# Aluminum floor thickness reccomendations



## daschmetterling (Jan 25, 2016)

We are going to use aluminum for our decking and wanted to get some reccomendations for thickness. The floor will go over 1 1/4" × 1/8" aluminum angle framing set 12" on center. I was leaning toward using 1/8" aluminum sheet. Would 0.090 be enough? I like the cost of 0.090 more than 1/8"! Here is a picture of the framing- it isn't complete, we are going to add two vertical supports to each "joist".
Thanks in advance for the advice!


Sent from my SM-N900V using Tapatalk


----------



## CedarRiverScooter (Jan 25, 2016)

.09 is plenty strong, IMO.

That will be one stiff boat!


----------



## daschmetterling (Jan 25, 2016)

Thanks CedarRiverScooter, I like that answer! Any thinner or would 0.090 be your reccomendation?

Sent from my SM-N900V using Tapatalk


----------



## AllOutdoors (Jan 26, 2016)

Go with .90 and be done. It's thin and light and you have plenty of bracing. It may flex some between the bracing but will be there for the long haul.


----------



## daschmetterling (Jan 26, 2016)

AllOutdoors said:


> Go with .90 and be done. It's thin and light and you have plenty of bracing. It may flex some between the bracing but will be there for the long haul.


Thanks AllOutdoors!

Sent from my SM-N900V using Tapatalk


----------



## RiverBottomOutdoors (Jan 26, 2016)

.090 will flex between the joists. Might feel a little mushy.


----------



## daschmetterling (Jan 26, 2016)

RiverBottomOutdoors said:


> .090 will flex between the joists. Might feel a little mushy.


RiverBottomOutdoors- thanks for the reply, unfortunately that is what I was afraid of. I definitely don't want to do the floor twice. Maybe 1/8" is the way to go. 
Hmmm, now we have conflicting recommendations.
Keep the comments coming- has anyone used 0.090 and regretted it?

Sent from my SM-T350 using Tapatalk


----------



## RiverBottomOutdoors (Jan 26, 2016)

How far apart are the joists?


----------



## daschmetterling (Jan 26, 2016)

RiverBottomOutdoors said:


> How far apart are the joists?


12" on center.

Sent from my SM-N900V using Tapatalk


----------



## RiverBottomOutdoors (Jan 26, 2016)

What's your plan for attaching the sheeting to the joists?


----------



## daschmetterling (Jan 26, 2016)

Rivets, I don't know the spacing. Any suggestions?

Sent from my SM-N900V using Tapatalk


----------



## Stumpalump (Jan 26, 2016)

If your going to cover it with carpet the small dings you get with .090 won't show. If it's going to be painted and worked real hard the 1/8 will look nicer. I like light weight and cringe when I see the heavy wood decks and flooring used here. I'd go .090 then paint it or vinyl it and live with a few dingers. I built a section of wood floor yesterday. 3/8" is all I ever used in 40 years and I remind people not to jump or come down hard on the floor. Never have had a problem and the flex on a hard wake hit is nicer on your body, boat and gear.


----------



## daschmetterling (Jan 26, 2016)

Stumpalump said:


> If your going to cover it with carpet the small dings you get with .090 won't show. If it's going to be painted and worked real hard the 1/8 will look nicer. I like light weight and cringe when I see the heavy wood decks and flooring used here. I'd go .090 then paint it or vinyl it and live with a few dingers. I built a section of wood floor yesterday. 3/8" is all I ever used in 40 years and I remind people not to jump or come down hard on the floor. Never have had a problem and the flex on a hard wake hit is nicer on your body, boat and gear.


Thanks Stumpalump! I am not worried about dings and cosmetic issues, I am mainly concerned about flexing and "soft" feel. 
These comments and feedback are great- thanks everyone, keep the opinions coming!

Sent from my SM-N900V using Tapatalk


----------



## RiverBottomOutdoors (Jan 26, 2016)

If you rivet it to each joist that will take some of the flex out of it. Rivets about 6 to 8 inches apart. Take everyone's opinions into consideration. We're all making educated guesses, but they are guesses nonetheless. Sometimes you don't know how it's going to turn out until it's done.

I used .090 on a previous boat to skin a deck and floor. I basing my guess on that experience. Good luck. Keep us posted. I like the wood free builds.


