Composite construction challenge

[GILow]

Hi all,

I’m fitting out the new boat interior using the composite construction approach.

The panels I am using are a honeycomb style panel, faced on either side so the cells are not open. This is the stuff here, but note that it has a much smoother face than the picture appears to present. (I’m using the 20 mm thick version.)

https://trojanfibreglass.com.au/prod...neycomb-panel/

I will be layering 3mm of CSM and vinylester either side for strength.

When I first looked at this material I was warned that the real challenge would be along the cut edges. The honeycomb matrix leaves big voids along the cut.

I dreamed up some ideas to deal with this but I was mainly unconcerned because very few of the cut edges needed to be sealed for my planned construction.

Now I’m revisiting my planned approach and wondering if there are better ways, particularly where I’m using the panels edge-on to support the cabin sole.

My initial plan was to lay up some CSM in a sheet to about 3 or 4 mm thick, cut the sheet into strips about 26 mm wide and glass these strips to the edge of the panels giving me a good bearing surface capable of holding a self tapping screw. (The joints would be under compression, glued with something suitable from Sika, but I want to cater for a knock down or roll over, so the screws seemed prudent. The cabin sole will be the top of the water tank so there may be some serious weight involved.)

Now I’m thinking about a plastic channel extrusion instead. Would that be a better approach, simply invert the channel over the panel and glass the whole lot in? How well does fibreglass stick to plastic I wonder? Are there better plastics for the job? Maybe small holes in the channel sides to help anchor it to the honeycomb sheet?

Any other approaches people have used and could recommend?

Matt

[Benz]

The usual dodge with edges of panels is to "Hog and Bog." You cut away "hog out" some of the core from between the panels and fill it with filler (bog). Then you can sand and round and paint the edge.
For your application, I'd cut strips of some material with substance, like Coosa or other high density foam to the same thickness as the panel, and hot glue them to the edge to hold them while I glassed the panel, making sure the glass grabbed the edging strips.
If instead of using CSM you used 1798 and 10-oz woven boat cloth, you'd have a lighter, stiffer, stronger panel, and some decent fibers holding on the edging strips, which you could then trim to the exact size you need.

[GILow]

Originally Posted by Benz

The usual dodge with edges of panels is to "Hog and Bog." You cut away "hog out" some of the core from between the panels and fill it with filler (bog). Then you can sand and round and paint the edge.
For your application, I'd cut strips of some material with substance, like Coosa or other high density foam to the same thickness as the panel, and hot glue them to the edge to hold them while I glassed the panel, making sure the glass grabbed the edging strips.
If instead of using CSM you used 1798 and 10-oz woven boat cloth, you'd have a lighter, stiffer, stronger panel, and some decent fibers holding on the edging strips, which you could then trim to the exact size you need.

Lots to think about here, thank you very much.

(And the hot glue gun is a great idea! That’s going straight on the shopping list.)

When you say to make sure the glass grabs the edging strips, do I take it you don’t wrap the glass around and over the edge strip? I thought maybe some of the thinner glass cloth types might be persuaded to bend around the corners.

[coopec43]

QUOTE Now I’m thinking about a plastic channel extrusion instead. Would that be a better approach, simply invert the channel over the panel and glass the whole lot in? How well does fibreglass stick to plastic I wonder? Are there better plastics for the job? Maybe small holes in the channel sides to help anchor it to the honeycomb sheet?QUOTE


Fiberglas doesn't stick to plastic at all.

Instead of plastic channel why not make up f/g channel yourself? (so simple!)

Get some correct width timber, round two corners, paint it with release agent (or wax it), then lay up CSM/resin over it. (I've just made up about 6 meters of 4 inch channel to use as reinforcements for the stanchion mounting)

You can buy it but why not make it yourself?

https://www.miyafrp.com/fiberglass-channels/

[Chotu]

I would definitely do what BenZ said. It’s the easiest way. The second part of what he was talking about.

Digging out the core and bogging sounds difficult. But making a frame around the core of something more sturdy like coosa or wood depending on your preference and glassing that edge frame to the panel face would be quick and it would support plenty of weight.

There really should be no need to go around the edge of that frame and back down the other side. You could have a separate piece of glass on each side. For your application. Because otherwise, you’re going to have to take a router and round that frame edge off to get the glass to take the curve.

All Boat construction projects should have a hot glue gun. It’s the fastest way to mock things up as well. For instance, if you are trying to make one of these panels into a non-structural bulkhead, the quickest thing is to take some little scraps/long strips of very thin door skin plywood, and hot glue them all to each other around the curve you are trying to do. Then take that template, and trace it out on your uncut panel. You’ll have a perfect fit pretty much first time. Saves countless hours.

