[PSUBS-MAILIST] Fw:

[Antoine Delafargue via Personal_Submersibles]

hello Hank,
nice idea.

Actually for my shell, I have tested red and yellow cedar, very light
weight wood used for wooden kayaks, and on my sub as outer shell,
covered by primer monocomponent polyurethane resin,
then fiberglass/polyester composite, and it holds reasonably well (at least
down to 50m).

For buoyancy gains, I would just coat the piece of wood (with round
edges) with the primer layer of PU resin which is not as strong
as glassfiber/polyester, but flexible to accommodate the potential wood
compression.
BTW once you start using this resin, you can t stop (called G4 or
Gravithane 2 in France). It contains solvents and unreticulated polymer
initially, so when you spread it on porous stuff like wood it penetrates
the material before the solvent dries and the polymer reticulates. So the
bond is very good, it will keep water out, and you can glue wood pieces
together like this. You can even strengthen the wood by penetrating the
first few mm on surface by diluting the resin first with acetone for a
first layer so it penetrates even better. But it does the same on skin so
do wear gloves if you do not want bionic plasticized hands for weeks
afterwards... the other issue is that unlike dual component resins it
expires a few months after opening (and store the bottles upside down and
always clean the tank's cap if you want to open it again).

my shell probably has a density of 0.7g/cc overall due to the glass fiber
and resins, when the wood is probably around 0.4g/cc
If I were to go for pure buoyancy tanks, I d probably end up somewhere
around 0.5g/cc which is comparable to the deep trawl buoys.

To check it holds pressure for my max depth of 120m, I cut a 5 square
centimeter piece and walked on it. did not compress.
regards
antoine





On Mon, Aug 22, 2016 at 6:31 PM, hank pronk via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Hi guys,
> I have forwarded a page with mechanical properties of Douglas Fir wood in
> this email.  There is a rating for compressive strength and it has a little
> f in the description.  Not sure how to interpret that.  Can I get an
> opinion on that.  I need to know the compressive strength in psi.  This
> could be a cheap form of buoyancy.  I would make a glulam  then fibreglass
> the exterior to waterproof the block.  Of coarse as always i would make a
> sample and put it in my large pressure chamber.
> Thank you in advance
> Hank
>
>
> On Monday, August 22, 2016 10:24 AM, xxx xxxxx <mp13 at live.ca> wrote:
>
>
> Douglas-Fir | The Wood Database - Lumber Identification ...
>
> http://www.wood-database.com/lumber-identification/softwoods/douglas-fir/
>
>
>
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>
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