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

Truck liner would work, some spay coatings, heck even a layer of butyl rubber would actually probably work pretty decent as a layer over the aluminum to water proof.

 

I understand that many people have applied truck liner type urethane coatings to aluminum boats with good leak sealing results. Probably not so good for weight.

I'd take glued and riveted aluminum over either one alone. But glue alone over rivets alone - I'd probably take rivets.

 

But a lot lighter than the thread title you opened. In reality the plate isn't that much thicker.

Alloy boats are painted with epoxy etch primer and then a high build below the waterline for boats that need antifouling ie. spend significant time in seawater. The epoxy is one of the best barriers for moisture and electrical conductivity. Polyurea can be very tricky to apply and keep on and it's expensive. It's main use is as an abrasion resistant coating.

I think you'd better define the size and displacement of the craft you have in mind.

 

I don't see how thicker metal would be lighter than thinner metal with a plastic coating, but it doesn't matter, cause the point was that an amatuer could produce a reliable result, while that is not the case with aluminum welding.
Rhino lining claims 35 to 65 lbs of weight for the coating used to coat a pickup truck bed depending on thickness.
I wouldn't be surprised at all if it actually did add some structural strength, but even without, I would trust that boat better than an amatuer welded aluminum boat.

I guess I'm thinking size wise on boats that are using 1/4" aluminum.
Let's just say for example that 35 lbs covers a 4x8 sheet of material.
A 4x8 x 1/8" sheet of steel weighs 164 lbs.
A 4x8 x 1/4" sheet of 5051 aluminum is 120 lbs.

For someone wanting to build a backyard boat like I am, I could easily use thicker aluminum, and bed liner coating to take care of the water proofing, and eliminate the rust factor.

 

If you find welding difficult, then don’t weld. Either hire someone to do it for you, or select a different method of fabrication/material.
Losing strength is relative. If the loss in strength has been accounted for in the design, so what? Also the loss of strength, as noted by Daiquiri, only occurs when not using O temper; as there is no chnage in the O temper. Even the H116 etc tempers, the loss is minor. Finally on this point, if you’re concerned about the loss of strength then, as noted, you must use the “as-welded strength” to be your design parameter, not the “unwelded strength”. Simple.

Why use a non-standard grade of ally?

Before even attempting to review your other concerns and answers based on other posters replies, what is it you are trying to do and why. Since you appear to be skirting around several and often unrelated issues, yet rolling them into one.

 

I'm just speculating that is seems there is a lot of people who might consider building an aluminum boat, but either don't trust their welding skills, or don't want to pay someone.

Just tossing the idea that maybe it could still be possible, using fasteners instead of welding, and a coating material, to not worry about leaking rivets and joints.

It is very possible I'm wrong, but it still seems enticing all the same.

 

I'd say it's quite possible but not worth the effort. OK so you rivet & coat the hull plate, how are you going to build the frames etc?

What are you going to gain?

Mike asked a very pertinent question - what size boat are you talking about? If it's a 5m runabout or similar, sure - glue it together with Sikaflex or similar and call it done. 12m ocean-capable sailboat, not for me.

PDW

 

The size of the boat is not something I considered when bringing this up, honestly.
The frames could be riveted or bolted as well.

I was thinking the gain would be for someone who is desiring rot-free/rust free construction, but doesn't have aluminum welding skills, or maybe doesn't want to buy a ton of equipment to build 1 boat. Or, maybe they're like me, and the above is true, plus I can't find anyone who is confident at welding aluminum.

For example,
When I thought of bringing this up, I was thinking of my own project I want; a trailerable houseboat cruiser.
I have experience with steel, (which is 90% chances what it will be built from). I don't have any aluminum welding experience, and I'd probably never use aluminum on any other projects. So it doesn't really make sense to buy a welder, learn to weld aluminum, and buy all the associated tools also, just for 1 project.
The next logical step, would be to hire someone. I tried, it was just not even close to affordable. Maybe if you live somewhere close to shipyards. There were a few guys I found that said they'd do it, but had about as much experience as I did. Not what you want for a boat, right?

Now there is also fiberglass, which really makes a lot of sense for a boat that you intend to trailer, as weight is always an issue. While I am still trying to learn about fiberglass, I currently have trouble talking myself into such a large fiberglass project, when my experience is non existant.

So, back to the riveted aluminum boat covered in a coating....
Basically, all the benefits of a welded aluminum boat, (questionable, depending on the fasters used), but without the quality control issue of welding aluminum. I don't know everything about aluminum, but maybe a different grade could even be used with rivets as no welding is done.


I don't have lots of answers or facts to back up a giant argument, I just thought it was a cool idea, and wanted to expand on it a bit.
Notice the thread was "insane thought of the day", not "you guys are all dumb, I have a better idea than all you", LOL

 

I would think that you could buy good used tig, use it for the boat, then sell it without losing that much money. I don't think there are that much other tools that would differ much from what you would need for your riveted boat too.
I have no real skill in welding alu but even if hard I think its learnable without needing THAT much effort.

 

Hello parkland

What type of hull shape did you have in mind?

Is this for lakes and rivers with calm to moderate conditions?

Would you use pontoons or...?

 

I don't think it's impossible, there are some amazing glues out there these days and combined with a decent riveting schedule, it'd probably work. I'd want the design done by an experienced engineer though and that might get costly.

As for aluminium welding, 2 very experienced people advised me not to do it for my hull. I took their advice and used steel. However except for a bigger welding plant (maybe) I honestly can't see a lot of difference in the tools needed. You can work aluminium with wood working tools fine.

IMO the biggest revolution for home boat building out of steel has been the advent of cheap plasma cutters. No way would I ever go back to using an OA torch for cutting plate.

PDW

 

If learning TIG welding aluminum is the issue, then MIG with a spool gun is easier (and faster). And I wouldn't rule out a combination where some things are glued and riveted and others are welded.

 

If a rivet leaks it it loose with the accompanying loss of structural integrity. Coating a hull with plastic or anything else because it leaks may keep an old clunker floating. However, if a new build leaks, it was done wrongly and the rivets should be peened over or replaced.

 

^^THIS^^

Wouldn't you want to know if your structural integrity has been compromised? Leaky rivets are an easy and obvious indicator that maintenance is needed. Easy to repair, and all a part of basic boat maintenance which should be done anyway.

Kinda like building firecrackers into the walls of your house to serve as a fire alarm...

 

That is true.
I was also thinking of actual bolts, and if those were put in, and loctite used on the threads, the joint might be more reliable than a rivet, at least to an amatuer.
I know there is the drawback of the bolt head sticking out, but depending on the layer coating it, maybe it can be hidden. For a dock or barge, that would probably be fine though.