New member, new boat builder trying to avoid moisture problems

[apolyshow]

Hello everybody,
I am a new member, and also a new boat builder from Greece.
I have 3 days now reading your posts to find as much I can, the best answers.
This September we have started a new boat ,36 ft length and today we have this result
91F6C1DD-913A-45C7-9D4F-38C31397C33E.jpg

Now, we are close enough to end the deck woods and I am wondering to install plywood.
C8E914A0-FB3C-47DC-A152-E015006F260E.jpg

Now my problem is , what kind of method to use for sealing correct the plywood .
I believe a 2 material (A+B) sealer and then an epoxy like WestSystem or CPES would be ok, but what is your opinion ?
is that too much or do I have to do something more to avoid moisture and rot?

Thanks a lot from now for your time,

[TerryLL]

Don't use plywood for the decking. This boat calls for laid planks running for and aft with corked seams.

Watch these videos: https://www.youtube.com/@SampsonBoatCo

[wizbang 13]

Leaky decks have killed more boats than rum, rocks and storms combined.
Plywood with dynel and epoxy will give to a stronger , lighter and drier deck. It will be a gift to the boat .
Two layers , 9mm over 12mm .scarph and stagger seams
( no fake wood planks on top of the ply). .

[apolyshow]

Leaky decks have killed more boats than rum, rocks and storms combined.
Plywood with dynel and epoxy will give to a stronger , lighter and drier deck. It will be a gift to the boat .
Two layers , 9mm over 12mm .scarph and stagger seams
( no fake wood planks on top of the ply). .

I am considering to use 15mm okoume plywood and use first a sealer a+b material and after that a westsystem 105/206 epoxy. But I don’t know if west system is going to have a good behavior after the sealer, I mean, if she is going to dry properly and seal the wood or not , because of the sealer.
Afterthis , I am going to use iroko wood with black Sikaflex and if west is not going to work properly, everything is going to be “in the air” and moisture then is going to be everywhere…
What are your thoughts?

[wizbang 13]

My thoughts?
ocoume is a poor choice because it has poor rot resistance .
putting iroko over ply is a mistake. Putting ANY wood over ply to make a fake theatrical deck is a mistake. Choose one or the other . Caulked decks leak . Period .
Using a single layer of ply is a mistake . Two lammed together are stronger than one .
Using a “sealer” under the west is pointless . West is a good product, but it does not do miracles .
The join in the cap rail looks sketchy.
These details should have all been worked out before the first saw cut.
Bruce

[TerryLL]

Agree with Bruce on this one. Okoume is light and a joy to work, but it is not at all rot resistant. It is appropriate for light day-sailers kept on a trailer and stored dry. Not a good choice as an inner deck where moisture may lay hidden for decades.

Also, Laid and corked decks do leak when not maintained, but seldom require complete removal when a rot pocket appears.

[Geftb]

Hello Apoly, welcome to the forum!
Fantastic progress for a September start!! How many are working on the project?
personally I would go with post #3.

Bruce, Looking at the rest of the joinery I would say that cap rail is temporary bracing, protect the end grains etc. At least I hope so

[apolyshow]

Hello Apoly, welcome to the forum!
Fantastic progress for a September start!! How many are working on the project?
personally I would go with post #3.

Bruce, Looking at the rest of the joinery I would say that cap rail is temporary bracing, protect the end grains etc. At least I hope so

Hello Geftb and thank you very much for your welcome and your kind words.
We are working only 2 guys and here you can see the first photo approximately at 10 of September after the first drawings.
C2D6CFAD-2D47-4300-9E5B-799DBE350E36.jpg

A lot of hot and a lot of work but now the rains and cold (and money ) have for a while stop us…

And if someone knows Italian here is an article about us from a website in Italy where we think to sail as a first journey before other countries
https://www.vaielettrico.it/dalla-gr...a-in-giardino/

I also think seriously the post #3

[Rumars]

You can use okoume for the deck, but it needs more precautions then a more rot resistant species like sapeli. You can also use a single layer of ply, but it's more difficult because you have to properly scarf the pieces, and thicker ply does not conform so easily to the deck curves. The ply needs to be fiberglassed for wear, okoume isn't very hard. Don't waste time trying to find dynel, it's not worth the trouble of importing it from outside the EU.

