deck recore with treated ply

[sscoll]

I've cut the top skins off both side decks of my Triton and find that after 46 years the combined moisture penetration amounts to less than a half dozen square feet per side. I'm thinking of using 4 inch squares of treated plywood in as much as its locally available. I remember someone having done something similar in the Triton MIR pages.

Anyone have an opinion about this?

Thanks.

Steve

[Rachel]

My feeling would be negative, based on a couple of thoughts (presuming you mean "lumberyard" treated plywood):

1) Treated plywood often seems to be poor quality plywood to begin with (voids, few plies per given thickness, wet/warped, etc.)

2) I would wonder if the treated/chemicals in the wood would make for an inferior bond with the epoxy/resin you are using to re-core with.

I guess, when it comes down to it, I would just rather use "real" core material meant for the job. Not that I'm all "Oh, one has to used this proprietary product," but just... considering the labor and expense with the resin and other materials.... why not? For example, a 2' x 4' piece of 1/2" core is less than $40 and can be shipped UPS (it rolls up to a small tube size if it is the scored variety).

To put it another way: What is your reason for wanting to use treated plywood? (Not asked as a challenge but just as part of my thought process.)

[sscoll]

Well, I take your view and agree. I've just been visiting with a buddy who has a ton of experience and suggested it. His point was that it took many years to degrade slightly and that when I'm 120 I may want to sell it and buy a bigger boat, or something to that effect. Hooper's said they might have some 3/8"... I'll go with balsa, it just seems squishy, even on the end grain.

You know they're planning a strip mine in the Penokee Hills?

Thanks for your points.

Steve

[Tallystick]

I'm recoring mine with polyester resin mixed with diatomite and fiberglass mat. Most of the top skin is being resused after tapering the edges and embedding them at the top of the mixture. I can do rough fairing while still wet, and then belt sanding for additional smothing, followed by a top layer of woven fiberglass. This is resulting in very stiff decks.

[Carl-A259]

Why not use the inexpensive balsa, it has already proved itself after 40 + years? The balsa didn't fail , the water intrusion thru improperly bedded deck hardware is what failed. I would and have used the scored balsa, I wet the balsa out with epoxy, bending it backward to open up the scoring and apply epoxy into the cracks to totally wet it out before laying it down on the deck. This does two things, helps to stop the spread of water damage if it should ever be present again and it stiffens the decks. ( I would think in theory, any way the repaired deck is always stiffer than the mushy one). If your plan is to use plywood why would you feel it is necessary to use treated plywood? The real plan is to keep the moisture away from the core. Easily attained thru proper bedding outlined on every sailing website, oversize drill, back fill, redrill, etc.etc.Just my thought.

[Rachel]

I'm recoring mine with polyester resin mixed with diatomite and fiberglass mat. Most of the top skin is being resused after tapering the edges and embedding them at the top of the mixture. I can do rough fairing while still wet, and then belt sanding for additional smothing, followed by a top layer of woven fiberglass. This is resulting in very stiff decks.

Tallystick,

Are you using any type of coring? Or are you saying that you are simply filing the space between the skins with polyester resin, mat and diatomite? (And, what is diatomite? I searched and got results for diatomaceous earth, which I know as a sort of sharp-edged "dirt" that will discourage slugs.)

I'm curious what your reasons are for not going with something more along the lines of epoxy resin, woven skin/reinforcement, and balsa or foam core?

Rachel

[mitiempo]

I think plywood is the worst core material to use - heavy and if water gets in the plies let it travel a long ways. I also wonder whether epoxy will stick well to treated ply. The best core material is end grain balsa.

Along with Rachel I wonder about the polyester and diatomite "core" tallystick is using.

[Tallystick]

Diatomite is diatoms or the bio-silica shells from plankton. It's similar to cabosil except the colloidal silica has been assembled into microstructures that are around 50 microns with an aspect ratio of 10:1 or so. I use that because it's a good reinforcing filler for the polyester resin, and the matting gives strength to the composite in all directions at longer length scales. It's comparable to how the aeromarine made their Triton decks I think. Aeromarine probably used a different silica filler, but I doubt the microstructure of the silica filler makes a huge difference. I use diatomaceous earth as my silica filler because I can get it for less than a dollar per pound, and it's a good, natural nautical material.

[mitiempo]

Tallystick

I understand now. But that makes for a heavy core - not to mention a lot of polyester. The purpose of the core in a deck is only to separate the skins, not to impart any strength of its own except to keep those skins apart.

