I would strongly disagree with this statement.  Richard's expertise is in strip and ply construction, but in my conversations with him I can detect no prejudice with regard to ply versus sandwich construction.   Economy is a major factor in building your own boat for most people.  Construction cost takes away from your resources for cruising and to a large extent governs the size of boat you can build.  Plywood is cheap and fast, and a well proven material.  The basic hulls and cabin could cost as much as double in foam sandwich.  Any designer builds for his market.  Richard's is a large market as a result of the design choices he has made, the material being one of them.

    Do keep in mind that while 900/900 glass over 1/2" foam may seem like a lot of glass, it is replacing not just plywood / glass, but plywood, glass and stringers.  These numbers are for a 33 foot cat (Eclipse).   They represent conservatism of the sort I respect.   

                                                                                                                                                    H.W.


On 08/31/2018 06:47 PM, 63urban 63urban@gmail.com [harryproa] wrote:

 

Richard favors ply so any numbers he uses for foam core should be taken with a grain of salt

Sent from my Bell Samsung device over Canada's largest network.

-------- Original message --------

From: "StoneTool owly@ttc-cmc.net [harryproa]" <harryproa@yahoogroups.com.au>

Date: 2018-08-31 10:26 AM (GMT-05:00)

To: harryproa@yahoogroups.com.au

Subject: [harryproa] marine ply

 

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

A:   Woods calls for 600/300 glass over Okume.    Assuming the same weight of resin, that's 1800
B:    I used 5 pound foam core, which I believe is H80
C:    Woods calls for 900 GSM each side, and I assumed another 900 GSM resin for a total of 2700 GSM and added the GSM of the foam itself for a TOTAL panel weight... For some             reason I  get a higher number this morning (3717GSM)
D:     I didn't use Rob's number because I was using Richard's number........ Richard is the designer of the boat in question.... I will go by his figures by default.

      I couldn't find the original text in an editable form easily, but I had saved a screen shot along with a note in red by way of explanation in a folder.   I've included it below.  Hopefully it will come through.


                                                                                            H.W. 






On 08/27/2018 12:24 PM, eruttan@yahoo.com [harryproa] wrote:

 

Stonetool; I looked at your calculations. I have questions...

Total GlassEpoxy Glass CoreEpoxy Core
5450 720 4730 9mm [1]
5630 300 600 4730 9mm [2]
6730 800 800 200? 4730 9mm [3]
2360 400 800 200 960 12mm

[1] 9mm Okoume 120gsm epoxy x 3 coats x 2 sides per Gougeons
[2] 9mm Okoume with outside glass, per RD
[3] 9mm Okoume Stonetool style
12mm H80 400gsm x 2 sides, per RD

Question A) Regarding your 9mm Okoume layup, how did you get to "Glass and resin total 1800 GSM"?

Question B) Regarding your 12mm Divinicell layup, did you assume H100 for core?

Question C) Regarding your 12mm Divinicell layup, how did you get to "Glass and resin totaling 3600 GSM"

Question D) Why did you not use Robs 1400GSM for your 12mm Divinicell layup?