There is no reason to use anything else then epoxy to seal the ply. The two part sealer is probably a polyurethane, and is just a form of paint. If it is an epoxy base it's thinned down (like CPS) and doesn't work as well as "normal" epoxy (100% solids).
Everything epoxied must be protected from UV, preferably with paint, if not, with varnish.
To seal, you paint the surface with unthickened epoxy, usually 3 layers. The edges of the ply are especially important and will need more layers, you paint it on until it stops absorbing it. The usual procedure is to seal the underside of the deck and fiberglass the top. With all those stanchions going trough the deck, I would also fiberglass the ply edges in advance. The deck is glued on with thickened epoxy and the screws removed and holes filled before fiberglassing. If you use stiched biaxial cloth you should follow up with a woven finishing layer.

Now comes the really important part, in order to maintain the deck integrity every single hole has to also be protected by having the fasteners going trough thickened epoxy. The procedure is to overdrill, fill, redrill to final size. This is something you must do every time you install something on deck.

If you want to install a wooden deck for traditional appearance, it must be done without screws, you glue the thin (maximum 9mm) planks onto the fiberglassed plywood using thickened epoxy.

With the current price of plywood and presuming you already have a lot of wood available, you could also think about a fiberglassed strip planked or cold molded deck.
I presume you plan to use carvel planking, maybe you should also think about strip or double planking with epoxy.

Thanks for the article, it's interesting, are you going to use a variable pitch propeller, or are you just accepting the inefficiency of the mismatch between normal and full power?

[wizbang 13]

Yea… those frame extensions that double as top timbers/ stantions…
that’s never a good idea
they are the first thing to rot

[apolyshow]

You can use okoume for the deck, but it needs more precautions then a more rot resistant species like sapeli. You can also use a single layer of ply, but it's more difficult because you have to properly scarf the pieces, and thicker ply does not conform so easily to the deck curves. The ply needs to be fiberglassed for wear, okoume isn't very hard. Don't waste time trying to find dynel, it's not worth the trouble of importing it from outside the EU.

There is no reason to use anything else then epoxy to seal the ply. The two part sealer is probably a polyurethane, and is just a form of paint. If it is an epoxy base it's thinned down (like CPS) and doesn't work as well as "normal" epoxy (100% solids).
Everything epoxied must be protected from UV, preferably with paint, if not, with varnish.
To seal, you paint the surface with unthickened epoxy, usually 3 layers. The edges of the ply are especially important and will need more layers, you paint it on until it stops absorbing it. The usual procedure is to seal the underside of the deck and fiberglass the top. With all those stanchions going trough the deck, I would also fiberglass the ply edges in advance. The deck is glued on with thickened epoxy and the screws removed and holes filled before fiberglassing. If you use stiched biaxial cloth you should follow up with a woven finishing layer.

Now comes the really important part, in order to maintain the deck integrity every single hole has to also be protected by having the fasteners going trough thickened epoxy. The procedure is to overdrill, fill, redrill to final size. This is something you must do every time you install something on deck.

If you want to install a wooden deck for traditional appearance, it must be done without screws, you glue the thin (maximum 9mm) planks onto the fiberglassed plywood using thickened epoxy.

With the current price of plywood and presuming you already have a lot of wood available, you could also think about a fiberglassed strip planked or cold molded deck.
I presume you plan to use carvel planking, maybe you should also think about strip or double planking with epoxy.

Thanks for the article, it's interesting, are you going to use a variable pitch propeller, or are you just accepting the inefficiency of the mismatch between normal and full power?

Dear Rumars thank you very much for your thoughts and the details that you post.
Extremely important and useful. Thank you for your time.Let me start from underside because it is important for me.

At underside I have put with D4 type glue a wooden veneer (maple) because I wanted to give a little bit of luxury . I am thinking to put west at this veneer and after west, 2 layers of Coelan varnish , so maybe I will protect the underside.

I am using plywood at top in order to decrease the weight because I already have a lot of weight down with all those ribs.
I am thinking a lot the idea of fiberglassing the ply to catch as much more I can the moisture and the rot.
Now as for the traditional appearance that I want to give at deck with iroko, the problem is that only glue will not give the curves that I need to give at planks of iroko, always according with deck curves…
So I have already buy inox screws and I will see how am I going to cover them but your idea is very strong , generally speaking.
The only thing that I am thinking about what you said, is that epoxy and west is doing much more good work, but from the other side , west is not so flexible and I am wondering if all the strengths that are going to push my deck (mast, ropes, walking, sun etc) if they are going to “brake” the epoxy and leave moisture to get in….

