[PSUBS-MAILIST] Fw:

Mon Aug 22 13:25:40 EDT 2016

Antoine,That is interesting indeed!  I was thinking I could maybe just coat the wood and I was also thinking to round the edges.  I can buy off cut laminated fir beams and coat them.  The nice thing about laminated beams is, the wood quality and proper dryness is all to a strict standard. Hank 

    On Monday, August 22, 2016 11:07 AM, Antoine Delafargue via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 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/ccIf 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.regardsantoine  

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 advanceHank

     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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