aluminum thickness questions

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200racing

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i am re carpeting/modding my g3(project thread to come).
the floor was carpeted 3/4 plywood. it soakes up water and weights alot. the floor supports are on 1 foot centers and foam even with the top in between. how thin of aluminum sheet can i use and not have a weak,sagging floor. it would be 48"x48"space.

also i am adding deck since it was a panfisher model. i want to use 2" aluminum angle would 3/16 be a good choice?
 
With your floor supports at a foot apart 1/8 inch thick Aluminum should be good enough. Theres quite a difference in weight between 1/8 inch and 3/16 inch plate and angle. I am going to use all 1/8 inch in my boat project. Floor supports and maybe decking if I can afford it.

Steve
 
My Fisher Marine has ribs on 22" centers (20¼" between ribs) filled flush to the top of the ribs with foam. I was surprised to see that the aluminum on top was only .036 (surprised enough to use calipers haha). So If your packing the space between ribs with foam, you can get away with some pretty thin stuff. 1/16th would be overkill based on what the manufacturer used.
 
JMichael said:
My Fisher Marine has ribs on 22" centers (20¼" between ribs) filled flush to the top of the ribs with foam. I was surprised to see that the aluminum on top was only .036 (surprised enough to use calipers haha). So If your packing the space between ribs with foam, you can get away with some pretty thin stuff. 1/16th would be overkill based on what the manufacturer used.

+1. When I put my aluminum floor down, I too used .063. I can't remember how far apart my ribs were, but I stuffed them with solid foam and it works beautifully. Riveted it down to the ribs. I don't have that boat anymore, but I do still get to fish out of it on occasion.
 
Now I am rethinking my flooring. Maybe I should go with 1/16 inch instead. I was going to go with 18" centers but might go with 24".

Steve
 
If you are going to go with 1/16", you had better put foam under it. 1/16" by itself isn't going to be nearly enough, even with ribs on 12" centers.

However, that opens up a whole other can of worms, and is a practice I'm not very fond of.
 
Agree with the other posters...if you are filling the space between the supports with foam you can get away with a very thin material, because it is fully supported underneath across the entire floor...where would you get any sag from?
 
My G3 uses .100" aluminum for the flooring on 12" centers. I'm sure there is foam under it, but there is no flex when walking on it. 1/8" would be .025" thicker and would work very well also.
 
JMichael said:
bassboy1 said:
However, that opens up a whole other can of worms, and is a practice I'm not very fond of.

Please elaborate as I'm hear to learn.

Traps dirt. Also traps water. By that, I'm not speaking of the issue of open cell foam holding water in the foam (provided one uses closed cell foam), but instead small amounts of water trapped between the layer of foam and the aluminum. While aluminum doesn't have an issue with flowing water, it does have issues with entrapped water w/o access to air.

The problem is that aluminum is constantly forming aluminum oxide on the surface. That feature of aluminum is what gives it a commercial value - the underlying aluminum by itself is very unstable, and without the oxide layer, would not be usable in most applications. In that oxide forming process, the aluminum is stealing oxygen from whatever it can - air and moving water, no big deal. But, when you have small quantities of entrapped water, without airflow, the water begins to lose some of the oxygen, and becomes acidic. This then goes right back, and starts to eat into the metal. Also, some pour in foams are slightly corrosive to the aluminum in and of themselves. I'm not sure how the sheet foam many use compares to that, so I can't say one way or the other in that regard, but it is something worth paying attention to.

In a freshwater application, the damage is probably going to be minimal. I'm sure we've all pulled apart older tin rigs that had aluminum sitting on foam, and seen the layer of white chalky corrosion. In most of those cases, the corrosion is not very deep, and the metal/foam combination had likely been touching for multiple decades, but all the same, it is not a practice I'm very fond of.
 
Thanks bassboy1. That explains a lot of what I found when I recently removed my floor, and why. "Traps dirt" is an extreme understatement, if what I found in mine is common. :lol: I only found one small area (approx 6"x14") with any pitting so it sounds like I was lucky there.

I don't want to hijack or derail the OP's thread, so could you PM me a link to any info on alternative routes to go if we want to maintain the safety factor of the foam flotation but avoiding the negative aspects of this. Thanks for the reply on this and any other info you can provide. I'm almost ready to replace my floor, so now would be a good time to find out as much as I can on this.
 
JMichael said:
Thanks bassboy1. That explains a lot of what I found when I recently removed my floor, and why. "Traps dirt" is an extreme understatement, if what I found in mine is common. :lol: I only found one small area (approx 6"x14") with any pitting so it sounds like I was lucky there.

I don't want to hijack or derail the OP's thread, so could you PM me a link to any info on alternative routes to go if we want to maintain the safety factor of the foam flotation but avoiding the negative aspects of this. Thanks for the reply on this and any other info you can provide. I'm almost ready to replace my floor, so now would be a good time to find out as much as I can on this.

I'll post it in the open forum, so others can read it as well.

There are two ways to provide adequate flotation without hurting the aluminum. One is air space. On many welded boats over 20' (over 20', for two reasons), the deck is often fully welded, and pressure tested, with the area below serving as flotation. I helped build a 25 footer with this style last year.
The reasons this method is only used on boats over 20' are: first off, and most importantly, the US government mandates that boats 20' and under have 2 pound per cubic foot density flotation foam. Secondly, seal welding the decks on a boat under 20' is no easy feat, given the thickness (or lack thereof) of the aluminum used on the smaller boats. One could probably count on one hand, possibly with fingers left over, the number of builders in this country who could build a 14' boat, out of .080, with seal welded decks, and not destroy the boat with warpage.

The second way, and this is most practical on the smaller boats, is to mold the foam outside of the boat, and encapsulate it with fiberglass, or a heavy plastic and tape. Then, (and don't forget this part), install it with spacers, to allow water and air to flow between the bundle and the metal.
 

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