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PostPosted: 09 Aug 2016, 19:08 

Joined: 24 Jun 2013, 09:37
Posts: 84
Hi

I did a search and didn't find a thread around this topic. If I'm wrong please point me in the right direction.

I have to replace both casting decks on my boat. Right now they are made using 3/4" home plywood. They are pretty soggy and soft.

My plan was to buy a sheet of 1/4" plywood or hardboard and after removing existing decks use them to create a template.

This would allow me to play around with the location for the lids for the under deck lockers.

Then using the template I was going to use 3/8" aluminum to create the new decks. I still need to figure out the weight comparison between a sheet of 3/8' aluminum vs. 3/4" marine plywood.

Anyone have any thoughts on the matter?


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PostPosted: 09 Aug 2016, 19:47 
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Joined: 29 Dec 2013, 16:46
Posts: 95
Location: York pa
Making templets is a great way to lay your boat out. I have used luan to do some things in my boat. It's light and cheap compared to messing up a sheet of aluminum. 3/8" aluminum is way over kill. If u have some structure under your deck now around 16" or less spacing 1/8" will be fine.

There is one cover on my boat right now about 24"x30" only bows slightly with me standing on.


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PostPosted: 09 Aug 2016, 21:23 

Joined: 06 Jan 2015, 18:39
Posts: 269
I used 9/16 ply for the first time creating my deck, and now will be replacing shortly after with 1/8 (.125) aluminum. I hated that it will get soggy...and have a different idea for the plan of the boat. Overall, it is a choice of yours, but a 1/8 sheet of aluminum is darn near the same weight as a 5/8 sheet of ply. (both are roughly 56-58 lbs) The reason for my doing it again in aluminum is it will be used as a duck boat for many years. and I don't want to have to continue to redo it. Also, 1/8 1x1 aluminum angle is cheap, solid, and takes up much less space for bracing than the comparable 2x2 I used for the wood deck. with my compartments i have on my boat, it is quite annoying to have so little space due to large braces.

It's all personal preference, but the aluminum 4x8 sheet, 50ft of angle, and rivets, will cost much less than the 9/16 ply 4x8 sheet, screws, and sealant did. Also, it will take less time to construct!

I was roughly 350 bucks into my wooden deck, and i have 150 into this aluminum one.


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PostPosted: 09 Aug 2016, 23:09 

Joined: 20 Jul 2014, 22:11
Posts: 88
Location: Oregon
3/8 is way over kill. I did aluminum compared to wood, I like the one and done fact of using aluminum. I used 1/16 on my floors, and 1/8 on a deck on the front.


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PostPosted: 10 Aug 2016, 08:58 
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Joined: 15 Mar 2014, 16:57
Posts: 1729
Location: CT
I'm sure it's talked all over on here...probably not too many dedicated threads to the comparison. I think comparing aluminum to plywood the main difference comes down to permanence of the aluminum vs. the plywood. 1/2" plywood weighs (~.75lbs per 1/4" sq. ft.) roughly the same as .100 aluminum (1.438lbs per sq.ft. typical for flooring/decking). You can get a little skimpy on the gauge of the aluminum if you've got it backed with foam & shave a little weight, but nothing that's going to make a major difference.

http://www.armstrongmetalcrafts.com/Ref ... eight.aspx

Now...your framing to support the deck is another story entirely - there you've got a huge weight savings in using 1/8" x 1" x 1" aluminum angle (0.28lbs/linear foot) vs. 2x4's (1.67lbs/ft) or 2x3's (1.25lbs/ft) and the savings only goes up from there as the aluminum will not take on water over time. Kills me to see people add decking with a lumber yard worth of weight beneath it in what is supposed to be a lightweight boat.

https://www.onlinemetals.com/merchant.c ... top_cat=60
http://www.osbornelumber.net/weights--measures.html

If you're looking to really keep the weight down you need to go with FRP (fiber reinforced plastic). Weighs roughly 1lb per sq. ft. but you need to be careful to make sure it's got your flotation foam backing it.



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PostPosted: 10 Aug 2016, 21:03 

Joined: 23 Jul 2016, 16:19
Posts: 9
I just finished mine last week using old street signs. Signs were approximately 1/8" thick. I'm 250 and they hold me fine.


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PostPosted: 10 Aug 2016, 21:44 

Joined: 06 Jan 2015, 18:39
Posts: 269
hitower wrote:
I just finished mine last week using old street signs. Signs were approximately 1/8" thick. I'm 250 and they hold me fine.

What is the dimension of the hatch. I'm using 125 aluminum soon and am not sure on the distance I need between framing to avoid stressing it too much!

