Lightweight Interior Construction Ideas

MiddayGun

Super Anarchist
1,094
404
Yorkshire
I'm looking to build some new shelving and cupboards in my saloon for a bit more stowage, and while I could just knock it up out of plywood, I'd like to try and save some weight if at all possible and try and come up with something a bit lighter than 12mm plywood all around.

Here's a rough idea of what I want to achieve, an extra shelf at the aft end & 2x lockers at the fwd.

Interior.JPG

I'm guessing foam core is the way to for this?
I'd like to veneer the visible surfaces at least with a real wood veneer which should look nice against my main bulkhead.

The 'bottom' of the lockers &  shelf I'll glass to the hull for some stiffness & it should also support i along the length, some questions I have:

  • Will 1 layer of 300gsm each side be adequate for this purpose? (with a veneer epoxy bonded over the glass)
  • For the non structural bits like the fronts & dividers can I get away with epoxy bonding the wooden veneer directly onto the foam rather than glass?
  • Do I need a 'balance' veneer on the back face like I would with plywood?
  • Does the core need to be solid in way of the fixings like hinges & catches?
  • I'd like to make all of it apart from the shelf removable for access, was thinking some hardwood stock bonded to the back face & then screws into the shelf / deckhead inner liner
  • Does it all need to be vacuum bagged to look good, or can I get away with heavy weights to hold it all down?

Assuming here the best thing is to make it in seperate pieces then assemble, I guess if I was feeling clever & I patterned it well I could make the shelf bottom and front from one piece of veneered foam core material & then kerf the backside so it could bend for a nice cuved transition between shelf bottom and shelf front.

Or if I'm completely barking up the wrong tree, are there better ways to do this? Framing etc.
I realise the weight savings may not be worth it, but I'm treating it as an interesting project / practice new skills etc.

 
With good fillets and solid stiffeners in the right places, you can probably do most of the job in 6mm plywood.  
6 mm okoume is about the same weight as 1/2” 5# foam with 300gsm glass each side side.  And a small fraction of the work and materials cost.  Not as stiff, though and curves are harder.
Some folk like varnished okoume, other woods are heavier or paint it and apply varnished mahogany edge moldings.

You can glass foam panels without vacuum on a flat table.  One side at a time, use peelply and squeegee it out flat.   

 
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SloopJonB

Super Anarchist
65,809
10,910
Great Wet North
Last winter I experimented with building a shelf for my boat using pink insulation foam.

1/8" teak ply epoxied to both sides and with solid teak end cap and fiddle rail ended up weighing under 1 Lb. per Sq. Ft. and was as stiff as 3/4" ply.

I would do it again for any non-structural panels. I plan to replace my engine box and berth flats with it in future.

 
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El Borracho

Sam’s friend
6,337
2,379
Pacific Rim
I'm looking to build some new shelving and cupboards in my saloon for a bit more stowage, and while I could just knock it up out of plywood, I'd like to try and save some weight if at all possible and try and come up with something a bit lighter than 12mm plywood all around.
My 1982 Santa Cruz 50 interior is primarily 6mm "Bruynzeel Mahogany" ply. Interesting appearance. Plenty durable. Really light. It's a dense flawless furniture plywood A/A (maybe A/B) sides. The edges are slightly radiused where they show. There are no frames of any kind. Everything is tabbed to the hull. A small amount of milled lumber for rails, fiddles, and whatever one calls the little boards that support shelf ends. Non-showy panels and bunks are 1/4" DF furniture-grade ply painted white. Countertop backing is 1/2" DF ply. No glassed surfaces. All joints are simple butts with 5/8" square gussets (?). Often glued and stapled. Sometimes screwed together.

Very few doors.No drawers. Much like what you have drawn. The shelves can be thin because the edges are supported by the tabbing in the back and the cubby face or fiddle* in the front. 

It is rather dark by today's standards. Today I'd maybe choose a lighter colored fancy wood.

100% of the volume is used. There are lockers and cubbys kinda secreted behind things. Some false bottoms in cabinets for deep storage. The entire hull surface is accessible except where it's behind 'easily' removable tankage. Gotta see one to believe it.....

* Whatever a solid fiddle shelf edge is called...

 

teamvmg

Super Anarchist
1,970
104
10mm  60kg/m3 airex foam with 300g cloth either side [Could go down to 200g but is tricky to work with]

Use epoxy, no need for vac bag

Use peel ply which would save weight and give finish good enough to paint or at least, need minimal filling/fairing for super glossy paint job

Lightweight filler in the cut edges and around hole for fixings

 

MiddayGun

Super Anarchist
1,094
404
Yorkshire
Cheers for all the ideas guys.
Guess I need to do some test pieces.

My experience with 6mm plywood has been that its been incredibly weak, but to be fair I've never actually bought decent quality gaboon stuff, just the local crap that I use for templates.
But I guess with good quality that's glassed to the hull & framed at cupboard opening size it should stiffen it up.

I'll do some test pieces and see what works for me. As I said, this isn't a 'must do' project, so I'm happy to play around and try some different ideas.

 
The good grades of plywood are very different from the cheap stuff.  6mm would be five equal plies rather than the three plies of lauan underlay or fir.

A well done fillet has structural value and is tidy, light and easy to clean.  Get Russel Brown's book on epoxy techniques.  The chapter on filleting is excellent.

 

Meat Wad

Super Anarchist
I'm looking to build some new shelving and cupboards in my saloon for a bit more stowage, and while I could just knock it up out of plywood, I'd like to try and save some weight if at all possible and try and come up with something a bit lighter than 12mm plywood all around.

Here's a rough idea of what I want to achieve, an extra shelf at the aft end & 2x lockers at the fwd.

