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BigSmile · 01-12-2016, 13:07

From under the deck margins, would you remove just the rotted core material, but leave behind the core that is delaminated from top &/or bottom skin, and delaminated in places from itself, and voided in places?

I think the delaminated and voided stuff needs to also come out, but I have been told otherwise. I've been told that, "it does not matter".

For me this does not compute, as I was under the impression that part of the core's job is to keep the bottom & top skins from moving separately, as part of how the deck "I-Beam" construction provides strength. So, how would that be possible with the delaminations of the top & bottom skins, and the delams within the core itself? Doesn't seem to me that these would afford the necessary stability.

And then isn't there that issue of water migration/osmosis that we all know can happen with voids?

Am I crazy?

toddedger · 01-12-2016, 15:53

No your not crazy at all. Core around the margins that hasn't gone bad is a lot more work to remove, but you need to get to a point where both skins are adhered to the core

Terra Nova · 01-12-2016, 15:59

Quote:

Originally Posted by toddedger

...you need to get to a point where both skins are adhered to the core

This...

BigSmile · 01-12-2016, 18:15

Quote:

Originally Posted by toddedger

No your not crazy at all. Core around the margins that hasn't gone bad is a lot more work to remove, but you need to get to a point where both skins are adhered to the core

Thank you for your input, cuz this just boggles my mind...

toddedger · 01-12-2016, 18:48

Now I'm not sure what I'm looking at in your last two photos. Usually core is balsa. Plywood usually ends up where hardware might squish balsa. Not sure but where you have that feeler gauge stuck looks like a lot more than a skin of glass on top. If it's just at the edge than the wood should be dug out and a new piece buttered up with glue can be slid in. Even if it were stuck on both sides the quality of the plywood looks suspect. I doubt the bond between the plys has much strength. But it's tough for me to say cause I really don't know what I'm looking at. I have redone deck core that was mostly plywood on some boats. Ericsson 39 is one that comes to mind. On that one I think I used about 75% balsa, but still mixed in plywood in certain areas where there was hardware, or where core needed to be slid in between glass.

If there is any void area water is not going to migrate into it unless you failed to seal the deck up properly to begin with. Osmosis is the result of glass being always submerged underwater. Not something you have to worry about on a deck.

BigSmile · 01-12-2016, 21:04

Quote:

Originally Posted by toddedger

Now I'm not sure what I'm looking at in your last two photos. Usually core is balsa. Plywood usually ends up where hardware might squish balsa. Not sure but where you have that feeler gauge stuck looks like a lot more than a skin of glass on top. If it's just at the edge than the wood should be dug out and a new piece buttered up with glue can be slid in. Even if it were stuck on both sides the quality of the plywood looks suspect. I doubt the bond between the plys has much strength. But it's tough for me to say cause I really don't know what I'm looking at. I have redone deck core that was mostly plywood on some boats. Ericsson 39 is one that comes to mind. On that one I think I used about 75% balsa, but still mixed in plywood in certain areas where there was hardware, or where core needed to be slid in between glass.

If there is any void area water is not going to migrate into it unless you failed to seal the deck up properly to begin with. Osmosis is the result of glass being always submerged underwater. Not something you have to worry about on a deck.

> It's a weather deck, lots of water sluices around. A long period on the same tack, and can be underwater for just as long. Leela, a similar vessel, has a great pic on her page Leela - The Highs, Lows, and Kisses in Between scroll thru the pics if the image of the wet weather deck doesn't show first.

I also understand that in freezing environments water will work its way into deck voids.

Core can be any number of things. The boat original construction was plywood. What you see glued down is a plywood "equivalent", Coosa.

The feeler gauge demonstrates how delamination still exists behind what has been bonded down. The red stuff is something being used as a fillet so as to glass up and over the foot on the coachroof/cockpit side, which has an additional 1/2" of ply. The feeler gauge was slipped into a delamination in the ply ahead of the glued core, and then turned and angled back behind where the core was glued down to show that the delam exists behind this work.

The original batch of pictures is of margin on the weather deck from both the gunnel side, and the coachroof/cockpit side. The gunnel side has 1/2" core. At the cockpit/coachroof, there is a 2nd layer of 1/2" ply core added on top of the deck core. This created the cockpit/coachroof foot that dimensionally lines up in the final finish with the 1/2" teak deck.

The teak decking did not extend all the way over to the gunnel side, it stopped a few inches before, and it had a curved finish edge. The space between the edge of the teak and the gunnel, channels water the length of the weather deck along the gunnel. Since there is no need for the teak on the gunnel side to join up against anything, there was no need for an extra 1/2" of core on this side.

The last 2 pics are of the coachroof side, the left one is from the port weather deck, and the right is the starboard weather deck.

Your observations about the plywood in the pictures are all spot on, which is why I'm so flabbergast at the assertion that it does not matter.

**minaret** · 01-12-2016, 22:13

Not crazy!!

ramblinrod · 02-12-2016, 09:17

Quote:

Originally Posted by BigSmile

From under the deck margins, would you remove just the rotted core material, but leave behind the core that is delaminated from top &/or bottom skin, and delaminated in places from itself, and voided in places?

I think the delaminated and voided stuff needs to also come out, but I have been told otherwise. I've been told that, "it does not matter".

