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What size plywood for floor?

HavAZd

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I got my old fiberglass tanks out and took the old floor out as well. It did not appear all that old but was put down with drywall screws, was not resined, and had mold on it.

So my question/s now...

How thick of plywood should I use for the floor. This is a Spectra 20 with 4 stringers and a jet, under 60 mph. I will resin the entire floor. I plan to put a ski locker in it as well. I have had answers from 1/2" to 7/8".

Is it necessary to use marine grade plywood? It seems to be special order only.

And regarding the ski locker, I see some with an aluminum lip edging that holds the lid. How about a wood 1" X 2" lip on which to set the lid? Thoughts?

I plan to work a lot on it this weekend if the weather cooperates.

Thanks :)
 

74 spectra20 v-drive

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Here is what I did for my floors. Use a good grade 1/2 to 5/8 plywood (I used 3/4) you should cover the bottom side with fiberglass cloth, make sure you use a 24 to 36 grid pad to rough up the wood prior to laying your cloth down. Let the cloth drape over your edges and grind to finish. You will have a solid floor for 30 years if you just resin coat the bottom the resin will flake off in a few years as I am sure you niticed this when you pulled your old floors up. If you are carpeting the top just give it a good resin coat and go I layed cloth on top as well, you encapsulate the wood this way. When you glass the floor in make sure you do not touch the side of the boat or you will eventually break through, leave a good 1/4in gap and glass to the sides it will hold no problem, lay some 1" strips of matt on the stringers and weight the floors down when you set them in, not too much weight or you push all the resin out and loose your bond. For you ski locker you can use aluminum or wood, if you glass a lip of wood to the bottom of the floor it is a better bond than screwing in a piece of aluminum. Once you are glassed in you can use a router and get a nice round edge as well and then make a lid to fit. If you size it right once you carpet a friction fit will hold it tight.
 
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Gelcoater

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Here is what I did for my floors. Use a good grade 1/2 to 5/8 plywood (I used 5/8) you should cover the bottom side with fiberglass cloth, make sure you use a 24 to 36 grid pad to rough up the wood prior to laying your cloth down. Let the cloth drape over your edges and grind to finish. You will have a solid floor for 30 years if you just resin coat the bottom the resin will flake off in a few years as I am sure you niticed this when you pulled your old floors up. If you are carpeting the top just give it a good resin coat and go I layed cloth on top as well, you encapsulate the wood this way. When you glass the floor in make sure you do not touch the side of the boat or you will eventually break through, leave a good 1/4in gap and glass to the sides it will hold no problem, lay some 1" strips of matt on the stringers and weight the floors down when you set them in, not too much weight or you push all the resin out and loose your bond. For you ski locker you can use aluminum or wood, if you glass a lip to the bottom of the floor it is a better bond than screwing in a piece of aluminum. Once you are glassed in you can use a router and get a nice round edge as well and then make a to to fit. If you size it right once you carpet a friction fit will hold it tight.
for what its worth ,i agree with 74spectra,if you choose not to glass both sides,maybe get 3/4 or 7/8. i would glass both sides,and beyond a knotless finish i honestly dont know if there are any diff. in marine grade ply. i do know a 4x10 sheet of 1" marine ply is heavy as hell, and atleast 2-3 times more $$$
 

stevel

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Hello I just installed new floors in my boat and used 3/4 marine plywood. The cost between marine plywood and a good quality non marine plywood is not much. I did a lot of research before I started and found that epoxy resin is worth the high cost, I used west system products. I do not think you have to glass the bottom if you use two coats of a good epoxy resin before you bond it to the stringers. I used 3m 5200 to bond the wood to the stringers then glassed over them. It is also a good idea to cut the wood at a angle where the ends of the boards will touch. west systems has good info on line and a great tech center where they will answer any questions you have. good luck
steve
 

Yellowboat

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your local plywood whole saler should have in stock or can get very quickly marine ply.
 

cakeeater ed

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The actual sq ft of plywood you use will not be a major factor in the performance of your boat (anchor,ski's, tools, spare parts,beer,food ice) will weigh more out on the lake than the small amount you save by going thin on the wood, go thick, use lot's of resin
 

HavAZd

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Thanks for the input. I bought 3/4 AC ply for the job, along with resin. I cleaned out the area where the old tanks were mounted yesterday. I also cut out the bulkheads between the stringers that were just in front of the engine and up near the dash. Both appear to have been replaced prior or put in by a PO. They weren't prepped well so I want to do it right.

