[PSUBS-MAILIST] Fw:

Mon Aug 22 14:27:57 EDT 2016

Sean,What are your thoughts on using type IV CNG tanks with 3,600 psi operating pressure as buoyancy tanks.  The tanks would have full pressure in them at all times.  They could also serve as reserve HP air if regulated to stay above ambient.Hank 

    On Monday, August 22, 2016 11:54 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Than you Sean,I have experimented with this idea already with uncoated wood and in 12 hr at full pressure the wood is no longer buoyant.  I do think though, if it was encapsulated reliably it could serve as a cost effective solution.  The trick of coarse will be encapsulating it reliably.  Also the blocks would have to be in safe locations so they don't get damaged.  I am quite comfortable with the compression of wood, fir in particular.  I use fir shims when I lift buildings and I can tell you how heavy a building is by how much the fir compresses.   BUT, you have a valid point.  I will have to test a lot.Hank 

    On Monday, August 22, 2016 11:27 AM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hank, the little f you are referring to I presume is the lb_f notation? This is an artifact of Imperial / US standard units, which in common usage do not differentiate between mass and force.  In SI, the mass unit is the kilogram, and the force unit is the Newton. In Imperial units, the mass unit is actually the slug, but almost nobody uses slugs on a daily basis. Thus, the US standard adopted the pound as a unit of mass, differentiating it from the force unit with the subscripts lb_m and lb_f. That they are equivalent only holds true in standard earth gravity, so in any other gravity field you need to divide the lb_f by 32.2 ft/s^2 to get the mass in slugs, and then multiply by the actual local gravitational acceleration to get the force in lb_f. All in all, it's a mess, which is why I prefer to stick with SI / MKS units for everything.  In any case, 1 lb_m is the mass that weighs 1 lb_f in standard earth gravity.That out of the way, getting to your actual question, be careful using published material property data, because it can be specific to shape or loading direction. Natural wood is an anisotropic material - it exhibits different mechanical properties in the grain direction than it does cross-grain. Dimensional lumber is usually milled longitudinally with the grain, so this may be what is quoted, but it is ambiguous. Also, while softwood lumber may have mechanical properties similar to that  of epoxy foams, the water absorption properties will differ, as I'm sure you're aware from your log salvage experience. Any coating you apply to encapsulate a block of wood will have different mechanical properties than the wood itself, which could lead to a breach of the waterproof integrity, and subsequent water absorption by the wood.  I would be very hesitant to consider this, unless you test a few samples experimentally, and also employ routine condition monitori! ng /density checks of such parts in service.Sean

On August 22, 2016 10:31:10 AM MDT, 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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