Deck re-core from below

[sailingunity]

Starting cutting the inner skin off today, but decided it wasn't worth it to go any further, as this doesn't look *that* bad, right???

[skipperpete]

Ouch, the deck must have had a bit of spring to it.
I had 60’ of deck exactly like that in your photo but replaced the balsa debris with Divinycell. It would have been impossible from beneath but was not too bad doing the job from above and I got to use the top skin of the deck again although in retrospect I wouldn’t do that again, far quicker to just re glass the whole deck rather than feathering: filling and fairing the joins and edges.

[sailingunity]

Originally Posted by skipperpete

Ouch, the deck must have had a bit of spring to it.
I had 60’ of deck exactly like that in your photo but replaced the balsa debris with Divinycell. It would have been impossible from beneath but was not too bad doing the job from above and I got to use the top skin of the deck again although in retrospect I wouldn’t do that again, far quicker to just re glass the whole deck rather than feathering: filling and fairing the joins and edges.

Yikes that sounds like a big job. I'm glad to do it from below, today I went and cut out 3', this weekend maybe a few more feet. It gives me time to work.

It would seem the coring was 5/8" end grain balsa. I still am undecided on what to replace it with, but it seems 1/2 and 3/4 are more common sizes.

[skipperpete]

My deck was 1” and after the re core it felt like walking on concrete, I was very glad when it was completed .....and I’d be happy to never see another 20 litre drum of filler in my life . The interior linings and bulkheads made it impossible to do any work at all from below. I don’t like balsa core at all after seeing the extent of rot and termite damage, the sheets of foam blocks were easy to sand and fair before grafting the skin back on and re glassing the seams. Make sure you have good ventilation below decks and I hope it all goes smoothly.

[sailingunity]

I have 2, maybe 3 bulkheads I'll have to work around, but I figured I would just remove the tabbing and re-tab.

The inner skin thickness was 1/4", which equate to 6 layers of 1708. Does this seem like overkill? With Vinylester resin and the better 1708, it seems like I could use less layers to achieve same strength as the original, which was no doubt polyester and probably alternating cloth/csm.

[Benz]

Originally Posted by sailingunity

I have 2, maybe 3 bulkheads I'll have to work around, but I figured I would just remove the tabbing and re-tab.

The inner skin thickness was 1/4", which equate to 6 layers of 1708. Does this seem like overkill? With Vinylester resin and the better 1708, it seems like I could use less layers to achieve same strength as the original, which was no doubt polyester and probably alternating cloth/csm.

My understanding is that the under skin of a cored panel carries the greater load--I wouldn't skimp too much on the material.
Without seeing how much area there is to cover and what everything looks like, it's difficult to say.

[Cheechako]

Originally Posted by sailingunity

I have 2, maybe 3 bulkheads I'll have to work around, but I figured I would just remove the tabbing and re-tab.

The inner skin thickness was 1/4", which equate to 6 layers of 1708. Does this seem like overkill? With Vinylester resin and the better 1708, it seems like I could use less layers to achieve same strength as the original, which was no doubt polyester and probably alternating cloth/csm.

My boat was thick like that on the inside also. 1/4"-5/16" in many places.
Too bad they didn't avoid coring at the bulkheads on your boat.

[sailingunity]

Originally Posted by Cheechako

My boat was thick like that on the inside also. 1/4"-5/16" in many places.
Too bad they didn't avoid coring at the bulkheads on your boat.

Built in 74, so perhaps some of those lessons hadn't been learned yet. Though I think many of the build techniques they used were pretty advanced for it's time, it has a relatively light length/displacement of 176.

[sailingunity]

At this point I'm really just thinking of recoring it with 5/8 Balsa, same as what was in there originally, though corecell is a close second. Vinylester resin will likely be my choice due to it's superior properties. I didn't do a fantastic job of cutting the bottom skin out, so I'm not sure I'll be re-using it. Perhaps I'll try harder as I go to be somewhat consistent in my technique.

The main thing steering me towards balsa, besides being so much cheaper, is simplicity, I don't need to buy extra backing plate material for the stanchions (though I will need to overdrill and epoxy the holes).