Finally as for the propeller I am going to use a variable pitch propeller in order to avoid any kind of drag power to stop the recharging of my batteries and the speed of my boat.

Thanks again for your kind words and your thoughts , they are really good and helpful!
Thanks my friend,

[john welsford]

I agree with plywood, and making sure you use a rot resistant species rather than okoume. But do make sure that every edge, and every hole for a fitting or whatever is sealed.
If you want a plywood deck to last forever, drill holes for fittings oversize, fill with epoxy then when thats hard, drill for the fitting through that.
Water in the end grain is not plywoods friend.

John Welsford

[Rumars]

If you already veneerd the plywood all you can hope for is that you did a good job, hopefully with a proper veneer press or vacuum. Put three layers of epoxy over it, and varnish. Coelan is overkill for the inside, but it's your money.

Epoxy is stronger then screws, and there is no flexibility in a plywood deck. The ply is glued to the deckbeams, carlins and beamshelf (you need to install blocking over your existing shelf), nothing moves.

Do not use screws, all modern teak deks you see on yachts are glued on, it's not my own idea. That's why there is a thickness limit of 9mm, this way the wood will not overpower the adhesive. If you need temporary screws when installing the strips those are put in the seams, then removed and the holes filled with thickened epoxy before installing the black caulking.
I'll try to find you some pictures of the process so you can understand it better.

[Paul G.]

Don't use plywood for the decking. This boat calls for laid planks running for and aft with corked seams.

Watch these videos: https://www.youtube.com/@SampsonBoatCo

Do NOT use a laid deck unless you like leaks. Good quality plywood glued and mechanically fastened will extend the life of this boat immeasurably. There is no need to "seal" with CPES. Use neat epoxy on any exposed endgrain. With ply you can fit it, mark where the paint goes and finish it before final assembly. A layer or two of heavy Biax will give it impact protection,

[debenriver]

While ply is a very good material for decks, I think you are going to have difficulty fitting around all those bulwark stanchions. I know it's too late now, but bulwark stanchions are (in yacht practice) traditionally fitted after the hull is planked and the deck is laid, dropped down alongside the frames rather than as an extension of them.

In that way the decking can come out over the top edge of the sheerstrake. Then the stanchions are dropped down through rectangular holes cut in the decking - the back (outboard face) of the stanchions is housed out the planking thickness over the decking (because it's almost impossible to caulk and pay once the bulwark planking is on). The other three sides have a caulking seam and are caulked and payed. You can also leave the beamshelf down (as you have) so as to get a good air flow behind and above the shelf. And the almost inevitable deck leaks around the stanchions won't trickle down behind the frames and rot them out from the back – a very common situation with stanchions that as simply an extension of the frames.

As you have it now, I would seriously consider solid timber laid decks with a good hefty covering board – Iroko is not perfect for the job but we built several yachts back in the day with Iroko decks – OK, they leaked from time to time but that was before the days of modern polysulphide paying materials, which are much more elastic than pitch. Either laid with the sheer snaped in to the king planks and margins, or fore-&-aft, snaped into the covering boards. The covering board will still be an absolute pig to fit and make watertight, but at least it can be in relatively short lengths and doesn't also have to fit up to the coamings etc., or deal with the deck camber like ply will have to.

If you do lay ply, then I would say that your 15mm is fine – either scarph the sections together or butt join then with butt straps bonded under. Personally I wouldn't lay solid decking over the ply and certainly not screw fasten it permanently – inevitably the plugs over the screw heads will wear and water will penetrate into the ply and rot it out. If you really must do it - do as Rumars says – 9mm max thickness all epoxy bonded, no permanent screws. Square edge planks. No caulking. Pay the seams with epoxy/graphite. But it's a lot of work. Even then I wouldn't lay a covering board, but rather keep the first deck plank inboard of the stanchions with the edge rounded over.

Cheers -- George

[Geftb]

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A lot of hot and a lot of work but now the rains and cold (and money ) have for a while stop us. 3

well, this is good. There is a lot of experience on this forum so take your time, read through and research each reply, make sure you understand what each person is saying, (there will be different opinions) and make a solid plan before going forward.
All the best.

[Rumars]

There are several ways to tackle the deck fitting problem. If the stanchion top timbers are not glued to the frames they could be removed and reinstalled after the deck is laid. All gaps are then filled with thickened epoxy.
If they are glued, the tops could be sawn flush with the beams and the offcuts reinstalled as stanchions using metal hardware (shoes or steel rods with barrel nuts, or even inletted flat bar.)

