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Replacing balsa in a stern


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I've done a lot of sterns (cue bad jokes), and one thing always popped up that I think could somehow be improved.  On a deck, you can put some epoxy on the balsa and work it so it flows between the squares and compartmentalizes Any future leaks.   Doing that on the stern is impractical.  Short of vacuum or infusing, does anyone else do any thing special? 

I mean,you could do the epoxy thing to the balsa before you put it in, but what a mess. 

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  • Grrr... changed the title to Replacing balsa in a stern

If you're working from the outside it's easy to paint epoxy into all the kerfs before laying it in place. Just set up a laminating table of some sort.

Working inside, not so much.

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Are we talking contour balsa on Scrim, then lay sheet on a convex surface ( we had a great big inflated Norwegian buoy in the workshop for this purpose) so all the kerfs are open,  plaster on good quantity of sloppy bog , making sure it goes into all open kerfs, flip onto mould and vibrate down into laminate ( an old 1/3 sheet sander covered in plastic works).

Called doing the job properly and doesn’t take much extra time.

But why balsa?

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1 hour ago, Zonker said:

<Foam> cough, cough

Balsa is good for decks if they don't leak. Last time I checked, unless you have a squared rigged pirate ship, about half of the transom is in the water. I wouldn't consider balsa for a transom. Maybe if I had scrap balsa on hand, couldn't buy foam, and it was someone else's boat.

You need to mix up the epoxy with microspheres to fill all of the scores. There is no point in "sealing" balsa with neat resin. If the thickened doesn't seal it, you've got bigger problems(water intrusion, skin delamination).

Go foam and never think about it ever again.

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What he said. 

Foam will likely not have the compression strength of balsa, so in he way of heavily loaded fasteners, pucks of Penske board would be a good idea. 

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Other than a backstay (where it really should be single skin) most transoms don't have heavily loaded fasteners.

Noah's or Defender should sell small pieces of Coosa or Penske board. Lots of people don't need a whole sheet. A 2'x4' quarter or 2'x2' 1/8 sheet would be nice.

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5 minutes ago, Zonker said:

Other than a backstay (where it really should be single skin) most transoms don't have heavily loaded fasteners.

Noah's or Defender should sell small pieces of Coosa or Penske board. Lots of people don't need a whole sheet. A 2'x4' quarter or 2'x2' 1/8 sheet would be nice.

Wouldn't outboard bracket mounts and/or rudder gudgeons for outboard/stern hung rudders count as heavily loaded fasteners?  (Asking honestly, not trying to be snide!)

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There are high-density foams used in high (compressive) load areas.  Had them under my cabin-top mounted winches.  Really strong stuff, yet still much lighter than  other options.

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1 hour ago, Crash said:

Wouldn't outboard bracket mounts and/or rudder gudgeons for outboard/stern hung rudders count as heavily loaded fasteners?  (Asking honestly, not trying to be snide!)

Yes of course; I didn't think of little boats. Most boats of 70/80's vintage would slap a piece of plywood on the interior as a backing plate (single skin) or as a core insert.

 

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1 hour ago, jamhass said:

There are high-density foams used in high (compressive) load areas.  Had them under my cabin-top mounted winches.  Really strong stuff, yet still much lighter than  other options.

My custom Nelson/Marek was built that way - high density foam in the hardware mounting areas, lower density elsewhere..

40 years now and not a hint of a problem. I'd never use balsa again.

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3 hours ago, SloopJonB said:

My custom Nelson/Marek was built that way - high density foam in the hardware mounting areas, lower density elsewhere..

40 years now and not a hint of a problem. I'd never use balsa again.

Where can someone buy this stuff if doing repairs?  We have some more recoring to do on our SC27 and have been using balsa because none of the local places stock foam.

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19 minutes ago, Rain Man said:

Where can someone buy this stuff if doing repairs?  We have some more recoring to do on our SC27 and have been using balsa because none of the local places stock foam.

Fiberglass Supply in WA state carries Divinycell.  I suspect they can ship to Canada.  I used to pick stuff up from them delivered to my Blaine mailbox, but the border closure kind of puts the kibosh on that for now.

Try Composites One in Langley.  They supply pretty much all the remaining local builders.  They even have the hard to get good stuff - Corecell. 

Mainly a distributor rather than a retailer, but I am told if you drop into their Langley plant, they will sell you stuff over the counter.  The rep we used to deal with is named Bob, can't recall his last name - but he knows his stuff and can be very helpful.

Almost forgot, Fibertek on Boundary Street in Van still sells Divinycell.  They just don't show it on their new web-site or haven't included it yet.  I was in their store a few months ago asking if they still carried it and they brought out a few sheets. 

