Fiberglassing my newly cored deck.

[Wind River]

I have recently removed the teak decks and re-cored the side and foredeck on my Hudson Force 50 Center Cockpit ketch. I am getting ready to lay down new glass and started pre-cutting the pieces.

To duplicate the thickness of the original layup I will be putting down 5 layers of 1708 bi-ax topped with two layers of 1.5 oz. CSM. That will get me the average 1/4" thickness of the skin I removed.

I'm sure the best scenario is one giant piece of glass per layer with no butted seams in each layer. Obviously that is not possible so smaller pieces will need to be butted together. The glass I have is 50" wide and there is a spot on the foredeck where it could be laid down at full width, but the 10 foot by 50" fabric is a bit unwieldy. The narrow side decks can be done in two sections per layer and rolled out as I go, so there is not much of an issue there. The transition from the side to the foredeck is where there will need to be more joints.

My question is how big of a deal are butt joints within the layup if they are staggered between layers? Lets say 6" or more apart?

What about small areas where the larger pieces leave a void? Is a small patch there anything to be concerned with?

Should I avoid butt joint at the expense of a lot of wasted fiberglass?

Am I concerned about nothing?

[Chotu]

You are absolutely fine doing butt joints because you have soany layers of glass... but stagger them as much as possible.

With 5 layers you're all good. No worries at all.

Not sure why you are putting the chopped strand mat down at all. A lot of extra work unless you are hoping for some smoothin effect from those layers. I'd just use the biax and then skim smooth it. It'll already be fair, it seems from the pics.

[Wind River]

Originally Posted by Chotu

You are absolutely fine doing butt joints because you have soany layers of glass... but stagger them as much as possible.

With 5 layers you're all good. No worries at all.

Not sure why you are putting the chopped strand mat down at all. A lot of extra work unless you are hoping for some smoothin effect from those layers. I'd just use the biax and then skim smooth it. It'll already be fair, it seems from the pics.

I believe there will be some sanding/grinding involved.

The original core was small squares of plywood and it varied in thickness from 15mm to 18mm. I had to pick a core thickness in between the two (5/8"). There are spots where I will need to build a little more thickness at the edge of the original glass than just the layup I have described. I hope it will not be too uneven.

I took the tip from Minaret in another post about using the CSM on top. The thought was, if I had to grind a little back down I wouldn't get into the structural part of the layup and also to hide the weave of the bi-ax cloth. Finishing off with peelply was also recommended to help ease the fairing a bit and soak up a little excess resin if needed.

[coopec43]

Quote "I have recently removed the teak decks and re-cored the side and foredeck on my Hudson Force 50 Center Cockpit ketch"

What was the existing structure? Did you lay several layers (X3?) of CSM glass over the existing glass? structure before laying the foam core?

Then what resin did you use to lay the core to the glass? When I laid the Divilette foam core on my deck I used Divillette (Divillette has the consistency of a putty)

DIAB Divilette High Viscosity Bedding Compound – Merritt Supply ...
https://www.merrittsupply.com/produc...ding-compound/

It is extremely important to get good "contact" so I used a rubber mallet to hammer the core against the deck/divillette. If the core is not fixed firmly against the fiberglass deck the core material will be ineffective.

There are quite a few clips on laying techniques on line.

https://www.google.com.au/search?biw...04.2_S_cDHtXRE

Clive

[Wind River]

Originally Posted by coopec43

Quote "I have recently removed the teak decks and re-cored the side and foredeck on my Hudson Force 50 Center Cockpit ketch"

What was the existing structure? Did you lay several layers (X3?) of CSM glass over the existing glass? structure before laying the foam core?

Then what resin did you use to lay the core to the glass? When I laid the Divilette foam core on my deck I used Divillette (Divillette has the consistency of a putty)

DIAB Divilette High Viscosity Bedding Compound – Merritt Supply ...
https://www.merrittsupply.com/produc...ding-compound/

It is extremely important to get good "contact" so I used a rubber mallet to hammer the core against the deck/divillette. If the core is not fixed firmly against the fiberglass deck the core material will be ineffective.

There are quite a few clips on laying techniques on line.

https://www.google.com.au/search?biw...04.2_S_cDHtXRE

Clive

The lower skin was fiberglass and pretty thin. I did not add any more layers to it.
As you can see in the picture, the old core was not doing anything for me, as in some spots the plywood was de-laminated down to individual plies.

The core I used is Coosa Bluewater 26 Urethane closed cell foam and bedded it with ArJay Core Bond by screwing it down to the lower skin. I tried to vacuum bag it but there were leaks in the lower skin or under the margins preventing a good vacuum. I will fill all the screw holes with thickened resin before laying down the glass.

I have documented most of this project on my Facebook page if anyone is interested:
www.facebook.com/SVWindRiver/

[coopec43]

The Coosa Bluewater 26 Urethane closed cell foam and the Arjay Polyester core Bonding compound appear similar materials to what I used but my closed cell foam was cut into squares approx 2in X 2in. and held together with a scrim backing. (that enabled it to follow curves in the decking)

Too late now but just walking/crawling around on the core material would have ensured a better "bedding" I suppose.

