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 Balsa Core Issues 
On the original setup, the fuel filter was between the tanks and screwed to the deck.  It's now hung temporarily from an outboard bolt (above the bilge pump) and exploratory holes have been drilled to find out the condition of the balsa core where it has been breached to install hold-downs for the various gear.
On the original setup, the fuel filter was between the tanks and screwed to the deck. It's now hung temporarily from an outboard bolt (above the bilge pump) and exploratory holes have been drilled to find out the condition of the balsa core where it has been breached to install hold-downs for the various gear.
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So, in addition to eliminating the deck penetrations, I'm hoping to clean up this mess.  You can just barely see the fuel filter screwed to the deck between the gas cans, which are screwed to the deck inside of the battery trays, which are also screwed to the deck.  All screws go into the balsa core.
So, in addition to eliminating the deck penetrations, I'm hoping to clean up this mess. You can just barely see the fuel filter screwed to the deck between the gas cans, which are screwed to the deck inside of the battery trays, which are also screwed to the deck. All screws go into the balsa core.
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I removed all the junk.  The holes were then coated with penetrating epoxy, left for 24 hours, then filled with an epoxy putty made from wood dust, then painted again with penetrating epoxy.  The bilge pump base was screwed and glued in place.  I tore it out, which ruined the base ($8) and will just glue it back in place to eliminate any penetration into the balsa core.
I removed all the junk. The holes were then coated with penetrating epoxy, left for 24 hours, then filled with an epoxy putty made from wood dust, then painted again with penetrating epoxy. The bilge pump base was screwed and glued in place. I tore it out, which ruined the base ($8) and will just glue it back in place to eliminate any penetration into the balsa core.
Viewed: 448 times.

Some of the screws had corroded and that colored the swarf.  Spooked me, so I got out my creepy medical tools.
Some of the screws had corroded and that colored the swarf. Spooked me, so I got out my creepy medical tools.
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This is a barbed needle that allows you to take biological samples by poking the victim.  The wood is good, although the fact that it is discolored shows that moisture was present.
This is a barbed needle that allows you to take biological samples by poking the victim. The wood is good, although the fact that it is discolored shows that moisture was present.
Viewed: 452 times.

Finally, the area can be cleaned up and repainted.  You can see that the four corners of the battery tray were also just screwed into the balsa core.  The goal was to fix the damage, relocate everything, and have a clean deck.  This was before I realized that the cockpit panel (on the right) was simply pop riveted into the balsa core.  My little project of protecting the balsa core just turned big.
Finally, the area can be cleaned up and repainted. You can see that the four corners of the battery tray were also just screwed into the balsa core. The goal was to fix the damage, relocate everything, and have a clean deck. This was before I realized that the cockpit panel (on the right) was simply pop riveted into the balsa core. My little project of protecting the balsa core just turned big.
Viewed: 429 times.

Here are the holes that concerned me next.  The seat box/cockpit liners are fastened to the deck with blind rivets.  Do these go into the balsa core?  Yikes!  The rivet heads have popped off and the caulking has failed.  Not a good sign if these go into the balsa core.
Here are the holes that concerned me next. The seat box/cockpit liners are fastened to the deck with blind rivets. Do these go into the balsa core? Yikes! The rivet heads have popped off and the caulking has failed. Not a good sign if these go into the balsa core.
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Even the rivets that looked good simply fell apart when bumped or drilled.  These are aluminum rivets with a steel mandrel.  Not a problem if they never get wet.  Oh that's right, it's a boat!
Even the rivets that looked good simply fell apart when bumped or drilled. These are aluminum rivets with a steel mandrel. Not a problem if they never get wet. Oh that's right, it's a boat!
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Exploratory drilling showed stained but essentially good wood near the helm seat box pop rivets.  I'm amazed, given what I found on the other side and the fact that these two rivet heads had fallen off.
Exploratory drilling showed stained but essentially good wood near the helm seat box pop rivets. I'm amazed, given what I found on the other side and the fact that these two rivet heads had fallen off.
Viewed: 329 times.

