Fiberglass or plastic over aluminum ? - (insane thought of the day)

Automotive definitely tests in salt spray, with thermal cycling -40 to 125C to drive the electrolyte.

I still question fiberglass on aluminum. It's easy to test, put a thin layer of fiberglass on a long thin piece of aluminum. Clamp one end and draw a line at the free end. Then heat and cool it. If temperature causes it to deflect like a bi-metalic strip there is an expansion difference that will cause it to distort and break the bond over large distances.

Resistance welding would be effective and relatively user friendly on thin aluminum plates. Autos spot weld aluminum all the time. There is seam welding but I don't think that is easy.

 

glass fairing

I think the idea of polyester resin and cloth or epoxy over aluminium is for corrosion protection and fairing. you can tint the resin and cellofinish for high gloss. any cracks from flexing can be repaired annually easily ,just use above waterline for show.

 

That is an excellent idea for a test.

 

cracks wouldn't be a good sign lol.
The purpose, or at least MY idea of the purpose of this, was to enable someone, most likely an amatuer, to build an aluminum boat hull without the burden of welding aluminum and the associated risks with quality control.



On another note,
Another technique I thought about last night;
Build the hull, say out of 1/4" thick aluminum and bolts.... Then apply truck bed liner to out side of the hull, the thickness of the bolts sticking out over the surface of the metal.
Then, grind away the bed liner material off the top of the bolts, so it's all flush, and use adhesives to apply a super thin guage aluminum over the entire hull. That sounds super tough and strong, and easy.
Aluminum-plastic-aluminum sandwich.

And because the outer layer would be really thin, if any damage DID occur, you could just grind the edges away, and apply a new aluminum panel over top.

 

Have you priced a 4x8x1/4" sheet of aluminum ? I think the main reasons that it would be hard for an amateur boat builder to build with aluminum would be the cost and it would be real hard to bend that thick of aluminum into a shape that would resemble a boat. You would also need some type of framework to attach the panels which would also have to be aluminum. I don't want to discourage anyone but I would definitely check into the cost of materials and work out a design for the boat before deciding what material to use.

Dave T

 

not even twice the cost of steel, plus steel needs expensive paint...

 

bizzar fame method!! you might as well rivet it and cover wih epoxy and 6 oz cloth

 

This is not a bad idea. It is similar to common wooden boat techniques where mechanically-fastened panels are supplemented with epoxy. The idea might not be the silver bullet you hope it is, though.

Here are some remarks about my thoughts:

Welding can be tricky, but is relatively straightforward compared to attaching dissimilar materials like aluminum and fiberglass.

It is possible to have a mechanically-fastened aluminum hull without any covering at all be watertight. The use of welded hulls is due to a number of perceived benefits.

Welding reduces strength in the heat-affected zone. Mechanical fasteners create stress concentrations. In the end, both introduce a certain weakness near themselves.

Repairing aluminum can require a fancy welder. Repairing this composite design is not necessarily more straightforward. How does one remove the glass? And have a useful surface for some more? Can you patch part of a panel or must you do the whole panel? I'm not saying it's hopeless, just that it isn't completely straightforward.

Using fiberglass is probably unnecessary. Some sort of epoxy can probably attain the same goal with less complication.

You say this alleviates the problem of aluminum reacting with dissimilar material -- how? Do you mean that mounting steel components will be to fiberglass attachments rather than to aluminum? If so, I think this reverses the relative strengths of aluminum and fiberglass.



I hope I haven't been too negative in expressing this perspective! I think this is a good idea and that such construction techniques could have their place.

 

I checked on the price of aluminum a 4x8x1/4" sheet the best price I found locally was $320 and $218 for 1/8". Do you have a specific plan for an aluminum boat that you plan to build. I still think that price and trying to form aluminum to any type of curvature would make it very difficult for an amateur builder to use, not only joining the seams and waterproofing. If you have a specific design I would like to see it. I think this would be most important before deciding the material to use. Maybe you have a better source and price for sheet aluminum if so let me know.

Dave T

 

I don't know exactly what I think, haha.
I guess it seems to me like I'd have more faith in an amateurs drilled and bolted boat, than the same guys welded aluminum boat.

I don't know what materials would be best, but basically the aluminum panels and frame would provide the strength, and the layer over top would be to make it watertight and act as a "repairable" layer. Since it doesn't provide structural strength, you could just grind it off, and patch it.

 

I got 280$ for a 4x10 sheet of 1/4" aluminum, and 104$ for a 4x8 1/8" of pickled cleaned steel.
Again, keep in mind that the steel is going to need expensive prepping and painting inside and out.

I'm pretty sure most wood designs could be used; most of them don't have very radical curves.
Thinking of a little wood boat I built a LONG time ago, it had mahogany wood hull, and I cut a million little 1x1x3 chunks of wood, and stapled them in all the corners. The same technique could be used here, as it's not even supposed to be water proof.

 

That was 1/8" aluminum not steel.

Dave T

 

?
No, what I wrote is what I was told, 280$ for 4x10 x 1/4" aluminum, and 104$ for 4x8 x 1/8 cleaned steel.

Too bad I didn't ask for the exact same dimensions, but thats what they had.

 

That's a pretty good price for a 4x10x1/4" sheet. I considered aluminum and other materials when I built my boat. I was thinking you could use 1/8" aluminum for curved sections and 1/4" for other parts I've had quite a bit of experience welding aluminum and have equipment to do it but decided on wood and eglass mainly do to cost.

Dave T

 

If you were using the "overcoat" method described in this thread, maybe the entire hull could be 2 layers of 1/8" aluminum. That would also allow all the joints to be staggered, and seems to me like it could be REALLY strong.