# Foam under the decking, pros and cons...



## MNHunter505 (Jul 20, 2012)

I got a voyager 16 ft and plan to install floor decking. Other than putting foam under the deck to ensure there is foam in the boat if it capsizes, are there any other pros? Does it make the deck sturdier? If I still have the factory foam, is there a need to add more foam for reasons other than flotation? 
Thanks in advance. Also, what size plywood for the deck?


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## sixgun86 (Jul 20, 2012)

See if you Factory foam has become water logged. Also marine closed cell foam is expensive. Some use Pool noodles which I know sounds ridiculous but they work! Foam could make your decking/etc more sturdy, not noodles though.. In regards to the deck, thicker the better but if you have ample bracing it could be unnecessary. Just don't use treated.

+ Boat won't sink. Hopefully. 

- Will cost $$


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## bluegillfisher (Jul 20, 2012)

will add support under thinner plywood. Quiets the dropping of tackle boxes. I have pink house foam under my aluminum deck. The PO used 5/8 PT plywood with beautiful astro turf as floor. The panels lifted out to clean leaves out. Guess it's all up to you and how you are going to use boat.


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## PSG-1 (Jul 20, 2012)

It's definitely a good thing, for numerous reasons. Flotation, first and foremost.

It provides rigidity for thin sheet aluminum floors, dampens vibration and makes for a smoother ride.


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## Buddychrist (Jul 21, 2012)

Why don't we make open cell spray in foam in a vacuum seal bag, technically it would be closed cell for extra flotation. 

Just thinking outside of the box


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## PSG-1 (Jul 21, 2012)

Too much chance of a hole being punched in a bag from vibration and jarring, and once that happens, water infiltrates the foam, and then you've got blocks of heavy, juicy foam in your boat.....you'd be better off with concrete blocks.

So, it's best to stay with closed-cell foam.


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## Buddychrist (Jul 21, 2012)

PSG-1 said:


> Too much chance of a hole being punched in a bag from vibration and jarring, and once that happens, water infiltrates the foam, and then you've got blocks of heavy, juicy foam in your boat.....you'd be better off with concrete blocks.
> 
> So, it's best to stay with closed-cell foam.



You haven't seen my vacuum sealer bags! I'm using a 1/2 horse industrial vacuum sealer and the bags it uses
are extremely thick. I'll post a photo of my vac sealer, when you turn it on the lights in the house dim and it sounds like a small car


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## acabtp (Jul 22, 2012)

Buddychrist said:


> You haven't seen my vacuum sealer bags! I'm using a 1/2 horse industrial vacuum sealer and the bags it uses
> are extremely thick. I'll post a photo of my vac sealer, when you turn it on the lights in the house dim and it sounds like a small car


no matter how thick a bag, i wouldn't trust it against the effects of vibration and time... even if it's extremely thick it still only takes one puncture for it to be ruined. you can poke all sorts of holes in closed cell foam and it will still won't absorb water.


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## bassboy1 (Jul 22, 2012)

Buddychrist said:


> You haven't seen my vacuum sealer bags! I'm using a 1/2 horse industrial vacuum sealer and the bags it uses
> are extremely thick. I'll post a photo of my vac sealer, when you turn it on the lights in the house dim and it sounds like a small car


Why bother with the foam, in that case? Bags of air would actually provide better flotation, as they wouldn't have the weight of the foam counteracting them. I'm not a big proponent of foam (there are better options for water displacement, which is all that is desired) in aluminum boats, but I'm also not real thrilled with the idea of plastic bags providing safe flotation. 

Foam does have the benefit of sound deadening and deck support, however it also is a major cause of corrosion when placed or poured up against aluminum. The important thing to do with foam would be to pour it in blocks, sealed in plastic (you are using the plastic to protect the aluminum, not to protect the foam from water), furred up from the hull with 1/2" plastic of some sort. This allows bilge water to flow where it needs to, and grants the aluminum the airflow that it needs to maintain the correct oxidation level, and as such, remain chemically stable.


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## Buddychrist (Jul 22, 2012)

The reason I say bagging the foam instead of just using bags of air is that there needs to be weight somewhere otherwise how are you planning on keeping airbags held in on an open deck Jon?

