Much seems to be being made of the lack of impact resistance of XPS with regard to use on the deck areas. The stuff is fairly tough by itself, add a glass sheathing, and it would take a major impact to have any effect, to suggest that dropping this or that on it will cause damage is a bit absurd..... I wouldn't be inclined to an outboard or a 60 lb anchor carelessly on it. Of course good design would be to have a thicker layup on top in the areas that might be subject to such loads. May cored decks have thin teak strips over them for looks and durability, or some of the laminate imitations that are now available. It's only logical to have additional layers of glass, or an overlay in areas of heavy use on ANY deck, and of course not everybody drops a winch handle from the top of a 60' mast on the deck ;-)
What is a bit discouraging is the fact that when something like this is brought up, so many people are so determined to make their case against it, rather than to seriously look at how they and others could benefit. Not so long ago Rob made a comment about my "closed little mind", in response to my reluctance to even consider the idea of foam cored hulls at all, much less below the water line...... and dismissing proas, Harry or otherwise, for my use.
Payload is a HUGE consideration to me, and as I'm looking at cats in the 30' range, and only about two designs fit my criteria, one with an 1800 lb payload and the other with 2640, made from plywood, the temptation of going sandwich construction if the initial cost can be made tolerable, for the possiblity of as much as 50% more payload, has forced me to turn my head.
An additional 800 to 1000 lbs payload without adding to boat size, and weight is a no brainer. My mind is hardly "closed", as I have progressed from considering only monohulls, having negative opinions about multihulls, based on reading, and the opinions of others, rather than on experience with them. Initially I was looking at trimarans, as I intend to step a single free standing mast, but payload considerations pointed me to catamarans, and figuring how to step a free standing mast on a cat. Proas have the same issue of payload and space per length as trimarans....... I'm not going to sail a 30' proa around the world ;-) The Harry Proa has many truly brilliant innovations, and I feel has made the proa a reasonable choice for many people, perhaps a better choice. I'm kind of an "idea vac".....If I can benefit from some of Rob's ideas and innovations, I will, and as always when I adopt ideas from others, I make sure everybody knows where they came from.... that's the least someone can do, and to do otherwise is the mark of a small man. We all build on the groundwork laid by those before us. In my own line of business, which I've been in for 35 years, I always offer help and the benefit of my experience to others who ask, sometimes those who are too proud to ask. People helped me when I needed it, it's a circle. In this respect Rob's a man I feel a real bond with... I'm not going to build one of his boats, but I'm already pointing out his innovative ideas and designs to others............. It's worked that way for me. I've helped others, and when they were over their heads, or knew someone else who was, guess who they went to....
H.W.
On 05/11/2018 07:40 AM, mcrawf@nuomo.com [harryproa] wrote:
<<When you speak of weight versus resiliency with regard to the upper portions of a boat, I don't really think it applies.>>
H.W.,
We're in agreement there. At least in the sense that there's a good case to be made for XPS or balsa in those locations. The talk about resiliency was for the rest of the boat.
I do know a designer/builder in Maryland who insists upon balsa core for the entire hull, but I can't follow him down that path. He's convinced that water intrusion will never be an issue if the boat is properly designed, built, and maintained, and I've seen too many cores turned to mush due to leaks no one knew existed. We've agreed to disagree, and since I don't have to purchase his boats, it's not a problem.
There's a fair amount of flat and nearly-flat surface deck area on the Ex 40 that might benefit from a thicker/lighter structure. It would be interesting to see what the weight and cost savings would be. I'll have to look into that in more detail when it's time to build.
- Mike
StoneTool owly@ttc-cmc.net [harryproa] wrote on 5/10/2018 8:37 PM:
Mike:
When you speak of weight versus resiliency with regard to the upper portions of a boat, I don't really think it applies. You don't hit docks and other boats with the coach roof or decks. In some places you want strength and stiffness AND you want light weight. That means a light weight core of greater thickness. If you made up two sandwich pieces of the same weight and dimensions except for the thickness of the core, and the same glass layers, but one had Divinicell H-80 for a core, and the other had XPS which is typically 2 pound per cubic foot versus 5 for H-80, and you tested both pieces in various loadings, the XPS sandwich would be in excess of double the strength in bending at least, and probably also in torsion. Tensile strength would be virtually identical.
I haven't done this, but I've done enough other things that I'm quite confident of it.
XPS that is not part of a sandwich does not bend well, and the thicker it is, the larger will be the radius at which it will fail. In a sandwich, the entire equation is going to change because failure always begins as a tensile failure on the tension side of a bend on bare XPS. With glass bonded to it, it cannot fail in tension before the glass does.
The performance of XPS in a sandwich has been demonstrated again and again. It becomes very resilient in bending
My "local" supplier (hundreds of miles away), carries no densities of marine construction foam less than H-80. Above the hulls themselves, H-80 is probably not the optimal core material. A thicker lower density core has many advantages. Divinicell H-35 might be the preferred choice in these kinds of situations, but in a place where XPS can be made to conform to the shape easily, I suspect that the advantages would be negligible....
H.W.
On 05/10/2018 11:48 AM, mcrawf@nuomo.com [harryproa] wrote:
H.W.,
So you'd say XPS deserves a place in boatbuilding the way balsa core does -- best perhaps for decks and cabintops, and less-than-optimal for hulls and topsides?
That would be a reasonable compromise.
Then, some folks will still go with balsa, or perhaps XPS, for the rest of the boat because weight means more to them than resiliency. Which is, of course, each builder's trade-off to decide upon.
Just out of curiosity, do you know how a sheet of XPS would handle the infusion process with curves? The building process for the Solitarry is pretty wild, at least in terms of what can be done ahead of time:
https://www.youtube.com/watch?v=DfhdRfBTt8o
I've never worked with XPS under 4", so I don't know much about its flexibility.
- Mike
Posted by: StoneTool <owly@ttc-cmc.net>
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