# What size Aluminum angle?



## Tech Sergeant Ken (Jun 28, 2009)

I am trying to figure out what size Aluminum angle I should use to frame the decking for my boat.

If I put Aluminum angle trusses spaced every 16 inches, could I use 1 x 1 x 1/8 angle for the trusses? Does going to 1-1/4 x 1-1/4 x 1/8 make it any stronger, or would I have to upsize the 1/8 to 3/16?

Is there an easy way to calculate, or a rule of thumb for spans, deflection under weight, etc?

Ken


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## ober51 (Jun 28, 2009)

Glad youve joined, but is there any way to join all these threads so all the information is in one place?


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## Tech Sergeant Ken (Jun 29, 2009)

Sorry, I don't know of any way to join the threads.

It's funny, I split the topics into multiple threads because I once got yelled at on a different website for combining too many topics in one thread. It was explained to me that for purposes of later searching, it is best if a new topic is created once the original question is answered.

It seemed to me at the time that the topics were distinct - 1) how to mechanically fit angle to make a joint, 2) how to best weld angle, and 3) how to size angle to support weight. Or course, they all have the same theme - angle.

I will leave it to this forum's administrator to decide if the threads should (and can) be combined, or should be left separate. I'm OK with either choice.

Ken


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## poolie (Jun 29, 2009)

I'm sure most of us over engineer our decks. I used 1 1/2 x 1 1/2 x 1/8 angle spaced roughly 15" apart. Combining that with 1/2" plywood for decking and mine is rock solid. Could I have used 1 1/4" instead... probably but I wouldn't have gone down to 1" x 1". 1" angle would need a lot of 'legs' going down to the floor to support any amount of load.


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## ober51 (Jun 29, 2009)

Ken, I didn't mean anything bad by it - I am just a fan of keeping things in one thread, that's all lol. All of your questions are important, so it's not a big deal. Maybe I was a bit jumpy, haha. Anyway, good luck!


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## Kurt Loup (Jun 29, 2009)

I'm using 1 1/2" x 1 1/2" x 1/8" tubing and angle on my project. So far, I have the rear deck 95% completed. I haven't attached the deck yet. I'll wait until I get the bilge pump mounted. It may look overbuilt, but I could feel some flex in the 1/8" plate before I added two additional support tubes. There's no flex now.

Kurt


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## Zum (Jun 30, 2009)

Sure does look solid...Kurt.
Nice job.


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## sparkbr (Jun 30, 2009)

kglade said:


> I am trying to figure out what size Aluminum angle I should use to frame the decking for my boat.
> 
> If I put Aluminum angle trusses spaced every 16 inches, could I use 1 x 1 x 1/8 angle for the trusses? Does going to 1-1/4 x 1-1/4 x 1/8 make it any stronger, or would I have to upsize the 1/8 to 3/16?
> 
> ...




Ken,

How long will your free spans be? what are you sheeting it with for flooring, and how big will the deck be?


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## Tech Sergeant Ken (Jul 24, 2009)

Brad:

Sorry for the late reply.

I found some software tools to help me make the calculations. The questions you asked about free spans, deck thickness, etc. are to me, a circle. I'd like to pick the free spans and deck thickness and size that would give me the "right" design without overdesign.

Anyway, I found that structural guys try to keep deflection in decks and balconies to less than 1/240 or 1/360. That means less than 0.1 inch deflection in a 36 inch span for 1/360.

I used beamboy to calculate deflection for a 300 lb point load, midway between my beam support points, and by trial and error found the answers I was looking for. I had to use "engineering power tools" to calculate the moment of inertia for the various angles and channels I was considering. Beamboy needs to know the moment of inertia for the beam, as well as the modulus of elasticity (10, 000, 000 /in2 for aluminum). Note, engineering power tools can do the deflection calculation, too, but does not display it graphically like beamboy does.

I know the addition of decking, especially vertical walls, makes everything stronger, but I don't know how to calculate that. I also haven't figured out how to calculate the deflection of a sheet of plywood or aluminum supported by beams.

beamboy is freeware. engineering power tools is $24.95 but works for 30 days for free but won't print or save data.
beamboy can be found at https://www.geocities.com/richgetze/
engineering power tools can be found at https://www.pwr-tools.com/

Anyway, to make the story complicated and real-world, I came across 84 feet of aluminum channel, 1 x 3, for free, and am trying to design the structure around this. I am puzzling over how to make the joints, but that is in another thread.

I am on the fence about aluminum vs. wood decking; today, I am leaning toward wood. I am thinking 16 inches between beams (like in a house) so the floor should deflect about like it does in a house. There is a really good picture here https://www.johnbridge.com/vbulletin/showthread.php?t=8921 that shows how grain direction affects deflection in plywood.

Ken


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## Jr Branham (Jul 29, 2009)

Here are a few pics of how mine was done. I did not do this, boat was custom built by boat builder in Arkansas. I wished I could weld aluminum......


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## 2007NNBS (Aug 3, 2009)

yes that is what i used for mine and it is solid


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