Personally I am not planning on installing any more foam in my boat. I would go with closed cell foam if i was going to do it at all but I was just thinking outside of the box


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## PSG-1 (Jul 22, 2012)

Buddychrist said:


> You haven't seen my vacuum sealer bags! I'm using a 1/2 horse industrial vacuum sealer and the bags it uses
> are extremely thick. I'll post a photo of my vac sealer, when you turn it on the lights in the house dim and it sounds like a small car





Sounds like an over-amperage condition an a circuit to me, if it's dimming the lights in the house. That could be a hazardous condition. Make sure to plug into a 20 amp receptacle, or at least into a 15 amp with nothing else on that circuit.


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## PSG-1 (Jul 22, 2012)

bassboy1 said:


> The important thing to do with foam would be to pour it in blocks, sealed in plastic (you are using the plastic to protect the aluminum, not to protect the foam from water), furred up from the hull with 1/2" plastic of some sort. This allows bilge water to flow where it needs to, and grants the aluminum the airflow that it needs to maintain the correct oxidation level, and as such, remain chemically stable.



Amen to that!! This is why I prefer to use foam board, because, unlike poured-in factory foam, the board allows water to flow underneath, through the gutter system of the boat. Factory foam always seems to be clogged in the gutters (anyone that doubts that...dismantle a few factory boats, and you'll see what I mean) Not only does this provide poor drainage, and not only can the foam begin to get saturated (even with closed cell foam) it also leads to poultice corrosion between the aluminum and the foam, eventually causing hull damage.


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## PSG-1 (Jul 22, 2012)

Buddychrist said:


> The reason I say bagging the foam instead of just using bags of air is that there needs to be weight somewhere otherwise how are you planning on keeping airbags held in on an open deck Jon?




Not sure, but I don't see how foam-filled bags are going to stay in the boat any better, particularly if you started taking on any water. If foam is not placed under a deck, or behind some kind of structural component, if you ever start sinking, you'll be watching the boat sinking under you, while the foam floats out of the boat, and away from you.


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## MNHunter505 (Jul 22, 2012)

One reason bags of foam would be better than bags of air is bags of foam won't be affected if punctured. 

Side topic...what size plywood is popular for the deck? I have a guy who is selling a 4X8X3/4 marine grade plywood.


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## MNHunter505 (Jul 22, 2012)

MNHunter505 said:


> One reason bags of foam would be better than bags of air is bags of foam won't be affected if punctured.
> 
> Side topic...what size plywood is popular for the deck? I have a guy who is selling a 4X8X3/4 marine grade plywood.



UPDATE to my side topic question...found out that it's too expensive for my budget, will go with the exterior plywood instead and switched this subject over to a pre-existing thread already started by someone else...feel free to jump in on that conversation too! thanks.


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## Backslider (Jul 22, 2012)

I used the blue board insulation. I liked it because its easy to cut and fit to the shape of the boat. The other board insulation probably is good for the same reasons. It has made the deck sturdier and more quiet.


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## MNHunter505 (Jul 23, 2012)

Backslider said:


> I used the blue board insulation. I liked it because its easy to cut and fit to the shape of the boat. The other board insulation probably is good for the same reasons. It has made the deck sturdier and more quiet.



Roger, I have decided to use it as well.


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## Butthead (Jul 23, 2012)

Pool noodles on my boat!


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## MNHunter505 (Jul 23, 2012)

Butthead said:


> Pool noodles on my boat!



aaahh, I like that! Hey, how are you going to attach the wood to your ribs?


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## xbacksideslider (Jul 23, 2012)

For decking, out of concern for weight and because I didn't want the weight of carpet and I wanted a veneer to stain, I decided on 1/2" solid core interior grade. It gets wet occasionally, so what? It dries, isn't sitting in a bilge . . .
Underneath the decking, contact cement out of a spray can sticks sheets of white encapsulated construction foam to sheets of the same stuff, and then to the bottom of the veneer. 

For flooring, I used 1/8" veneer underlayment, backed up by that same white plastic film encapsulated construction foam. Built up slices of sheets of foam under the floor veneer to change the V floor to a flat floor and to support that 1/8" veneer, for a flat light floatation floor.


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## bassboy1 (Jul 23, 2012)

MNHunter505 said:


> One reason bags of foam would be better than bags of air is bags of foam won't be affected if punctured.



Now we're back to square one - the bags get punctured, and the foam gets waterlogged, and you have the concrete blocks that PSG mentioned.  

