| 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.

    The original question regarded ply construction alternative for an HP hull, something Rob had not offered.  I presented the information I had with regard to my own project (intended), without making judgments or any intention of actually equating those specifications directly, just to show what Woods had done.   I do agree that it seems excessive, and would suggest that Richard is not by any means "expert" with foam core composite design.  We have a number of suggested substitutions for foam core to plywood, all of which differ, Rob's being by far the lightest, though he offers it to substitute for the plywood only, not taking into account the stringers.  Richard's figures replace both ply and stringers with 12mm foam and 900/900 glass.   This is obviously not a template for reversing Rob's HP to plywood..... the result would be rather absurd I think.   It is simply information to file away, and add to one's "body of knowledge".  

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.

I am only on this forum to learn what I can to help me construct my boat of choice "efficiently".    It should be obvious that if one were to peel the hide off the boat in question and lay it on the floor, while it would lay flat, it would be anything but square.  Both the top and bottom edges would be curved, and not in a way that I am capable of calculating based on the plans, and the bow and transom ends would be angles that could not easily be laid out in the flat.  I do not yet have the plans.... Things are still evolving.   A plywood skinned boat is normally built by fitting each skin panel in place over formers with stringers.   There will be no scalable drawings or table of offsets to precut these pieces.     What this means is that while making a flat infusion of the hull sides is possible, I am left with the need to create a template that will lay flat so that I can infuse to the final shape (more or less).   The other alternative, which you no doubt would agree is absurd, is to make a 30' panel and attempt to trim to fit.   The lower hull beneath the knuckle

will be done in cedar strip over temporary bulkheads.   The stripped lower hull is typically glassed outside, and removed from the form, and glassed inside.   Everything above that will be sandwich, as per the option of building them with plywood.  My inclination is to use low cost "sacrifice material" for bulkheads, and stringers as needed using the provided offsets for the foam version which has 1/2" foam rather than 1/4" ply.   The actual bulkheads would be sandwich, and would be inserted later..... perhaps not even in the exact original locations and shape in some cases.
     Ideally, I would like to generate the data to allow others to do the same thing....  A reference line and table of offsets could allow someone else to duplicate the shape on a melamine table.   The design of the Eclipse hull does not have the simplicity of the HP hulls that lend themselves to "intelligent infusion", nor do I have any intention of redesigning the boat itself.   

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?

Rob is not in the business of designing cats, and an HP does not scale to my requirements realistically.   Richard has offered me a solution that works for me in the form of Sagitta built on Eclipse hulls.... longer than I really want, but it will allow me to easily have the mast where I want it, and leave me with a huge cockpit.  The fatter hulls offer greater displacement, and if I build the upper works using infusion, I gain more.

                                                                                   H.W.

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Posted by: StoneTool <owly@ttc-cmc.net>

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