[pcford]

Leaky decks have killed more boats than rum, rocks and storms combined.
Plywood with dynel and epoxy will give to a stronger , lighter and drier deck. It will be a gift to the boat .
Two layers , 9mm over 12mm .scarph and stagger seams
( no fake wood planks on top of the ply). .

I did a boat about forty years ago. "Fake" teak over plywood. Where do you come up with these "ideas?"

[wizbang 13]

I did a boat about forty years ago. "Fake" teak over plywood. Where do you come up with these "ideas."

Pat, Did this boat have a butterfly hatch ? Did it live in a boathouse? Did you put ten coats of Epifanes on her? We’re you wearing a silly Greek fisherman hat ? Tell us more details and maybe we can help you.
Bruce
edit… oh sorry man, I thought you said “fake Teat”

[willin woodworks]

I did a boat about forty years ago. "Fake" teak over plywood. Where do you come up with these "ideas."

OK, tell everybody how you did it.

[Nicholas Carey]

I am considering to use 15mm okoume plywood and use first a sealer a+b material and after that a westsystem 105/206 epoxy. But I don’t know if west system is going to have a good behavior after the sealer, I mean, if she is going to dry properly and seal the wood or not , because of the sealer.
Afterthis , I am going to use iroko wood with black Sikaflex and if west is not going to work properly, everything is going to be “in the air” and moisture then is going to be everywhere…
What are your thoughts?

If you are doing a plywood deck and epoxy-coating it, what would be the purpose of a "sealer a+b material" applied to the plywood first? The epoxy coating is your sealer. And anything you put on the wood is likely to weaken the epoxy/wood bond.

A 2-layer plywood deck, sheathed with epoxy and either dynel or fiberglass fabric will last a long time. Here's a piece by Our Host (WoodenBoat magazine) on a good process for doing a plywood+epoxy+fiberglass deck:

https://skills.woodenboat.com/articl...-plywood-deck/

You might find it useful to get a copy of the Gougeon Brothers' book, The Gougeon Brothers On Boat Construction book, available from them as a free PDF, or you can buy the hardcover book:

https://www.westsystem.com/the-gouge...-construction/

On a related note (and given the cost of teak), this stuff looks quite interesting: MarineDeck 2000.

Cork planks, 9mm thick x 36 or 50 mm wide x 1.88 m long, though they're actually a cork composite: cork granules compressed under very high pressure with polyurethane adhesive and UV inhibitors. Also available in wider widths for margin boards and king planks. Bonded to the substrate with Simson (Bostik) marine adhesive/bedding compounds.

https://stazo.nl/en/stazo-marinedeck/

The stuff looks pretty tasty, too:

deck-1.jpg

deck-3.jpg

deck-2.jpg

cork-decking.jpg

[John B]

I'm sitting on a boat with teak overlay on ply , it was built in 1974. It's time for it to go but geez, nearly 50 years isn't a bad life and I'm not going to be changing any plywood when I get rid of the teak( which is now at the end of its life through wear.)

[pcford]

Pat, Did this boat have a butterfly hatch ? Did it live in a boathouse? Did you put ten coats of Epifanes on her? We’re you wearing a silly Greek fisherman hat ? Tell us more details and maybe we can help you.
Bruce
edit… oh sorry man, I thought you said “fake Teat”

No to all above. That is if I understand your questions.

[apolyshow]

If you are doing a plywood deck and epoxy-coating it, what would be the purpose of a "sealer a+b material" applied to the plywood first? The epoxy coating is your sealer. And anything you put on the wood is likely to weaken the epoxy/wood bond.

A 2-layer plywood deck, sheathed with epoxy and either dynel or fiberglass fabric will last a long time. Here's a piece by Our Host (WoodenBoat magazine) on a good process for doing a plywood+epoxy+fiberglass deck:

https://skills.woodenboat.com/articl...-plywood-deck/

You might find it useful to get a copy of the Gougeon Brothers' book, The Gougeon Brothers On Boat Construction book, available from them as a free PDF, or you can buy the hardcover book:

https://www.westsystem.com/the-gouge...-construction/

On a related note (and given the cost of teak), this stuff looks quite interesting: MarineDeck 2000.

