Latest Lightweight, Rot Free Panels for Projects

[Chotu]

Originally Posted by Breaking Waves

I don't know if my experience will help at all, but .....20 years ago I made a complete cored interior - made it up in modular components in my shop over a winter while a yard was building the hull.

It seemed like a 'well-solved problem' even back then already.

You could buy pre-made panels, but I made mine just copying what I thought were the best practices from the higher quality guys. I used a 4x8 'press' rather than a vacuum set-up, seemed both simpler and faster for making a bunch of panels.

I used foam (urethane) and honeycomb cores, and ply and glass and formica skins. Interior 'design' was varnished to about waist level and then white above that - so varnished nice plywood skins for lower cabinetry, and generally semi-gloss white painted fiberglass skins above. Formica where esthetic was less important.

I generally used 'peg and glue' for the joins, with some nice solid shaped mahogany corner pieces in a few places for esthetics.

Looking around today for best practice examples, I am a bit surprised at how little the cored panel world has changed. I would consider Dragon Plate who are very technical/high stiffness to weight oriented (and ofc very expensive), as someone who has likely got the good core options sorted out given their skins are quite expensive.

Attachment 205766

This is pretty helpful. Thanks!

And yes. It's crazy how there isn't anything premade for this. Even the dragon plates need finishing.

One thing all the detractors need to remember is I have severe allergic asthma and just about had to give up boats all together.

Air pollution and epoxy are the main triggers. So let's keep that in mind. I have quite a sensitivity to airborne chemicals.

[jimbunyard]

Originally Posted by Chotu

It's a shelf to hold dishes. Ha ha. It doesn't matter AT ALL what it's made out of as long as it holds the dishes and weighs nothing.

It doesn't need any tensile strength. That comes from what I'm laminating to the outside of it. It needs compressive and shear strength. And it's got lots of it. The one I'm using as a test panel approaches divinycell in compressive strength. Sheer feels pretty good too, but the Numbers would be better.

But you had it right on the contact cement. Doesn't work at all.

Note:. I ALWAYS use destructive testing when testing out a panel.

'Nothing' is a relative term. You're in for a surprise if you think a laminate has no need of tensile strength; what do you think holds the sandwich together?

Given the time and effort to use the construction method you plan, the pennies and ounces you save on XPS over 5 lb PVC or polyurethane will be forgotten when you have to replace the cabinets in 5 years due to delamination and substructure attachment issues. If you use the boat hard, the inadequacies will likely manifest themselves even sooner.

Obviously just my opinion.

[Watermelon123]

Anyone who would like to find a low cost, lightweight , and strong option for panels on a boat should seriously consider XPS.

I have made a number of panels for testing and use on my boat and 12’ catamaran dinghy all with great success.

There are many people as well as opinions on these forums as well as many backgrounds and experience levels.

I love the quote one engineer put up that one simple test is worth 1,000 opinions.

I have built a hatch as well as a companionway hatch from standard Dow 15 psi compression XPS. I put filets on the inside. I laminated a layer of 17 oz biaxial cloth on both sides. I also can jump up and down on it without any suggestion of compromise. Btw, I’m 6’4” and weigh 230 lbs. I have also built shelving spanning over 30” on which to store tools and cans of paint. Also I built the foredeck of my 12’ cat dinghy from XPS clad in 1/8” luan door skins.

Epoxy resin works well for this job. Never let the epoxy get hot it will melt the XPS. This is a weak point for the XPS. I’d not paint a finished panel black or a dark color and leave it in the tropical sun. I sand the XPS with 40 grit and vacuum before laminating.

Hope this helps you. Rob

[exMaggieDrum]

Just FYI if it is important: the cabinet maker/woodworker in my old yard said that Starboard and the like will hold screws long term better than most wood with much less prep required, such as accurate drilling of hardwoods. It is heavy though.

[Breaking Waves]

I was not super experienced or knowledgable about core panels when I built mine. It all held together perfectly (for 75,000ish miles of high latitude sailing); except for one particular panel - the cored cabin sole right at the base of the companionway steps, the loaded edges of this sole panel crumpled. I occasionally 'jumped' off one step up onto this section of sole - so it was taking dynamic impact loading. It could have used less span/more cross floors underneath but it was a section my wife used for galley storage and she did not want extra floors in it. I originally had just 1 ply glass wrapped the edges, then I routed some foam out and epoxy filled it and wrapped it - which still crumpled. I finally routed it out again deeper and put in 2" wide solid wood strips to replace the edge foam and that worked. It was just this section - the rest of the sole was fine with the original design.