----------



## daschmetterling (Jan 26, 2016)

RiverBottomOutdoors said:


> If you rivet it to each joist that will take some of the flex out of it. Rivets about 6 to 8 inches apart. Take everyone's opinions into consideration. We're all making educated guesses, but they are guesses nonetheless. Sometimes you don't know how it's going to turn out until it's done.
> 
> I used .090 on a previous boat to skin a deck and floor. I basing my guess on that experience. Good luck. Keep us posted. I like the wood free builds.


These are great comments! I appreciate everyone's ideas, and I like that they are coming from experience. 
Yes, I like the idea of wood free, too. We are trying to build something simple, durable, easy to clean, low maintinence, and hopefully not too expensive!
Thanks again



Sent from my SM-N900V using Tapatalk


----------



## lckstckn2smknbrls (Jan 26, 2016)

Have you thought about putting some aluminum angle running front to rear of the boat tying all the joist together and giving support to the floor in between the joist. Are you going to put foam under the floor?


----------



## daschmetterling (Jan 26, 2016)

Yes, we have thought about that, but haven't decided yet. Once we get the vertical supports in, we can check stability. Tying all those joists together woild definitly stiffen it up, good point. Maybe doing that and then using 0.090 would be enough? 
We are planning on using pour foam and leaving an open channel in the middle for drainage and to run pvc conduit. 

Sent from my SM-N900V using Tapatalk


----------



## CedarRiverScooter (Jan 26, 2016)

Doesn't the floor sheet tie the tops of the joists together? Maybe just tie the ends of the floor to something solid.

Any foam going under the floor? That can take some spring out of it too.


----------



## daschmetterling (Jan 26, 2016)

CedarRiverScooter said:


> Doesn't the floor sheet tie the tops of the joists together? Maybe just tie the ends of the floor to something solid.
> 
> Any foam going under the floor? That can take some spring out of it too.


Good point about the floor tying the joists together. Yes, we will be pouring in foam.
Thanks again!

Sent from my SM-N900V using Tapatalk


----------



## lckstckn2smknbrls (Jan 26, 2016)

daschmetterling said:


> CedarRiverScooter said:
> 
> 
> > Doesn't the floor sheet tie the tops of the joists together? Maybe just tie the ends of the floor to something solid.
> ...


I was thinking the aluminum angle in between each joist will keep the aluminum floor from sagging between the joist.


----------



## wmk0002 (Jan 27, 2016)

What is the width going to be and will the floor be purely fastened to the lateral angles? 

I do aerospace stress analysis and have a program at work I can use to model a section of the floor and get stresses and max deflections. It will act under the assumption that the lateral angles it attaches to are completely rigid and I will have to make an assumption on the load to give it. I would imagine a single 300 lb load distributed over a small area, like 4" x 4" at the very center, would be good enough. I could get results from that and then model in some additional bow/stern angles and see how much it drops.


----------



## daschmetterling (Jan 27, 2016)

wmk0002 said:


> What is the width going to be and will the floor be purely fastened to the lateral angles?
> 
> I do aerospace stress analysis and have a program at work I can use to model a section of the floor and get stresses and max deflections. It will act under the assumption that the lateral angles it attaches to are completely rigid and I will have to make an assumption on the load to give it. I would imagine a single 300 lb load distributed over a small area, like 4" x 4" at the very center, would be good enough. I could get results from that and then model in some additional bow/stern angles and see how much it drops.


Wow - thank you! What a tremendous offer! 
The hull is tapered, so the width is between 55" - 45". Mostly right around 55"
Yes, we were only going to fasten (rivet) the floor to the joists every 8" or so.
Thanks again for sharing your time and expertise! 

Sent from my SM-N900V using Tapatalk


----------



## wmk0002 (Jan 27, 2016)

No problem. It isn't very difficult plus it will be a good exercise for me as I soon plan on buying a new open floor plan 1648 flat bottom and will be installing my own floor down on it's ribs. I will probably have time to do it tonight so hopefully I can have some results for you tomorrow morning.


----------



## daschmetterling (Jan 27, 2016)

wmk0002 said:


> No problem. It isn't very difficult plus it will be a good exercise for me as I soon plan on buying a new open floor plan 1648 flat bottom and will be installing my own floor down on it's ribs. I will probably have time to do it tonight so hopefully I can have some results for you tomorrow morning.