But they do seem to be transitioning to servicing the local film industry rather than DIY fiberglassers and their new web-site emphasizes that end of their business more.

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On 10/1/2021 at 1:50 PM, jamhass said:

There are high-density foams used in high (compressive) load areas.  Had them under my cabin-top mounted winches.  Really strong stuff, yet still much lighter than  other options.

I've read that for deck core, Island Packet uses. basically, resin and microballoons, maybe with some glass fibers added. I wonder about it vs. high density foam, Coosa board, etc.

I have a pending transom project too, a 19' outboard powerboat.

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On 10/1/2021 at 4:09 PM, Rain Man said:

Where can someone buy this stuff if doing repairs?  We have some more recoring to do on our SC27 and have been using balsa because none of the local places stock foam.

Industrial Plastics and Paint. When I worked there they had several types of foam.

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On 10/2/2021 at 5:53 PM, blurocketsmate said:

I've read that for deck core, Island Packet uses. basically, resin and microballoons, maybe with some glass fibers added. I wonder about it vs. high density foam, Coosa board, etc.

I have a pending transom project too, a 19' outboard powerboat.

That's not really core then, is it...that's a solid glass deck with a high resin content...

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  • 3 weeks later...
On 10/2/2021 at 5:53 PM, blurocketsmate said:

I've read that for deck core, Island Packet uses. basically, resin and microballoons, maybe with some glass fibers added. I wonder about it vs. high density foam, Coosa board, etc.

I have a pending transom project too, a 19' outboard powerboat.

This product sounds like Coremat- it used to be available in thicker form, now I usually see it in 4mm sheets.

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On 10/1/2021 at 2:13 PM, Zonker said:

Yes of course; I didn't think of little boats. Most boats of 70/80's vintage would slap a piece of plywood on the interior as a backing plate (single skin) or as a core insert.

 

Correct - that was what was in the stern of my 7.9.  I replaced it with a piece of solid fiberglass.  Pictures of process to follow  - just because a lot of the time people don't follow up and show what they did =).

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So short story (with pictures! Wooooo!).  Found someone very interested in my boat.  Sent him all the pertinent information, but he's quite a distance away from me.  So he asked a very reasonable question if I could grab a moisture meter and check the whole boat.  The boat was shrink wrapped (and has been for 2 years ish).  7 or 8 years ago I pulled everything off the boat and repainted deck and topside.

Anyway.  I borrowed a moisture meter and started checking.  Everything looked good.  Then I got to the stern.  32%.  Crap.  32%.  Crap.  So.... I made a map. 

port stern (Large).jpg

Starboard Stern  (Large).jpg

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So - he agreed to buy it, assuming I repaired the stern.  He would pay for the repair.  I had a local marina that I use extensively quote it so we knew the ballpark price range, and away I went.  Deal in place, everyone happy. 

I had my son crawl up and get moisture meter readings on the deck too to make sure, and everything looked good.  Or so I thought.

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I mean.  You have to go until you hit dry balsa.  Right?  I promised to make it good.  And.  Well shit.  So - I got sick of the morning dew collecting on the shrinkwrap and running down.  It meant I had to tape the whole repair closed each day, and the was a pain in the ass.  So I pulled the shrink wrap on the boat, and took the opportunity to get up there myself and moisture meter it.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shit.

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Both decks were wet around the chainplates.  The cabintop was wet in the middle of nowhere.  No hardwear even near by.  How the hell does that happen.  So, I started cutting. 

 

And cutting.  I opened the side decks at least 2 feet long on both sides and a foot wide before I got to dry balsa.  Then I cut a square out of the cabin top.  And.....

 

20210918_121131 (Large).jpg

20210918_121104 (Large).jpg

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SHIT.  SHIT.  SHIT.  The balsa there was perfect.  So, I just opened up the cabin top deck for nothing.  Shit and damn.

 

So now I had some thinking to do.  I sold this guy a bill of goods.  A dry boat.  We agreed to fix the stern (at cost, no markup).  But now we've got the decks and they are wet.  That's not the bill of goods that I sold him.  So I guess I'm fixing these on my dime, because it's just the right thing to do.  Even if I cancelled the deal, I can't sell it to someone else without disclosing the problems and lowering the price.  Morals, right?

So now I have to fix it all.  This is not what I planned on doing for my month of September and October, but I'm sticking to what I said and I'm gonna sell this fellow the boat I promised him.  Sooooo....  working begins.