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PostPosted: 11 Aug 2016, 08:49 
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Joined: 15 Mar 2014, 16:57
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Location: CT
Where do you guys find street signs? You can't get them from the DOT in CT. Or don't you want to answer on a public forum? :roll: :-



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For Sale - Custom Hand Tied Jigs, Bladed Jigs, Custom Rods

2002 Alumacraft 1436LT w/ 1984 Mariner Tiller Converted to Remote & 55# Minn Kota Terrova 12v (removable)

1985 Bass Tracker III - restoration posting coming soon w/ 1988 Mercury 60hp 2-Stroke & 55# Minn Kota Terrova 12v shared w/ my 14'


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PostPosted: 11 Aug 2016, 11:39 

Joined: 06 Jan 2015, 18:39
Posts: 269
I've got a stack of them I've found at various spots. one property I hunt was an old gravel pit and the owner said I can take anything I find on the land because it's all junk... I found probably 30 different signs all the size of a large stop sign.


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PostPosted: 11 Aug 2016, 15:01 

Joined: 01 Jun 2016, 14:11
Posts: 127
Location: Croom, FL
hitower wrote:
I just finished mine last week using old street signs. Signs were approximately 1/8" thick. I'm 250 and they hold me fine.


Funny!!! I work on the hiways and "come in contact " with alot of "extra" street signs that are sometimes left on the road.

Was just talking to my wife and pointed to a road sign and said "look" she said "what" i said "that aluminum decking we need to purchase is pretty expensive right?" She didnt get it. Lol


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PostPosted: 11 Aug 2016, 20:55 

Joined: 23 Jul 2016, 16:19
Posts: 9
The opening is about 15" wide, just enough to fit my gas tank in there. As soon as I get more fuel line.

I have a recycle center by me that has these periodically, the new signs need a reflective face to be legal. So these show up as they're replaced.

Carpet mostly done now, we're doing rubber mat on the floor.


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PostPosted: 11 Aug 2016, 20:56 

Joined: 23 Jul 2016, 16:19
Posts: 9
Can anyone help me as to why my pics keep being posted upside down???


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PostPosted: 15 Aug 2016, 20:14 
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Joined: 15 Jul 2012, 22:18
Posts: 147
Location: Union, MO.
I've found that if I try to post with my iPhone it will do that. I now download pictures from my phone to the laptop, go into the picture file on the laptop and orient them correctly then post on here from the laptop. May not be the best solution but it works for me.


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PostPosted: 15 Aug 2016, 21:40 

Joined: 05 Oct 2008, 12:14
Posts: 4122
Location: Algonquin Il
onthewater102 wrote:
Where do you guys find street signs? You can't get them from the DOT in CT. Or don't you want to answer on a public forum? :roll: :-

My neighbor is a supervisor at the county hwy dept. When I needed some aluminum to make patches he got me a few signs that had been run over that I could cut up.



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PostPosted: 15 Aug 2016, 22:00 

Joined: 24 May 2015, 23:01
Posts: 102
One thing that hasn't been mentioned here in the comparison between aluminum and plywood, and "...decking with a lumber yard worth of weight beneath it in what is supposed to be a lightweight boat."... Is the flotation of the plywood and the lumber yard worth of weight. While aluminum bracing and support does indeed save weight and space for more flotation which will be required, the specific gravity of wood in water is considerably less than that of aluminum and lessens the need for flotation.

From the Boatbuilder's Handbook put out by the U.S. Coast Guard:

Quote:
Material ------S.G.----factor----weight Cu. Ft.
Aluminum-----2.73----0.63--------170
Yellow Pine---0.55--(–0.81)-------34
Fir Plywood---0.55--(-0.81)------ 34


So, for every square foot of 1/8" aluminum (@ "1.438 # sq.ft.") we need to add .015 cubic foot of flotation to meet requirements.

And, for every square foot of 1/2" plywood (@ 1.269 # sq. ft.) we can remove 0.017 cubic foot of flotation and still meet the requirements.

This is why many boat manufacturers still use plywood decking.

I learned all of this researching for my boat project. Because I asked questions about the new weights of my boat after my modifications, and whether I would be "legal" viewtopic.php?f=21&t=40637#p415433. No one gave an answer, so I started hunting around... Y'all are fantastic! The answers are right here on this site, through links to the U.S.C.G. site in the topic HOW MUCH FOAM DO I NEED? viewtopic.php?f=3&t=25283

Until Jim fixes the link in the HOW MUCH FOAM DO I NEED topic, the correct link to the U.S.C.G. boatbuilders manual is: http://uscgboating.org/regulations/asse ... TATION.pdf


Last edited by oakchas on 16 Aug 2016, 20:16, edited 1 time in total.

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