Stringer Sistering Question - 1998 Falcon Thunderbird

[Dan_A]

1998 Falcon Thunderbird

Finally have my project boat back in hand.
I have cut out all the rotted stringers, however they were only partially rotted. They were fully encased in fiberglass but at some point a previous owner threw some screws through the floor into the stringers allowing moisture to penetrate. The rot runs from the front of the engine bay to the foot locker, and only in the two innermost stringers. Everything else is completely solid. I have read a lot of posts about stringer repair over the last year and see that most recommend taking the cap off and doing a full replacement. In this case I do have the means to do this so I have been looking at the method of sistering butt joints adhered with epoxy. It seems it would work in this case.

My current question is this: When using this method, are the sister boards adhered to the hull with thickened epoxy along with the primary stringer, or do they “float” over the hull and just act to support the joint?

 

[76SeaRay]

I did a couple of small sister boards on the outside short stringers (about 5 inches tall) at a butt joint. I bedded those to the hull along side the stringer. I have to do two more, one on each of the main stringers that are 10 inches tall. There were original sister boards on the main stringers that were not bedded, however, the stringers in my boat were hit or miss on bedding from the factory (quick and dirty build) so no surprise the sister boards were not bedded. When I put in the small ones, I bedded the stringer first, let them set, then added the sister board. I felt that way the stringer carries the main vertical load and not the sister board.

All this said the recommended joint is a scarf joint at (I believe) 12 to 1. I don't have a way to make a 12 to 1 joint. I plan to use a 45 degree cut at the joint in the main stringers (original from the factory was a butt joint) and use a sister board also. I forgot to cut the 45 degrees before I put in the first main stringers so it will be difficult to cut the ends at 45 degrees already in the boat. Most people I think make the joint out of the boat and install the one long stringer but in my case I am working from the back to the front of the boat because I didn't want to remove too much of the old stringers all at once and risk losing shape of the hull. So, I couldn't put in one long piece. My stringers are all made from 3/4 inch marine plywood and so are the sister boards. They are glassed with PB between the sister and stringers and screwed to the stringer on both sides of the joint.

I am by no means an expert. This is just what I am doing and it seems to make sense to me. Maybe others will weigh in on other views. I am not sure if there is a right way or wrong way.

 

[kcassells]

You can apply woods to both sides of stringer and take 2 sides of ea. pc. and cut to a 45 degree angle. So 2 pcs of ply axtend @ 6" past joint and all sides are 45 cuts. The glass will roll and conform to the 45 edge.
Make sure all woods are wetted out and dry.
Next peanut butter or 5200 the wood on with clamps or screws.
Let it dry/set up and go over with glass. If 5200 you need to make sure it gases off prior to glassing.

Rehab SportCraft 222 1983 deep V hull cuddy walkaround

Hey now,,, Not much to report. Grinded down all the nubs from making the filets on the starboard side hull. Yea that's right..I said it, I need to use the correct lingo. Gonna clean up and do some glass tom. or the weekend. Just remember...the grinding really never ends. Keep the work as...

forums.iboats.com

 

[kcassells]

Going back I did angle off the bottoms and raised @ 1-2" above stringer which allowed glass to transition.

 

[JASinIL2006]

You can apply woods to both sides of stringer and take 2 sides of ea. pc. and cut to a 45 degree angle. So 2 pcs of ply axtend @ 6" past joint and all sides are 45 cuts. The glass will roll and conform to the 45 edge.
Make sure all woods are wetted out and dry.
Next peanut butter or 5200 the wood on with clamps or screws.
Let it dry/set up and go over with glass. If 5200 you need to make sure it gases off prior to glassing.

Rehab SportCraft 222 1983 deep V hull cuddy walkaround

Hey now,,, Not much to report. Grinded down all the nubs from making the filets on the starboard side hull. Yea that's right..I said it, I need to use the correct lingo. Gonna clean up and do some glass tom. or the weekend. Just remember...the grinding really never ends. Keep the work as...

forums.iboats.com

View attachment 351735

This looks like a pretty good fix. That joint is probably stronger than the wood on either side of it.

 

[Dan_A]

You can apply woods to both sides of stringer and take 2 sides of ea. pc. and cut to a 45 degree angle. So 2 pcs of ply axtend @ 6" past joint and all sides are 45 cuts. The glass will roll and conform to the 45 edge.
Make sure all woods are wetted out and dry.
Next peanut butter or 5200 the wood on with clamps or screws.
Let it dry/set up and go over with glass. If 5200 you need to make sure it gases off prior to glassing.

Rehab SportCraft 222 1983 deep V hull cuddy walkaround

Hey now,,, Not much to report. Grinded down all the nubs from making the filets on the starboard side hull. Yea that's right..I said it, I need to use the correct lingo. Gonna clean up and do some glass tom. or the weekend. Just remember...the grinding really never ends. Keep the work as...

forums.iboats.com

View attachment 351735

Having a boat day today, should be moving on to rebuilding the stringers soon. I see you mention using PB or 5200 to adhere the sister boards. I was planning to use thickened west epoxy. Are the other options better or just less expensive?

 

[kcassells]

to me poxy the way to go.