I decided to replace the vertical piece of plywood with solid glass.  I happened to have a chunk of hull (3/4") laying around that had about the same curvature.  So after a lot of grinding, gluing, and bogging I got that in place along with the balsa wood.

112462589_20210930_185355(Large).thumb.jpg.88132a2c311ce6f5037340942c83b488.jpg

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That picture is a little misleading, but that center piece is solid from the bottom all the way up through the top.  I used a fein to remove the material up the rail in the center area are up behind the gelcoat, but left the outer skin in place so I didn't have to make a template to know where the pintel/gudgeons had to reattach.  I beveled the glass so it fit in like a key, filled the area with silica and resin, then slide the glass into place.  That squeezed out the extra bog, then I used that to get all the balsa in place.  Did the whole thing in a single shot.

I also installed solid fiberglass strips on the left, where the mounting point for the outboard motor was.  Might as well do it the way I'd do it if it were my boat (which is kinda still is).

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I opened up the side decks as well.  I inserted solid fiberglass squares where the chain plates pass through, and the rest got the solid balsa job.  Stern was 3/4" thick, but the side decks were all 1/2".  I patched up the hole in the cabin top as well (damn it damn it damn it).

I was careful to only make cuts in the decks and cabin top in the non-skid.  That's easy to redo.  You just need to stay away from the gloss portions around it (what we call the shiny).  But still, that cut into the cabin top meant I was redoing a section 8 feet long and 2 feet wide.  Sigh.

So we feathered the glass around the cuts 2 inches, deck and stern. Used 2 layers of glass in both locations, and started fairing it.

 

20211005_161941(1) (Large).jpg

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The colors you see in that picture are the white (underneath) microspheres.  The really dark black is a spray on fairing compound to show you the low areas.  The white after than was awlgrip primer.  You want to put a coat of primer across the whole stern and sand it.  That way you are sanding a consistent material without any hardness differences that will cause waves where the softer material wears away faster.  The beige you see is 3M marine fairing - the stuff that cures in 15 minutes so you can sand it.

We used an a long piece of 1/8 aluminum to gage the flatness vertically, and to bend around the stern.  What we discovered - and boy did it piss me off, is that the mold in the rear of the S2 (I assume all of them) went from convex on the right to concave on the left of the stern.  By like 1/16" of an inch.

So we sanded.  And faired.  And longboarded.

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And FINALLY - time to paint.  We did the non-skid areas first.  2 of the 3 came out gorgeous.  Below is a picture of the new versus the old. 

20211019_104525 (Large) (Large).jpg

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The third, in true murphy fashion, had problems.  We were doing this all outside, uncovered, in the fall.  So the temperature swings meant we were pretty limited in the time window each day, and we had to dodge constant rain too.  It just so happens that the cabin top non skid had 2 problems.  First - it was obscured by the sun by a tree.  And it got some water on it overnight (even while covered).  So in one area the paint didn't adhere as well as it should, and in another it got a little chalky.  So, that had to be ground completely down again.  Because I'm not doing shitty work and trying to pawn it off on someone.

So, we went back to the stern and finished the fairing.

 

 

20211012_164302 (Large).jpg

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Soon after than, we were ready to paint the stern.  And we did.  And not less than 30 minutes after we painted the stern (we had tarp up and wrapped around the boat to create a tent), the stupid combine in the stupid corn field right next to me start doing their stupid harvesting.  Dust EVERYWHERE.

20211017_140410.jpg

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The kicker was, from one angle it looked great.  From another angle, you could see the corn husk dust everywhere.  I considered lighting their field on fire to help spare them the time of harvesting it (what are neighbors for, right?), but no.....

So, it was time to call in the big guns.  Called a person of a person who had a heated and enclosed shop.  Resanded the stern and resanded the cabintop deck, and made a run to the shop.  Painted it overnight.  We were careful with everything.  We pulled the tape of the edge while the paint was still wet so it could blend from the rear into the side and not leave a tape line. And finally... SUCCESS!

 

20211031_120349 (Large).jpg

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I wouldn't normally post all this baloney, but since I'd been giving the fellow almost daily updates on our progress everything was right at hand and I hoped someone else would get a kick out of it.  Anyway, I cleaned the sides of the boat yesterday, and the finished product turns out pretty damn nice for a 37 year old boat with a 7-8 year old paint job.

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nice work, fun read. thanks for posting. 

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Nice to see an honest man.

You are an increasingly rare, even endangered subspecies.

Homo Sapiens Honestus.

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32 minutes ago, Grrr... said:

Finished with hardware.  What I'm happiest with is you can see no waves in the reflections of the motor mount. 

20211101_180255.jpg

A good example of what the rest of us try for.

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