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  #1  
Old 04-20-2007, 02:04 PM
NanookofNJ NanookofNJ is offline
 
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Replacing Floor on 17' Aluminum runabout

Hello. First time poster. Thanks for any info in advance.

I am in the process of replacing the front platform floor on my 17 aluminum Sea Nymph. The old floor appears to be 1/2 or 3/4 inch plywood with no resin or epoxy and was finished with a rubber backed marine carpet. Much of the wood is now rotten, but I was able to take out the old carpet to use as a template for the new flooring I'll be putting in this weekend.

A few questions:

1. Type of plywood. What is the best kind of plywood for this application. I was going to go with exterior grade (X) at either 3/4" or 1/2"(if it's strudy enough to hold a person up there). I've heard conflicting advice. Some say I could go with exterior, others swear by marine grade at over $100 a sheet, and there's a lot of conflicting advice about pressure treated in regards to it eating aluminum, warping, and a long drying time. Just wanted to see which would be my best, and most cost effective route.

2. It was also suggested that I apply either an epoxy or polyesther resin to the exterior plywood before screwing it down to the ribs of the boat. Which of these, epoxy or polyesther resin would be best for a plywood application? Is there an "all in one" I could buy that would allow me to roll or brush it onto the ply? Would I need hardeners or activiation chemicals for either of these?

Many thanks. I hope to get the wood cut tomorrow and start on the resin/epoxy soon after. Your help is greatly appreciated.

Nanook
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  #2  
Old 04-20-2007, 02:48 PM
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marshmat marshmat is offline
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Hi Nanook (doesn't that mean 'polar bear'?),
AC exterior grade should be fine for your application. Marine grades generally have higher grade veneers in the middle, and sometimes stronger glues, but for your job I don't think it's worth the extra cash. A coat of epoxy (paying special attention to the edges) would go a long way towards preventing rot. (AC exterior is preferred over AB; the former has the worst veneer on the outside where it can be easily sealed; the latter has the worst veneers in the middle.) West System epoxy is a good choice for the beginner, it's very easy to use if you buy the cheap pumps that come with the kit, and follow the directions.
I wouldn't use pressure-treated for this. Modern pressure treating chemicals are quite effective against rot; unfortunately they are horrendously destructive to aluminum.
And this is a boat- it's a deck, not a floor
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Old 04-20-2007, 02:53 PM
NanookofNJ NanookofNJ is offline
 
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Thanks so much Matt!

Unfortunatley, the only place that sells any kind of fiberglass material within an hour of me is selling a polyesther resin in gallons(I'm guessing with a catalyst??). Would this resin be comprable to the West System epoxy you mentioned? Or should I be looking at epoxy only? Would I need a hardener for that? And is the application doable with brush or roller?

Thanks again, have a nice weekend!

Nanook
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Old 04-20-2007, 03:02 PM
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marshmat marshmat is offline
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Oh, poly will work. It just isn't as strong, waterproof, or easy to use as epoxy.
The catalyst for polyester is methyl-ethyl-ketone peroxide. It always comes with the resin; the mixing ratio is usually on the order of a few hundred to one. This makes it really, really important to be thorough with the mixing.
For coating a plywood sheet you'll probably only end up buying a litre or so. The stuff keeps for a while, if you end up doing fibreglass projects later. A cheap, crappy plastic-bristle paint brush works for applying it; so does a plastic spreader. Whatever tool you use will be toast after one use. Acetone is needed for cleanup.
You might want to consider laminating one layer of fibreglass cloth on each side of the wood, if you want a really permanent solution.
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Old 04-20-2007, 03:13 PM
NanookofNJ NanookofNJ is offline
 