I used CSM against the core followed alternate layers of WR and CSM. (Never lay up WR against WR but you would know that )

Clive

[Wind River]

Originally Posted by coopec43

The Coosa Bluewater 26 Urethane closed cell foam and the Arjay Polyester core Bonding compound appear similar materials to what I used but my closed cell foam was cut into squares approx 2in X 2in. and held together with a scrim backing. (that enabled it to follow curves in the decking)

Too late now but just walking/crawling around on the core material would have ensured a better "bedding" I suppose.

I used CSM against the core followed alternate layers of WR and CSM. (Never lay up WR against WR but you would know that )

Clive

I don't think that Coosa board is anything like what you used. Coosa has woven roving inside the board that makes it a structural board. It is a direct replacement for plywood in this particular situation. It's only shortcoming is that it doesn't hold a screw very well. It is rigid like plywood but in this case it didn't have to follow many curves other than a little bit of the crown on the fore deck.

I drilled holes through the Coosa board to allow the screws to pull up the lower skin to the core and not bite into the core. I'm pretty sure I got a good bond. Not as good as if the vacuum bag had worked but I am confident I will be better than the original build.

[coopec43]

What a magnificent looking yacht. (I love the Errol Flynn looking yachts)

[Benz]

Putting some CSM or woven cloth (like 6-oz boat cloth) over biax is essential; otherwise, if one tears out (as when you drill a hole through), it will pull out along its whole length. I prefer 6-oz woven E-glass, since it will take less fairing compound to smooth than the CSM.
Butting the seams in fine, otherwise you get lumpiess.
Coosa board is a bit overkill, but certainly doesn't hurt--it's not like weight is an issue.
Looks like you're doing a fabulous job.

[ontherocks83]

Is there any reason not to go solid fiberglass for the deck? Once you had the old coring removed, why not just add more fiberglass onto the inner liner?

[coopec43]

Originally Posted by ontherocks83

Is there any reason not to go solid fiberglass for the deck? Once you had the old coring removed, why not just add more fiberglass onto the inner liner?

Solid glass would be flexible whereas a cored deck (or hull) is very stiff. An added bonus is that foam is insulation from the hot overhead sun.

Clive

[Wind River]

Originally Posted by Benz

Putting some CSM or woven cloth (like 6-oz boat cloth) over biax is essential; otherwise, if one tears out (as when you drill a hole through), it will pull out along its whole length. I prefer 6-oz woven E-glass, since it will take less fairing compound to smooth than the CSM.
Butting the seams in fine, otherwise you get lumpiess.
Coosa board is a bit overkill, but certainly doesn't hurt--it's not like weight is an issue.
Looks like you're doing a fabulous job.

According to Coosa Composites, the Bluewater 26 is about 30% lighter than plywood of the same thickness.

Bonus for lighter, stronger and waterproof!

[Chotu]

Ok. Everything looks good to me! You did the best you could with the core bonding. Sorry to hear about the leaks in the inner layer of existing glass. But you got it done with screws.

I'm not sure I agree with the poster talking about not using just biax. I've used just boss all over the place as per the plans and not once has it pulled in any way drilling it or cutrying it.

Might be a polyester issue? Because it doesn't do that with epoxy.

[coopec43]

Originally Posted by Chotu

I'm not sure I agree with the poster talking about not using just biax. I've used just boss all over the place as per the plans and not once has it pulled in any way drilling it or cutrying it.

Might be a polyester issue? Because it doesn't do that with epoxy.

Perhaps we are talking at cross purposes because bi-axial cloth often has CSM already stitched to it to ensure a good bond between layups. Maybe people are not aware of that?

As for me I just use Woven Rovings and CSM with Polyester and Fiberglass Cloth with epoxy.

Fiberglass Biaxial Cloth is a #1708 E-glass Biaxial (+/-45 degree) Cloth with 3/4 oz mat backing. The fiberglass rows are held together by light nylon stitching which do not affect the structural integrity of the cloth.

Clive

[Chotu]

Originally Posted by coopec43

Perhaps we are talking at cross purposes because bi-axial cloth often has CSM already stitched to it to ensure a good bond between layups. Maybe people are not aware of that?

As for me I just use Woven Rovings and CSM with Polyester and Fiberglass Cloth with epoxy.

Fiberglass Biaxial Cloth is a #1708 E-glass Biaxial (+/-45 degree) Cloth with 3/4 oz mat backing. The fiberglass rows are held together by light nylon stitching which do not affect the structural integrity of the cloth.

Clive

Ah. That csm layer is for polyester layups. Epoxy layups are just the biax. There is no need for the extra CSM stitched on when you are doing an epoxy job. It just adds weight and no significant strength.

Biax should just be biax when building in epoxy.