| I apologize for my tardy response. You didn't bother to include the original text which explains things fairly well I think.  

First, no apology is needed. Second, the bottom right of every one of the list emails it a link to all the posts in the thread. Sorry you had trouble finding them.

Here is your post.
https://au.groups.yahoo.com/neo/groups/harryproa/conversations/messages/12842

I often get things wrong, but I found the wording and prose confusing, so I asked questions. So, I guess, we disagree on how well you explained.

To be clear, the context is Chris posed this question to Rob...
"My question is how much extra would one of the larger Harrys (say the 50) weigh if plywood was used instead of foam and glass? Would that level of extra weight ruin the handling and performance?"

To which you directly replied...
"Here is an actual comparison I made on the two building systems per square meter for the Woods Eclipse hulls based on the actual figures."

So I ask, did you intend to compare two different core RW layups plans and some sort of flat infusion, and use that to infer the delta for doing Robs Intelligent Infusion in ply?

| I did not use Rob's numbers or Gougeons numbers, I used Richard Woods numbers as he is the designer of the boat in question.

The boats and designer you injected into a thread about ply as an alternative core for HP designs? Ya, I noticed.

But it is an interesting compare and contrast, is it not?
Richards planning number seems quite a bit heavier/expensive no matter the hull material. Several well respected other sources suggest it is heavier/more expensive than they expect/suggest. By a lot. Perhaps it is required for a 8 Ton 30' cat. I don't know.

Certainly we know of a not 8 ton 30' boat built in 1966 that seems to be fine without following this RW plywood layup plan. A world famous epoxy/composite company has a slightly heavier/tougher, perhaps updated, plan than this boats plan based on over 50 years experience. Seems reasonable to me a slight change makes sense, but perhaps RW knows more than they do. But it does not seem reasonable that RW layup plan is needed, as it seems boats without it from 50 years ago did pretty well.

Also you said...
| This is based on Richard Woods real published figures from the plans, supplied by a builder, and from his bill materials.

| The cost of foam sandwich is high compared to ply/epoxy. Probably at least double when everything is taken into consideration, and there are complications. It appears to me that to build entire hull sides on a table will require that a template be made, which would involve constructing temporary bulkheads, stringers and strongback from "sacrifice material" and laying on some sort of light paneling such as used trailerhouse paneling to get the shape.

The reason I found this confusing is two fold.
1) You flow from comparing RW core materials to a critique of what you imagine flat infusion to be, when RW does not do flat infusion. Or does he?

2) It seemed you implied that ALL foam sandwiches are expensive, when, perhaps, you meant JUST Richards sandwiches. Because Robs, and others, are very competitive with wood, and much lighter (and faster, cleaner, healthfull, easier to build). Even when compared to reasonable ply layups. You don't have to compare them to a RW ply layup to make them look good.

You continue...
| That's a pretty substantial project by itself. Half bulkheads could be used of course, and simply attached to a floor, as all 4 sides will be the same except the cutout for the bridge deck. You need the actual table of sufficient length, and there are the sacrifice materials used for infusion.

This confused me. Why do you assume what it takes to do? Are there not enough Pictures on harryproa.com to show you that this guess is baseless? Certainly Steinar's flat infusion WW hull did not need most of what you suggest. And what it did need is not needed in a plans build. Rob has said enough times that you don't need things like this nor over 1000m of sticks to build his boats. I guess the cost of sticks in a ply build alone covers most of the foam? Finally, you always need space to build a boat. Robs boat need the least space I have ever seen.

There are lots of pictures and descriptions on harryproa.com. You don't have to guess how flat infusion is done. If that is not clear, you can ask. Its not like it is a secret. But all you detail is needed for a ply build. At least, that's what I am told.

A collection of asides;

Rob, you never answered Chris's question. "How much extra would one of the larger Harrys (say the 50) weigh if plywood was used instead of foam and glass? Would that level of extra weight ruin the handling and performance"

Rob has suggested a build of quality ply core Intelligent Infusion is more expensive than foam, here https://au.groups.yahoo.com/neo/groups/harryproa/conversations/messages/12834

I humbly suggest if 700kpa XPS core does well, its cheaper and lighter than anything so far.

Chris, I humbly suggest there is no "uncertainty in [the] direction" of foam core. I have (vigorously) discussed a new core option, but the typical Divinycell cores work excellent.

P.S.
Stonetool, you have been doing your analysis of your desired boat for some time. You have a good idea of your cost and desires. You have talked to RW about modifying his plans to meet you your needs.

Why not ask Rob for a design and total package price to meet your Statement of Requirements?