woven fiberglass fabric how much?

[PAR]

The multi part acrylics and polyurethanes employed in the automotive industry must be applied on a 'glassed surface or you can expect some cracking. In a perfect world, just epoxy encapsulation alone should be enough, but in the real world there's more then enough movement (without fabrics) to test the tensile strength of the paint film and cracking results. If using an LPU or a WR-LPU, then you'll need to 'glass the surfaces.

I also have issue with the taping schedule you've mentioned above. It suggests insufficient taping at critical locations. For example a minimum structural seam on 8 mm plywood (like a chine) would be 2 layers of 12 ounce (340) biax on the inside, over a 3:1 fillet and a minimum of 1 layer of 12 ounce biax on the outside, preferably two layers. This would be a 6" (150 mm) tape with a 30% overlap on the centerline of the joint.

[metin_mehel]

Ilan, After aplying primer, should I sand the surface? Or should I start painting before primer dries?
Thanks.

[metin_mehel]

Par,
Do you have any test result of a chine under load with tape and without tape?
Does it increase strength or just fatigue strength(durability)?
I just applied one fiber layer inside chine. Do you think it fails?

[Ilan Voyager]

Thanks PAR for reminding us these good principles.
After applying the primer you must wait it's completely dried. Never paint on a fresh primer it would be a disaster. About sanding; it the substrate was well prepared and the primer well sprayed there is no need of sanding if you paint in a short delay AFTER DRYING. After 24 hours always sand.

PAR will answer the same : "composite"chines must be glassed on the 2 sides.
With glass only inside the joint will crack and the plywood fails by delamination inside the wood.
There is very little literature about this kind of joints. Happily it's very easy to engineer by a crude test; make a chine as you were planing to do. Try to break it: if it fails at the joint, there is not enough glass. If the plywood fails elsewhere but not in the zone of the joint, the glassing is strong enough.

PAR gave you a good scantling for glassing the chines. You can replace the BIAX by cloth cut at 45 degrees.
To simplify the same 200 gr cloth can be used. Four layers inside over a fillet. The largest layer about 160 mm wide, the less wide 100 mm. The first layer to apply over the chine is always the smallest, and the last the largest. It seems complicated, in reality it's pretty fast and simple as you put the layers fresh on fresh.
Outside it's the same, and very easy with a light cloth which will pass the angle without difficulties. It's good practice to sand in the plywood a slope of about the thickness of the glass layers and to round the chine. The fairing will be easier. Hard to explain, very easy to make on a soft plywood as okoume.

[PAR]

Metin_mehel, there is no such thing as a taped seam boat without the tape. Stitch and glue is just the assembly technique, the building method is "taped seam" and it completely relies on fillets and tape to work. It's fairly simple engineering and some simple rules of thumb can be applied, but only non-loaded panels can avoid the taping schedule. In these cases the fillet is cosmetic and used to smooth out corners for easy cleaning, shedding water, etc. A structural fillet can be applied to a corner without tape and it will create a flange that eliminates stress risers and improves local stiffness, but has limited elongation properties without the tape.

On very small craft you can use regular cloth cut on a 45 degree bias as Ilan has mentioned, but I don't on anything that will be loaded or receive cyclic strains. Regular cloth is a weave which places the fibers in the fabric in a sinuous orientation, within the cured matrix. Under load these fibers have to stretch before they can absorb loads, often reaching their breaking point, because they are pinched by other woven strands crossing them. Biax is two layers of uni-directional fabric that are lightly knitted together, so the separate strands participate in loading situation immediately, without stretching, making for a much stronger fabric, particularly over a chine, where you can expect considerable loading.

[Ilan Voyager]

You're right Par but it's just a 5.8 m little cat with a no race design for small coastal cruising.
In the States you have low prices and high wages. Metin is in Turkey with low wages and high prices. That means that everything costs to him, with his probable acquisitive means, at least 3 times more than for a US guy. Cloth cut at 45 degrees is largely enough for such a small boat. Biaxial will cost to him a fortune. The epoxy resin has costed to him already a little fortune. (like if you were paying your resin 200-250 bucks a gallon). If he had money he wouldn't be on Boatdesign asking for cheap solutions. A rich guy in Turkey does not put his hands in resin.
There are economic realities...
An example a 180 amps MIG welder will cost in the States about 600 USD and the weldor using it can ask 20 USD an hour even at the far end of the Nebraska; so the weldor pays it in 30 hours of work, lets say 45 including price of consumables. The same MIG welder will cost in Mexico 900 USD and the weldor can get at best 8 USD hour, so he will need 113 hours to pay it. The argon mix will cost 3 times the american price and the metal wire 2 times...counting these price he need in reality 200 hours to pay it. That's economic reality.

[metin_mehel]

I made a strength analysis on the boat geometry, max stress around a chine is 10Mpa. I am not sure but okume's tensile strength is 20 or 40 Mpa. In Gougeon Bro. book the simple test method as Ilan dealed, making a simple two part connection by a fillet. If breaking is at fillet therefore I should expect failure. I will test this. This is good idea.
Is there any way to cover the chine by a layer made by fiberglass&polyester? 18lt polyester is around35$ and 1m2 - 200gr/m2 fiberglass woven roving is 1$.
Forsure the failure from fillet may start from the thinest crossection of the fillet. Therefore stress consantration on these area should be spreaded on a larger adjacent surface. These ensures both strength and the life of the fillet.
Thanks guys.

[Ilan Voyager]

Originally Posted by metin_mehel

I made a strength analysis on the boat geometry, max stress around a chine is 10Mpa. I am not sure but okume's tensile strength is 20 or 40 Mpa. In Gougeon Bro. book the simple test method as Ilan dealed, making a simple two part connection by a fillet. If breaking is at fillet therefore I should expect failure. I will test this. This is good idea.
Is there any way to cover the chine by a layer made by fiberglass&polyester? 18lt polyester is around35$ and 1m2 - 200gr/m2 fiberglass woven roving is 1$.
Forsure the failure from fillet may start from the thinest crossection of the fillet. Therefore stress consantration on these area should be spreaded on a larger adjacent surface. These ensures both strength and the life of the fillet.
Thanks guys.

The test can be used in any kind of joint. It's primitive engineering, as it doesn't calculate the strength of the plywood. It just assumes that there is not solution of continuity in the joint, nothing more.

The lone thing that bothers me is the polyester you want to use, simply because polyester does not cure on epoxy, and also polyester glues badly on wood. Never laminate polyester after any epoxy.

[metin_mehel]

I will buy more tapes for external coat. I just applied one layer inside and I will coat two layers outside of chine. Finally I will coat it fiberglass fabric (200gr/m2) hope it works now. Ilan do you know sail force calculations?

[PAR]

The inside of the chine joint carries the vast majority of the load and this is where the fabric reinforcements need to be. Of course externally you need reinforcement too, but not at the level of the inside. Which is why I suggested you could get away with 2 layers of 12 ounce on the inside, with just a single on the outside. Personally, I wouldn't risk the issue with such a modest savings of material and effort, but on a light, small boat or a racer, then it's sometimes worth the risk.

[metin_mehel]

Unfortunately I already finished. There will totaly be 3 coat on outside. Two tape and one fabric. This boat will use sails and may have big loads on the hull.