that means going on deck to get from Cabin TO CABIN?)

 

Thank you very much jehardiman,

I try to avoid that confusion, but I have to say that it is not always so easy for a novice would-be boat builder like me... This is because of my lack of experience, of course, but also because "the parts of the structure that support sea loads", the "skeleton", are not always well defined in the plans. Sometimes the same parts are also parts of the "skin" (i.e. not the skeleton itself, the longitudinal or transverse frames) of the whole structure, like the transom, the roof of the pilot house, the floors ( sometimes integral structural parts of the whole hull, but not always), even the panels of the compartments.( I remember being in one plastic production boat squeezed between two others in the marina. When we closed one or two doors, it stopped making funny noises, as the doors themselves were apparently contributing in the integrity of the structure only when they were kept closed !) So in the naive mind of an amateur boat builder, there is always a confusion about what exactly is skeleton and what skin, and how much each one is contributing in the integrity of the whole boat.
Now, there is much hype about plans of "frameless" metal boat construction, but nobody tells you what structural parts give what portion of the required rigidity to the boat, beyond the rigidity that would have had as a closed shell structure, formed by the welded steel plates of the hull s skin. It would be great if we could insert the 3D plans into the proper software program, calculate and see the distribution of the various loads (with the help of a finite element analysis method, for example). Then even a novice like me could understand something about the contribution of a certain structural part, and if, why and how many frames, transverse or longitudinal, are required to keep the boat in one piece. And only then we will sail in a "frameless" boat and not need the help of pilot Jesus Christ.

 

Xarax;

They are ALL contributing to the structural integrity of the whole vessel. Wether the skin plating, a gunnel flange, or a winch backing pad. The "sleketon" is for more than just providing the form on thich the hull plates are bucked.

Simlpy, there are three major loads that need to be resisted by a vessels hull.

1) Primary Loads. This the total longitudinal bending moment forces from hydrodynamic and hydrostatic forces. The loads are primarly carried through the shell. Think of standing on an upright empty soda can...as long as the shell is straight and intact it will support your weight. Twist or bend the shell...the can collaspes due to loss of symetric section shape which overloads a portion of the shell and begins a cascade failure. Now again try stepping on an upright soda can...reach down and with a sharp nail keep putting holes in the shell...the can eventually collaspes by because the loss of area causes the primary loading to exceede the yeild strength of the shell.

2) Secondary loading. This is the transverse loads generated by the primary loads. They are normally carried by the transverse frames and bulkheads. What this does is to break the shell panels up into to short lengths that will resist buckling. Go back to our soda can...cut the ends (bulkheads) off. Now stand on the can shell...it collaspes immeadietly! Why?...the ends provided fixity for the shell. Without bulkheads or frames, the shell cannot support the longitudinal load without buckling.

3) Tertiary loading. This the the actual hydrodynamic and hydrostatic load normal to the skin. The skin has to suport this load without deflecting or sheering. Lets lay our soda can down on its side...now step on it in the middle....it collaspes because the bulkheads are too far apart...it losses section geomety. If you step on it near one end it will support weight until the bulkhead collaspes. Now again try stepping on an upright soda can...reach down and dent the side of the shell...the can collaspes by buckling because the tertiary load caused deflection exceeding the euler buckling quotient of the shell between frames/bulkheads. Going back to our first example where we put holes in the can skin, this is another tertiary load that the skin is expected to resist to prevent damage from flooding the vessel.

Additionally, there is attachment loading which functions similar to tertiary loading. These are the loads placed in the hull by things attached to it such as masts, stays, engine power transmission loads, and the dynamic loads of heavy masses attached to the hull. Going back to our soda can...weld a rod to the skin...then step on the can...now bend/push/pull the rod....see when and how the can collaspes.

 

Beautiful exposition. It should be published somewhere. Brief, simple and deep, about a quite complex issue.
Thanks a lot jehardiman !

 

From a PM sent to me:

The answer is still no. Buckling is a function of the section modulus and material modulus to yeild strength, not the load.

The maximum unsupported length of a steel panel with 2x20 cm longitudinals is 39.9 feet and even then the skin would need to be 24mm minimum.

To build an unsupported steel panel of 60 feet, you would need as a minimum 34 mm plate, longitudinals of 22mm x 390mm capped with a flange 34mm x 400mm spaced on ~2m centers.

If you put in ONE transverse frame the skin thickness drops to 25mm with 15mm x 300mm longitudinals.

If you put in TWO transverse frames, the skin now becomes 17mm with 10mm x 215mm longitudinals.

If you put in THREE transverse frames, the skin now becomes 11mm with 8mm x 165mm longitudinals.

Give up on it xarax.... Yes; building a vessel without transverses can be done; but smart people gave up on it long ago.

 

I think frameless could be developed creativly. Waterpipes and fuelpipes and others not transfering media with to big temerature diference from the hull could serve as frame, so could a deck, fuel tanks, water tanks and engines bolted directly to the hull could serve as a frame. The hull's construction would determine stiffnes, deck rails.
Try to make eatch component a structual part.

If you don't nead a class to ishue a certificate you can do quite crazy things.

Annyway there is ways to save weight on the frames and it won't steal mutch space.