Ply Deck on Ferro yacht

[AlexR]

Hi All,

Not sure if this topic has come up prior(i cannot find a thread on it)

I am replacing the ply deck on our ferro yacht, has anyone tackled this before?

My question is around the hull to ply deck join and what everyone/anyone else has done on the edge whee the deck and hull join.

Much appreciated

[jeepers]

https://www.fastenal.com/content/doc...agna-Crete.pdf

http://tex-crete.com/pdf/Flooring/ep...0_11-07-06.pdf

How big is the boat?
How much of the deck needs replacing?
How much of the deck is cementitious F/C &/or steel &/or wood ?
How much of the cabin structure sides & roof need replacing?
Who is doing the job? Yard, Contractor, Owner
There are also the $$ factors A.) What is the market value of the boat worth? B/) What is the boat worth to you? C.What is your budget? (You can pm this to me if you prefer)

NB.This (Deck repair & replacement) is a common issue of F/C boats with wood decks. Especially owner built.
I have noticed that "most" F/C boats under 40-45' have wood decks & cabin structure. Many have Fiberglass coatings & repairs.
There are many Youtube videos of wood & composite decks being strengthened, repaired & replaced by epoxy &/or fiberglass
"Most" F/C Boats 45+' have steel or cement (FC) decks & cabin structure.
"Most" F/C boats with cement (F/C) decks & cabin structure "generally" need less maintenance than steel.

[AlexR]

Hi Jeepers, cheers for the reply.
The boat is 43ft, wide beam.
I am doing the job myself, and replacing the whole deck, the current deck is 12mm marine ply with fibreglass over it. The deck sits on top of the outer rub rail. However water has made its way in there.
Id like to change the way the deck and hull join, and would love photos or videos of others. I have looked on YouTube however cannot seem to find a ferro hull to wood deck join.
Cheers Alex

[Wotname]

Whatever you do, please make sure you seal all the end grain (i.e. edges) of the ply with resin (preferably epoxy). You can't overdo the edge sealing but you can "underdo" it. Ply is great stuff if it keep dry and the edges well sealed.

Also any penetrations should be treated in the same manner as you would in a foam core deck.

[Fore and Aft]

AlexR I would heavily coat the underside of the deck with epoxy before gluing the sheets down to the deck beams. I usually mark the deck beam positions on the plywood so I am only resin coating the areas inbetween the beams.

Wotname is right about sealing the end grain and I wonder if you could bevel the plywood deck edge so you can heavily glass it onto the rub rail which I assume is timber? Two layers of 450gm double bias would seal it well. The last deck I did for myself I covered all the glass with peel ply (Then removed it) and that was basically all the finishing I did on the non skid areas. Then the gloss areas got a coat of filler to smooth out the fiberglass.

Not knocking ferro but this is basically a love job you are doing and I cannot see you increasing the yachts value.
Another good idea is to get on the phone and find the best deal on plywood in your area. I brought 112 sheets of plywood for our yacht and got a big discount. The same with the epoxy and fiberglass a bulk buy got me a big discount. Big enough that the interest on my visa card still did not cancel out the savings.

Cheers

[AlexR]

Wotname thanks for the advice, i will definitely be sealing the end grains on the ply.

Fore & Aft cheers for your advice, would you resin the whole sheet and then add a thickened epoxy to the deck beam before mounting?
The rub rail is wood yes, would it not be better to fibreglass over tge deck and down the hull directly to the cement and the mount the rub rail ontop of the fibreglass??
I am curious at looking into a couple of potions giving me a good seal.
Cheers

How

[Fore and Aft]

AlexR I can't say I have ever glassed on to concrete before......but in my head I am thinking if you glassed over the edge of the plywood , 50mm down the concrete sides, then bolted the timber rub rail on top of the fiberglass using sikaflex the fiberglass might hold onto the concrete hull. Sort of a timber/sikaflex/fiberglass/concrete sandwich. I could see that working, particulary if you use a good glass like 450gm double bias. I would use one layer of double bias on the deck and two layers on the deck hull radius. As for the epoxy on the plywood underside you could just wet out the full sheet and then straight away lay the plywood on top of the deck beams that have been covered with epoxy glue. I would also consider getting a good grade exterior plywood with two good faces. The two good faces make it so much to easier to work with.

Cheers

[Wotname]

I also haven't glassed to FC before but if I was and if I didn't seek further advice, then I would make sure the FC was super clean and abraded by using a concrete cleaner (HCl acid) and then using epoxy.

Epoxy has a very high mechanical adhesion to most surfaces hence the need for the surface to be both clean and rough.

Maybe google can advise if there is a cheaper solution available than epoxy and that gives the same adhesion.

[HankOnthewater]

Fibreglass resin will stick to concrete, but epoxy resin does it much much much better. I would would not use fibreglass resin on concrete or on old timber.

