Extruded Polystyrene (XPS)

[gabdab]

Hi,
looking at this site I read the builder is using a non conventional type of foam which
he patiently tested :
http://www.trinardo.com/y.a.t-yetano...dofoamcompare3

As he mentions it being fine for small vessels I wonder if doubling the size of his design (42') is still possible.
Being the price so convenient compared to alternative foams it would really solve some budget problems.

[rwatson]

He doesnt test for water absorbtion that I can see. This wouldnt matter for a trailer based boat so much, but for 42 feet, it would be a major issue.

[gabdab]

I guess you need extensive tests to be safe.

[rwatson]

are you doing ply or strip plank?

I found a tech sheet that said there is zero water absorption at
http://www.finnfoam.fi/client/frontpage//english.pdf

you could get a small piece and sink it in 20ft fo water for a week. That would give you some usefull info

[seagull369]

I wrote the coast guard on the use of prefabbed extruded polystrene sheets (the kind you'd find in Home Depot) for floatation purposes about a year ago. The answer I received was that it's perfectly fine to use for that purpose as long as it does not come in contact with gasoline. This, therefore, would exclude its use within a floor that contains a gas tank.

I'm not sure what you want to use the stuff for, but if you'd like more info., go to Dow's website below and enter the search "buoyancy"

http://dow-styrofoam.custhelp.com/

[zigzag]

Re the high compression foam, I have also investigated possibilities to replace divinicell, Seems the shear strength is much lower in a bending situation, the compressive is however much higher. This however could easily be overcome by inserting some timber stringers or if it is a large deck scenario use notched matrix timber with the foam in the voids. anyone have the time to make some tests?

[KnottyBuoyz]

Originally Posted by zigzag

Re the high compression foam, I have also investigated possibilities to replace divinicell, Seems the shear strength is much lower in a bending situation, the compressive is however much higher. This however could easily be overcome by inserting some timber stringers or if it is a large deck scenario use notched matrix timber with the foam in the voids. anyone have the time to make some tests?

I've got the time if I could get my hands on some samples. Anybody speak Finnish?

I'm a little concerned about resins bonding well with this type of foam.

[zigzag]

I did do some quick tests with thin plywood (1/8 ) poplar on either side of the foam. I used gorilla or Purbond single pack PU. the bond to the foam does not need to exceed the shear strength I would opt for some sika flexible PU on the foam and epoxy on the embedded batten. Mike Leneman used standard extruded polystyrene foam on the L7 deck. Might pay to get some feedback.

[gabdab]

are you doing ply or strip plank?

Not sure yet..

http://www.surfersteve.com/polystyrene.htm

In this page there is a link to xps usage in surfboards making .. preatty price for :
$46 for a 8'x4'x3" sheet

One more alternative is to use 2lb./cubic foot (25psi - pounds per square inch) extruded polystyrene foam (XPS) - Dow Square Edge, or "blue board". Please try to keep and open mind, and disregard much of the information you might have read online etc., about this foam. The delamination problems which have caused some builders to stop using this foam can be solved by following the directions below. A very good board can be made with this foam if you will simply build the board a little differently. This foam does not have the water absorption problem that expanded polystyrene has. Extruded polystyrene is stronger (pound for pound) than polyurethane, or expanded polystyrene (most surfboard polyurethane is about 3lb/cu.ft.). If you build with this foam using conventional methods, you are much more likely to have delamination problems.
Please allow me to insist you do the following:

1. Use an epoxy glue joint/s (in place of a stringer/s) - one is o.k., two is better.
2. Finish the blank by sanding lightly with #20, leaving hundreds scratches and small pits.
3. Add about 5% more resin to the laminate after dragging the excess resin out of the cloth.

The extra resin will fill in all the pits and scratches left on the rough blank. I realize it is hard to scratch and tear the foam of a blank you worked so hard to perfect, but do not skip this step. The pits and scratches greatly increase the bond, and with the glue joint/s, will minimize the delamination problem to a level equal to other foams. As with all boards, but especially XPS, avoid exposing an XPS board to a car interior on a hot day with the windows rolled up. This foam is available in sheets 8' x 4' x 3" and 8' x 2' x 4" thickness maximum, so you may have to glue (epoxy) two sheets together. It is possible to make two good boards out of one 8' x 4' x 3" sheet, if you bend the foam as in the paragraph below. XPS was available in 2006 for $46 for a 8'x4'x3" sheet.

[gabdab]

another usage (hovercraft):
http://www.hovercraft.com/content/in...roducts_id=165

[naturewaterboy]

Originally Posted by gabdab

As he mentions it being fine for small vessels I wonder if doubling the size of his design (42') is still possible.
Being the price so convenient compared to alternative foams it would really solve some budget problems.

You can't take a design and just scale it up, or you may find you and your crew swimming back to shore . There's a little (no, there's a LOT) more to designing a boat than that.

[gabdab]

Yes, I am little concerned about resizing a design.
I saw a post somewhere on this forum about it .






Wikipedia mentions the coast guard having built a 6 person raft in xps in the '40s .
That must be preatty big as size.

[gabdab]

Reply from Finnfoam.
Should I use the skin on non skin type :

Hello,

We have F700 / 50 mm on the storage. We could cut also thiner boards from that 50 mm, but then there will be lost little material.

F700/50 mm with skin (thickness tolerance -2...+2 mm) is 9,5 €/m2 -> 190 €/m3 (vat 0%) + freight costs.

F700/10 mm without skin (thickness tolerance -0,5...+0,5 mm) is 2,38 €/m2 -> 238 €/m3 (vat 0%) + freight costs.

You have to use epoxy resin, because polyester resin will corrode polystyrene foam. Here you could see also one project - sun electricity boat http://shalom.ponkala.net/ .

[pcfithian]

I recently built the cuddy roof for my Tolman out of 1" XPS foam with a 1/8" exterior luan skin on either side, making a foam sandwich. The attached pictures show the foam layer and also the upper skin. It also shows the support bows made from 2 layers of 1/2" plywood at the front, middle, and back.

I used 3M's Fastbond 30 water based contact cement. I found this method to be fast, low cost, and strong. The roof is incredibly stiff. The advantage of using contact cement is that no vacuum bagging or clamping is required, only a laminate roller to ensure adequate contact between the foam and the skin as shown.

The sides showing the exposed foam edges will be scraped back 1/2" or so and filled with a wood flour/epoxy filler, then faired and glassed over, reducing shear load on the foam.

[rwatson]

What does
"Special Note When bonding wood veneers, success is dependent on many variables such as
environmental conditions, bonding process, type of base material, type of veneer,
adhesive type and top coat finishing systems to name a few. For un-backed wood
veneers, water based contact adhesives are not recommended. It is the user’s
responsibility to thoroughly test any adhesive for its suitability in bonding wood
veneers. It is also recommended to follow the veneer manufacturers
recommendation and industry guidelines."

What does "unbacked" mean ?