Dynel over ply deck?

[psk125]

I am replacing the sole (deck? cockpit floor?) on a center-console runabout, and am thinking about covering the 5/8" marine plywood with a cloth/resin combination to keep it drier this time. Many Woodenboat articles mention people using dynel on their decks. I also hear Vectran is a possibility, as is, of course, the standard fiberglass. I would plan to tab into the hull with some 4" fiberglass tape, but for the large, flat expanses is a different material better? I think just one layer of fiberglass cloth (not counting overlaps) would be sufficient. Would dynel and vectran work with just one layer, or are more necessary? Thanks in advance for any advice.

[Bayboat]

I would use Dynel, two thicknesses, for the cockpit floor. Paint each layer with epoxy. Lap it up about 1" around the perimeter and screw-fasten a 1" or 1-1/2" batten with bedding compound against the Dynel. Trim with a razor blade or exacto-knife. I put 2 layers of Dynel on my cabin top ten years ago and it's still fine.

[brad9798]

agreed ...

[paladin]

make sure the edges ALL AROUND the plywood are well sealed, bottom, edges and topsides...with the same epoxy that you are using with the cloth....

[RodB]

First, know that Dynel or Xynole polyester (which I prefer over Dynel cause its easier to work with and every bit as effective) both use lots of epoxy and that costs money (like three times what 6 oz cloth would require. There was a detailed study by the Gougeon Brothers where they tested many variations of fabrics for impact and abrasion resistence for use on the decks of the Ticonderoga... The results were quite illuminating. I studied it carefully before deciding to just go with one layer of Xynole cloth for the bottom sheathing of my skiff. Those numbers showed one layer of xynole cloth was several times more abrasion resistant than 6 oz fiberglass cloth...and several times more impact resistant. The next best think I could have done was to use an exotic fabric like Kevlar...or use two layers of Xynole, or polypropylene , or Dynel...or a combination of two of these. I figured the weights and cost of these various fabrics..and decided one layer of xynole polyester was plenty of protection for hull sheathing my 18 foot....800 lb hull. If I was building a 28 foot sailboat, I would use two layers of Xynole as sheathing...

I would say that one layer of 6oz cloth and epoxy would be adequate if you are not particularly hard on your boat...and if the ply is supported well underneath....so that there is little flexing. My 18 foot skiff has 1/2" ply Okoume flooring that is glassed on the top surface(4 coats of epoxy and 6 oz fiberglass cloth) and double coated with epoxy on the bottom surface. There is a generous support system of stringers running underneath it and it ties into cleats along the sides of the hull about 5" above the chine. There are 4" wide 3/8" ply strips to tie all floor panels together...as shown in the photos... My cockpit floor is as solid as a rock!



FYI...all surfaces of wood here were triple coated with epoxy...the top surface here of the hull bottom was glassed and had extra coats of epoxy applied where water would stand during use of the boat.



Note the electrical gray PVC used for steering and control chases...blocks of Honduras Mahogany were glued to the hull bottom and the screws for the clamps were screwed into the blocks only...no holes were made in the hull bottom. Naturally the scews in the blocks of wood were slathered with epoxy upon installation.



Note sheetrock screws were used for the glue up...and removed later...and holes filled.... all joints between panels were taped with 4" 7oz cloth tape....


Completed with all joints filled with epoxy and taped (photo does not include the joints along the sides of the hull yet). The hull sides joints with the floor were taped with biaxial tape...as I had it left over and It was so strong (was overkill).


In addition to primer and paint (Kirbys) ...a non skid of ground walnut shells of a proper grit....(about $15/50lbs) sprinkled in paint was applied to most of the surface. I really like this type of non-skid because in reality it is only wood particles in paint...atop a solid glassed panels...so it is very water proof and easy to re-do.




ONe final note...I have gotten negative feedback from two pro builders on the use of Dynel or Xynole for a deck covering/non-skid because if the fabric weave is left exposed enough to offer a good non-skid, it traps dirt so easy and is a bitch to keep clean. I used Xynole on the bottom of my hull for sheathing and it made for a great abrasion resistant barrier...but I buried the weave and applied two additional coats of epoxy and graphite powder at the end to make the hull bottom slick and tough.

Good luck,

RodB

[pipefitter]

Dynel is overkill for a sole of a boat unless you just like doing things as such. I used 6oz fibreglass as well and after it's all said and done,it really just keeps the plywood from checking in making the finish last longer.You will be hard pressed to damage deck finishes to where dynel would ever be necessary. Mine is tabbed to the hull as well and it would take some serious impact to damage it. If that were to be the case,what I had used to subdue the plywood surface whether dynel or glass would be the least of my worries.

Also agree with Rodb about the structural considerations. If it is riding on the strength difference of glass vs dynel holding everything together collectively or the difference thereof,there is other problems with the construction that should be addressed unless the hull was designed initially with that material choice in mind.

I was told by another builder that unless someone is experienced with cloth laminations,that fibreglass,being that it wets out to near total transparency is easier to see lamination/wet out problems that may not be as easily seen with dynel such as starved coating and blisters.

[RodB]

I totally agree with Pipefitter...and in addition...fabrics like xynole and dynel give alot before they fail...ie., stretch....and take a lot of epoxy to be saturated.... that is why they make a good sheathing... but when used as sheathing...they are usually not meant to be a structural element to any great degree. If structural considerations are in the mix... fiberglass should be used if it has been calculated in the design because of its stiffness ie...it is used as a structural element...

I did not say it above....but implied that dynel was overkill...Pipefitter said it outright...and i agree wholeheartedly...especially in smaller boat like yours.

RodB

[psk125]

Thanks for the advice - particularly on the strength overkill and the difficulty of keeping "nonskid" dynel clean. The old deck was 5/8" ply ring- nailed over floors 24" apart with 'glass over it, so fiberglass w/epoxy helping it stick better should work for another 20 years this time. Especially once we replace the "pour-in" open-cell foam they used in the original construction. It seems to have absorbed every drop of any leak, and held it up against the ply until much of it turned into black strands of chopped vegetal matter.

[Gold Rock]

Those of you who know, what's your opinion/experience of polypropylene fabric such as Vectracloth? The ad copy sells it like polyester (Xynole, Dynel, et al). Is there a 'free lunch', or does it have significant liabilities relative to the others as a deck covering? I've never laminated with anything other than 'glass, but I'm getting ready to recover my decks, so this thread is very timely. Thx.

Chuck

[Brian Palmer]

It seems to me that a layer of dynel and epoxy will be more brittle than glass and epoxy because of the higher resin content.

I just put a layer of 6 oz glass and epoxy over part of my plywood cabin top this weekend, and I did the same a couple years ago with another area but used dynel. I have to say that the glass seemed like a better reinforcement since it used a lot less epoxy to saturate the cloth and fill the weave. This cabin top is fairly thin, so I need something that could flex without cracking.

The glass also seemed easier to handle during the wetout and did not move around as much as the dynel when I used a plastic speader to spread the epoxy around and work it into the fabric. I also really liked that it turns transparent so you can check the wet out.

--Brian