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Thanks again! Turns out the local boat place carrys West System Epoxy and hardener as well and is less then 20 miles from me. Unfortunately, it's $85 a gallon for the epoxy and $30 for a quart of the hardener. I'm only doing a 4' x 5' piece, you think I could go with less then a gallon of the epoxy for this application?
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Old 04-20-2007, 03:50 PM
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marshmat marshmat is offline
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You'll only use a few cups on this project. But the stuff is incredibly handy to have around, probably one of the most versatile materials you can have on hand in a shop.
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Old 04-21-2007, 11:58 PM
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alan white alan white is offline
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I guess this is a renegade answer, but I am going to guess that the reason your plywood panel failed to begin with has to do with the method of capping off a potentially wet cavity with relatively unprotected wood and then gluing or stapling a piece of carpet to it. Yer fighting city hall for no good reason.
What about taking a paltry third of your budget and doing something shipshape like a red cedar or fir deck with a 3/16"" space between 1x6 boards? Varnished mahogany sounds outragious, but a 3x5 ft area of Spanish cedar would be maybe $100 for stock and fasteners, and another $17.00 for a pint of varnish. Even Honduras would come in under $200.
Cleat them together underneath and finish with a quart of Deks Olje or something if speed is an issue.
I like solutions like this. Production boats are built as you see them because they can't afford real wood craftsmen on their assembly line. That's all.
To duplicate what they did is only copying a process meant for assembly lines and so it is material intensive at best and inferior at worst.
You are the labor, so why not do something labor intensive and cheap on materials? In your circumstance, lacking the CNC ply cutter and a massive roll of carpet, template, glue rollers, spray rigs, and jigs, you'll probably spend more time matching the original construction anyway.
Which would be cheaper, look better, last longer, feel better underfoot, and give you the greatest sense of accomplishment? Which job would have made you choose one boat over anpther?

Alan
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Old 04-22-2007, 03:40 PM
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PAR PAR is offline
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Most of the stuff has been covered here. Epoxy coated plywood will tolerate much more abuse and resist moisture ingress better then anything else.

That understood, you're likely much better off using a more traditional method, such as Alan has mentioned. I like cedar or pitch pine (unless you can afford teak) for these types of floor board. I'd use less wide pieces, so cupping and checking is less an issue, say 3" max width if you're using one by stock (measures ~3/4" on edge). Both cedar and pitch pine age beautifully, can accept oil or harder finishes (varnish or polyurethane), are lighter then plywood, provide good under foot traction (the whole point) and looks a bunch better then indoor/outdoor carpet, plus will not rot out whatever the carpet is applied to.

If you design the floor boards in a clever way, so they can be removed, you can use this space as stowage and also remove them to keep the belly of the beast clean. I think you enjoy the look and use of "slat" style of floor boards, much more then a generic hunk of Astroturf coated plywood.

You could just by a few 2 x 4's and cut the edges off in 3/4" thicknesses. This gives a thinner width board (so you'll need a few more), but it's the cheapest way to get good looking quarter sawn lumber for floor slats. A few 8' - 2" x 4"s will likely get you'll little project done, which is darned economical.
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Old 04-22-2007, 06:41 PM
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alan white alan white is offline
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Going on...
Concurring (strongly) here with the narrower (3") boards and suggesting fir 4x4 ripped to get 3/4" quarter-sawn boards 3 1/2" wide (4 per 4x4 used, and maybe 3 1/4" width after jointing and resawing. I went through a stack at Home Depot to find a 4x4 for a mast extension. Found a beauty with the exact same annular width as the 30 yr old original. Seek and ye shall find.
How I would do it...
Two #8-1 3/4" flathead stainless screws per board into PAINTED pressure treated 2x4s (under-cleats) ripped to 1 1/2" x 1 11/16".
Was it $11.00 I paid for the 4x4x8? If so, 3x5 ft will use 2-30" x 36" panels so the end scrap of the 4x4 will be only about 5", and the whole thing will use 24 boards 30" long. That's two 4x4x8s, $22.00. Paint and varnish and screws and 2x4, $50.00, total of $72.00 give or take. That's 8-10 coats of varnish, PT wood sealed, done.
Babe magnet. They go for the real woody boats.

In fact, paint the underside of the boards too, all before assembly, and a quart of Ben Moore polyurethane deck paint in two coats, no primer, after acetoning the PT (which should be the dry pieces they used for stickers, not the wet ones they sell---- grab a few---- not at Home Depot--- they will get confused and frightened).
Lifting holes (half a circle out of two adjacent boards)are nice, and maybe 3/16" rope hinges (black braided nylon, knotted underneath), and two pieces instead of one for lighter lifting and less moving of stuff, and a place to put the hinges. Oh yes, and let in the rope hinge channels so the rope lies flush like staples.




A.
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  #10  
Old 04-23-2007, 04:16 PM
NanookofNJ NanookofNJ is offline
 
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Thanks for the info guys. I applied the 1st and 2nd coats of poly to the newly cut plywood yesterday. The slat tip is great and all, but this is a fishing boat with pedestal, livewell, battery, and dry storage compartments up there. So function over beauty works for me.
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  #11  
Old 04-23-2007, 05:02 PM
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alan white alan white is offline
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But why did it rot?
What about the other panels?
Is the design flawed?

Alan
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