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dutch ob 20

dutch OB 20

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Jan,

This discussion is beyond my level of expertise, so I can't comment.  But, I will say this, your project is amazing.  The precision, quality and rate of progress of your work is very impressive and fun to watch.  Keep up the good work and keep posting. 

Carter 

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Hi
With some help from google translate  (;  I have read your reflections and advice and this is what I have done so far
Before I put the plywood on the hull, I provided the inside with a thin layer of glass fabric (100 gr/ m). So the bodum is from the inside out glass and 9 mm plywood
The side is made of two layers of 4 mm plywood with a layer of glass on the inside of each layer

And this is what I intend to do with the outside
My hybrid fabric is 120 cm wide and I can overlap at the keel and the chine flats and then have two layers of 190 gr / m in those places and I think that is strong enough

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9 hours ago, HighDesert said:

Jan,

This discussion is beyond my level of expertise, so I can't comment.  But, I will say this, your project is amazing.  The precision, quality and rate of progress of your work is very impressive and fun to watch.  Keep up the good work and keep posting. 

Carter 

Thank you Carter and I keep posting photos on the forum

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Typing from the bleachers here...

 

One of the main advantages of using carbon is for weight savings.  The stuff is very expensive in comparison to glass.  To me, it doesn't make sense to use carbon (especially alot of it) in a hand layup.  Unless you are very good at epoxy work, you are almost assured to use too much resin...which will negate the weight savings you were hoping to get from the carbon in the first place.  I feel that carbon fiber should be bagged in order to gain it's full advantage.  

 

My other "issue" with it is the fact that it's so stiff.  One of the best attributes of a wood boat is how it rides in comparison to a "glass" boat.  It just seems that some of that soft wood feel would be lost with carbon in the hull skin.  Maybe that's the wrong way of thinking, I don't know.

 

With all that said, you can get an aramid/eglass blend that might work better for you.  I suspect that it would be less expensive than the carbon weave.  Regardless, you may want to consider adding glass over top just so you don't have to deal with sanding over aramid.  

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One other item to pay attention to is carbon fiber unless oriented correctly does not like to go around corners. You may want to dry fit first and be sure the cloth will lay flat. There isn't enough resin in the world that will hold the cloth down. It has a mind of its own

My 2 cents

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Thanks Graham for that reply.  That is the kind of info I had hoped to get as a reply to my comment.

On 12/21/2018 at 6:42 AM, Designer said:

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

 

 

By ding resistance are you saying the added hardness protects against minor damage? Do you think the Kevlar/Aramid adds anything to this property?

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Jan,

 

I like that thin layer of glass on the inside of the planking. It helps to prevent water from getting into the ply and it adds stiffness to the skin and adds to the impact strength. Yes the 120cm wide fabric will be perfect.

 

Hightechmarine brings up an important point. I do not know what radius your fabric will wrap around without bubbling so I would do a test sample. I tell everyone that the round of a pencil is the minimum that you need. It is really annoying to see bubbling on either side of the chine corner. If it does happen, I have been able to save it with peel ply. If you do not have peel ply some clear plastic is worth a try.  It does not always work but when it starts to bubble there is nothing much you can do but repair it later and wished that you had made a bigger roundover. The down side is that the sharper you can make that chine edge the more efficient and drier it will be. I build the rounded over chine corner back to a sharp edge with colloidal silica thickened epoxy. If you have any milled fibers, I would add some to the mix. The rounded corner allows the water to wrap around the chine instead of breaking away clean.

 

Dave,

 

My guess is that being about half the weight and thickness, the ding resistance will be about the same as 10 oz glass. While we are on the subject, sheathing the outside does not add much to the stiffness to the planking. Glass on the inside does and adds to the impact strength but does nothing for ding resistance. The reason is that the forces are generally inwards putting the planking under tension. Glass fibers have much more tensile strength than wood fibers. Sheathing on the outside will be in compression and the thickness of the glass is quite thin so does not add much extra thickness to the planking. Thickness increases stiffness in all materials.

 

 

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Further to Grahams advise - I noticed Appendix E of the Gougeon Brothers Boat Building Book also merit use of inner layers of composites on plywood.

Section also covers Aramid/Kevlar inc some test panel comparisons - with suggestion to utilise on inside where it can be put in tension (kevlar's main advantage over other fabrics).

 

Back to original topic - I have used this particular hybrid fabric before and have successfully pulled it over a 'pencil round' edge with no bubbling (utilising peel ply).

My suggestion would be to always utilise peel ply with this fabric - as is can end up somewhat 'textured' finish/surface if you don't.

 

 

 

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