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dutch ob 20

dutch OB 20

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9 hours ago, lenm said:

I have used plenty. What do you want to know?

 

Hi Lenm

I have enough experience with epoxy with glass fabric but not with a hybrid fabric
Do I first have to coat the wood with epoxy than to apply the fabric in the wet epoxy and then a layer of epoxy coating
Or can the fabric on the (no wet epoxy) wood and coat through the fabric on the wood

Dutch 20 OB

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Either method will work with this fabric as it is not too thick at 200gm.

When compared to a typical 200gm glass - I find this hybrid takes more epoxy to wet out.

It is much stronger than a 200gm glass though.

I had a layer of this fabric on a SUP which fell off the roof racks on my truck.  It bounced off the pavement with minimal damage (skin still waterproof).

Make sure to protect it with a UV clear coat or paint because kevlar can degraded under UV I believe.

 

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Composites aren't my forte, so I won't make any specific recommendations.  But I know enough to say the word strength has little meaning if not further described.  Kevlar in general adds puncture resistance to a laminate.  Hinckley uses it in off-shore boats for that reason.  White water kayaks are often Kevlar.   Carbon fiber can create rigid shapes with little weight.   We now have cloth blends using 2 or even 3 materials woven together in different ways for different characteristics. The definition of quality is to conform to requirements.  What are your expectations of this layer?

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I agree - strength can have different meaning depending on context.

I find there is a lot of 'anecdotal' information floating around on the internet when it comes to composites.

Lots of opinions and theory with no physical tests to back up their statements.

Back to the subject composite, I have some test panels somewhere where I tested this hybrid variant against some benchmarks.

Will see if I can find results, however, not relevant here as involved PVC sandwich rather than plywood.

 

 

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The reason I mention the characteristic of laminates is that with the advent of new products we as boat builders may come to choosing new hybrid fabrics over glass.  But there has to be a good reason to spend more money. 

 

Aramid/Kevlar adds a safety factor.  Simply put, it is harder to hole your boat. It adds some abrasion resistance over glass as well.   https://compositesplaza.com/products/aramid

 

Carbon produces stiffness/rigidity with little weight added.  I am considering a thin wall, hallow, wooden mast wrapped in a carbon sleeve for my Lapwing. I have been talking to Graham about this. As  I get older this project gets closer to the top of my list of things to do. But I question whether one layer over a surface will add much that glass won't.  It will save some weight though.   https://compositesplaza.com/products/carbon

 

I agree, there is lots of anecdotal "information" floating around,  that is why I don't make a recommendation here.  But we as technical craftspeople need to understand enough to make decisions for ourselves. I don't mean to distract from your original inquiry about application technique, this just seemed like a good time/place to talk about alternatives to the more common glass clothes we plywood boat builders have used. Does a modern blended material fabricate offer characteristics worthy of the price?

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Seeing that I designed the boat and specified the sheathing material I thought that I should comment. 

 

There are three main considerations that I wanted to meet for sheathing the hull as well as the cost and weight and availability. I specified 10 oz (400 g/m2) finish cloth which meets all three points adequately. This does not mean that is the only choice. I see that our builder has gone up scale and bought a more exotic cloth. I do not have the mechanical properties for it except that it is half the weight and we know that it is stroger thickness for thickness. My guess is that it will be strong enough.

 

The most important part is the chine joint which holds the boat together. I specified two layers of 10 oz glass (400 g/m2 inside and out over the chine joint by 2 1/2" (6cm) including the chine flats. This gives an adequate safety margin allowing for the variables of home built and qualities of glass and epoxy. I felt that it would be practical if the bottom was glassed 2 1/2" passed the chine first,  the edge sanded to a taper and then the sides were glassed down over the chine and chine flats br 2 1/2". Laying the glass this way would meet the strength requirement of the chine and have no seams to fair and later print through on the shiny sides. I see that the spec. sheet shows that the fabric is a meter wide. It is just a bit too narrow  to reach 6 cm up the sides and lap the keel in the center of the boat, I would lap the chine by 6 cm and patch the gap at the keel line.  

 

The second consideration is ding resistance. I think that this fabric should as well as the 10 oz glass.

 

The third factor is keeping the moisture out of the wood. Wood does not rot if the moisture content is kept below about 22%. Epoxy is the best vapor barrier that we have but it is not 100% vapor proof. With all semi permeable membranes more thickness is always better. Keeping the wood dry under the epoxy also reduces movement of the surface which reduces print through in the paint. 

 

So how does our carbon kevlar fabric stack up against our low tech glass fabric? I think that it is equal or maybe a bit better in 1 and 2 and is lighter which is always a good thing. I think that glass comes out a bit ahead in three. It does cost more but some of this is offset by using less epoxy. Kevlar does not feather well, it just fuzzes up when you grind it. Fortunately it is not too thick and you may just have to fair it just with fairing compound.

 

If I inherited this boat I would be happy with the choice. If I was building the boat I would choose glass.

 

I agree with the previous post and lay the fabric dry and wet out through the fabric. This allows you to keep the thread lines nice and straight which is important foe maximising the mechanical properties. It is easier because the fabric is perfectly and trimmed in advance so that once you start mixing epoxy it takes less time and there are no distractions. 

 

 

 

 

 

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I will add a couple of comments that may or may not apply to this particular build,  even though the subject has been covered well over the course of many threads in the past. The issue of wetting down thru and wetting up thru fabric does have some if, ans and butts from my observation. Certain glass types like combo matt biaxall do not always wet down as easily and can starve the wood if you are not careful and mindful about a possible need to rewet another coat while in the wet stage.

 

This is where I personally wet the plywood after dry fitting the fabric and then reroll it on a tube or a pvc cone to reapply after a wet out coat of resin. Meranti plywood will require more resin as the grain is more course than the fancier plywood. Its more durable while being  small amount heavier, but not objectionable IMO depending on the design and what you plan on doing with the boat.

 

Of course dainty boats that reside on trailers and used on sunny days in rivers and big sounds and bays and yes even Bay River will not see the abuse as when a boat is used in rocky regions of the world and beached on a regular basis.  So types of glass and certain plywoods can be to your advantage. I like this type of glass and I have been considering using  it in an application where I have used thinner plywood than I would normally use in a like build before.  Please let us know how it wets out.

 

That's my story and I am sticking to it. B)

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Oyster makes good points. I have never had much trouble wetting out carbon but the thing that bothers me is that it does not change color like glass and you never know for sure if it is properly wet out as it is still black. I just over work it to make sure that it is done. fortunately at 5oz it wets out easy.

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One other thing. When the boat sells someday and the surveyor puts his meter on the hull the meter will read off the chart. The carbon fiber is conductive thus triggering the meter. Keep good records to show the construction method.

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