# Aluminum framing



## Givey1982 (May 8, 2017)

I am thinking of adding some aluminum framing to my boat as opposed to using wood. My question is for those who have done this did you weld the aluminum, brazen it or design it to bolt together?

Thanks


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## Johnny (May 8, 2017)

those that have access to a welder - weld
those that know how to use a pop-rivet gun - uses rivets
all is good if done correctly


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## Buckethead (May 8, 2017)

I used 3/16" aluminum or stainless steel rivets. I also used stainless bolts/nuts with nylon washers and 5200. Did most of my fabrication in 2012 and 2013, no leaks, no connections trying to come apart, still holding up well. Fabricating with aluminum means no rotting and basically you'll use the same tools.


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## Shoedawg (May 8, 2017)

I used pop rivets and bucked some in my all aluminum framing. If you know how to weld aluminum, go for that, but it's a skill you must be proficient in. Welding aluminum is not like welding other metals. Stainless steel bolts work as well. Rivets are very strong and are cheaper than buying stainless steel bolts, nuts, washers in bulk, unless you can find a good deal.

Wood on the other hand is easier to work with for most, but with the right tools, patience and seeking knowledge, aluminium is pretty easy to work with. I had no experience with working with aluminum until I did my build. There is not a single piece of wood framing in my build. I didn't want to spend the time dealing with rot, and having to replace it some time down the road. With aluminum, rot worries don't exist, plus there is a weight savings compared to wood. 

Go with Aluminum. You will be glad you did.


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## overboard (May 9, 2017)

Rivets, SS bolts, SS screws, if you plan to never take it apart, or as parts on a removable piece, then welding is an option. I added extensions to a deck, made a small deck, and installed floors without any welds or any wood.


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## Captain Ahab (May 9, 2017)

I used all SS nuts (nylock) bolts and sheet metal screws - works great


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## rachbra (May 9, 2017)

What size angle aluminum will support people while make flush decks with the boats platform. I have seen it on here a bunch, they make sweet compartments out of all the open space in the boat by framing with angle aluminum. I was just curious if i make something similar that could hold 2 or 3 guys fishing. I wanna keep the weight a minimum so what size would support a human?


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## captpetej (May 10, 2017)

thickness of material is only one factor here. Structure is the big variable. Triangles are the strongest shape there is. IE you can use thin material, and lots of structure to get strength, or you can use material thickness with less structure to obtain roughly the same strength.

Design, size, and amount of storage will all factor here.

.095-.120 wall aluminum is plenty thick to make work easily, all will need supports strategically arranged for strength. 

I'm sure folks have gone thinner as well .065 comes to mind... and will hold up to human weight... if supported...


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## minuteman62-64 (May 10, 2017)

I bedded the joints in 5200 and then pop riveted them together. Since I was working in the bow "V", with limited room, I justified (to myself) the purchase of a HF air operated rivet gun. Turned out to be a great purchase.

W/regard to load bearing, the shape is more important than the thickness. I used a structural grade aluminum angle, 1 1/2" x 1 1/2" for almost all of my members. It has held up great - no issues with a 200 lb. person (me) standing in the middle. I think I posted some photos on here a couple of years ago.


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## minuteman62-64 (May 10, 2017)

Yessss. My mind is still sound. Here (hopefully) is the post: https://www.forum.tinboats.net/viewtopic.php?f=3&t=39542#p401683


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## pmshoemaker (May 11, 2017)

Please excuse my ignorance -- this is my first of probably about a million questions. I just took possession of a 1984 PolarKraft 16ft. johnboat that I am dying to get to work on. I picked up a trailer, got it titled/tagged -- now it's on to the big show -- this weekend I'm going to shovel out the leaves and the gunk, cut down a few little trees that have grown around it since it was last moved 25 years ago, and start getting it fixed up. My question is this -- I am very intrigued by the concept of using aluminum. Do you attach the framing through the sides of the boat with rivets? Or do you just attach the framing to the supports on the inside edges? I guess this question goes for wood construction, too. I just can't see from any of the pictures on any of the posts. Hopefully I'm articulating this clearly -- do you actually put rivets through the side of the boat?


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## Shoedawg (May 11, 2017)

pmshoemaker said:


> do you actually put rivets through the side of the boat?



You can if you use solid rivets and buck them properly and even coat the rivet shaft with some 5200. The entire bottom of my tin had leaky rivets in her. I drilled them out and replaced them with new, solid rivets (bucked them) and coated with 5200. Had her in the water for 7 days on a fishing trip and not one leak. 

You could also use pop rivets above the waterline as well, and again, seal the shafts with 5200.


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## pmshoemaker (May 11, 2017)

hmmm -- thanks Shoedawg. I have a grand total of 0 hrs. of experience working with rivets. When you say "buck," is that the process of squashing them with a metal backstop of some sort? (please excuse my novice terminology... but I'm a novice when it comes to rivets and such). Also, will the 5200 break down over time, leading to leaks? Or is it pretty long-lasting stuff?


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## TDobb (May 12, 2017)

As far as what size aluminum framing to use it depends on a couple of factors. Span distance between connections and anticipated weight at the midspan, along with distance between framing members. Another factor you want to consider is what material are you going to use for the decking, plywood or aluminum and what thickness.

A couple scenarios below assuming a 200 lb guy is going to be walking around in the boat.

Lets say you wanted to go with 1/8" aluminum decking. You would want your framing to be 16" OC. If you have short spans, say 42" or so, you could pretty easily use 1.5 x 1.5 x .125 aluminum angle. Now if you have long spans, you might be best to run a couple larger profiles the long way near the outside edges and run smaller angle perpendicular to the long span to save material cost and weight. If you could somehow tie that long spanning member back into the structure of the boat at a couple of points along the way you could probably do it with 1.5 x 1.5 x .125 square tube, but if you had to span 8 feet only supported at the ends, I would probably bump it up to a 2 x 3 x .125 rectangular tube with the long leg vertical.