These cored panels are nice to work with - one man can handle a 4x8 sheet pretty easily, they save a ton of weight in the boat, and they should stay dimensionally stable and never rot or swell.

[Chotu]

Originally Posted by jimbunyard

'Nothing' is a relative term. You're in for a surprise if you think a laminate has no need of tensile strength; what do you think holds the sandwich together?

Given the time and effort to use the construction method you plan, the pennies and ounces you save on XPS over 5 lb PVC or polyurethane will be forgotten when you have to replace the cabinets in 5 years due to delamination and substructure attachment issues. If you use the boat hard, the inadequacies will likely manifest themselves even sooner.

Obviously just my opinion.

Given this process will work with any foam, what's the next one up from XPS?

[jimbunyard]

Originally Posted by Chotu

Given this process will work with any foam, what's the next one up from XPS?

Given that this is not a question that can really be answered without considering all the parameters you've outlined, let me give you a reasoned answer, taking into account those parameters as I understand them.

To begin with, the XPS board I assume you are referring to is the pink or blue stuff available from the big box stores. If so, the 'tensile shortcomings' I have qualms about can perhaps best be illustrated by the this thought experiment. Screw a coarse thread drywall screw into a panel of 1/2" XPS and one of, say, 5 lb density, unreinforced 1/2" PVC foam. The one in the XPS can be pulled out much more easily than the one in the PVC.

I've had no construction experience with the higher end XPS, like Dupont Panel Core, but have some with it in refrigeration applications. It seems tough enough, but I could find no references for it's use in your application, nor any indications of price. It would be surprising to me if in the quantities you need there is much difference there in it and the PVC or PU.

The limitations in glue selection and comparative tensile strength remain, even in the higher densities.


As for the right selection for your application, without actually seeing what you're doing, one can only make assumptions, so here goes.

Given that you seem, with good reason, to prefer not to use epoxy, the most common method for laminating formica turns out (anyway) to be the best; solvent-based contact cement. (This also eliminates the use of polystyrene)

So the choices are unreinforced PVC or polyurethane, or reinforced polyurethane. Seems that, across the board, the reinforcement adds about 30% to the cost, so the trade off comes down to how much stiffness you want in the final structure/how much you want to pay, and to a much lesser extent, weight savings (3-5 lbs/cu ft vs 15-20 lbs/cu ft).

Rather than bore anyone any more with hypotheticals, instead I'll tell you what I'd do based on what you've told us so far.

Contact Miami fiberglass suppliers, and find the one that offers the best price on both the Coosa and PVC foam. I'd use Coosa for the shelves and walls because I'd only have to laminate the exposed surfaces. For the doors I'd use 5 lb unreinforced PVC laminated on both sides and edges.

For the placement of the 'screwing blocks' I'd lay out all the doors on the full size sheet of core (before lamination) and then glue a full strip of quality multi-ply hardwood plywood, say 3" wide, along the hinge side of the core, laminate both sides, re-lay out the doors, cut them out 1/16-1/8" oversize with a metal blade on a quality, variable speed orbital jigsaw, trim them to size with a router, edge trim them and install. For the fascia where the door mounts, I'd use 3/4" multi-ply hardwood plywood, formica laminated on exposed surfaces only, to aid in gluing if you choose not to use mechanical fasteners.

Though I'd prefer mechanical fasteners, with reasonably close fitting, glue can be used to fasten the cabinets sides to the hull or substructure. Though I've never used it, I've fought with removing methylacrylate type glues enough to know that their bond is tenacious, though it is expensive. Perhaps this is a good application for it. Thickened epoxy is available in self mixing, caulking gun tubes as well, though your allergies may preclude it's use.

There are numerous shelf mounting and adjustment systems out there; if you can find one that adds to the strength of the whole rather than using the strength of the cabinet alone to support the load, so much the better.

A final note on laminating. I may be mistaken, but it seems that you were contemplating applying contact cement to the panels, assembling them and vacuum-bagging them 'wet'. This will not work; the bond is made on contact after both coated sides are dry.

While vacuum-bagging after bonding isn't strictly necessary, it certainly wouldn't hurt anything.

Obviously there are many different ways of approaching this, but given what you've described, based on my experience something along these lines will be your most cost/time/longevity efficient solution.

[Breaking Waves]

Doors ..... for cabinet “doors” We used mesh fabric with twist lock closures .... very light very, easy to make, good ventilation. Used on a lot of high end race boats.

