aluminum hull any ideas

I plan on building the HB20 as designed by Bateau boats. The boat is ment to be built stitch and glue plywood. I would love to construct the hull from .125
or point .019 aluminum. I think it would work. If anyone has ideas, input or considerations please send the along.

gracias,

amigo

 

Hello, amigo,

It is not clear the figures you have mentioned are simply thickness of the sheets or some other standard specifications.
If you mean .125 inches, that is about 3 mm thick. It should be workable. Thickness of .019 inches is only about .5 mm which is too thin to make a hull.

Regards,
Syed

 

Go on the amateur aiircraft sites and find the supliers for riveting gear.

A set of trimmers is about $35, a good amateur rivet gun is about $75, and rivet sets are about $20. Get a Cleeco pliers $7 and about 30 Cleecos.

Now with a GOOD set of sheers , and a smaller air source youre ready to build boats .Many suppliers have marine grade rivets.

"EAA" is a good place too start."

FAST FRED

 

sorry i ment to type .190 aluminum for th hull.
but i do like the rivet idea.

 

There's lots of info on the web on building with aluminum. It can be cut and worked with common woodworking tools, and anything over .125 can be welded. Just remember, .125 weighs about the same as 3/4" plywood.

Check out the metal boats forum on this site, and the "Metal Boat Society" forum.

Sal's Dad
(currently building W Atkin's Rescue Minor in aluminum)

 

The problem with using sheet aluminum as a substitute for plywood in a taped seam design, is the sheet aluminum require a lot more reinforcement then the plywood. Aluminum flexes like crazy, compared to a taped seam or stitch and glue plywood hull. I recently made the conversion from an aluminum design of mine to plywood

(http://www.boatdesign.net/forums/showthread.php?t=10388&referrerid=2040)

and the differences in plywood were astounding. The plywood boat was over a 1/3rd lighter, requiring additional ballast to bring her down to her lines. The wooden sister also had 2/3rd's fewer pieces, because I could stress the skin, making it a full stitch and glue boat. It also takes a fair amount of material understanding and engineering to make these conversions. Just keeping the welding distortion to a minimum will drive a designer nuts in a small craft, using sheet aluminum construction. This is one of the two major reasons rivets are the choice in production built aluminum hulls. The other reason is weight of course. Eighth inch is about as light a gauge you'd want to weld up, but you can rivet much thinner panels at a tremendous savings in weight.

 

Thickness is the main driver in bending stiffness, which explains why plywood, or any wood for that matter that's 3/4" thick, will have much more bending stiffness (not to be confused with stiffness in the engineering sense of the word expressed as Young's modulus) than a thin piece of metal, even though that metal has orders of magnitude more tensile strength and modulus of elasticity. The way you build to take advantage of a high tensile strength material like a metal is to use the material as the skins of a sandwich structure. That's why it is such a popular way to build boats.

Jimbo

 

Par mentioned that sheet metal requires a lot more reinforcment in a tapered seam design than if it was built in plywood. What if the shape of the boat was square. The sides are 90 degrees to the bottom, i guess it is a "punt" or "jon boat" 20' long x 8, wide. does this shape also require more reinforcement?

Jimbo mentioned "sanwich structure" what does this mean?

gracias

amigo

 

I am not sure what he meant with tapered seam construction but

A square section boat doesn't seem any better - actualy worse because a square can skew into diamond shape.
The problem still exists that the flat surfaces don't have much rigidity. Think of square profiled beer can and squeezing it - would go flat very easily.

Compound forms (curbed in two directions as in sphere versus cylinder) would give much more rigidity but is beyond ordinary joe's skills. Still aluminum at 3mm would quite easily wobble - aluminum boats seem to have quite a dense reinforcement rib cage inside the hulls.

I don't know jack - just speculating here...

 

Aluminum is like GRP , usually strong enough , but seldome stiff enough.

An ALUMINUM BOAT WOULD NEED STIFFINERS Usually L shaped material or U shaped , riveted where it contacts the hull.

FAST FRED

 

right

also:

Sandwiched means structure where you have stronger skins and lighter material in between. Such as aluminum or fiberglass surfaces with foam in between. Typical core materials are honeycomb, foam, balsa etc. As the layered board has way more thickness it is much mores stiff (think bending this kind of structure and you'll understand that the amount of compression on skin layers is way more than on thin sheet.

Sandwich in ascii:


===========================
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
===========================

 

there out exists an aluminium composite material made with 2 exterior aluminium sheets with plastic inside.

http://www.alpolic-usa.com/Products/MCM.html

http://www.alucobond.com/

someone has hull experience with it?

 

Tape folks, taped seam, not tapered. 'Glass tape, set in epoxy, over the seams.

Aluminum is a quite flexible material, which requires panel reinforcements when used in sheet form. Welding causes distortion, particularly in thin sheet goods, which also is another requirement for reinforcements on the panels.

Clever use of shapes can reduce the reinforcement needs slightly. Aluminum also can be formed quite easily, unlike other metals. Rolling a bilge turn or even a round hull is much easier and something not generally available to plywood or steel paneled hulls.

Aluminum's unique qualities also require a good understanding of the material's properties. I have never seen an aluminum cored hull, but reason it could be done, but there would be issues. The inner and outer skins would be thinner and welding couldn't be practical on craft below 40' LWL, the skins would be just too thin. Attachment of the skins, to insure no shear can take place, would be a concern. Attachment of the structural elements and reinforcement to a thin inner skin would also keep me up a night. Adhesives are a wonderful thing, but I feel much better with a solid stack of dimes lined up along two adjoining pieces, particularly when hove off a rocky lee shore with a gale building outside.

 

The old Viking lap strake method would seem ideal for constructing a light weight stiff hull, with rivets , no welding.

The riveting process does not require the same skills and knowledge , or e$pensive machinery to weld thin aluminum.

Is this ever done ? 30 to 50 ft?

FAST FRED

 

The only way to make a sandwich structure is by bonding (gluing) the components together. It is no accident when you get lasting paint or adhesive bonds on aluminum; it takes specific steps and chemicals. Without these, the bonds WILL fail. Corrosion can creep in under the bonds even after correct surface treatment and cause glue bonds on aluminum to fail. For this reason alone, aluminum skinned sandwich would be a poor material choice from which to build a boat hull, which is probably why nobody does it.

Other high tensile, high modulus materials (like fiberglass, carbon fiber, etc) which are corrosion resistant make more sense for the skins of a sandwich structure in marine use.

Now an aluminum monocoque would work, if you didn't mind riveting all those little pieces and giving up quite a bit of interior space. Other than that, you must use a thickness of aluminum sheet goods that has sufficient bending stiffness to build a hull without so much internal reinforcement, like 1/4" thick or so. Then that 40' length threshold look pretty realistic.

Jimbo