Now if you wanted to go with .060" aluminum sheet for decking, your supports would have to be much closer together, like 8" OC. .090" decking you could probably go 12" OC.

If you are doing plywood, 1/2" marine grade I would go 16" OC, 5/8" you could probably go to 20" OC, and 3/4" would span 24" OC. The disadvantage with going to thicker plywood though is that it is much heavier than the aluminum framing required to go with thinner plywood.

The type of boat can also play a roll as well. One of the things I remembered along the way in my build is that my boat (1976 Lund S-14) is very tippy. That said, the perimeter framing in my boat I went a little lighter (1 x 1 x .125) than noted above in some areas because as I step on the decking the boat rocks just from the weight being off balance. There isn't enough resistance from the water or the weight of the boat to cause bending in the members as the boat just rocks out of the way.

It is really all in how you frame things to be honest.

Could you get by with doing 1 x 1 x .125 angle for your main floor framing? Yes probably, but it might not be as rigid as you'd like. Could you frame everything with tube shapes? Sure but it will be way overkill for most stuff unless you are trying to get by with .75 x .75 x .0625" tubes (Don't do that, way too thin).

On rivets, a 3/16" aluminum rivet is good for about 240 lbs of shear, which is the direction across the shank of the rivet. In tension, a 3/16" aluminum rivet in my experience is only good for about 75 lbs, when using 3/16" pilot holes. If you step up to 13/64" pilot holes to make it easier to install, you get even less pull out strength from them. Basically what I am saying here is use rivets so the load is transfered through the side of the shank rather than the length of the shank. If you need to fasten using the length of the shank, switch to a sheet metal screw or a self drilling screw, they hold much better in tension.

If you have an air compressor to use, buy a pneumatic rivet gun. They run about 40-50 bucks on amazon and the very first rivet you sink with it will make you smile. On my boat I sank about 250 3/16" rivets. Just thinking about doing that with a hand rivet gun makes my forearms ache. The pneumatic rivet guns are so fast and so easy. I would have paid $250 for one with how much satisfaction I had over a manual popper.

No matter what way you go, remember to have fun and wear safety glasses and hearing protection. Gloves would be good too working with aluminum. I tore myself up pretty good any time I didn't have the gloves on (stubborn idiot). 

Take care,
Tom


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## TDobb (May 12, 2017)

By the way, those numbers above for span distance on aluminum sheet for flooring were provided to me by the structural engineer that sits next to me. I design aluminum framing for curtainwall (exterior walls on sky scrapers) for my day job and work with structural engineers all day every day to ensure what we are doing will work. He ran numbers for the aluminum flooring option as I was considering going that route. I ended up sticking with plywood for the flooring but looking at it now, wish I had gone aluminum. Plywood is a WHOLE LOT cheaper than aluminum sheet though, even marine grade plywood, about 1/3 of the cost of 1/8" aluminum sheet.


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## Shoedawg (May 12, 2017)

TDobb said:


> Plywood is a WHOLE LOT cheaper than aluminum sheet though, even marine grade plywood, about 1/3 of the cost of 1/8" aluminum sheet.



Yes it is. But going with a aluminum sheet vs a wood floor pays off BIG time in the end.

1. No rot issues
2. No buying the sealant to protect the wood (time and money)
3. Weighs far less than wood (making the boat lighter)
4. No replacing wood floor after some years
5. Really not that hard to work with
6. Strong

I picked up my sheet (a 10x10) for around like $114 from a aluminum dealer. Stay away from those BigBox stores, they will rip you off.


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## TDobb (May 12, 2017)

Shoedawg, how thick was that aluminum? A 10 x 10 sheet for $114 is a steal of a deal. I was looking at discount steel in Minneapolis and a 4 x 8 x .125 sheet comes in right around $150. If your sheet was .125 you dang near got that at scrap price, that would be 175 lbs of sweet clean metal.

But yes, all of those factors you mention are definite benefits for aluminum. 

I just couldn't justify the extra cash over plywood for my project as the previous remodel I used standard CDX plywood and after 7 years when I pulled it it looked like the day I put it in. I didn't use any sort of sealant when I installed it the first time around either, just laid carpet right over the plywood. My boat is stored in the garage 100% of the time when it is not in use so keeping it dry was advantageous, but I fished in the rain plenty of times over those 7 years.


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## Shoedawg (May 12, 2017)

TDobb said:


> Shoedawg, how thick was that aluminum?



Here is what I ran with:
5052 Aluminum Sheet 5x10x.090

.90 was plenty thick for my needs. I used it for all my decking, floor and sides. I was not worried at all about flex in the floor or decks. In fact, I have very little flex, which is not noticeable at all. With the right structuring (per your boat's footprint/layout) .90 is not a bad option to use. I felt .125 was too thick for my needs.


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## Shoedawg (May 12, 2017)

pmshoemaker said:


> hmmm -- thanks Shoedawg. I have a grand total of 0 hrs. of experience working with rivets. When you say "buck," is that the process of squashing them with a metal backstop of some sort? (please excuse my novice terminology... but I'm a novice when it comes to rivets and such). Also, will the 5200 break down over time, leading to leaks? Or is it pretty long-lasting stuff?



Yes bucking is "squashing" a rivet with a metal backstop and a hammer. 

5200 last a long time and there should be no worries about it leaking, if applied properly. A rivet that has been bucked properly will not allow a leak. Coating the shaft of the rivet first with 5200, then bucking it, just adds some peace of mind and helps prevent leaking if the rivet gives a little.

Eventually some rivets will leak overtime, but can be easily fixed.


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