Should I stick with plywood or go for foam core?

[rwatson]

The seeming preference for plywood over proper (read PVC) sandwich construction on the forum continues to puzzle me, you have a clean, seamless construction that is virtually free of framing in some cases, opposed to something that is all joins and framework, it is just a no-brainer, except the foam sandwich one-off is more difficult to execute.

Yeah, expense is the big thing, but you still have all the 'furniture', the bunks, benches, seats, compartments etc in any boat. Whether they are structural or not, its still got to to be done.

In sandwich construction you still have to make all the moulds, and then put a few back, or a whole new set, afterwards.

 

[groper]

Im a carpenter by trade and i can make my boat furniture faster with foam sandwich panels than i can with plywood...go figure... foam core is much more expensive but also lighter and thus a higher performance boat will result and nothing to ever rot...

I dont see any difference in "difficulty" either, i think its more "familiarity" with plywood which is why so many people shy away from the foam core methods... they just dont know how it will behave as most have never used it before, whereas almost anyone and everyone has built something from plywood before finishing high school... Curiosity gets the better of some people and they investigate the foam core option, then they read their first quote for the foam and fall over backwards, it usually seals the deal in favour of plywood in all but the most extreme of high performance requirements...

 

[rwatson]

..... usually seals the deal in favour of plywood in all but the most extreme of high performance requirements...

Absolutely.


And, its not just getting experience with foam - its the sheer amount of work.

yes, you can build furniture faster with "foam sandwich panels than with plywood.", but you missed out mentioning the "making the foam sandwich" part of the process.

Sure, once you have the flat panels, its a doddle, but unlike plywood, which is substantially done when you buy it, you have to make the sandwich panels yourself.

Making up the smooth, flat panel tables for the panel layup is a big time sink for a one off project, as well.

Yes, I know you can buy them prebuilt in some locations on earth, but not usually, and the prepared panels come with a big price premium.

 

[groper]

Well you missed the part about needing to encapsulate the ply in epoxy and the subsequent finishing work after that... large peices need to be joined together from multiple sheets etc and a timber frame needs to be built.... it all balances out in the end, the labour involved is about the same. Its more about price and suitability for task with regard to shape and mechanical properties that should drive decision. ..

 

[rwatson]

A hollow core door, two saw horses & plastic sheeting is fine for interior sandwich panels - it's a low cost way to get started making your own. Moe

.... and , and ???

Its not as easy as buying just buying the form materials, and you probably know it too.

For a start, even internal panels are rarely bigger than a door panel. So you have to get several of them, and set them up on a trestle fully flat, level and secure.

Plastic sheet you buy from the hardware store has folds and creases that all muck up the layup. You are far better spray painting a new mdf doorskin for a decent finish, after filling in the gaps beteen doors. Thats no 60 minute exercises. And I would always go for melamine covered mdf in preference.

Then, if you are putting a foam backing on the layer of glass, you usually need a small vacuum setup to ensure contact during cure, so you might as well do both sides at once - thus all the paraphenalia setup. If you dont do vacuum to both sides, you have to turn the half made panel over, and you cant put 'ooze holes' in the first glass surface to make sure that the foam is contacting the second glass layup with no air bubbles.

Compare that with chucking a premade, half the cost, sheet of quailty plywood on the back of the truck.

There is no comparison for the one off, amateur built boat.

oh - and did i mention cost ????

 

[El_Guero]

Check out the foam on the NZ Americas Cup Boat after impact.

They are super lightweight, but a plywood wouldnt have suffered that much damage.

And the Oracle answer is

"that depends".

In this case not depending upon the data architecture, but the materials.

3mm ply wrapped in glass would struggle to out perform 25mm foam core wrapped with carbon fiber.

Broad and prejudiced statements do not do learners any good. They walk away thinking foam is weaker than ply, but that depends upon which ply, which foam, and which wrap, the underlying re-inforcement, And which process .... infusion takes foam up a notch. And most importantly, the quality of work done by the craftsmen and the original design of the NA.

Ply is stronger than foam .... Steel is stronger than steel. Forget to mention 1 inch steel built on 1 foot bulkheads, stringers, and ribs is stronger than quarter inch built on 18 inch bulkheads, stringers, and ribs.

So, I read this thinking, "Am I learning anything of value?"

How is nothing of value good for the art and science of marine engineering? How will we encourage some 17 year old kid to devote his, or her, self to the future of nautical engineering and build the next great product?

The sail boat each of us wishes we had today, just like a couple of kids did for us at Apple in computing?

Or, a couple of mid twenties engineers and sales people from IBM did at Oracle? And just think what Ellison's vision did for the business world, and for sailing, yesterday?

wayne

 

[FixItWise]

The Gougen Bros 30+ year old catamaran might disagree with you - and dozens of other old plywood/epoxy boats around the world.

There are plenty of problems with foam, mostly caused by problems in construction true. Its far from a total problem solver, as well as being a lot more expensive to build.

Check out
Core Materials in Boat Building: Reviewed in the Light of History - Structural Issues - by David Pascoe http://www.yachtsurvey.com/core_materials.htm

Thanks. Great read. Got me thinking about building with wood core. Even though I swore I would never own another boat with any wood in it. As a woodworker, I appreciate the simplicity of working with wood.