>>|I will actually make another attempt at contacting him, since we are both in Sweden.
>I look forward to hearing how it goes.
I was able to get hold of him, and he offered to answer some questions!
This is my translation of the relevant parts of our conversation:
From me:
Hi Kjell
I'm very curious about your experiences with XPS as core material. I'm looking at building my own a trimaran, or maybe even a proa! Questions:
You have done a test which compares the H60 with Finnfoam 700 in a vise with good results. Have you made any other comparisons?
Did you have any issues with the adhesion of the epoxy to the core? Or delamination?
The XPS tensile strength is lower than the H60. An australian who built a pedal powered catamaran with XPS tells us that in a pinhole through the skin, where water entered, the skin began to delaminate from the core. And the area just grew, which it usually usually with divinycell according to him. He believes that temperature cycling and possibly ice formation has caused the core to be torn away from the skin, due to its relatively low tensile strength. Finnfoam 700 seems to have 0.3-0.5MPa compared to H60 1.8MPa. How you observed something related to this on your hull now after storing it for many years?
How did you like to work with the XPS when you built the boat? Would you recommend building with XPS?
You planned to build the deck in wood to get a classic wooden boat feeling, and I agree that wood is beautiful. But was it also due to the fact that you were unsure whether the XPS would withstand the loads on the deck?
Nice lines on the hull! what software did you use?
How much did you pay for a square meter of Finnfoam 700 10mm?
Sincerely
Björn
From Kjell:
Hi Björn
The Finnfoam XPS I used has a higher density than what typically found in the hardware store. Finnfoam tried to market 700 for rail insulation. I paid about 10 SEK/m2 when buying a cube meter in 10mm sheets.
The vise test method is an easy way to compare differences in compressive strength of different materials. The principle is similar to Mohs scale.
[Regarding additional tests] I did a test where I laminated the cores I wanted to compare with vacuum infusion of epoxy and fiberglass, with the idea to drop a steel sphere (free falling) one each sample. This had given some strength (Joule) in order to compare the different samples with respect to adhesion and the ability of the sandwich material to withstand shocks, delamination.
Now, I did not get that far, but I made some tests by hitting with a hammer and found that XPS had the ability to recoil - there was no delamination. H60, on the other hand, was very brittle and unable to spring back, causing delamination of the skin.
(Mind that divinycell is available in higher grades than the H60 which I used.)
A sandwich construction is extremely complicated, especially for a boat construction, if we are targeting low weight. The skin must have different thicknesses depending on where on the boat is used. Below the waterline there is a risk of grounding, and a lady with high heels could walk on the deck.
For a sandwich to handle a certain spot load - a certain thickness of the skin is required so that it is not punctured (supporteded by the core). The sandwich has two surface layers, where both needs to be able to handle these spot loads. On a 6m LOA boat, the weight of epoxy and fiberglass of both skins becomes significantly more than if you would build the boat from plywood, and only have a thin skin. (Plywood is tough.) If you study at smaller raceboats, 6-7 m, they are usually made with a solid fiberglass layer, not sandwich. A sandwich adds no value for small boats.
I chose to use XPS to be able to give the boat the shape I wanted. To save weight, my conclusion is, it's easier to join weight watchers and get rid of a few kilograms body weight :)
If I had started today, I would have built it differently. I would have based it on a mould made from cheap XPS from the hardware store. I would have shaped the XPS, applied a release agent (clay), add fiberglass, and remove from mold. Voilà! a single-layer hull that can easily be strengthened up in some places.
The australian you mentioned probably used regular XPS, which is not like Finnfoam 700. My hull is rock solid!
I designed in different CAD SW for Linux, which are free.
-FreeShip (cousin of DelftShip). I prefer Freeship, because it is better to export 2D to DXF, DWG.
-2D CAD DraftSight to create 2D drawing from FreeShip.
Today, there is also ONShape, which seems to be very competent 3D cad.
FreeShip is absolutely amazing for boat construction - amazing software.
All the best
Kjell
>Does H60 not recover from being crushed? Did the F700 reinflate? The F700 has 30% less compressive strength, but looking at that pic, you would think the opposite.
>So I don't understand that pic.
>So I don't understand that pic.
According to the specs,
H60 has 0.9MPa nominal, 0.7MPa minimum.
F700 has >= 700kPa, i.e. 0.7MPa minimum, with no nominal specified. So minimum compressive strength is the same. And it looks like on these sample, the H60 was closer to minimum, while the F700 had more margin. So the F700 was the stronger one in his vise.
Regarding pricing mentioned above:
10 SEK is roughly 1 USD, EUR, GBP, for 1 m2 or roughly 10 sq. feet!
On Mon, May 21, 2018 at 3:48 PM, '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
|In case you haven't seen it, in the following link you can see how the 700kPa (100PSI) XPS compares to other XPS and Divinycell H60 in compression..
|
|http://www.trinardo.com/y.a.t-yetanothertrinadofoamcompare3
Yes, I did see. This pic of the F700 vs H60 troubles me.
http://www.trinardo.com/_/rsrc/1472867876393/071021_Material TestDSCN3008red-medium.jpg
In this pic, H60 and F700 were stacked and compressed excessively.
Does H60 not recover from being crushed? Did the F700 reinflate? The F700 has 30% less compressive strength, but looking at that pic, you would think the opposite.
So I don't understand that pic.
The builder does make the point that XPS has a much finer cell, so the laminate will be lighter. I will add, the excess epoxy to fill a more open cell foam is a very weak and heavy choice. If one wanted a lighter composite, one could skim coat voids with microballons and epoxy, I imagine. But I don't know how to make the skim coat infusion bond have strength!
While there is some concern that the lack of texture will make a weaker foam laminate bond, I do not think that has been shown a reasonable concern. The foam laminate bond is not high stress, and is quite weak, as a peel test shows.
|I will actually make another attempt at contacting him, since we are both in Sweden.
I look forward to hearing how it goes.
__._,_.___
Posted by: =?UTF-8?B?QmrDtnJu?= <bjornmail@gmail.com>
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