Cork planks, 9mm thick x 36 or 50 mm wide x 1.88 m long, though they're actually a cork composite: cork granules compressed under very high pressure with polyurethane adhesive and UV inhibitors. Also available in wider widths for margin boards and king planks. Bonded to the substrate with Simson (Bostik) marine adhesive/bedding compounds.

https://stazo.nl/en/stazo-marinedeck/

The stuff looks pretty tasty, too:

deck-1.jpg

deck-3.jpg

deck-2.jpg

cork-decking.jpg

Dear Nicholas what a wonderful answer ,thank you very much for all the info.
I already after reading your answer send a message at STAZO and no I am trying to find Dynel’s product.
My workers are saying that fyber is not something that we need but I am thinking it very much after I show the article.
Thank you very much I will download the magazine .

[apolyshow]

I'm sitting on a boat with teak overlay on ply , it was built in 1974. It's time for it to go but geez, nearly 50 years isn't a bad life and I'm not going to be changing any plywood when I get rid of the teak( which is now at the end of its life through wear.)

John had you made any special job like for example fiberglass into plywood or anything else?
Did you had any problems with moisture, or water inside through deck or rot ?

[John B]

John had you made any special job like for example fiberglass into plywood or anything else?
Did you had any problems with moisture, or water inside through deck or rot ?

There are no issues but I didn't build the boat , it was a professional build by a prestigious boat builder in 1974. My expectation is that it has an epoxy glued ply deck, and the teak was glued down with weights and screws in the caulking rebates. All the fastenings were then removed , holes filled and the rebates/ grooves caulked. So now I have worn teak glued to ply , no screws, no leaks or rot , but the teak is past its use by date.
I don't know what the ply is but it's whatever the best type was in 1974.
I have work to do but rot is not one of the jobs.

[Paul G.]

There are no issues but I didn't build the boat , it was a professional build by a prestigious boat builder in 1974. My expectation is that it has an epoxy glued ply deck, and the teak was glued down with weights and screws in the caulking rebates. All the fastenings were then removed , holes filled and the rebates/ grooves caulked. So now I have worn teak glued to ply , no screws, no leaks or rot , but the teak is past its use by date.
I don't know what the ply is but it's whatever the best type was in 1974.
I have work to do but rot is not one of the jobs.

Its only about 80 boat dollars if you get your man to do it!

[apolyshow]

.

A 2-layer plywood deck, sheathed with epoxy and either dynel or fiberglass fabric will last a long time. Here's a piece by Our Host (WoodenBoat magazine) on a good process for doing a plywood+epoxy+fiberglass deck:

https://skills.woodenboat.com/articl...-plywood-deck/

Where can i find to buy Dynel product ?

[Nicholas Carey]

Where can i find to buy Dynel product ?

Dynel is a trademarked name synthetic acrylic fabric.

You can but it from Jamestown distributor, and from composites suppliers.

https://www.jamestowndistributors.co...ct-detail/4214

It will require significantly more epoxy to wet out than fiberglass fabric, and it tends to "float" in the resin. It's used on decks because it's tough and abrasion resistant, and since it's a proper woven fabric, looks more like a painted canvas deck.

[wizbang 13]

Xylene and Dynel are very similar .
Apparently they are different fabrics, but they behave in application and service about the same.
One is a tighter weave, which one… I forget by now.

[pcford]

Xylene and Dynel are very similar .
Apparently they are different fabrics, but they behave in application and service about the same.
One is a tighter weave, which one… I forget by now.

actually: "Xylene is a colorless, flammable liquid with a sweet odor. Exposure to xylene can irritate the eyes, nose, skin, and throat. Xylene can also cause headaches, dizziness, confusion, loss of muscle coordination, and in high doses, death. Workers may be harmed from exposure to xylene."

[wizbang 13]

Oh ya got me Pat
I meant xynole
izzat it? Zat howitz spelt?
didja sheath a boat with it 40 years ago?

[pcford]

Oh ya got me Pat
I meant xynole
izzat it? Zat howitz spelt?
didja sheath a boat with it 40 years ago?

I don't fool too much with plastic materials. That is, if I understand your comment. (?)

[Rumars]

Where can i find to buy Dynel product ?

Only from the USA, it's not usually imported in Europe. For your application it's completely unnecessary, since you want to skin your deck with iroko. Even if you wouldn't, dynel and other similar fibers are a waste of money for decks. Their only useful for repeated high wear areas, for example a kayak keel that is regularly dragged over sand and stones. Not to mention that if you use epoxy you can't have it exposed to UV, on deck and topsides the paint is the critical component, not the fiber type.
As I said before, forget dynel, use fiberglass. Just like kevlar, Dynel and Xynole are hyped up by people who don't understand when and how to use it.