For head door, we made a sliding door - no need for hinges or screws.

The people recommending coosa board - how do you recommend finishing it for “nice” interior use? Back when I last tried it, it was a real pain to get a good paint finish. Is Formica laminate the real solution for it?

[Chotu]

Jim, I'm not going to quote the whole post you made but thanks!! Reading it over a few times to get a good mental picture of the details. Still going over the description of how to do the screw blocks. I'll get it, but I'm definitely mentally challenged when it comes to finish work like this.


I should mention what I'm doing is making cabinets. Picture a galley. A stateroom. They all have cabinets to store things in. That's what I'm making.

The hull, bulkheads, cross beams, everything is done and the boat has already traveled around 1000 NM. Just making boxes to store crap in, basically. Lol

For areas that are loaded or have cyclical loads or impacts (like the shower base/pan/floor) I'm using the same thing the hull is made from. Corecell and fiberglass panels.

For speed of assembly and lightweight characteristics, I'm looking for 3-5lbs foam and to bond the Formica so it's looking good upon installation without all the finishing involved in other methods. Still very lightweight but good enough to make some shelves.

Anyone have any insight into lower cost PVC or polyurethane foam in 3-5lb density? Brands? Off brands?

[Chotu]

Originally Posted by Breaking Waves

Doors ..... for cabinet “doors” We used mesh fabric with twist lock closures .... very light very, easy to make, good ventilation. Used on a lot of high end race boats.

For head door, we made a sliding door - no need for hinges or screws.

The people recommending coosa board - how do you recommend finishing it for “nice” interior use? Back when I last tried it, it was a real pain to get a good paint finish. Is Formica laminate the real solution for it?

I was going to actually leave everything as a cubby hole, which I had on my last Catamaran. Then I was thinking it was so lightweight, doors may be ok. But good point on not using doors on the cabinets at all.

The issue I always have with sliding doors is where do they go?? Ha ha. Seems every time I want to do one, it's got nowhere to slide to. But I'm going to look a little harder on that.

What hardware did you use to do the sliding doors? I'm quite challenged with this finish work and need remedial help. Lol

Coosa is out. Too heavy and porous.

[Breaking Waves]

Originally Posted by Chotu

What hardware did you use to do the sliding doors?

Real simple, really no “hardware”, routed channel in mahogany with uhmw strip in channel, above and below door, wooden knobs both sides of door, all there was too it. Slide easily With knob but enough friction did not slide on its own. As you say - challenge is space to make door work. For me toilet was forward of compartment facing aft, and shower aft end of compartment. Shower compartment had enough wall space for door to slide into.

But a normal door with hinges would not break your weight budget if this did not fit your interior layout






I'm quite challenged with this finish work and need remedial help.

Ive see some pictures, you do excellent work. perhaps just need to remember to keep it extra simple

........

[Chotu]

Originally Posted by Breaking Waves

........

Thank you!

Question for all:

What's the absolute cheapest structural foam available? The boat is already built. I'm making cabinets to hold clothing, napkins, some cups and food.

[Chotu]

Originally Posted by Breaking Waves

........

Thank you!

Question for all:

What's the absolute cheapest structural foam available? The boat is already built. I'm making cabinets to hold clothing, napkins, some cups and food.

[Matt Johnson]

I've used Air-Cell 6lb which I think was under $100 a 4'x8' sheet. But that was years ago and my memory is foggy on the price. I may be way off, but I remember that it was significantly cheaper than Core-cell. Maybe worth a call.

https://fiberglassflorida.com/fiberg...reen-foam.html


Matt

[Chotu]

I wanted to report back my findings regarding XPS foam

I found the right adhesive and made some test panels with that as a core. To me, it was a failure.

Over a short amount of time, the XPS foam went from being fairly rigid to kind of soft. That’s not a good quality in a core material.

With my fingers alone, I could squeeze the edges of the test panel and deformed them. Especially on the corners where there was a point. That’s not good enough to make doors for cabinets. Might stand up for cabinet walls, but I don’t want to risk it with all of the labor involved.

Going to have to pony up for the more expensive foam core. I still want the speed of installation, so I still plan to adhere Modern formica to the core. Then I have a finished piece right away. I have some pretty good I have some good techniques for zero bond line. so it should look very professional.

and of course, no epoxy involved.

Given that I won’t be using poly styrene foam, I should be able to use contact cement. I will do another test panel soon. And I will report the findings. This should be a really useful way to make cabinetry. Fast. Durable. And looking really nice. So I’m sharing it with everyone.