cracked shear seam

I brought my Shearwater 17 hybrid in to touch up the varnish and when I took the rigging off I found that water had gotten past the screws in several spots staining the wood. I drilled the holes oversized and filled them with thickened epoxy. Tonight I drilled out the epoxy with an 1/8" bit and started to screw the rigging loops back in (nylon strapping with the supplied brass screws). I hear a cracking noise and I see that the shear seam has split! The deck to hull glass overlap seems to be ok, but I can see the separation. I'm thinking I shouldn't have used the same holes and the epoxy was stronger than the seam or I didn't drill a big enough hole for the brass screw.

How should I fix this??

My thought as of the moment is..first, have an adult beverage and calm down. Second, redrill the holes, refill with epoxy, third, from the inside of the boat apply fiberglass tape to the shear clamp.

Argh! Advice please! TIA

Dan 


15 replies:

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RE: cracked shear seam

Hi Dan,

Hold the beverage in one hand and take a photo with the other.  Post the photo so we can understand the problem.  Then finish the beverage.

Don't worrie

Lou

RE: cracked shear seam

I hope this clarifies it...

RE: cracked shear seam

First pic is the outside, second is the inside

RE: cracked shear seam

What is that white stuff I'm seeing in the interior photo?

RE: cracked shear seam

John,

The thickened epoxy I used to glue the deck to the hull has whitened over the course of the summer (last year). Not sure why.

The dark line in the white is the split. 

Dan 

RE: cracked shear seam

Dan,

How deep did you drill with the 1/8 drill bit ?  You need to drill the full depth of the screw.

If you just drill through the deck and not into the shear clamp, then the screw will act like a jack screw.  The theads of the screw will grip the deck but the point will push against the shear clamp. 

If you drill through the deck and into the shear clamp the full depth of the screw, then the screw can not push against the shear clamp.

Good luck and keep us posted

Lou

RE: cracked shear seam

Lou,

You and Joey from CLC had the same thought and I think that is indeed the problem. I hesitated to drill too deep and the screws bottomed out in the holes.

His solution is to put the screws back in, widening the gap, slit the glass at the shear line, pour in some unthickened epoxy from the inside of the boat allowing it to run out and then remove the screws, hence tightening the gap. I think I am going to do this. I will probably use a strap or 2 around the boat too. Then, I think I will put a small fillet between the shear clamp and the deck just to strengthen things up a bit.

Should I risk using the same holes again? 

I had planned to do 1 more coat of varnish on the hull anyway so hopefully it won't be too ugly. 

Thanks,

Dan 

RE: cracked shear seam

I have followed Joey's advice and I think it will work out fine. On closer inspection I think I did a pretty crappy job glueing the deck to the hull. Not sure why the thickened epoxy whitened like that. I put a small fillet between the deck and the sheer clamp as far in as I could reach.

I also think I may have compromised the joint when I screwed in the rigging the first time around. I saw areas where the glass looked stressed. I suspect I didn't drill the holes deep enough as I was worried about drilling all the way thru the sheer clamp. The screws may have been the only thing holding the deck on ;-)

Any thought on what size drill bit should be used for these screws? 3/4 by 8, I believe.

Dan 

RE: cracked shear seam

Hi Dan,

According to the chart I keep by my drill press, for a traditional #8 screw, the shank  hole is 5/32, and the pilot size is 7/64 for hardwood and 3/32 for soft wood. The bronze screws that came with my kit appear to match the chart pretty well. I would think the hardwood size would be the better choice as the eopxy shouldn't give.

I drilled through the shear clamp, taped the bottom of the holes and filled them with epoxy. 

It just so happens I am in the process of drilling and filling the holes in my deck today for rigging and a rudder on my MC 16.5 hybrid.  I drilled through the shear clamp, taped the bottom of the holes and filled them with epoxy.  I haven't drilled the screw holes yet but I plan to drill the 5/32 shank hole through the deck and the smaller hole through the shear clamp.   

Seeing your post makes me wish I had gone with the carbon fiber straps or something similar that doesn't put holes in the deck.  I will probably go that route on my next boat.

Nate

 

RE: cracked shear seam

Nate,

I know what you mean. I used Eric Schade's flush holddowns in my wife's SW16h and I started thinking I should retrofit them on my boat...next winter maybe. 

RE: cracked shear seam

Dan,

That is a beautiful boat, I love the design! My wife saw it on a previous post and wants me to copy it on my next boat.   Immitation being the most sincere form of flattery. 

 Good luck with your repairs, I would like to know how it turns out.  That had to have been frustrating. 

Maybe no one will notice.  I made quite a few mistakes on my boat, but usually nobody notices them unless I point them out. 

 

RE: cracked shear seam

Thanks Nate

Truth be told I stole, er, borrowed the design right out of the catalog 

http://www.clcboats.com/shop/boats/kayak-kits/light-touring-kayaks/shearwater-16-hybrid-sea-kayak-kit.html 

RE: cracked shear seam

It is possible your shear seam was weak to begin with.  The white appearance of your fillet may be due to water vapor intrusion.  Was it covered w/clear exoxy after it cured?

Also, your shear seam is not glassed over.  In a kayak with a shear clamp, planing the lower inside edge off, i.e. you end up with a triangular shaped shear clamp instead of a rectangular one, will greatly ease glassing over this area.  Done before the deck is on is recommended. The small area at the bottom of the shear clamp can then be filleted slightly and a smooth glass tape interface will result from the deck/shear clamp/hull side.  I believe that this should always be done in at least the middle third of any glued on deck as good composite design practice.

You can see what you are doing using a mirror, cell phone camera or a camera connected to your laptop & a small shop light.

I have been out of the loop for several years in cancer treatment and a Valley Fever lung problem & not allowed to be around any VOC's, so I thought I would catch up with building processes.

Dirk

RE: cracked shear seam

Thanks Dirk,

No, the shear clamp was not coated after it cured. The epoxy is thickened with cellofill which accounts for some of the whiteness, but I did notice it becoming more white after the inside of the cockpit got wet a few times. This winter I did clean it up a bit and along with my repair put some more epoxy on the seam. I suppose I could still chamfer and glass the seam at some point.

 Be well,

Dan 

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