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OB 20 build from aband


acreew

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Hello everyone,

I purchased a partially completed OB20 hull and am pondering next steps. Read on build thread (Dutch OB20) where the builder apparently alternated glass between the planks (glass/plank/glass/plank) when planking the sides. (tried to contact Jan directly but did not hear back)

 

1) is this advised? What would be the benefit?

2) What is the best way to accomplish? (it would seem that you would glass the plank material prior to cutting, but not sure if this would impact how the planks would conform to the shape of the hull, etc. etc...)

 

Thank you in advance for any thoughts.

 

Will

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Do not glass your plywood before gluing up your hull layers. And for sure don't use 5200 between the layers, which is and has been promoted by some rebuilders of older multi layer hulls.  I think you are talking about using wetted out glass in lieu of mixing up cabosil and epoxy between the layers of plywood.  I would ask Alan and Graham about that. That method has been used in the past on many one off cold mold hulls when the building method came about, even using chop matt and wet it out in hopes to avoid voids, and an easier method of glue up instead of all the mixing. But these days when using jigs and building boats created by designers, the hulls are fairer and the engineering is better for the minimum amount of added weight too. So the glue ups require less filler materials. You will end up with a much heavier boat , especially if you use biaxal and accomplish nothing really if you use finish cloth.  Now I have used 403 fibers in areas that has more concave shapes instead of the cabosil. But as long as your fits in your layers are good, you should not need the 403, which is more dense.

 

There are alternative methods of laminating layers of plywood to achieve a solid bond in lieu of using a bunch of screws and washers , a common practice. In the not so extreme flares in particular look up Raptor staple gun and plastic staples.  They work really well in the small tumblehone area in the aft sections and in the bottom panels if you need to laminate layers. When the glue is cured, just knock off the extra if any and you are good to go. They save you tons of work in your finish section of your build.

 

These will minimize your work on your final layer in the flatter areas. We also use golf tees to fill holes that has had the larger screws and washers You sanding is more uniform when sanding simular materials.  The Raptor staples work in a simular way.  

. This gives you a cleaner finish of simular products under the glass to minimize some print thru that can happen when using thickened cabosil in the holes before glassing and possibly dished out areas around the harder areas of the cured glue and wood.. You can also skin over any compression areas with a mix of 406 and 410, . There will be some shrinking if you use more 410 from west system or glass beads in the mix. So let cure and check your areas before glassing.  Do most of your fairing before your finish glass goes on.  

 

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Thank you Oyster for the very detailed response. I do plan on getting the raptor gun and staples. Below is the section of the dutch ob 20 thread talking about adding glass to the planking:

 

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

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  • 2 weeks later...

Hello all,

 

I have dry fitted the last stringer on the sheer clamp (previous two were already installed.) There is a significant at least 1/4 inch overlap Of the recently added stringer. The overlap occurs mostly at the forward temporary frame and forward bulkhead. Prior to gluing the stringer in place I wanted to get your input as to whether this is to be expected or how to fix this issue. The new stringer Is touching all internal frames.

 

Thank you in advance for any help you can offer.

 

Well

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You are doing the right thing by making sure that you are not going astray. This is a critical stage and if you get it wrong it will be harder to get right. Having said that, I cannot see if you have a problem or not. The object is to be able to fair the sheer to the stringers and stem so that the planking will lay down flat to your bevels. The other hard part is to get it so that when you trim off the planking, there will be just the right landing for the gunwale to go on and look right in 3D.

 

There some sectional views in the plans showing a cross section of these parts. 

 

Feel free to call Alan or I and maybe we can talk you through it.

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  • 2 months later...

Hi Wil

 

I haven't been on the forum for a while, so I missed your question.

 

I first coated the entire 4 mm plywood sheets with thin glass and epoxy. Then I cut the sheet into pieces.

In the photos of my build you can see that I use a temporary wooden strip between the chine batten.

This used to clamp the two layers of plywood together with screws during the drying of the epoxy.

I used stainless staples for attaching to the chine batten.

 

Is this an answer to your question?

 

Greetings Jan

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