Originally Posted by brian eiland
I'd like to know more about this subject as well. I've written directly to Derek to ask about his alleged quote on this material.
+++++++++++++++++++++++++++++++++++++++++ Here is a reply I got back from Derek: Foam core is ideal for all kinds of reasons - a few -
PVC does not rot or deteriorate and is monocellular. Water does not permiate through the foam.
The cut cells fill with resin and provide both a complete contact with the skin as well as backing up the thin skins.
Where two sheets come together, the join will fill with resin if not already glued.
In the 47 years I have been specifying foam it has been 100% reliable. The most damage I have seen or been told of has been through the outer skin but not the inner skin.
Easy to cut, sand, bevel, join, bend, taper thickness etc. Cost of the basic sheets may be slightly higher but the very low wastage due to being able to put offcuts together more than offsets this. There are lots of things that simply cannot be done with any other materials.
Honeycomb is claimed to save weight (a minor amount) but it does not have the record of PVC foam. Some cells are likely to get filled with water. A shower following a hot sun on the deck will act like a powerful pump. Some people say - we would not use below the wl but that is where by my theory there is less likely to be a problem. 8mm diam cells, unbacked thin skin is more vulnerable to damage and water ingress.
I do have a serious problem with Nida. Their consumer style comparison puts nida top and balsa second and PVC foam way down the list. Ie a material can be unsuitable on one count, which should rule it out entirely but it can still be top on the numbers count. Repeated emails to their MD and to their chief designer does not get answered.
Balsa should never ever be used in any boat. I learned this from own experience 40 years ago and there have been numerous instances since. My question, what is there to gain? Better shear strength but the PVC does what you need so what is gained. Balsa is heavier than the foam we use and is less resilient and more likely to break the skin to core connection.
Water will get into both honeycomb and balsa. it is only a question of time - ie a time bomb as there is little or no indication of the problem till it is too late. A very nice looking 55 cat, built in Brazil, was slipped alongside a 36 power cat of mine in New Caledonia, to have a soft spot at a chain plate investigated. Two days later, the whole hull side skin had been removed and no one had looked at the other side. A new owner as well.
The nice part of KSS is that most parts lose the flat panel look. This particularly includes the hulls. We would never call the KSS workshops, flat panel clinics - though all parts do start as flat panels.
Why go for steel? I have designed for steel and ally but hate the stuff. Noisy and dirty while building, taking a lot more than twice the time, lots of finishing and then build another boat inside.
Why go for polycore? How will you ensure that the water that will get in does not run between the polycore sheets. Resin infusion is the magic, but not for any system I have seen to use honeycomb.
We built lots of foam monos. Can easily do hard chine monos.
+++++++++++++++++++++++++++++++++++++ Here is a reply I sent back to Derek: Kelsall wrote:
Foam core is ideal for all kinds of reasons
So what foams do you recommend for deck constructions...particularly for tropical climates?? If I remember correctly there are not that many that come recommended for use as deck cores?
I believe there are also a number of these foam cores that are NOT recommended for use with dark colored hulls?
And aren't there a number of these foams that don't take kindly to being bonded to with polyester resins? Isn't this questionable bonding in some instances, combined with the brittle nature of many of these foams the reason that some of these sandwich structures delaminate. Upon delamination can't the water migrate along the skin-core boundary?
Perhaps you have experienced far fewer problems with these foam core structures as you have learned what best foams to utilize, and you have built your sandwich structures in more ideal controlled conditions (on flat tables with infusion and bag pressure), than traditional one-off hand-layup conditions. But isn't that the same premise that the kit-boat guys are touting with their Duraflex and Polycore prefab panels.?...regardless of the core type.
Balsa appears to hung in there as a core material because of its superior ability to stand up to deck temps of the tropics. But too many post-construction penetrations without proper sealing have led to many problems with balsa cored structures. And a considerable number of new construction proper skin adhesion problems turn up. That why I recommended against the use of balsa-cored Duraflex construction upon a recent inquiry about same. As I read even more forum submissions on various type of cored constructions I was finding some problems with foam cores as well.
Concurrently I am finding fewer problems with polypropylene cores, those cores that I had for years ignored as inferior. I've had to do some reconsidering, and thus far I'm liking this material much more than I would have ever thought possible. I also like its 'toughness' and elastic ability to give without brittle failure.. Kelsall wrote:
Water will get into both honeycomb and balsa. It is.....nice looking 55 cat.....
Sure the cells PP honeycomb are 'hollow' and can hold water, but that appears to be restricted in a very local manner....and absolutely no rot. Subsequent water migration should be stopped by the moisture barrier scrim layer that is termo-fused (not glued) to the cell edges.
You did not mention whether that cat was a balsa cored or PP cored vessel??
I'm looking at redesigning a couple of monohull motorsailers, and my preference for building these is steel hulls with prefab poly-honeycomb decks and superstructures. Kelsall wrote:
Why go for steel?
Steel hulls are perceived as low simply technology, low cost, very high durability construction....you can bounce off of those stray floating containers, or rocky outcroppings without fear of slicing or puncturing thru that outer fiberglass skin of a cored vessel.
And since we are not that overly concerned with weight in the monohull construction as we are with multihulls, why not utilize this very marketable material for that worldwide cruising owner. Besides steel hull maintenance has become much easier with modern coating materials.
I would consider an all sandwich construction per this gentleman when he was building his 65' schooner of 3” Nide-core (WWW) http://www.soundingsonline.com/boat-...lletproof-boat
….but I would still be willing to bet that most clients will opt for steel in the hull itself.