Thank you again, and there is really no rush. I am glad this will be a good exercise for your boat build! I look forward to seeing what you come up with, and I suspect many readers on tin boats will be interested, too!

Sent from my SM-N900V using Tapatalk


----------



## wmk0002 (Jan 28, 2016)

Wanted to say I didn't have a chance to do it last night. I should tonight though.


----------



## daschmetterling (Jan 28, 2016)

wmk0002 said:


> Wanted to say I didn't have a chance to do it last night. I should tonight though.


No problem, it is not a rush, and I am just grateful you are going to do it! It is great to have data to work with.

Sent from my SM-N900V using Tapatalk


----------



## wmk0002 (Jan 29, 2016)

Alright, I finally have some results for you. I assumed 6061-T6 aluminum. I'm not sure what specific alloys people commonly use for home boat mods based on pricing and availability so I just went with the aerospace standard. However, it doesn't make a ton of difference. The 2000 through 7000 series alloys all have virtually the same stiffnesses which is what drives deflection. They do have different strengths and 6061 is actually one of the weaker ones we commonly use, but it is still plenty strong for this type of application.

For the model, I created a simply supported plate model that was 54" x 12" based on your dimensions. The 54" edges were simply supported (essentially models them as just resting on your angles and assumes angles are super stiff or "rock solid"). The 12" edges were left free. I wasn't really sure what the best load to apply was but went for a totally unrealistic point load of 300 lb at the very center. Then tried it with a 300 lb load at the center but distributed evenly over a 4" x 4" section. I ran this configuration with both 0.090" and 0.125" sheet thickness.

I then added some bow to stern running supports/stringers. I added three rows evenly spaced at 13.5". I applied the same loads as above but this time at the mid-point between the center stringer and the next one over. I ran it it with both thicknesses.

So, for some numbers...
For the first configuration without the stringers I got deflections of: 1.10" for the point load and 0.97" for the distributed load at 0.090" thick; and 0.41" for the point load and 0.36" for the distributed load at 0.125" thick.
For the configuration with stringers: 0.69" for the point load and 0.58" for the distributed load at 0.090" thick; and 0.26" for the point load and 0.21" for the distributed load at 0.125" thick.

The thing I failed to do was apply a load between the edge and the first stringer for configuration two as that would be critical since it loses some support there since I left the sides free. I know it will be a little worse than what I got. 

It's kind of hard for me to make any kind of recommendation based on these results since I am not really familiar with how supportive the foam you plan on adding will be. It has the potential to help a lot. However, assuming the foam does provide somewhat significant support, I would think adding in 3 or 4 rows of stringers down the center and one down each side near the edge and using a 0.090" sheet would be more than fine. By the same token, going without stringers and using 0.125" over foam will probably be comparable. Keep in mind 0.125" AL weighs about 40% more than 0.090" so weight may be a wash either way.


----------



## wmk0002 (Jan 29, 2016)

FWIW, last month I emailed and asked Alumacraft what gauge they use for the flooring in their MV1648 NCS and was told 0.080". Those models also have factory foam under the floor. So maybe someone with that model can chime in on how sturdy their floor feels and can give you the spacing of their ribs for comparison. 

Also, this is the foam I have seen mentioned on here and that I have been researching for use on my future boat. https://www.uscomposites.com/foam.html You may be able to contact them and get a better idea of how structurally supportive it is. Thinking back to some of the poured foam I have encountered under decks on other boats, I can believe how it can provide a lot of support. 

Using the Alumacraft info from above, I'm really leaning towards the mindset that 0.090" sheet with no stringers would be fine if the right foam was used AND done so that it is near flush with the installed floor/deck. 

Sorry I can't be of more help.


----------



## daschmetterling (Jan 29, 2016)

Can't be of more help?! Are you kidding me? This is incredible information! Thank you so much. It will probably take me the weekend to digest it all! I'll keep everyone posted on what we decide, and how it works.
Thanks again!

Sent from my SM-T350 using Tapatalk


----------



## Fishfreek (Jan 29, 2016)

I just measured the ribs on my MV 1648 NCS. They are closer together in the front at 9" on center and then spread to 13" on center towards the back. I am 270lb and with the factory foam under the floor I feel almost no flex. Of course I get a bit but it is not something I notice as I walk around. I also measured the floor thicknes and came up with .085 but on a set of non calibrated calipers. Hope this helps.


