Cracked at the Gunnels

[funbun]

Okay I finally have made some headway into this boat, but ran into a major problem. I went out this morning and the scarf joint completely failed on the starboard gunnel. What to do now?

I scarfed this with epoxy/powdered limestone. Was it the limestone mixture, or was it that too much stuff got squeezed out?

 

[dawallace45]

A scarf joint is very stiff compared to the rest of the length of timber , placing the scarf right on the frame like you did was more than it could take , you put a piece of gunnel that was too stiff to bend properly right where it has to bend , if you put the scarf a foot or two further back towards the bow it would have been fine

David

 

[Kayak Jack]

Funbun, a gunnel has its maximum stress at the center of the boat, and lessens towards the ends. I'd do joinery as far away from the center as I could. I wouldn't rule out a glue starved joint, but am only guessing. I had a cockpit coaming pop off of my first kayak I built. I'd screwed down the clamps too tightly and had squozenened out too much glue. (Conjugation examples: rise, rose, risen - squeeze, squoze. squizzen)

On this, maybe you could crank it back into shape, reglue, and clamp it. Add a "decorative" splint on the outside and maybe inside too?

 

[funbun]

Well, I have plenty of materials. I may just start all over. I haven't put the bottom or anything.

 

[Kayak Jack]

Maybe this hull can be stood upright, shelves added, and you have a new bookcase? Matt has some plans for that.

 

[funbun]

Yeah, that's about all this hull is going to be good for.

 

[Kayak Jack]

Well, Christmas is coming. Hasn't your wife been begging you for a new bookcase? Now, you can fulfill her wildest dreams in spades1

 

[seedtick]

we don't match up scarf joints perfectly when we glue, but pull the pieces back about 1/32". That way you leave a gap that you cannot squeeze out the glue no matter how much pressure you use

Never used limestone as filler but from what I've read, it should be OK. Just be sure you're used a very fine limestone (like talcum powder) and not hydrated lime

 

[funbun]

Yeah this is the super fine power stuff. I use it in my garden all the time and thought it would be fine.

 

[funbun]

How do you keep the epoxy solution from running everywhere. Maybe I didn't have it thick enough? It had the consistency of pancake mix.

 

[JEM]

Powdered limestone? Not sure if that's the best thickener to use for a bonding application. Woodflour or fumed silica would be better.

 

[funbun]

Thanks, JEM. I need to order a few more supplies anyway. Is 5 lbs enough for a 14 ft jon boat?

 

[oldsparkey]

Thanks, JEM. I need to order a few more supplies anyway. Is 5 lbs enough for a 14 ft jon boat?

Plenty for several boats. You mix the wood flour with the epoxy so it resembles almost a runny P"Nut butter mix. Not to runny , not to stiff , Just right.
As a fillet for over the seams then it is thick , almost like real P" Nut butter.

 

[john the pom]

I had only gathered about half as much woodflour as I reckon I needed for my last build. Added a pound of plain flour as in baking. Didn't have to mill it any finer. Mixed it thoroughly. BTW have heard that self raising flour would be too oily compared to plain.
My logic was that it has to be cellulose based as it is/was plant material just like wood. Seems as good/strong as as the last build.
Cheer John.

 

[swampwood]

The picture is of the outside gunnel sliced at the beam.
I used a silica, woodflour and epoxy mixture, C- clamped them together until they setup.
The wood is white oak.
There are actually 4 splices in the center area, but the inside and outside splices are staggered about a foot apart.
None have failed yet anyway.