I'm half thinking of yanking the engine while I'm at it so I can clean up the whole thing. It's raining steady now so today is shot (no room in the garage) but I do want to use the boat when the weather gets really nice.

I came across some other issues that I would like to fix while the boat is at this stage so was thinking about changing the thread title. I don't know if I can do that.

My turning fin was bent so I took it off while I have it uncovered. I'm wondering if I need that at all. This is my first jet boat so I am not sure if one is needed on a 20' cruiser. The only time I had this boat out after buying it, it seemed to want to 'hunt' at high speed (well, 50 or so, high as it will go). Might that bent turning fin have caused that?

Also, there is a bulkhead about 3' behind the bow. It too looks to have been added by a PO. It is loose. I'm wondering if Spectra put those in to help support the deck or what.

Computer research might be all I get done today with the crappy weather.

74 Spectra V-Drive: I saw the thread on your boat. That is awesome! :bowdown: Mine won't be quite that nice. If I can get the interior done this year, maybe next year or so I can go after the outside. It has been painted but not prepped or painted very well. Looks pretty good from 50'. :D
 

74 spectra20 v-drive

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HavAZd, it sounds like you are going at your project with the right mind set, really mine is no big deal, I am just stupid enough to tear everything I get completly apart (I won't mention my house remodle in 2000)

The center bulk head on the Spectra 20 was for deck support, and most of them over time brake loose, you will want to fix that.
Talking about bracing, I have seen at least 10 of these boats that have a dip in the top deck about two feet forward of where the deck ends at the dash. If you lay a level along the non skid, start at the dash and lay towards the deck you will see a dip, I would guess that yours is dipping as well, I had a 1/4inch plus dip in mine. There is a lot of weight sitting on top and they just (I my opinion) didn't brace it well enough, or make the top deck stiff enough. I added bracing in that spot and hung the boat by a chain attached to the deck where the dip was to get the dip out prior to glassing in the side supports.
 

HavAZd

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HavAZd, it sounds like you are going at your project with the right mind set, really mine is no big deal, I am just stupid enough to tear everything I get completly apart (I won't mention my house remodle in 2000)

The center bulk head on the Spectra 20 was for deck support, and most of them over time brake loose, you will want to fix that.
Talking about bracing, I have seen at least 10 of these boats that have a dip in the top deck about two feet forward of where the deck ends at the dash. If you lay a level along the non skid, start at the dash and lay towards the deck you will see a dip, I would guess that yours is dipping as well, I had a 1/4inch plus dip in mine. There is a lot of weight sitting on top and they just (I my opinion) didn't brace it well enough, or make the top deck stiff enough. I added bracing in that spot and hung the boat by a chain attached to the deck where the dip was to get the dip out prior to glassing in the side supports.
I'll fix that bulkhead...don't want a dip in my deck. :eek:
 

RiverDave

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I've only done one floor, and we did it out of 3/4 marine grade..

I think 1/2 would be too thin.

RD
 
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3/4 marine grade..

RD
X100... And glass both sides... Use 1X2 on ether side of the ski locker and through bolt it to each side, on the bottom. Then take the ski locker hole and clearance it out so the wrapped carpet clears and you are good to go.
 
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HavAZd

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What kind of resin did you decide on.
I bought 3M Bondo fiberglass resin at Home Depot. My neighbor is helping me out and suggested that was fine. I bought that before I posted for any input on this site.
 

stevel

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Please do not take this the wrong way but the stuff at hd is not going to be good for marine use. If i were you look at the benifit of a good epoxy resin it can flex some with out cracking. If you have ever looked at wood in the boat that looks like the resin has small cracks in it, that is because the resin gets very hard and brittle over time and when the wood flexs the resin cracks and lets water in and then the wood rots. Also I would not use screws to hold down the floors just bond it with 3m 5200 and glass them in. Good luck with your project
steve
 

NAFLASH

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I agree with the statement above regarding epoxy resin, howeever is it much more expensive and most epoxy resin's require a post cure at a higher temperature. Granted you won't need that but it does help.
 

stevel

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The west system resin i used was just under $100.00 a gallon. I replaced all the floors on my 21 foot open bow and used two gallons. you only want enough resin to coat the wood. It is a common mistake to use to much resin. You can use a bondo squegie to spread it on the wood.
 
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