[GILow]

I’m assessing these approaches against getting the cabin sole level. Pros and cons for each. Part of the challenge is that I think the edge strip will need to go on after I’ve put the floor stringers in place, as I think the stringers will need to be faired and levelled in situ. Can’t see how I can get a level before they are attached to the hull, too many variables.

Much to think about, thank you all for the input.

[Benz]

Originally Posted by GILow

Lots to think about here, thank you very much.

(And the hot glue gun is a great idea! That’s going straight on the shopping list.)

When you say to make sure the glass grabs the edging strips, do I take it you don’t wrap the glass around and over the edge strip? I thought maybe some of the thinner glass cloth types might be persuaded to bend around the corners.

You could wrap the cloth around, but like Chotu said, you'd need to bullnose the edge pieces. Also, when you wrap glass around something, the top parts delight to stay in place, but gravity is working on that underside as well, and getting a perfect lamination becomes tricky. Better to make your edge pieces wide enough that you'll have to trim them, and after then you'll have a perfect fit.

[Chotu]

Originally Posted by GILow

I’m assessing these approaches against getting the cabin sole level. Pros and cons for each. Part of the challenge is that I think the edge strip will need to go on after I’ve put the floor stringers in place, as I think the stringers will need to be faired and levelled in situ. Can’t see how I can get a level before they are attached to the hull, too many variables.

Much to think about, thank you all for the input.

If the boat is out of the water, and I don’t know if it is, level the boat’s waterline.
Then go to a hardware store and get a laser level. Worth every penny. I used to want to build my boat. Everything is within 1/8 of an inch or less.

You can shoot a perfect plane for your cabin sole that way.

[GILow]

Originally Posted by Chotu

If the boat is out of the water, and I don’t know if it is, level the boat’s waterline.

Then go to a hardware store and get a laser level. Worth every penny. I used to want to build my boat. Everything is within 1/8 of an inch or less.



You can shoot a perfect plane for your cabin sole that way.

Boat is in the water, but lasers are still perfectly useable. I’ve got enough to reenact that lame movie with Connery and Zeta Jones.

https://youtube.com/watch?v=jA19wgJxabE&feature=share

I ummmed and aaahed about whether to do this job in or out of the water. In the end I decided I’d rather the hull was in its “natural” shape for the installation of the floors and stringers, otherwise the whole lot would be permanently under some kind of tension or compression from the shape change.

[GILow]

Originally Posted by Benz

You could wrap the cloth around, but like Chotu said, you'd need to bullnose the edge pieces. Also, when you wrap glass around something, the top parts delight to stay in place, but gravity is working on that underside as well, and getting a perfect lamination becomes tricky. Better to make your edge pieces wide enough that you'll have to trim them, and after then you'll have a perfect fit.

Agreed. The little buggers peel off the second you look away.

[Jim Cate]

Matt, this is way out of my expertise zone, but could you not rout out the core to a constant depth (12 mm?) and then glue in a fitted length of some hardwood to bring the edges flush? Or use low density FRP ripped into strips (not G10, but cheap stuff).

Seems that this would give good sealing and a decent load bearing area, cheap and quick.


Jim

[s/v Jedi]

That core material is amazing. Like others wrote, I would hot glue hardwood strips to the edges before glassing.

That said, look at the type of hot glue gun you use. I have been dismissive of them until someone convinced me to buy a real one and try again… results are amazing and plywood tears and delaminates instead of letting go.

This is the one I got: https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

[GILow]

I’m really trying to avoid having any timber down there. Being a water tank I’d be constantly worried about wood rot.

I’m going to play around when I get the laminating bench setup and try each of the approaches suggested so far. I’ll report back.

[GILow]

Originally Posted by s/v Jedi

That core material is amazing. Like others wrote, I would hot glue hardwood strips to the edges before glassing.



That said, look at the type of hot glue gun you use. I have been dismissive of them until someone convinced me to buy a real one and try again… results are amazing and plywood tears and delaminates instead of letting go.



This is the one I got: https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

Good tip on the glue gun, thank you. I can’t find anything remotely as powerful at Bunnings (our equivalent of Home Depot), the highest wattage was a DeWalt at 95 Watts. A big improvement on the 10 Watt model I guess. I’ll look around some more.

[GILow]

Originally Posted by Jim Cate

Matt, this is way out of my expertise zone, but could you not rout out the core to a constant depth (12 mm?) and then glue in a fitted length of some hardwood to bring the edges flush? Or use low density FRP ripped into strips (not G10, but cheap stuff).

Seems that this would give good sealing and a decent load bearing area, cheap and quick.


Jim

The FRP in strips was just the approach our good friend Max was advocating, but being Max he also advocates making my own panels.

It is on the list of techniques to test.