I'm not trying to be critical here - just furthering an interesting, all the while constructive, debate.


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## PSG-1 (Jul 23, 2012)

Backslider said:


> I used the blue board insulation. I liked it because its easy to cut and fit to the shape of the boat. The other board insulation probably is good for the same reasons. It has made the deck sturdier and more quiet.




Correct. The blue, or the pink foam board is what you should use. 

You can also use the white styrofoam 'bead board' but it is more likely to break apart into those annoying little styrofoam balls, and it's not nearly as tough as the blue or pink foam board. 

Typically, 1 & 1/2" board will fit underneath an inner deck, if the ribs are made of square tubing.

If they are the older, round type of ribs, 3/4" is probably going to be a better fit.


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## MNHunter505 (Jul 24, 2012)

Anybody use 1/2" plywood for decking and have good results or is it standard to use 3/4". trying to save some weight. Thanks.


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## PSG-1 (Jul 24, 2012)

I would think that if you use the correct thickness of foam board, where it's flush with the top of the ribs, you could definitely use 1/2" plywood and it would be adequately supported.

Same as with using 1/16" aluminum sheet for the floor with foam underneath, as opposed to using 1/8" with no foam underneath to support it.


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## MNHunter505 (Jul 24, 2012)

PSG-1 said:


> I would think that if you use the correct thickness of foam board, where it's flush with the top of the ribs, you could definitely use 1/2" plywood and it would be adequately supported.
> 
> Same as with using 1/16" aluminum sheet for the floor with foam underneath, as opposed to using 1/8" with no foam underneath to support it.



Yea, that is what I was thinking! I might have to give that a try...


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## Butthead (Jul 24, 2012)

MNHunter505 said:


> Butthead said:
> 
> 
> > Pool noodles on my boat!
> ...



I just put a few screws through the wood into each rib and did a staggered pattern down the length.

x x x x x
.x x x x
x x x x x
.x x x x
x x x x x

It may have been overkill, but I'd rather over do it then have to fix it later.


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## MNHunter505 (Jul 25, 2012)

Butthead said:


> MNHunter505 said:
> 
> 
> > Butthead said:
> ...



I read a post by someone who put industrial velcro on the top of the ribs and then set his floor down. That way it can be removed easily. I am thinking of giving it a try.


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## Butthead (Jul 25, 2012)

MNHunter505 said:


> I read a post by someone who put industrial velcro on the top of the ribs and then set his floor down. That way it can be removed easily. I am thinking of giving it a try.



That's definitely an option if you want it easily removable. I think the regular black adhesive backed Velcro is rated at 2lbs of holding force per inch so I wouldn't recommend putting it all the way across and on every rib or else it could be a little challenging to pull it up when needed.


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## MNHunter505 (Jul 25, 2012)

Butthead said:


> MNHunter505 said:
> 
> 
> > I read a post by someone who put industrial velcro on the top of the ribs and then set his floor down. That way it can be removed easily. I am thinking of giving it a try.
> ...




Very true, I will have to stagger 3in lengths across the ribs. Here is a question, how are guys securing there alum framing to the boat? I know they pop rivot the pieces into the belly/bottom ribs but what about the sides of the framing that touch the inside of the boat walls...?
https://www.tinboats.net/forum/viewtopic.php?f=21&t=13160&start=45


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## xbacksideslider (Jul 25, 2012)

MNHunter505 said:


> Anybody use 1/2" plywood for decking and have good results or is it standard to use 3/4". trying to save some weight. Thanks.



I used 1/2" for my casting deck and 1/8" over styrofoam board for my floors.

As for the 1/8", I punched a hole in it with the gear shift lever when I dropped the outboard down onto it too quickly.


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## MNHunter505 (Jul 26, 2012)

xbacksideslider said:


> MNHunter505 said:
> 
> 
> > Anybody use 1/2" plywood for decking and have good results or is it standard to use 3/4". trying to save some weight. Thanks.
> ...



Wow, that stinks! 1/8" seems a little thin for a deck...I think I will stick with 1/2" on all flooring.


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## xbacksideslider (Jul 27, 2012)

Yep, dented/punched it, but it's 30 or 40 pounds lighter than 1/2" and the floor pieces are one piece, easily removable to a clean and dry inner hull.


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