# Aluminum VS Ext Plywood for Casting Deck and Floor



## FuzzyGrub (Jun 3, 2011)

I am comfortable with using ext grade plywood for decks and floor. I've used it on other projects and very happy with results. I could handle doing sheet aluminum, but only with standard fastners, since I don't have the welding equipment or tallent. I am not concerned about wood rot. Primarily interested in calculating the amount of weight savings if going through the extra work (for me) of going to sheet aluminum. I couldn't find any info on minimum aluminum thickness for span length recommendations. My floor spans are 14" on center, and would like similiar span for casting decks. Does anyone have what the minimum and/or recommended sheet aluminum that should be used? and its corresponding square foot weight? If there is a specific thread on that here, a link would be much appreciated.

Note: Support framing would primarily be aluminum. 
Also: Floor covering will not be carpet. Some form of paint, possibly bedliner type will be used.


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## shawnfish (Jun 4, 2011)

i just had the same question not long ago. use search engine and type weight and look for my thread, a week ago i think...good info!


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## shawnfish (Jun 4, 2011)

its on page 3.....weights.


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## FuzzyGrub (Jun 5, 2011)

Thanks, I found it. All my searches were coming up with too many hits. Looks like 0.125 aluminum would be the right thickness. I don't have a break to bend and make the thinner sheets stronger. I generally use 5/8" ext grade plywood and there would not be a significant weight savings going to aluminum.


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## heavyduty (Jun 5, 2011)

I just had a floor put in my new Alumacraft 1442 NCS. Using closed cell foam to fill the space between the ribs and make it flush with the top of the ribs, I then used .062 aluminum. My ribs were roughly 14" apart also. I'm 320lbs and it supports me just fine. I used the .125 to extend the front casting deck since it was not fully supported with foam like the floor.
HD


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## FuzzyGrub (Jun 5, 2011)

heavyduty said:


> I just had a floor put in my new Alumacraft 1442 NCS. Using closed cell foam to fill the space between the ribs and make it flush with the top of the ribs, I then used .062 aluminum. My ribs were roughly 14" apart also. I'm 320lbs and it supports me just fine. I used the .125 to extend the front casting deck since it was not fully supported with foam like the floor.
> HD



I found some other projects that were doing similiar with 1/4" plywood and even 1/8" luan. I did some testing with some 1" blue closed cell foam and very thin alum sheet that I had on hand, layed on the floor in the basement. Was able to walk on it no problem. The foam is all the structural support. I wonder what the thinest anyone has ever covered it with? The boat would need 1.5" foam. Basicly the top layer is just to protect the foam.


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## nomowork (Jun 6, 2011)

I just finished my floors today. I made them out of 1/2" plywood (okay so they're actually .451").

I made a box type frame out of scrap 2 x 4s and 1 x 1s for the deepest center part of the hull and a box frame of double stacked 1/2" plywood for the rear flatter section. I primed them and painted with exterior concrete non-skid porch paint. Kind of interesting to see how they will hold up.


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## FuzzyGrub (Jun 6, 2011)

nomowork said:


> I just finished my floors today. I made them out of 1/2" plywood (okay so they're actually .451").
> 
> I made a box type frame out of scrap 2 x 4s and 1 x 1s for the deepest center part of the hull and a box frame of double stacked 1/2" plywood for the rear flatter section. I primed them and painted with exterior concrete non-skid porch paint. Kind of interesting to see how they will hold up.



Our '67 Starcraft has been in our family since new. It took over 30 years for that plywood to start to feel soft. A few years latter, when I repaced the floor, the plywood was still intact enough to use as a pattern. Starcraft had used 5/8" ext grade plywood, and only painted the top. The soft and rotton spots were caused by waterlogged foam. That stuff never drys out, and kept constant wetness against the wood.

When I replaced and for modification, I primed and sealed all surfaces, and the edges twice. Then all surfaces with one coat of porch poly. The top surfaces got multi-coats with traction additives. Has held up well, and cleans up very easily. I have to deal with a fair share of mud in early spring and late fall on our primary fishing river. Plus, its easy to give it another coat every couple of years.

I have used some 2 by's for some structure support, but it has always been from top of floor to deck, not below where it could have extended contact with moisture. The way pine end grain wicks water, I couldn't put that much faith in the primer/sealer, and especially in an area that I would have to tear everything out of to fix/replace. 

Anyway, for my current project, I am being very careful with weight gain. As such, I am toying with the idea of laying 1.5" closed cell foam between ribs. I need to add floatation back from removed bench seats, anyway. Water drainage will be from front to back in the strakes, under the foam, but would also provide some channeling around foam. A thin layer of aluminum sheet over the top, with a bedliner or tough coat type paint for the finish. The question in my mind, is how thin of aluminum can I get away with and how will it hold up?


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## nomowork (Jun 6, 2011)

I made my floors so that it could be easily removed in case of an emergency of some sort. The center floor section has two "finger holes" to lift the floor out and the sub floor is not attached to the hull. The rear floor section is all in one piece with the sub floor bracing built as part of the floor. If any water gets inside of the boat, hopefully the sub floor is high enough that the wood won't get too wet. If the water is that choppy, I won't be out there. 

I'll try and post some pictures later on my "Another rookie" thread.


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## heavyduty (Jun 7, 2011)

I believe James River Jets uses .050 alum in floors and sides when backed by foam. That's the thinnest I've heard of. No experience but I think I'd steer clear of luan. Drop a battery on a corner, anchor, anything with some weight on an edge and I think it would puncture thru luan but just dent alum. 
HD


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