White Oak For Motor Rails

[Mannanj]

I'm making some progress on my Barrelback build. I've made some sawdust making the frames, and am getting ready to start the building frame.

I have an 8/4 x 12in.x 16ft. White Oak timber that I'm thinking of sawing into 2x4s for the Motor rails. I remember reading something about glueing being somewhat difficult but couldn't find any answers in the archives.

Do any of you that have done this before have any advice pro or con about using this pice of lumber for the Motor rails? Any help is most welcome.

[gdcarpenter]

For what it's worth I built all the frame components on my ZIP using white oak. My transom is 2 pieces of 8:4 white oak with a horizontal joint roughly half way up. Heavy but strong. I used Titebond III for many of my white oak joints, with the caveat that they were very tight fitting joints.

If in doubt rough up mating surfaces with 80 grit and wipe with acetone if you wish, but white oak is not particularly oily. I have had no issues and my ZIP is over 2 years old and has been in some serious chop. I say go for it.

[lakeracer69]

I would use 60-80 grit sandpaper and acetone as the previous poster suggested. I would also laminate a full length piece of 1/2" marine plywood to them as well. It will help to control splitting and warping.

YMMV

[Bill Edmundson]

Mannan

I like 2 layers of wood for the motor stringers. The glue issue with white oak appears to be in saltwater. Sanding the matching surfaces with 80 grit is a good idea. I also "lace" the joint with screws. But, what do I know? I'm just a retired structural engineer. If you use 2 pieces on each stringer I don't think the plywood layer is doing much.

Bill

[Cyclone]

I have been using kiln dried white oak with around a 14% moisture content and MAS Marine epoxy. I followed the recommendations from MAS and coated both the mating surfaces of the white oak with the mixed epoxy. I then mixed in colloidal silica with the the remaining epoxy in the cup to thicken it to a pudding like consistency. I then apply the thickened epoxy to the same mating surfaces prior to assembly. The glued surfaced of the wood were clean as they had just been prepared.

I made longer pieces of white oak by scarf joining shorter pieces. I used a 10:1 ratio for the scarf joint length to the given thickness of the material. Later I ripped these long pieces into narrower boards on my table saw. Each time I did this I had a left over strip that was too narrow to for any of my needs. I used these strips to test the strength of the glued joint. I placed the strips across 2 bricks spaced about a foot apart with the joint at the midpoint between the bricks. I would then break the strip with a mini sledge hammer. The wood always broke on either side of the scarf joint as the glued lamination was stronger than the surrounding material. These tests helped to confirm that my glued joints were good.

[Mannanj]

Mannan

I like 2 layers of wood for the motor stringers. If you use 2 pieces on each stringer I don't think the plywood layer is doing much.

Bill

The drawings call for 2x4 nominal which means 1and 1/2 by 3 and 1/2 in with a 3/8 plywood face. The timber I want to use is a solid 2in. thick and finished both sides. Do you think re-sawing and laminating would be sufficient without the plywood facing? This would net about one and 7/8 in thickness, the same as the drawings.

[Roberta]

I used white oak and 3/8" Okoume plywood on each side of the motor stringers for the Torpedo. I roughed up the oak with 50 grit and epoxied the plywood using System Three Gel Magic, some locating screws, and ring shank nails about every 6". This was done about a year ago and so far they look great. They came out nice and flat and straight. They were clamped to my very flat table during curing. Check out the process in the beginning pages of the "Roberta's Torpedo" topic.

Roberta

[jprice]

I did what Bill said.
It's virtually impossible to find a piece of lumber that long that's going to be straight and true. If you laminate them and orient the layers so that any bow or curve is working against each other, you end up with some pretty straight and solid pieces in the end.

[tsmitherman]

All the above comments are good, but unless I've missed it, there is one important point that was not covered. When using epoxy on white oak, you need to use MINIMAL clamping pressure. The White Oak does not absorb the epoxy nearly as well as most other boat woods, and if you over clamp, it will starve the joint and make it weak. This would not apply if you are using Titebond or some other glue.

The saltwater issue is only a problem if you use resorcinol or plastic resin glue (I forget which one it is, but one of them reacts with a chemical in the white oak if you place it in saltwater).

Bottom line - stick with epoxy and roughen up the surface of the oak, then use just enough clamping pressure to hold the parts in place.

My only joint failure in my build occurred when I clamped two very smooth white oak boards with epoxy. I tightened the clamps as hard as I could (a lesson learned from using other glues). The joint pulled apart a few days later.

[kens]

All the above comments are good, but unless I've missed it, there is one important point that was not covered. When using epoxy on white oak, you need to use MINIMAL clamping pressure. The White Oak does not absorb the epoxy nearly as well as most other boat woods, and if you over clamp, it will starve the joint and make it weak. This would not apply if you are using Titebond or some other glue.

The saltwater issue is only a problem if you use resorcinol or plastic resin glue (I forget which one it is, but one of them reacts with a chemical in the white oak if you place it in saltwater).

Bottom line - stick with epoxy and roughen up the surface of the oak, then use just enough clamping pressure to hold the parts in place.

My only joint failure in my build occurred when I clamped two very smooth white oak boards with epoxy. I tightened the clamps as hard as I could (a lesson learned from using other glues). The joint pulled apart a few days later.

True,
white oak is so dense that it doesnt absorb much resin, thus more difficult to get a good bond. Especially true of 2 pieces of white oak epoxy to each other, I had a oak-to-oak failure as well.

Oak also is the most unstable of all species when subjected to moisture (it swells up a lot), thus when it swells up, the glue line (epoxy) remains stable and the glue joint is now stressed. The oak swells but the epoxy doesnt. This had lead to many oak/epoxy failures, any water salty or not will swell oak!!!!

I used some white oak in my build and will pass on using any more of it for structure.
The best use of oak I ever saw is Ray Macke trimming his interior with it, beautiful.

West System Geoudeon Bros. does not recommend hard dense wood for stringers. They advise mahogany or other softer wood that glues better and will absorb some vibration. Oak tends to transfer vibration rather than absorb.
I built my stringers of Cypress laminations, and I like it.

[Mannanj]

Is my reasoning correct that the acetone wipe down helps the oak absorb the epoxy a bit deeper into the grain of the wood than it would normally??