----------



## daschmetterling (Jan 29, 2016)

Fishfreek said:


> I just measured the ribs on my MV 1648 NCS. They are closer together in the front at 9" on center and then spread to 13" on center towards the back. I am 270lb and with the factory foam under the floor I feel almost no flex. Of course I get a bit but it is not something I notice as I walk around. I also measured the floor thicknes and came up with .085 but on a set of non calibrated calipers. Hope this helps.


This is incredible- thanks so much for measuring the spacing and floor thickness and chiming in! It is wonderful to have all these data to help with this decision! I know this thread will be useful for others, too. Thanks again!

Sent from my SM-T350 using Tapatalk


----------



## uncndl1 (Jan 31, 2016)

Great progress so far, thank you for sharing. Have you decided which pound of the pour urethane foam you are going to use? i.e. 2#, 3#, or 4#. Best regards.


----------



## daschmetterling (Jan 31, 2016)

uncndl1 said:


> Great progress so far, thank you for sharing. Have you decided which pound of the pour urethane foam you are going to use? i.e. 2#, 3#, or 4#. Best regards.


We haven't ordered it yet, but we are planning to go with the 2#, based on comments here. 

Sent from my SM-N900V using Tapatalk


----------



## daschmetterling (Jan 31, 2016)

uncndl1 said:


> Great progress so far, thank you for sharing. Have you decided which pound of the pour urethane foam you are going to use? i.e. 2#, 3#, or 4#. Best regards.


Thank you! This group has been such a great resource!


daschmetterling said:


> uncndl1 said:
> 
> 
> > Great progress so far, thank you for sharing. Have you decided which pound of the pour urethane foam you are going to use? i.e. 2#, 3#, or 4#. Best regards.
> ...




Sent from my SM-T350 using Tapatalk


----------



## riverrat717 (Feb 1, 2016)

Be careful foaming. High expansion rate with that foam. Far as a drain channel goes...you may want to use a pipe or conduit to act as a mold cavity to run to your drain plug. ANYWHERE you don't want foam, use lots of car wax on that surface and the foam won't stick.


----------



## daschmetterling (Feb 1, 2016)

riverrat717 said:


> Be careful foaming. High expansion rate with that foam. Far as a drain channel goes...you may want to use a pipe or conduit to act as a mold cavity to run to your drain plug. ANYWHERE you don't want foam, use lots of car wax on that surface and the foam won't stick.


Great advice, thank you!

Sent from my SM-N900V using Tapatalk


----------



## RiverBottomOutdoors (Feb 1, 2016)

Putting in any storage?


----------



## daschmetterling (Feb 1, 2016)

RiverBottomOutdoors said:


> Putting in any storage?


We are going to put in storage under an elevated deck on the bow. 

Sent from my SM-N900V using Tapatalk


----------



## wmk0002 (Feb 1, 2016)

riverrat717 said:


> Be careful foaming. High expansion rate with that foam. Far as a drain channel goes...you may want to use a pipe or conduit to act as a mold cavity to run to your drain plug. ANYWHERE you don't want foam, use lots of car wax on that surface and the foam won't stick.



Don't take this to the bank, but I think I have seen where a drop tarp, like for painting, was used to line the inside. Supposedly wax on top of it works well.


----------



## daschmetterling (Feb 1, 2016)

wmk0002 said:


> riverrat717 said:
> 
> 
> > Be careful foaming. High expansion rate with that foam. Far as a drain channel goes...you may want to use a pipe or conduit to act as a mold cavity to run to your drain plug. ANYWHERE you don't want foam, use lots of car wax on that surface and the foam won't stick.
> ...


Good to know- i'll look into it. Thank you!

Sent from my SM-N900V using Tapatalk


----------



## Shoedawg (Feb 12, 2016)

daschmetterling said:


> wmk0002 said:
> 
> 
> > riverrat717 said:
> ...



I purchased some 2lb pour foam from US Composites a few months ago back (have yet to get into the pouring stage). For draining issues, underneath your floor, you can try using some aluminum flashing. They are sold in rolls of various feet and widths and very affordable.