Hmmm, by having the deck siting on top of the rubrail.... that may be asking for trouble: we all bump into something at times, and if the rubrail gets knocked then the plywood deck does get a bump as well, not a good idea. The plywood AND its edges need to be protected from that.

Maybe you could make a drawing how the deck was fixed to what, and then some of us and make recommendations how to improve on that. Hmmm, 12 mm thick plywood might be marginal as well on a 43 ft boat, also depending how far the support beams are apart, or how many layers of glass you add to that.

BTW, I had a ferro boat myself for 20 years, and worked on 3 or 4 others as well.

[jeepers]

Were there Ferro/cement bulkheads cast in place when the hull was made?
The physical/engineering properties of concrete(& steel) and wood(& fiberglass) are very dissimilar. Wood & fiberglass have similar coefficients of thermal expansion. Concrete & steel almost identical. Concrete has minimal tension strength.
There needs to be beams between the hull sides just under the deck(& bulkheads from hull side to hull side). To resist the hull top edges being flexed or compressed
A boat is not a static structure.It is subject to many forces including torsion.
I would construct a labyrinth seal at the top of the hull sides with a chamfer or step on the outside corner of the hull. The labyrinth seal groove can be cut with a Diamond masonry blade.
Any wood would be treated with 2-4 coats starting with a "thinned soaking" sealer of either fiberglass resin & acetone &/or epoxy.
Plywood end or edge to edge has none or limited sealing design. Any & all wood sheeting would be edge/end routered to accept a 1/4" hardwood tongue. This is similar in principle to making biscuits but is continous. This makes a continuous Tongue & Groove joints & seals. These connections would have copious resin/epoxy applied as an adhesive/seal during installation.
You may find a "Toe saw" helpfull in removing the rotten deck & frame work. Eg.
https://www.harborfreight.com/power-...saw-62420.html
I use the above saw for cutting rotten sole out.
In my opinion;
Making the following assumptions.
The rest of the boat is in good condition, has value, will probably last another 40-50 years or more. (Which is not a limit, but a historical observation.There exists a 160 year old F/C boat, a dinghy made in France 1860, that is still usable )
If the boat was 38' & under I would probably replace the wood with a 3/4" plywood "continuous" membrane. Since the subject boat is 43' I would install a non organic "cover" that is in theory a form to cast a F/C deck on top of it. This cover or form could be made from ribbed fiberglass sheets or steel or plastic. This would be an excellent opportunity/application to use recycled plastic.

[AlexR]

Originally Posted by Fore and Aft

AlexR I can't say I have ever glassed on to concrete before......but in my head I am thinking if you glassed over the edge of the plywood , 50mm down the concrete sides, then bolted the timber rub rail on top of the fiberglass using sikaflex the fiberglass might hold onto the concrete hull. Sort of a timber/sikaflex/fiberglass/concrete sandwich. I could see that working, particulary if you use a good glass like 450gm double bias. I would use one layer of double bias on the deck and two layers on the deck hull radius. As for the epoxy on the plywood underside you could just wet out the full sheet and then straight away lay the plywood on top of the deck beams that have been covered with epoxy glue. I would also consider getting a good grade exterior plywood with two good faces. The two good faces make it so much to easier to work with.

Cheers

Ive bought some good marine ply with both outer surfaces looking good. 450gm double bias will hold, i was in fact considering 2 layers on the whole deck and sides, both for strength and because the deck is only 12mm.

The sides give me anxiety 😂, i would prefer hiding the edges of the deck to avoid any impacts. Ill get the laptop on today and draw up a little drawing of what i am thinking.

[AlexR]

Originally Posted by HankOnthewater

Fibreglass resin will stick to concrete, but epoxy resin does it much much much better. I would would not use fibreglass resin on concrete or on old timber.

Hmmm, by having the deck siting on top of the rubrail.... that may be asking for trouble: we all bump into something at times, and if the rubrail gets knocked then the plywood deck does get a bump as well, not a good idea. The plywood AND its edges need to be protected from that.

Maybe you could make a drawing how the deck was fixed to what, and then some of us and make recommendations how to improve on that. Hmmm, 12 mm thick plywood might be marginal as well on a 43 ft boat, also depending how far the support beams are apart, or how many layers of glass you add to that.

BTW, I had a ferro boat myself for 20 years, and worked on 3 or 4 others as well.

Ill be using west system epoxy.
Let me draw up a little picture and post it.

[jeepers]

What model or plan of boat is it?
Is it a center cockpit or aft helm, does it have a pilot house.
What condition is the cockpit /helm station in?
How much of the deck is rotten & needs replacing?
Can you post/provide photos of the deck/project?

Could you put a rub rail below the hull deck joint?