[Quetzalsailor]

I fretted about using treated lumber when I made new engine beds for the Morgan 27. However, I paid attention to the local Watermen in Rock Hall, MD. They habitually use treated lumber and ply under polyester resin and glass for engine beds and whatnot in their workboats, and none of what I observed looked bad in their world of work and hard knocks. Now, I understand that polyester really doesn't bond all that well to wood and Gougeon touts their epoxy as superior for that reason. All the various glues are problematical, given time, poor initial applications, poor initial fits, and enough varying moisture levels in chunky enough pieces of wood. Even marine grade plywood will fail eventually given these conditions (I've got a 1975+/- Italian-built Mahogany Flying Dutchman where the marine plywood decks and other components were reduced to veneers but the cold-moulded hull remains repairable) (I also, last week, used the lumber out of a 1964 Hinckley B-40 mast for the rub rails on the FD I'm rebuilding. The urea resin scarphs failed as I trial-installed the parts onto the hull and I had to clean 'em up and re-scarph using epoxy.)

The pressure-treated lumber and epoxy engine beds in the Morgan did fine for the 5 years I owned the boat after I did the repair and I'm still in touch with the current owner, another 7 years later. The lumber is totally encapsulated in epoxy-'glass. The ordinary plywood I used for the core in the cockpit sole did as well, too.

I conclude that: 1, There is really no reason to be tempted to use pressure-treated material if it's going to stay dry. 2, That pressure treated lumber does not cause a problem to epoxy or polyester (a pretty limited basis for the conclusion!) 3, If you fear water intrusion, using pressure-treated lumber won't hurt, and may save your bacon. And, of course, 4, Pressure treated lumber and plywood is really pretty crappy stuff! Unlike the pressure-treated Okoume marine plywood, ordinary pressure treated yellow pine is the worst of the worst cheap woods available.

[Tallystick]

Mitiempo, yes it does add some weight. Around 10 gallons of resin, 30lbs of diatoms, and maybe 20lbs of matting. To me the main benefit of an all glass deck is that it's monolithic, with much less potential for interfacial delamination between dissimilar materials over time.

[Rachel]

Mitiempo, yes it does add some weight. Around 10 gallons of resin, 30lbs of diatoms, and maybe 20lbs of matting. To me the main benefit of an all glass deck is that it's monolithic, with much less potential for interfacial delamination between dissimilar materials over time.

I have to say that I am still in favor of a more "traditional" deck re-coring. Granted, I have not had the chance to see many re-cores that are more than ten-years old in order to analyze long-term performance, but I don't see major potential for delamination (or the more common de-bonding) with a "proper" re-core job. Even the sloppy, probably hastily built original decks would likely have held up fine if they were not subject to water intrusion.

Actually, original decks can be a good example of what works and what doesn't work. For example, I'm just finishing up a small re-core on a 48-year-old balsa-cored boat, and the only problems were where there was clearly water intrusion due to obvious mistakes in small areas (such as someone mounting spinnaker pole chocks straight into the core with little bedding). 90% of the deck core was dry and tightly-bonded to the skins, and the skins themselves were not delaminated (not that that is really part of the discussion but you mentioned delamination).

Nowadays we know how to isolate* the core from water intrusion, and, as owners working on our own boats, do not have the pressure of "assembly line" and profits to consider. Not that our time is not worth something, but taking a few extra hours to improve the details of the job is nothing in the grand scheme of a re-core. So our re-cored decks should be that much better than the originals. In addition, we can use epoxy with its superior secondary bonding (vs. polyester).

So, based on that and other examples, I can only think that a "properly" (in quotes because this is in my opinion) done core job will last exceptionally well, and be lighter and probably more rigid (skins/tension vs. slab). To me a cored deck in good condition is monolithic, no?

Rachel

*Not that no-one knew, and some boats did have isolated core even then; but many of the plastic classics had deck hardware that went straight into the balsa core.

[Tallystick]

My main thinking on this was that from what I've read EC Tritons used balsa and have deck core problems, while WC Tritons used all glass and deck repair is uncommon. So it seemed reasonable to emulate that construction method. Core skin construction is stiffer on a weight or material used metric, but an equally thick solid cross-section is stronger and stiffer overall. My boat had a partially repaired deck with part of the top skin delaminating on the poorly repaired areas, so that also made me feel like making it solid and be done with it.

[mitiempo]

Tallystick

3/16" skins with 1/2" balsa in the middle is a great deal stiffer than 3/8" solid glass as you are in effect creating a "I" beam. Weight in the core is not necessary and in the wrong place on a boat's deck. To replace balsa with polyester and fossilized algae is a weight gain that doesn't make sense to me.