For me this does not compute, as I was under the impression that part of the core's job is to keep the bottom & top skins from moving separately, as part of how the deck "I-Beam" construction provides strength. So, how would that be possible with the delaminations of the top & bottom skins, and the delams within the core itself? Doesn't seem to me that these would afford the necessary stability.

And then isn't there that issue of water migration/osmosis that we all know can happen with voids?

Am I crazy?

It is a little difficult to comment on photos without the context of seeing the surrounding area.

But in general, the strength of composite construction is highly dependant on the bond of the skin (FRP) and core (Plywood, balsa, foam, honeycomb, etc.).

Break that bond (delamination) and much of the structural strength and integrity is lost.

However, one doesn't have to remove "good" (dry, wet, or even rotted) delaminated core) as long as the skin(s) are still good.

1. "Sound" the delaminated area to determine the extent of the delamination.

2. Drill small clearance holes in the perimeter of the delaminated area through the skin and just into the core, about every 4".

3. Inspect the core "sawdust" to ensure it is not wet. (If so, do drying step 7.)

4. Drill a hole the size of a your shop vac discharge in the centre of the area just through the skin.

5. Pry up the centre area and apply shims between skin and core.

6. Plug in the shop vac discharge, turn it on, and verify air blows out of each hole. (Soapy water on your finger tip and check for bubbles).

7. If core was determined wet (step 3) run the shop vac until all water is blown out and then for 48 hours. (Don't leave unattended.) Try some additional core drill samples to ensure it is now dry.

8. Screw a self tapper (waxed threads) into each perimeter / core test hole.

9. Pour low viscosity resin into the centre hole. (I use polyester.)

10. Put on chemical goggles. Plug in and turn on the shop vac again. (Don't let the nozzle out or resin may fly.)

11. Remove each screw in turn until resin comes out, and then screw back in.

12. When resin has been forced through entire void, remove shop vac nozzle from centre hole.

13. Tape a bottomless paper cup around centre hole.

14. Remove shims from under centre hole.

15. Press down skin (slowly gently) from perimeter to centre hole, collecting resin from the cup as it oozes up.

16. Place sand bags on area around centre cup, collecting excess resin as it works its way out.

17. When resin is cured, remove cup and screws and fill holes.

Also works on underside, but apply pressure (step 16) using flexible panels (e.g. plywood, thickness depending on area, to follow compound curves) with jack posts, and leave the bottom in the collection cup. ;-)

Note: Catalyze resin for sufficient pot life that it won't kick before resin injection / extraction is complete.

Cheechako · 02-12-2016, 09:26

On a Union 36, once you start removing that plywood it might never end! But yes, in theory you should replace any that is not bonded. For those areas that are dry an alternative might be injecting epoxy resin to re bond it.
I think you have to ask yourself how far to go, are you going offshore? or just restoring a boat to use locally?
Unbonded plywood is not proper, but not going to be a problem for local sailing either.

guyrj33 · 02-12-2016, 10:15

I like the idea of using vacuum to pull resin into voids. This could also be accomplished with vacuum bagging techniques. It really works well when properly set up.

Elie · 02-12-2016, 10:29

Brandon from Sheen marine, thank you very much.
So much destruction occurs when one tries to replace wet balsa core that your proposed approch is almost magical. Yet very logic and seemingly working, without major glass work. I presume tha the bleed holes on perimeter are small (1/8. 1/4?. Is a 2x8 ft area is too big for this solution?. Can it be done is steps, smaller area at a time?. What about the idea of using a refrigeration vacuum pump to glue back the skins after drying?. Have you tried your method of drying core?. Does it works all the time?...
Thanks again.

Terra Nova · 02-12-2016, 10:36

Quote:

Originally Posted by Elie

...your proposed approch is almost magical...

Drying out a wet core, in 48 hours, using a shop vac, would be truly magical...if it were even possible.

DeepFrz · 02-12-2016, 11:08

Don't use any plywood in any area that you don't want to compress unless you coat it thoroughly with epoxy and use an anulus at every bolt hole. Injecting neat epoxy to fill voids will result in hard, brittle spots. Injecting a lesser resin will result in hard brittle spots with little ability to adhere to the core. If the core plywood was wet it really should be replaced.

BigSmile · 02-12-2016, 11:25

Here's couple more pictures to help with context.

Delams are not isolated, visual inspection shows them.

Thanks for the details on vacuum. I'll have to study that more, and may have some follow-up questions.

Sailing inside the bay and the stresses on the rig and boat structure are no different than ocean. It can blow a hardy 40 consistently, and I've been out there when it's gone from 5 to 54 in the snap of a finger.

So, I just couldn't rationalize a minimized solution because of possible "lesser" sailing. Everything is (well most everything now) all open, exposed, visible, accessible, so I also can't imagine spending the $$s without a complete solution, ie, getting failed wood out from under margins and re-coring. And to your point, it's a no go with delaminations that break the continuity of the bond from skin to skin through the core. At least in our view. I'm not sure what engineering the folks who are saying "it does not matter" are using. And since they won't engage in conversation about it beyond it does not matter, I'm not able to understand the position. Was hoping that someone here would be able to tell me what I was missing, but I think I'm largely hearing from the community that delams from skins or in core, even if under margins are not sound.