Composite panel construction?

[Sos]

I want to make a composite panel as part of a hard cockpit cover on our catamaran. It will be 900mm wide x 1960mm long and I want to put a 10 x 10 raised lip around the top edge to stop water dripping. It will have solar on it and walking access to the boom.

Can anyone advise what thickness foam core and layup I will need?

Also can anyone point me towards any YouTube videos on how to do this!

Thanks...

[coopec43]

My preference is for Divinycell or Airex core. I'd probably opt for 10 -15 mm thickness core.

I'd use polyester resin (be very careful with he hardener as it is dangerous)

As far as glass is concerned I'd use CSM (Chopped Strand Matt) You guys use a different way of measuring the weight so I can't advise. (Your supplier will be happy to advise)

Just noticed

The most popular weights are . 75 oz and 1.5 oz. In the US, chopped strand mat is nearly always sold or specified in ounces per square foot
I'd use x2 layers of 1.5 oz top and bottom. If you are going to attach solar panels you will have to replace the foam with ply(?) squares 3 inch x 3 inch(?) where the bolt will pass through the panel.

https://www.youtube.com/watch?v=OwABZT2pIn8

[Sos]

Great info thanks.
I am hoping to get a good gloss finish so was going to use peel ply. Would it still be advisable to use chop strand if I want a fair finish?
I know whatever I do there will be a lot of sanding. I am thinking of a spray paint finish to match the boat colour better.

[Chotu]

Originally Posted by Sos

Great info thanks.
I am hoping to get a good gloss finish so was going to use peel ply. Would it still be advisable to use chop strand if I want a fair finish?
I know whatever I do there will be a lot of sanding. I am thinking of a spray paint finish to match the boat colour better.

Peel ply won’t help you get a good gloss finish. It makes a tooth for the next layer to mechanically bond to. Not what you’re looking for.

A better way will be to just go wet on wet. Fast.

Make a perfect core in the exact shape you want for the whole hard cover out of corecell, Airex, divinycell, etc. use thickened resin to make the core the exact shape and size you want the final product to be. Join all foam panels and fair the core so it’s perfect and looking just like the hardtop you want.

Scuff up any thickened resin you use to build the core. Put in the pieces of wood coop suggested where your hardware will go. That’s for compression strength. Or... leave it all foam and just epoxy your solar mount hardware to the surface of the finished product.

Now it’s ready to glass. If using polyester you need mat. 1708 is a very common fiberglass availablei n the states. It has mat and cloth together already. Leave the mat side up and laminate it to the foam. Mat side up is to get as smooth a surface as possible. Before it completely hardens, spread thickened polyester with microbaloons and a little bit of silica (or a pre made fairing compound) over the whole thing in as smooth a layer as you can. This has your entire hard top done and ready to sand smooth and paint in one step.

The difference with epoxy is you don’t need the mat. So 1708 isn’t needed. You can use 8oz cloth or something a little heavier than that instead of 1708 and follow the same procedure above.

Wet on wet, not peelply, is the way to get this done most easily.

For core, 3/4 to 1” is the minimum I’d use. 5-6lb core minimum. You want some stiffness. Thicker core makes it stiffer. Id actually use 1”.

[mikedefieslife]

I've been looking at building my hardtop. Nidacore is a popular choice but for ease of working I think PVC closed cell foam is a better choice brand name is unimportant there's plenty to choose from. Not much in it price wise, but the with the foam cutting and shaping is much easier. There's no edge filling needed either.

I would use Polyester resin and 19mm core.

[Sos]

Thanks Chotu, I will look further into 1708 or similar. How would you apply the fairing compound, over such a large area, to get a smooth finish?



Mike, I agree that the PVC closed cell foam looks better - will look into that.


Cheers

[Rucksta]

Have you considered a premade panel?
The high initial cost could pay for itself in reduced finishing.


Chotu seems to be onto it.

P.S. Wide squeegee on a long handle works for quickly spreading the polyester filler around

[Chotu]

Originally Posted by Sos

Thanks Chotu, I will look further into 1708 or similar. How would you apply the fairing compound, over such a large area, to get a smooth finish?



Mike, I agree that the PVC closed cell foam looks better - will look into that.


Cheers

Applying your fairing compound is like applying mud to Sheetrock. Whatever tools you would use for Sheetrock work are perfect to spread on the fairing compound.

It won’t be smooth. It’ll be the best you can do. Then it’s easy sanding (relatively) because that’s what fairing compound is made for. Easy sanding. You can knock it back to smooth quickly.

[Chotu]

Sorry for all the imperial states units. Thought you were here at first.

[Matt Johnson]

I have a few plans in front of me right now for similar sized hardtops. One is 20mm foam core (6lb) and 1200g of biaxial; one is 19mm with 900g Triaxial; and the final is 25mm with 600g biax.

These are the base specs with no additional reinforcements added... I don't have those details yet.

We used 1/2" 3lb foam and 17oz cloth (two layers on top) on our small dodger top and there is no way you'd be able to walk on it. With the span you are looking at, I'd go for 25mm 6lb, double up the edge and think about an additional beam between upright posts.

Matt

[coopec43]

I think you'd find this helpful.


https://www.boatdesign.net/threads/h...r-build.44839/

[Fore and Aft]

A nice way to finish the edge is with a peice of PVC pipe that has been cut down the middle, forced onto the edge of your panel then glassed. I did this with our hard top and put a couple of garden hose fittings in the corners so we could catch water as well.
Cheers

[Fore and Aft]

I just noticed that on the edge of our hard top we used 50-60mm diameter PVC pipe. It's real nice to grip when you are standing at the aft end of the cockpit.
Another thing I used was the PVC T peices on the edge so I could slide the stainless steel uprights into them. I did'nt want the uprights at 90 degrees so I cut the T peices at the base and wedged them to the angle I wanted then glassed them.
Cheers

[Sos]

Thanks everyone for the great info.

Think I will go with the 25mm thickness.
It will be supported on all 4 sides.

Also going to add hose attachments for water catching.

This is what I am trying to achieve -

[coopec43]

Originally Posted by funjohnson

We used 1/2" 3lb foam and 17oz cloth (two layers on top) on our small dodger top and there is no way you'd be able to walk on it. With the span you are looking at, I'd go for 25mm 6lb, double up the edge and think about an additional beam between upright posts.

Matt

Two layers on top..... OK
How many layers on the bottom?

What you are suggesting is an absolute overkill surely?