You state that a previous repair was failing. I wonder if it might have been because polyester was used instead of epoxy, which should always be the first choice for secondary bonds.

[galleywench]

I guess people do use PT in some boat applications, but it always seems wet and slippery to me and I can't imagine that the bond would be as good as with straight marine ply or balsa. Not to mention that it is heavier than regular plywood and if it is well sealed in the first place, what is the point (I think someone already mentioned this).

It never even occured to me that you could do solid decks like Tallystick is doing (or has completed). It seems rare to hear of such a thing, but when you add up the weight, it doesn't seem like a huge amount. I haven't done any stability calculations (and don't intend to) to see what that additional weight (<200 lbs) would do but I wonder if it would be noticeable? I certainly notice when a 200 pound person walks around on my deck, but spread out over the whole boat?

It would certainly simplify a bunch of steps in the recore process, but I don't know if I could afford the extra epoxy (I've used somewhere north of 15 gallons on my recore with balsa). I assumed that the main reason why everyone (or most everyone) did cored decks was a stability thing and not so much material cost. The I-beam effect that's provided with a core is nice and from a material perspective is cheaper, but more labor intensive.

[Tallystick]

Solid is stronger and stiffer than I-beam of same thickness. Now if you took all the material in the solid and made it into an I-beam (which would than be thicker) it would be a stronger I-beam. But if you are just talking about fixed thickness, the extra material in the solid does increase strength and stiffness, but not as much as if you had added it to further separate the I-beam instead of the :"missing" part of the I-beam. I don't find the small increase in weight to be problematic for me, while YMMV. My boat won't be doing any racing.

[mitiempo]

Weight in the wrong places adds up. 200 lbs extra in a deck that is 2 1/2" above the waterline = a vertical moment of 500 ft/lbs. To maintain the same vertical center of gravity (righting ability) 500 lbs is needed 1' below the waterline or 250 lbs 2' below the waterline.

Stability is important if you are racing or not.

[Rachel]

I really don't know if the extra weight would be a problem in the grand scheme of things, so I can't comment to that.

On the other hand, on the subject of stiffness in fiberglass-only decks: Most of the "solid" glass decks I have seen have some sort of framing inside the boat to stiffen them (deck beams, etc.). That seems like a valid way to go about making a boat deck, if one prefers to substitute a more flexible panel and beams for a cored structure. I don't know how thick a fiberglass-only deck with no other support would have to be in order not to be too bendy.

But... Talleystick, it sounds like you are re-creating the thickness of your (adjacent) cored deck by filling with mat and diatomaceous earth and polyester resin, if I understand you correctly (?). So it's sort of a cored hybrid using polyester/mat/diatomaceous earth for the core?

I'm really not sure what to think of that, or how it will hold up, but for myself I would probably feel enough doubt that, since I have easy access to the "proper" materials, and since it's a lot of work either way, I would use a more "traditional" approach vs. experimenting (in fact, that's what I did do, both times [two different boats, not a failed repair]).

Just my thoughts on it.

Rachel

PS: In re-reading, I just thought of one more question I had while reading your initial post about your deck work, Talleystick.

Most of the top skin is being resused after tapering the edges and embedding them at the top of the mixture. I can do rough fairing while still wet, and then belt sanding for additional smothing, followed by a top layer of woven fiberglass. This is resulting in very stiff decks.

You mention re-using the original top skin, and then going over the whole (?) with woven cloth. I don't know the thickness or type of cloth you are using, but are you also going to be tabbing across the cuts? Maybe that is not necessary if you are covering the whole shebang with say, a couple of layers of 1708 (but then that seems like it would negate the benefits of re-using the top skin).

So to summarize, I was just wondering how you are handling the seam between the original top skin and the pieces you are re-using.

[Tallystick]

Anyone have pics of the WC Triton deck cross-section, or know if the thickness is different than EC decks?

[Tallystick]

Oh yeah for the seams, I'm wrapping the wetted matting around the seams so it overlaps around an inch on either side. It's fairly easy to spread around into position with a paint stirrer or spreader. That z-tabbing I guess you could call it is needed to transmit the load along the fibers instead of filler. I sand both sides of the top skin with 60 grit just prior to embedding it.

The starboard side of my boat was badly soggy and I had only planned on fixing that, but now I'm also doing the port and redoing the previous repair around the foredeck. I'll take some pics this weekend.

