XPS core again

There seems to be the assumption that only a thin fiberglass layer would be used on the bottom.......... Part of the design of a boat is to utilize the materials properly for where they are used. The design in question that this is very loosely based on would ordinarily have 1/4" ply on the bottom........ and that's not particularly rugged. I would not use either of these materials without a beaching keel of some sort. The idea that someone mindlessly assembly something without taking such things into consideration is a bit silly. Perhaps rather than visualizing something mindlessly stupid and projecting that on the builder, it might reflect better on those making comments to suggest HOW to make the material work, and perhaps allow that some thought is being given to such issues. There are some useful comments being made, but a number that reflect projection of their own lack of imagination and problem solving ability on others.

 

The problem is that the material cannot work as you wish. A thick fiberglass layer on the bottom and on the sole deck is essentially solid frp with an xps mould.

To suggest good intentioned people discussing the constraints of xps have a psychological problem is really offensive.

 

Holy cow!! You worked with Rutan? I bow, I grovel. I abase myself. Rutan... I have relatively few heros, Rutan is among them. Kurt Tank, Lemmy and the guy who invented Macrostatistical Entropy are some others.

 

There is another one. The late Martin Hollmann. He is one of the pioneers in composite design and was in the same circa when Burt started. He wrote several books on Composite Aircraft design that I am still using to date. His book laid down the foundation for the new method of composite engineering.

 

I must have this book

 

1. Composite Aircraft Design 2. Modern Aircraft Design Vol 1 3. Modern Aircraft design Vol 2. Although he was in the background, he designed most of the Lancair composite aircrafts, the most popular design at the time along with the Rutans EZ canard flier.

 

Well, I've certainly put some 7725 Rutan Special to good use on boats, that's for sure. It's nice to work with.

 

My neighbor has an unfinished Rutan ez flier? in his pole barn. He made one mistake with it and quit.

 

Anybody who has mechanical properties of XPS? The one posted by Stefano lacks some properties that is needed to analyze this core using accepted method used in the Marine industries. I need Tensile strength and compressive modulus.

 

https://www.ridoutlumber.com/wp-content/uploads/2016/12/Dow-Blue-Board.pdf

use square edge

or

https://www.dupont.com/content/dam/...oam-brand-square-edge-pis-43-D100047-enUS.pdf

 

I see Owens Corning Foamular gives this number:

Compressive modulus 6895 kPa

And a corresponding density XPS number I saw for tensile strength was 110 ~ 120 kpa.

 

Seems rather low. 110 kPa = 0.11 N/mm2 (Mpa). It should be in between Styrofoam EPS 0.45 and Diab H80 2.5. Seems like 1,100 to 1,200.

 

That does sound low now that I think about it.

I see BASF styrodur, which is a 2lb/ft3 XPS, gives the number 0.4 MPa.

And I found a number for Foamular FM-250 of 300kpa. That's all a two pound foam.

I found the same foam listed elsewhere as 360kpa, too. Not sure which is correct but that must be the ballpark.

 

Foamular comes in a few different versions.

Here is the data for 150, which is 15 psi compressive strength.

https://dcpd6wotaa0mb.cloudfront.ne...lation-Product-Data-Sheet.pdf?v=1621376715000

The 250 would be better for anything really.

https://dcpd6wotaa0mb.cloudfront.ne...lation-Product-Data-Sheet.pdf?v=1620255197000

 

Lancair air was a customer of mine, Lance Neibuaer was an amazing guy to listen to.

At lunch there was an occasional brain storming session with several of his friends and other designers, I just sat and listened.