plywood question

[bonz_d]

Just started tearing out the decking in my 16' Alumacraft Classic, the previous owner did a horrible job last time. Found a remenant piece of ply still in the boat from the original decking which measures and looks like 1/2". The last job was done with 5/8". To do this more correctly I need to be able to slip it under the Livewell on one side and the Rod box on the other. Again which the PO didn't do.

So here are my choices which are available at my local Menards.

1/2" AB Marine ply. $50.00 a sheet
1/2" ACX which looks like 4 ply but dosen't state if it's 16/32" or 15/32". $29.00 a sheet
1/2" ACX Premium which looks like 5 ply and again dosen't state. $33.00 a sheet
1/2" BCX which is 15/32" and only 4 ply. $24.00 a sheet.

This hull has 5 stringers on 10" centers with a 1.75" flange on top so I really don't think using 1/2" ply is going to be a problem. So which of the 4 would be the best choice and has anyone seen whether it makes a differeance as to which side should go up or down?

 

[jbcurt00]

Plywood ALWAYS goes writing down or in, AWAY from primary exposure.

I suspect the Marine ply is 15/32" too, or actually metric, but the other 3 are definitely 15/32". 15/32"ply IS the new 1/2" ply under the current lumber measuring system where 2X4's are 1.5 X 3.5 +/- 1/16-1/8".

 

[jigngrub]

All 4 choices will work, with the more expensive being the better. How long they last will depend on what you do to them to seal them and what you plan to finish your deck with. The cheapest sealed with 4 coats of epoxy resin will last longer than the most expensive sealed with spar urethane or varnish.

The side with the stamp or writing should go down, unless they both have writing , then it doesn't matter.

Make sure you run the plywood with the face grain (strength axis) direction at a 90* angle to the stringers, or to be more clear... don't run the grain of the plywood in the same direction as the stringers.

 

[bonz_d]

So how much if any differance is there between 4 ply and 5 ply?

Jig you've worked with it I know so how thick is the vynil flooring? I was able to get one side cleaned out and a pcs. of 5/8" ply just barely fits under the boxes. Coat it and cover it and it will never fit. I understand about the grain but unfortuneately I will probably have to. Otherwise there is no way I can do it with just 2 seams and I really don't want to have a bunch of pcs. seamed together.

The plan right now is 2 seams/joints. 1 down the center to the end of the livewell then one midship from port to starboard. I can cut and place the forward pcs that fits under the helm and forward portion of the rod locker and then in 2 pcs. fill the rear portion of the deck and still be able to slide them under. That rear section is only a little more than 6' and 2' of that is under the splashwell.

 

[jc55]

Router it down to desired depth or can you trim the floor flanges of the things you need to slip it under? I'm a 3/4" fan personally.

 

[jigngrub]

Nautolex vinyl is 1/16" thick.

Just so you know, if you run the grain with the stringers your plywood will sag causing valleys between the stringers unless you install additional framing or support the plywood with foam.

 

[bonz_d]

Thanks. Don't know why I always spell vinyl wrong. Alway! May be able to do it with 3 seams if I put one under the splashwell. Will have to remeasure.

Sorry jc but 3/4 will never work. These pcs. have to fit 6" under the rod locker and 6" under the livewell. The rod locker and flotation box on the starboard side is almost 9' long and the livewell and flotation box on the port is 6'.

 

[bonz_d]

Still haven't heard any input on the number of plys. Which is stronger? 4 or 5 ply? I would think the more the better.

 

[jigngrub]

5 ply is stronger and better.

4 ply would be the same as 3 ply, just thicker.

 

[Axkiker]

I will throw my very uneducated first time builder input in here. For my build I used Advantech. Its some new osb type stuff which is designed to be very water resistant and stronger than plywood of the same size. You can google advantech and find their website which will give a good comparison between it and other sub-floor materials.