The problem is finding 5/8 of any material is quite difficult. I found a place in Canada that seems to have 5/8 coated balsa (Noahs). Jamestown doesn't even have it on their site, though I could try calling them. There is one local fiberglass place I'll try on Monday.

I plan to replace the coring at the bulkheads too, my plan is to cut out the tabbing, and re-tab it to the new inner skin. Getting the coring material in there might be tricky, it might be the one place I save the inner skin as well since glassing that area might also be hard.

[Benz]

^^ Why not use 1/2" foam and make it fatter with a couple extra layers of glass cloth?
Nothing gives me the shudders more than balsa core. No one ever said: "I had to re-glass my deck 'cause the foam core rotted."

[sailingunity]

True enough and like I said I am thinking about core cell as well, I've heard good things about it. It just makes the installation process a bit more complicated. I like that it's lighter and absorbs less resin.

However the are concerns with heat I hear

[s/v Jedi]

Yes there have been rudders that turned out to be hollow shells with a puddle of molten foam core at the bottom.

Balsa is fine but no deck penetrations. There shouldn’t be a core material at the stanchions to start with, the core in deck and hull should be tapered out to a solid area around the deck/hull joint that has enough room for the stanchions.

Again, my recommendation to try to put the balsa on the cut off skin first. You can use some hot glue while fitting. Also, simple to repair the cut off skin.

I found the Fein Multimaster the best tool for cutting skin from the underside. The circular saw is impossible where there is not enough room and almost impossible when there is. I like not having straight cuts which helps to get it back exactly where it came from.

[wingssail]

Originally Posted by sailingunity

At this point I'm really just thinking of recoring it with 5/8 Balsa, same as what was in there originally, though corecell is a close second. Vinylester resin will likely be my choice due to it's superior properties. I didn't do a fantastic job of cutting the bottom skin out, so I'm not sure I'll be re-using it. Perhaps I'll try harder as I go to be somewhat consistent in my technique.

The main thing steering me towards balsa, besides being so much cheaper, is simplicity, I don't need to buy extra backing plate material for the stanchions (though I will need to overdrill and epoxy the holes).

The problem is finding 5/8 of any material is quite difficult. I found a place in Canada that seems to have 5/8 coated balsa (Noahs). Jamestown doesn't even have it on their site, though I could try calling them. There is one local fiberglass place I'll try on Monday.

I plan to replace the coring at the bulkheads too, my plan is to cut out the tabbing, and re-tab it to the new inner skin. Getting the coring material in there might be tricky, it might be the one place I save the inner skin as well since glassing that area might also be hard.

I have used ordinary soft wood, such as pine, cut into blocks to fit awkward places. If you can't find the exact 5/8, you can sand down (or plane) thicker material or build up a thinner piece a bit with epoxy filler.

[Sailorman97]

Originally Posted by sailingunity

At this point I'm really just thinking of recoring it with 5/8 Balsa, same as what was in there originally, though corecell is a close second. Vinylester resin will likely be my choice due to it's superior properties. I didn't do a fantastic job of cutting the bottom skin out, so I'm not sure I'll be re-using it. Perhaps I'll try harder as I go to be somewhat consistent in my technique.

The main thing steering me towards balsa, besides being so much cheaper, is simplicity, I don't need to buy extra backing plate material for the stanchions (though I will need to overdrill and epoxy the holes).

The problem is finding 5/8 of any material is quite difficult. I found a place in Canada that seems to have 5/8 coated balsa (Noahs). Jamestown doesn't even have it on their site, though I could try calling them. There is one local fiberglass place I'll try on Monday.

I plan to replace the coring at the bulkheads too, my plan is to cut out the tabbing, and re-tab it to the new inner skin. Getting the coring material in there might be tricky, it might be the one place I save the inner skin as well since glassing that area might also be hard.

Noah's has a Buffalo NY warehouse and they can ship out of there. Saves the customs and import hassles.

[sailingunity]

Originally Posted by Sailorman97

Noah's has a Buffalo NY warehouse and they can ship out of there. Saves the customs and import hassles.

That's good to know, thanks!