Cross beam dimensions

[checkoutmyjunk]

New here, my first post....

I did a number of searches and did not come up with the answers I hoped to find.

I picked up a 1970 "homemade" pontoon. It has a wooden frame and my original plan was to trash everything but the toons. I would add some new aluminum cross beams and new marine grade ply on top of that. I planed on it having a dual purpose, primarily it would serve as a dock, the secondary purpose was to serve as a barge. Because I wanted to pull it in and out and do some supply runs for my island, I wanted it to be a registered unit so that I could drop a motor on without the boat cops getting upset with me.

I stated my search for cross beams and quickly realized that online sellers are asking between $45 and $65 a piece, at 16" centers I would need about 17 of them. That puts me over $1K in the beams alone. I see that hat is the best bet and even confirmed that with the engineer here at work but I also think that C channel would work for my application.

Here is where I am hoping for advice:

I can get enough 2" x 1" C channel for under $200 with a thickness of .130" (just over 1/8") but I am not sure that would be heavy enough?
Another option id 3" x 1.5" C channel for a little over $500 with a thickness of .258" would doubling my cost net me a much better performance?

I do not plan to hang a big motor on this rig, right now I have a 30hp tiller that I plan to use, but I do have a line on a cheap 70 that I might try later.

[willy13]

Make sure it's structural aluminum not architectural aluminum. Architectural aluminum will have a sharp bend in the channel side profile that becomes a stress riser under load. Structural aluminum will have a small inside radius. Do a search you will see the difference.

[willy13]

My guess, and I stress guess, is at 16" of center and if the 2"x1" is indeed structural aluminum, that should do it and save weight. The 3"x1.5 at .25" thick is over doing it, which is fine, as long as weight is not a concern.

[TheWhisker]

When I re-did my deck, I replaced 4 of the beams where the plywood came together (they met in a channel originally and I didn't have the expertise -or maybe the patience is a better word- to router the edges so they fit in properly). I used 0.125" (1/8) c-channel and it's actually thicker than the rest of the cross beams so I'm not worried about it. Mine were 2-1/4" height and my beams are 16" centered as mentioned. It is 6063 but I'm still comfortable with it.

[TheWhisker]

Make sure it's structural aluminum not architectural aluminum. Architectural aluminum will have a sharp bend in the channel side profile that becomes a stress riser under load. Structural aluminum will have a small inside radius. Do a search you will see the difference.

But that is correct... my replacement channels have that sharp bend and if that's a concern when replacing *all* the beams, it is worth noting. I didn't want to sound like I was arguing with or contradicting willy13.

[bansil]

How far do you have to go and what would wt be on it? A couple atvs, coolers etc? Why not build a wooden deck on it? Use 2 x 4 x 8 ft on 2 ft centers and then grab either 5/4 wood or synthetic decking? I would measure all the supplies first may be too heavy

[bansil]

Most decks last 20/25 years with exposed wood

16 pc 5/4 x 6 x 16 pressure treated is $270 or so

2 x 4 x 8 about $6 x 18 ~ $108

screws? maybe $50 total

I just spent $428 for material and $72 in beer/ice and hot dogs and buns....so for $500 you can have a picnic work weekend

Best part is no cutting required, I guessed on material qty's so you will have to make a paper napkin drawing to verify

[checkoutmyjunk]

How far do you have to go and what would wt be on it? A couple atvs, coolers etc? Why not build a wooden deck on it? Use 2 x 4 x 8 ft on 2 ft centers and then grab either 5/4 wood or synthetic decking? I would measure all the supplies first may be too heavy

Good point!

Loads:
I would take a single garden tractor, or golf cart at a time.
I do need to haul building materials, in that case 1000lbs at a time, I mean I still have to move it all by hand once I get it to the island.

Distance:
The two ramps I use are a red C hair more than a mile drive.

[checkoutmyjunk]

Most decks last 20/25 years with exposed wood

16 pc 5/4 x 6 x 16 pressure treated is $270 or so

2 x 4 x 8 about $6 x 18 ~ $108

screws? maybe $50 total

I just spent $428 for material and $72 in beer/ice and hot dogs and buns....so for $500 you can have a picnic work weekend

Best part is no cutting required, I guessed on material qty's so you will have to make a paper napkin drawing to verify

[bansil]

Oh....yeah baby, plus that top frame would look good at walking height with canvas tarp stretched over it and wet down with resin, waterproof and light wt. Maybe a gallon of poly resin would do it, make sure to post pictures this will be fun