How many layers of Dynel

[Paul Maselli]

The restoration of the Elliot white is going strong. The entire backbone has been rebuilt and refastened. Every Floor Timber and 40 % of her steam bent ribs are new. Every Bronze fastener from the shear down has been replace. The Iron Shoe hangs on 22 new 3/4" 316L Stainless Steel Studs. We're hanging new garboards.... :cool:

Now from the shear up:
The deck will be oak laminated beams & carlins. Followed with 1/2" cedar T&G covered with 12mm Meranti Ply laminated with scarfed seams.

My question is simple. 1 course or 2 course of Dynel in West Epoxy. BTW The hull is 34ft x 10ft-8in wide. A formidable area to cover, Essentially a full laminated and glues plywood skin atop Cedar. Does the benefits of a second lay down out way the cost of materials and labor? smile.gif

[boatbuilder.org]

One layer of Dynel will be fine.
---Joel---

[Buddy]

I agree, one layer. The dynel isn't creating strength or stiffness in your deck, or performing anything like traditional canvas bridging over a "moving" pieces on a T & G or strip deck...Really it's just creating a matrix to hold a watertight paint system together, and provide some impact resistance protection against puncturing that system from dropped sharp objects and dragging abrasive ones.

[boatbuilder.org]

The Dynel "swells" and one layer will give the thickness of several layers of 6 oz. cloth

[Paul Maselli]

Thanks guys, keep the fine opinions coming. I tend to agree, I've done far more than my share of layup work but haven't used dynel in 20 years. Have used more than my share of that itchy stuff F/G. :( . It's just that when I call Defender someone over there (probably driven by selling more dynel) :rolleyes: made a strong suggestion that multiple layers were req'd to prevent surface cracks...

Sometimes Too much thinkin is no good. I'll agree with you guys and go with my gut.

[NormMessinger]

I'd be interested to hear Joel's opinion regarding dynel vs. glass for preventing surface cracks.

I used dynel on the deck of Prairie Islander but to give a rough, canvas like look. I sure don't like the way it handles. And, it is so rough when the epoxy is cured that I'd think it would be difficult to get a smooth finish if one is desired.

[holzbt]

If you are worried about cracking put a layer of 10 oz. cloth down first under the dynel. I don't think you would gain much by using multiple layers of dynel, except that you'd make the epoxy distributors happy.

[boatbuilder.org]

Originally posted by NormMessinger:
[QB]I'd be interested to hear Joel's opinion regarding dynel vs. glass for preventing surface cracks. QB]One of the reasons I went to it is that it is supposed to be a bit more "elastic". A problem area in plywood construction is the end grain. I do a lot of rounded edges and the end grain of plywood, though sealed and glassed, moves a bit because of the layered plys. One straight grain, one end grain etc. I have decided the movement is thermal related because it only seems to happen in areas the get direct sunlight. Over the years this movement continually causes stress on the "brittle" glass covering causing what I call a "zipper". This only my opinion and I have no tests or scientific data supporting the theory. It may be more caused by the fact that the corners tend to get sanded more and the glass just becomes a bit thin, I can't say for sure, but I know with Dynel you have a thicker cake of material that is not as easy to sand thin as glass. Any thoughts...?
---Joel---

[NormMessinger]

Thanks, Joel. I learned to use glass and epoxy when I built a Long EZ airplane, one of Burt Rutan's designs and much of what I "know" to be true comes from that experience. My boats have not recieved enough exposure to really test the materials.

[Todd Bradshaw]

Interesting Dynel factoid:

Dec. 11, 1950
"Dynel will be to wool what nylon is to silk." With this glowing sendoff Joseph G. Davidson, president of the Chemicals Division of Union Carbide & Carbon Corp., last week showed off blankets, socks, draperies, knit goods and imitation fur made of the newest synthetic creation of Union Carbide (manufacturers of Bakelite, Prestone, Vinylite).
Made from natural gas, salt and air, dynel can be dyed, woven with other fabrics or used alone. Davidson says it is washable, mothproof, almost shrinkproof, and resistant to strong chemicals. At $1.25 a lb., manufacturers may find dynel a cheap substitute for wool, which, for similar use, sells at $2.15 to $3.50 a lb. Since dynel orders already far outstrip the company's annual production of 2,000,000 lbs., work was started last week to double the output. If dynel catches on, Union Carbide hopes to expand to as much as 40 million lbs. a year.

[NormMessinger]

Factoid or actually true?

Dynel really confuses my preconcieved misconceptions about epoxy composite construction. I can accept that it is highly resistant to abrasion, just taking the Forum's word for it. It sure works to give a rough texture as a deck covering. But it feels in hand rather stretchy which suggests that it would not be as strong in tention as glass but have no idea how that translates to after saturation. Joel's use suggests my imagination is on the wrong track. One thing seems sure, dynel has not caught on in the boat-stuff catalouges I've had my hands on. Only Defender had it when I bought though I see Jamestown now carries it as well.

P.S.--I just went googling for dynel, polypropylene, etc. Oh, woe! Sure revealed my ignorance.

[ 02-04-2005, 10:33 AM: Message edited by: NormMessinger ]

[George Roberts]

Paul Maselli ---

I don't think that Dynel is ever the best choice. An equivalent weight, cloth plus epoxy, of glass is usually a better choice.

I don't know whose scantlings you are following so I am unable to determine if 1 layer or 2 layers of Dynel (or the glass equivalent) is necessary.

I expect that cloth and epoxy on one side of the plywood is not the best of practices.

[AngWood]

Natural gas, salt, and air?

Don't see many Dynel sweaters in the stores these days.

[Todd Bradshaw]

Yeah, but the ones you do see REALLY resist abrasion well! Quite a few of the early versions of synthetic fabrics later exhibited unexpected characteristics that made them much less desirable than their manufacturers originally thought they would be. Some had such bad breathability and/or moisture vapor transfer that they became sweatboxes. Others, like some of the fleece fabrics, especially acrylic, tended to pill horribly very early in the garment's lifespan. Early polypropylene underwear was marvelous at vapor transfer but tended to pick up body oils and sweat. The fiber itself absorbed so little moisture that the water in the washing machine couldn't get it wet enough to wash the stuff out, causing it to get pretty ripe after a while. Early Gore-Tex was a nightmare. I don't know much about Dynel's history, but the last person who wore a Dynel sweater probably also had a bee-hive hair style, reinforced with Dipity-Do....

[Todd Bradshaw]

The folks at Lowrance Electronics once told me that if you want to see if a sonar transducer will shoot through your hull bottom (mine was cored and I wasn't sure) without drilling a hole, you put a blob of Dipity-DO on the floor and set the transducer face in it. If it will work through the Dipity-Do, it'll work when glued down.