From my limited experience the stuff is great. Its heavy as heck when compared to other similar materials but I didnt care about that. Its extremely strong and knowing it limits the amount of water absorption made me happy. It has NO voids and is typically straight as an arrow. Its a little higher than the normal ply at roughly 33.00 a sheet but not as high as true marine.

I did some adhesion comparisons between advantech and a typical plywood. My very unscientific findings were that there was no difference. I have some pics ill try to post if I can ever get the pics off my phone.

 

[jigngrub]

I will throw my very uneducated first time builder input in here. For my build I used Advantech. Its some new osb type stuff which is designed to be very water resistant and stronger than plywood of the same size.

Its extremely strong and knowing it limits the amount of water absorption made me happy.

Not trying to take anything away from your Advantech, but...

Advantech is classified as Exposure 1 grade for moisture resistance, from their site:

Can I leave AdvanTech panels exposed to the weather?
AdvanTech panels carry an Exposure 1 bond classification. This means that they are intended to withstand weather exposure during the construction phase of a project. However, the panels are not intended for permanent exposure to the weather. AdvanTech panels, like most other wood products, are susceptible to decay if exposed to long-term high moisture conditions. Proper conditioning or ventilation of crawl and attic spaces, as well as correct installation of roof and wall coverings and application of flashing and caulking, will minimize problems due to excessive moisture

Pretty much the same as most plywood, even the stuff we call Exterior grade which really isn't true exterior panels.

When they say Advantech is stronger than plywood they're only comparing it to 4 ply plywood which is about the same as 3 ply. 5 ply plywood is stronger and that's what most 3/4" plywood is and the better 1/2" is.

 

[bonz_d]

Thank for the education jig! Think I'm leaning towards the 5 ply. The marine grade would be nice but I can get 3 sheets of the 5 ply for what 2 sheets of the marine would cost. Besides, it's going to be covered and not varnished and left exposed.

Also don't see many places to pick up Nautolex online. Only found 4 places. One of those only sells it up to 12' continuous lengths.

 

[jigngrub]

I got mine at Defender, they had the cheapest price I could find on the net.

Continuous length doesn't really matter, you're going to cut it up anyway.

 

[bonz_d]

That is the website I saved! how costly was shipping?

 

[jigngrub]

They were the lowest on that too. Good service and quick delivery.

 

[bonz_d]

That's good to know. Guess I'd better get busy cleaning out the other side. I'll see if I can get a picture up of the section I have uncovered.

 

[undone]

Vinyl does not protect the plywood very well, it should still be coated with epoxy.

The vinyl tends to get holes and tears in it over time, these let water in and it can't escape, so it rots. The bottom of the plywood is also exposed to water with very little chance for it dry out.

 

[sheboyganjohn]

Not sure where you are finding 4 ply, all the plywood I know of has odd numbers of plys. More plys are generally better since the grain direction is alternated with each layer and if you have a void, it is not as big as it would be if you had fewer thicker layers. As for running with the grain to prevent sagging, that does not exactly make sense since the grain does not run the same way with all the layers. Maybe if there are only 3 layers that my be an issue, but I don't see it with plywood that has lots of layers.

 

[bonz_d]

Vinyl does not protect the plywood very well, it should still be coated with epoxy.

The vinyl tends to get holes and tears in it over time, these let water in and it can't escape, so it rots. The bottom of the plywood is also exposed to water with very little chance for it dry out.

Thanks for the advice but this isn't my 1st rebuild. Just the 1st one with trying to use 1/2" ply which was origanally used.

 

[bonz_d]

Not sure where you are finding 4 ply, all the plywood I know of has odd numbers of plys. More plys are generally better since the grain direction is alternated with each layer and if you have a void, it is not as big as it would be if you had fewer thicker layers. As for running with the grain to prevent sagging, that does not exactly make sense since the grain does not run the same way with all the layers. Maybe if there are only 3 layers that my be an issue, but I don't see it with plywood that has lots of layers.

2 of the examples I've listed I've already looked at and yes they are only 4 ply. Also the 5/8" that is being removed is also 4 ply.