View attachment 376314

I'm guessing foam core is the way to for this?
I'd like to veneer the visible surfaces at least with a real wood veneer which should look nice against my main bulkhead.

The 'bottom' of the lockers &  shelf I'll glass to the hull for some stiffness & it should also support i along the length, some questions I have:

  • Will 1 layer of 300gsm each side be adequate for this purpose? (with a veneer epoxy bonded over the glass)
  • For the non structural bits like the fronts & dividers can I get away with epoxy bonding the wooden veneer directly onto the foam rather than glass?
  • Do I need a 'balance' veneer on the back face like I would with plywood?
  • Does the core need to be solid in way of the fixings like hinges & catches?
  • I'd like to make all of it apart from the shelf removable for access, was thinking some hardwood stock bonded to the back face & then screws into the shelf / deckhead inner liner
  • Does it all need to be vacuum bagged to look good, or can I get away with heavy weights to hold it all down?

Assuming here the best thing is to make it in seperate pieces then assemble, I guess if I was feeling clever & I patterned it well I could make the shelf bottom and front from one piece of veneered foam core material & then kerf the backside so it could bend for a nice cuved transition between shelf bottom and shelf front.

Or if I'm completely barking up the wrong tree, are there better ways to do this? Framing etc.
I realise the weight savings may not be worth it, but I'm treating it as an interesting project / practice new skills etc.
Very cool, If I were going to keep my boat, I'd like to do that too. I was thinking like an Olson 30 / SC27 type interior. Mock up in cardboard and use foam (maybe some stringers like surfboards), biaxel and carbon. The boat was built with just bulkheads and stringers.

Some great ideas here.

 

El Borracho

Sam’s friend
6,337
2,379
Pacific Rim
The cored glass panel and epoxy fillet approach seems like a great amount of work. Especially the sanding and finishing. The thin furniture ply is very easy to saw, construct and finish. A brief touch with sandpaper, a coat of varnish and you're done. Compare that with sanding and painting inside cubbies...ugh. Finishing the tabbing is plenty painful enough. Do it before mounting the faces. Seriously mask the wood. Figure out how to make perfect tidy tabbing. Perhaps use vinyl-ester vs. epoxy since life is short.

Is the finished weight difference significant? Doubt it. The foam core method won't be zero weight... 

I use a portable table saw in the cockpit with a very expensive carbide blade. Cutting the pocket openings has been a challenge. A hole saw and fine coping saw seems to work best. Pretty easy to neaten up the wiggly coping saw lines with a sanding block. Mahogany breaks out kinda easy so the sabre saw is problematic.

Tip on varnishing inside cubbies: Varnish on a little cloth wiper works remarkably well.

Foam core would be great for counter top backing, bunks, and the engine box.

The old world DF ply is nothing like today's retail stuff. Seriously dense and aromatic with pitch. Sands to a perfect finish.

But, yes, wood is so last century...

 

toddster

Super Anarchist
4,139
939
The Gorge
I've recently made several pieces from 8mm okume.  It's about as far as I'd like to compromise between load bearing and weight, but that includes some work-tops. YMMV.  BTW, for both the old and new oval-opening lockers as shown in the drawing, I've made bypass doors out of 1/8" ABS sheeting. Very light weight and conceals the jumble within.  A slight curve to the track prevents the doors from rattling or sliding on their own.  I'll pretend that I planned that on purpose.  

But for even lighter weight and organization within the lockers, I've had thoughts of sewing fitted shelving (hammocks) and pockets from leftover sailcloth and the like.  

 

MiddayGun

Super Anarchist
1,094
404
Yorkshire
Very cool, If I were going to keep my boat, I'd like to do that too. I was thinking like an Olson 30 / SC27 type interior. Mock up in cardboard and use foam (maybe some stringers like surfboards), biaxel and carbon. The boat was built with just bulkheads and stringers.

Some great ideas here.
If you google the interior of the Maxi 1050, that's where i got the inspiration from. 
I already made a mock up with several other ideas but I discarded them as I didn't like them. 

It goes against the grain a little bit boxing in the stiffening web, but its all removable & I think a shelf or cupboard butting up against it looks wrong. 

Some great ideas here, seems like plywood is the way forward on this one, lightweight stuff anyway. My wallet should be happy about that one. 
I actually have bypass sliding doors in the galley and it looks good, not so sure about them in this application though, I'll have a play with the model and see if I can try the idea. 

 
Part of the reason for the variety of techniques being proposed here is that folks are putting a different value on lightness.  If it doesn’t matter, you’ll use a lot of 3/4” plywood and if it matters a lot, you’ll start with nomex  honeycomb.  I’ve found it useful to have in the back of my mind the price I’d pay to save a pound.  One way to arrive at this would be to ask how much the value of the boat would be diminished if it were 1000 lbs. overweight.  Divide by 1000 and that’s the marginal value of a pound saved.  I’d guess values of $100/lb. for a light foiler, $50 for sporty things and $10 for a 4KSB.    Factor in a value for your time and you have the basis for evaluating alternative approaches.

 

Nodrog

Member
404
37
Auckland
My 2c worth, a veneer either side of 80kg foam, or veneer one side, 200gsm glass the other, is going to be plenty strong and lighter than 6mm ply, and will still look great, but..... There's a lot of work in getting there, including a vac pump to do it well, and yes, anywhere you attach a fastener you'll need to reinforce the core too, and finish the exposed edges. It could be an interesting project if you want to do it that way, but ply's pretty good! 

The fillets in a job like this add up to a sometimes surprising amount of weight too, they're the same whatever panel you use. They also add a massive amount of strength, so even 4mm might be sufficient if you don't need to support too big a panel, or be able to act as a grab handle in a rough sea. By the time you're down to 4mm ply I understand its pretty hard to get much lighter using cores. 

 
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