Seat box removal, showing the exploratory drilling on the port side that made me decide to remove everything.  The dark holes indicate bad balsa core.  The outer holes are marked
Seat box removal, showing the exploratory drilling on the port side that made me decide to remove everything. The dark holes indicate bad balsa core. The outer holes are marked "OK" with a red marker, although I may find that's a bit hopeful when I go further.
Viewed: 367 times.

CD 16 seat box/cockpit panels removed.
CD 16 seat box/cockpit panels removed.
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Once the port side seat box was removed, I could tell that there was a substantial problem.  You can see a white line of caulk that kept water (and dirt) up against the pop rivets.  I'm not sure what the little strip of caulking was intended to do.
Once the port side seat box was removed, I could tell that there was a substantial problem. You can see a white line of caulk that kept water (and dirt) up against the pop rivets. I'm not sure what the little strip of caulking was intended to do.
Viewed: 198 times.

I drilled out the mounting holes where the failed pop rivets had been and started drilling radiating holes to determine the extent of the damage.
I drilled out the mounting holes where the failed pop rivets had been and started drilling radiating holes to determine the extent of the damage.
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I was still digging out failed balsa six inches away from the leak.  This is a good photo of the waxy look of wet balsa.
I was still digging out failed balsa six inches away from the leak. This is a good photo of the waxy look of wet balsa.
Viewed: 229 times.

This shows the flotation foam behind the starboard panel.  I intend to reuse most of it, but fastened into place with spray foam.  When loose, they act as wedges against the panels and may have contributed to the pop rivet failures.
This shows the flotation foam behind the starboard panel. I intend to reuse most of it, but fastened into place with spray foam. When loose, they act as wedges against the panels and may have contributed to the pop rivet failures.
Viewed: 365 times.

Pop rivet heads that just fell off during removal.
Pop rivet heads that just fell off during removal.
Viewed: 337 times.

Pulling corroded rivets out of the core after the heads had been drilled off (or the heads had already fallen off).  Here is another picture showing that the bead of caulking could hold dirty water behind the panels and contribute to the leaking pop rivets.
Pulling corroded rivets out of the core after the heads had been drilled off (or the heads had already fallen off). Here is another picture showing that the bead of caulking could hold dirty water behind the panels and contribute to the leaking pop rivets.
Viewed: 360 times.

When pulling the rivets, there is no way to avoid some damage to upper laminate, but that won't matter because this will be drilled out and filled with epoxy.
When pulling the rivets, there is no way to avoid some damage to upper laminate, but that won't matter because this will be drilled out and filled with epoxy.
Viewed: 349 times.

These rivets all have rusty mandrels, indicating high levels of moisture in the core even areas where the rivets didn't appear to have leaked and the wood appears okay.
These rivets all have rusty mandrels, indicating high levels of moisture in the core even areas where the rivets didn't appear to have leaked and the wood appears okay.
Viewed: 355 times.

When actually leaking enough to cause rot, they look more like this.
When actually leaking enough to cause rot, they look more like this.
Viewed: 328 times.

For some rivets, I had to drill down and then pull out the remains of the rivet.  This balsa seems okay even though the adjacent test hole was discolored.
For some rivets, I had to drill down and then pull out the remains of the rivet. This balsa seems okay even though the adjacent test hole was discolored.
Viewed: 320 times.

Going aft, you can see the change on a rotten fastening.  The pop rivet holes on both sides were okay.
Going aft, you can see the change on a rotten fastening. The pop rivet holes on both sides were okay.
Viewed: 318 times.

Here's the wet swarf from a bad hole, even though the boat had been in the garage for several months.  All of this had to be dug out and then the hole dried out.
Here's the wet swarf from a bad hole, even though the boat had been in the garage for several months. All of this had to be dug out and then the hole dried out.
Viewed: 344 times.

Additional holes needed to be drilled, radiating out from the rotten hole to determine the extent of the damage.  I could have drilled smaller holes, but I wanted a really good look to make sure that the rot had not spread.  The balsa surrounding the center hole was soggy, but not yet rotten.
Additional holes needed to be drilled, radiating out from the rotten hole to determine the extent of the damage. I could have drilled smaller holes, but I wanted a really good look to make sure that the rot had not spread. The balsa surrounding the center hole was soggy, but not yet rotten.
Viewed: 346 times.

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