[galleywench]

Weight in the wrong places adds up. 200 lbs extra in a deck that is 2 1/2" above the waterline = a vertical moment of 500 ft/lbs. To maintain the same vertical center of gravity (righting ability) 500 lbs is needed 1' below the waterline or 250 lbs 2' below the waterline.

I knew I could count on someone to do the math :)

[mitiempo]

Mat has no strength worth mentioning by itself. Its main use is to fill voids between layers of roving when laying up a hull in the traditional way. Biaxial 1708, as mentioned by Rachel, would be a much better choice. Also, if using polyester instead of epoxy, re-using the top skins is not a wonderful idea. If you are covering it with other cloth and polyester resin the work to fair will be the same as if you had not re-used the top skins - and a better bond is achieved between the new polyester and the core you are using than with the old polyester cores.

Re-coring a deck ant attaching hardware properly is a well established and written about project. I see no benefit to trying to re-invent the wheel when proven methods exist.

The stability numbers I posted are factual. Putting 200 lbs 2 1/2' above the deck is the same as hauling a 25 lb weight 20' up the mast - a vertical moment of 500 ft/lbs.

[mitiempo]

To give you an idea of an un-cored deck and its issues a neighbor has a Spencer 35 built in 1964 with un-cored decks. If you aren't sure what type of boat that is it is the same model the late Hal Roth sailed - Whisper and very similar to an Alberg 35. Actually Whisper was 2 boats away from my neighbor's boat in production and it didn't have cored decks either. The Spencer is a solid boat and they didn't build them lightly. But when you walk across the foredeck it flexes a bit - plenty strong enough but a bit springy. On a 35' boat it is never good for boat show visitors to find the deck flexes, no matter how strong it is. The later version, the MkII, had a cored deck without the flex.

[Rachel]

It's comparable to how the aeromarine made their Triton decks I think. Aeromarine probably used a different silica filler, but I doubt the microstructure of the silica filler makes a huge difference. I use diatomaceous earth as my silica filler because I can get it for less than a dollar per pound, and it's a good, natural nautical material.

I would have thought that Aeromarine's Triton decks were simply "solid" layups of fiberglass;, i.e roving, mat, and polyster vs. having an inner "core" of any type, but I don't know that for a fact.

Anyone have pics of the WC Triton deck cross-section, or know if the thickness is different than EC decks?

I feel like I remember seeing a few photos of Aeromarine-built Tritons that had some type of stiffening in the V-berth area to support the foredeck. What I don't know is if that was put in at the time of build or added later. I would imagine the decks are thinner, as I can't imagine them building a boat with 3/4" thick fiberglass decks (estimating thickness of cored deck), but I don't know.

Here is one photo I was able to quickly access of an Aeromarine-built Triton, "Head Over Heels." It looks as though there is some sort of stiffening of the "stringer" type under the foredeck but I can't be sure. The (other) Aeromarine Triton I'm remembering had something more like traditional deck beams running athwartship and didn't look like this one.

[Tallystick]

My boat has a single stringer going in the other direction from those in the photo, from the bow back along the centerline to where the forecabin starts. I used epoxy and cloth to reinforce the wooden beam before building over it with the matting and thickened resin. The top layers of cloth could be epoxied, but I don't know if it will make a difference.

To minimize the weight effects, hopefully my fluid tanks can be located to balance it out. Looks like there are lots of good archives to sort through that may have advice on that.

[Rachel]

My boat has a single stringer going in the other direction from those in the photo, from the bow back along the centerline to where the forecabin starts.

I believe that is usually (and maybe always, although one hesitates to make blanket statements covering them all) present on the east-coast built Tritons, which have cored decks.

The comments and photo I put in my last post were about Aeromarine-built ("west coast") Tritons.

[mitiempo]

Tallystick

When the Triton (and almost any other boat) was designed the tanks were always low down. Of course. they are only effective as ballast when full. You can't count on that all the time so as ballast they are not always useful.

If you add too much weight topside you could always shorten the rig.<g>

(why are there no smilies on this forum?)

[Rachel]

(why are there no smilies on this forum?)

It's a hallowed Plastic Classic Forum tradition. We have to express ourselves in words, with the occasional text-based emoticon. The horror! ;) <---occasional use, which makes them work like a dash of spice, in my opinion.

Rachel

[mitiempo]

Ok Rachel - I'll work with it. <g>

[Tallystick]

My boat only has the stock water tank. It didn't come with a fuel tank, and I am thinking of adding a holding tank and maybe kerosene tank. I've removed the stock galley and icebox, so it's somewhat of a blank canvas. Sorry to divert the tread off topic.