Its pretty easy to bend, shape and cut too. Basically you would shape a conduit to run along the bottom of your boat, creating a drainage channel for water/clean up. See my second grade drawing below to understand what mean:



To keep the foam level with your floor, I would first add some plastic trash bags to the *bottom *of your floor first (tape it). From there, pour the foam over your choice of drainage/bottom side of boat (in my case, the alum. flashing) and *QUICKLY* place your floor over the foam (plastic bags down) before it starts to expand. Get some weight on the top of the floor and keep even pressure on it. Let the foam do its work, while watching for any rises/shift it may produce in the floor while it is expanding.

After the foam has cured/stopped expanding, then you can remove your floor and take off the plastic trash bags. The bags (per US Composites) shouldn't stick to the foam, thus given you a pretty even foam platform that will now support your floor and you have drainage as well.

You can then, mount your floor. I wouldn't use PVC piping for draining. The diameters (IMO) of most large piping just don't do that good of a job. Plus sticks, leaves and other crap can get stuck in them, impeding good drainage.

I am in the same boat (haha) as you are with floor thickness. I am leaning towards .090 myself. It seems most guys on this forum use that size for their floors.


----------



## richg99 (Feb 13, 2016)

I filled the two inch cavity between my "joists" with loose cut blue foam sheets. It added flotation and also firmed up the aluminum top sheet.

I cut the pieces of foam skinnier than the openings. My thought was to let water freely flow in and out. I didn't want to trap water. 

I did add a vinyl covered piece in 1/4 inch ext. Plywood on top. 

richg99


----------



## daschmetterling (Feb 13, 2016)

Thanks everyone for your comments and suggestions (and even aerospace engineer calculations!).
Originally I was trying to decide between 0.90 and 0.125 aluminum sheet- and it seems like 0.090 is the way to go there. But now we are leaning toward using aluminum diamond plate, and this comes in 0.100 or 0.080 thinknesses! More to decide! Weight is pretty negligible between the two, about 16 lbs difference in a 60" x120" sheet. But 0.01 is about $50 more expensive than 0.080. In the whole scheme of things, kind of a wash. The reason we are thinking of diamond floor plate is the traction and maintenance idea. We won't need to add traction nor paint, and we figure the aluminum will get dull and dirty pretty quickly. For work we use unpainted aluminum boats all the time, so it seems normal to us!
We can always paint it it we want or need. We are trying to build a simple, cheap, durable low maintenance fishing boat, because we will use it hard, and probably not maintain it as well as we should!

Sent from my SM-N900V using Tapatalk


----------



## daschmetterling (Mar 7, 2016)

After a lot of debate, we ended up going with rigid insulation for flotation and 0.100 aluminum floor plate. 

View attachment 1

View attachment 2

View attachment 3

After riveting the floor every 8", it is really solid. If you stand between the joints it does flex, but not too the point of feeling spongy. I am glad we went with the 0.100.
You can read more details about the floor and the boat on my build thread.
Thanks everyone for your help and suggestions!

Sent from my SM-N900V using Tapatalk


----------



## richg99 (Mar 7, 2016)

Looks good. I put the same blue foam below decks on mine.


richg99


----------



## daschmetterling (Mar 7, 2016)

richg99 said:


> Looks good. I put the same blue foam below decks on mine.
> 
> 
> richg99


Thank you! We ended up getting a lot of foam in there, more than we calculated we needed to float the weight of the boat and motor. Hopefully, we will never need it!

Sent from my SM-N900V using Tapatalk


----------



## surfman (Mar 7, 2016)

daschmetterling said:


> After a lot of debate, we ended up going with rigid insulation for flotation and 0.100 aluminum floor plate.
> 
> View attachment 1
> 
> ...



You will be able to float a tank with all that foam.


----------



## richg99 (Mar 7, 2016)

Unless/Until the boat fills up with water, that foam isn't doing a thing except adding some stiffness to the deck.

BUT...when you do take a big wave over the side, you will be very happy that you put it in. Ha Ha regards, richg99


----------



## daschmetterling (Mar 26, 2016)

Here are some more pictures of the flooring installed, 0.100 aluminum riveted every 8". I am glad we went with 0.100, I don’t think I would go less than 0.090. View attachment 1
View attachment 2


Sent from my SM-N900V using Tapatalk


----------

