Help! Marine Plywood For Stringers!!!

[AJSVFORCE]

I Am Trying To Find Marine Plywood Long Enough To Replace My Stringers That Run The Length Of The Boat And Cant Find Any Plywood 15' Long! Do I Have To Splice The Eight Footers?
Please Help!!!

 

[jonesg]

Re: Help! Marine Plywood For Stringers!!!

yes, long scarf joints work well.

 

[Yacht Dr.]

Re: Help! Marine Plywood For Stringers!!!

Hello Force..

pics are kinda needed in this application.. are you scabbing ?.. or bulkhead to trans ?

YD.

 

[AJSVFORCE]

Re: Help! Marine Plywood For Stringers!!!

These are the stringers that run from stern to bow.I am new at rebuilding boats and woodworking.

 

[PiratePast40]

Re: Help! Marine Plywood For Stringers!!!

Butt joints are just fine with plywood. Keep your joints as far apart as possible. After all, you're just making more ply's. I used resin and mat to bond mine but some say the mat isn't necessary. I used screws to hold them together and let it set up for a day. Then removed the screws finished up ripping to the exact width and length. Then went back and filled the screw holes in with resin.

 

[88BLiner]

Re: Help! Marine Plywood For Stringers!!!

Yes you will need to join two 8' pieces. I would suggest the method that PiratePast40 described above.

 

[jonesg]

Re: Help! Marine Plywood For Stringers!!!

butt joint is no good for this, you're using the wrong terminology.
I think you meant lap.
the only butt joint with any strength is a scarf, the longer the better.

 

[PiratePast40]

Re: Help! Marine Plywood For Stringers!!!

butt joint is no good for this, you're using the wrong terminology.
I think you meant lap.
the only butt joint with any strength is a scarf, the longer the better.

In this case, I'm talking about two layers of plywood with the butt joints having backing pieces (the second layer). I'm not sure of the term but believe the lap joint would be the piece (that also has butt joints) that forms the second layer. When plywood is manufactured, the pieces inside the layer are butted against each other anyway so this is the same construction method. If this were a single piece of wood, then I would agree that a scarf joint is far superior.

 

[Mark42]

Re: Help! Marine Plywood For Stringers!!!

In this case, I'm talking about two layers of plywood with the butt joints having backing pieces (the second layer). I'm not sure of the term but believe the lap joint would be the piece (that also has butt joints) that forms the second layer. When plywood is manufactured, the pieces inside the layer are butted against each other anyway so this is the same construction method. If this were a single piece of wood, then I would agree that a scarf joint is far superior.

I agree with using a simple butt joint with overlapping "scabs" . I think its actually called a scab joint, but I'm not sure. Ive seen this method on a number of project boats on these forums. No one ever complained about failure.

I also wouldn't bother with marine grade ply, unless the boat was built with it. Seeing as most boats do not use marine grade plywood, chances are yours wasn't either. If not, I would choose a pressure treated plywood for anything under the deck and for the transom. It would really be a disaster to find out that one stress crack or one bad lamination that lets water in starts rot right away. I look at pressure treated ply as an extra insurance policy for all the labor you put in. Also there are a number of documents by the APA that recomend pressure treated ply in boats, you should take a look at them if you haven't already:

Bonding Fiberglass to plywood:
http://glen-l.com/wood-plywood/fiberglass-plywood.html

Preservative Treated Lumber study:
http://www.glen-l.com/wood-plywood/boatbuilding-plywood.html

 

[AJSVFORCE]

Re: Help! Marine Plywood For Stringers!!!

Thanks for the help.
What i need now is a detailed list of materials and the methods of their use.
I have a pretty good Idea of what needs to be done. But what exactly is used in each application and why is what i have been trying to figure out so i dont waste money using the wrong resin or wrong fiberglass for the certain application i am working on.

 

[rockyrude]

Re: Help! Marine Plywood For Stringers!!!

While pressure treated has it's advantages, you need to find the old CCA treated, the new AC2 eats most fasteners unless they're stainless. The other problem is that most all pressure treated needs to dry a good month in order to get any kind of a bond with the resins.

 

[Mark42]

Re: Help! Marine Plywood For Stringers!!!

While pressure treated has it's advantages, you need to find the old CCA treated, the new AC2 eats most fasteners unless they're stainless. The other problem is that most all pressure treated needs to dry a good month in order to get any kind of a bond with the resins.

The notion of PT wood having poor bonding and eating fasteners is a common misconception. Although there may be an issue with aluminum. Stainless steel, galvanized and silicon bronze fasteners are not affected.

Regarding bonding and the APA tests:

All tests on the untreated and treated specimens at the 65% relative humidity failed predominately in the plywood, indicating a good fiberglass bond. This indicates that the treatment did not have an adverse effect on bonding at this moisture level. Furthermore, the strength of the treated and untreated plywood were similar.

65% humidity! Geeze, the pressure treated ply I get from the lumber yard is drier than that!

Read the whole APA test document here:

http://glen-l.com/wood-plywood/fiberglass-plywood.html


Here is a quote from MicroPro, producers of AC2 pressure treated wood regarding fasteners in AC2 wood:

Fasteners- MicroPro? technology offers many benefits including significantly improved corrosion performance. MicroPro AC2? pressure treated wood with MicroPro technology exhibits corrosion rates on metal products similar to untreated wood. For best results, use stainless steel or Midwest Manufacturing Premium Triple Coated Fasteners.
Fasteners (and other metal products) for use with MicroPro AC2 preserved
wood products include:
- Stainless Steel Stainless steel fasteners and connectors are recommended for use with treated wood in other severe exterior applications such as swimming pools, salt water exposure, etc. - Type 304 and 316 are the recommended grades to use.

Other fasteners and hardware as recommended by the manufacturer
There may be additional products (other than stainless steel or hot-dip
galvanized) which are suitable for use with MicroPro AC2 treated wood.
Please consult with the individual fastener or hardware manufacturer for
recommendations for use of their products with MicroPro AC2 treated wood.

 

[ondarvr]

Re: Help! Marine Plywood For Stringers!!!

I'm not sure why the worry over the possible corrosive affects of PT, nothing being secured by screws or bolts on a boat should be anything but SS anyhow. On a tinny I can see issues, but on a glass boat it makes no difference.