RE: [PSUBS-MAILIST] Syntactic Foam Attached to a Metal Hull

["James Frankland" <james@guernseysubmarine.com>]

hi all.

i keep sending a message to the group but it never arrives, even though im receieving all the messages ok.  Can someone please reply to me so i can test my mail is working!  Thanks!

Is there an limit for attachments on the mail list?  I'm trying to send one to you all thats a whopping.....94k, so surely this should be ok?

James F.


----- Original Message -----
From: Brent Hartwig [mailto:brenthartwig@hotmail.com]
To: personal_submersibles@psubs.org
Sent: Mon, 6 Aug 2007 20:31:34 -0700
Subject: RE: [PSUBS-MAILIST] Syntactic Foam Attached to a Metal Hull

Jay,

In the case of the K-250 restoration, the foam would not be there to increase the general operating depth of the hull, although it would likely do allot towards doing just that if one wanted to do the figuring and testing. I've read materials on how much stronger a steel pipe was in regards to being more resistant to external pressure, when covered in syntactic foam of a specific type and thickness. Syntactic foam gives me insulation and noise reduction, as well as allot of collision protection.

Condensation comes from the water in the air reacting to a very cold surface. So if the metal is sealed in by epoxy primer and/or a Rhino type coating, which in turn is sealed in syntactic foam, the air has no access to the steel.  Look at the steel sections as being potted with epoxy, since the syntactic foam, I'm considering is cast with an epoxy.  Also since the foam insulates the the interior of the sub from the usually very cold exterior water, you shouldn't have much trouble with condensation in your sub compared to normal. Also syntactic foam will not have the mold problems that other types of insulations have.

I like to design my subs to have more none compressible buoyancy then generally needed, so I can add allot more weight to the multiple drop weights. I don't want to put the weight all in one drop weight, so I can have a more controlled assent, as well as if one drop weight doesn't work for what ever reason, the sub will have back-up drop weights. Having more weight down low gives me more stability above and below the surface.  If I design the sub the way I'm thinking, then if say the person(s) inside the sub were in SCUBA gear and/or breathing from a regulator when the sub was full or partly full of water, and all the ballast tanks were full of water, they could release one or more drop weights and still take the sub to the surface without getting out.

Your very right in that syntactic foam can be a pain when one wants to reconfigure a sub. With the R300 he designed it carefully enough that we hope he doesn't need to do any major changes later. Some times to get the performance one wants, you need to use materials that can be hard to work with. If I think I want the foam to come of in easy to remove sections in the K-250 then I can just cast them in sections with PVA mold release behind them and then bolt them onto tabs that are added to the ribbing.

The syntactic foam on the Bionic Dolphin was brought up, since it's depth rating is plenty for most PSUBs, and it is cast with a flexible eurothane that would flex with a steel hull better then a resin cast foam would.

I value your input allot Jay, since it makes me think.  Please don't stop, we need you. ; )'

 Thanks again.

Kindest Regards,

Brent Hartwig


From: bottomgun@mindspring.comTo: personal_submersibles@psubs.orgSubject: RE: [PSUBS-MAILIST] Syntactic Foam Attached to a Metal HullDate: Mon, 6 Aug 2007 19:36:06 -0400






Brent,
You shouldn?t consider syntactic foam as a structural material in combination with a steel hull.  This would be considered a composite composition and to work properly, the Young?s modulus of the two materials should be close.  If you were to pursue this idea, your sub?s hull would be very difficult to work on in the future since the syntactic foam against the hull would have to be removed for maintenance or welding.  A well developed hull that is not going to extreme depths in the ocean should not need syntactic foam for buoyancy (we are usually worried about how much lead we have to add) as the hull is not real thick.  The R300 is a unique case as the design strived for the minimum volume to theoretically obtain the optimum hydrodynamics for speed.

You have to be careful installing foam inside against a hull.  Condensation will collect behind it and result in corrosion that is not obvious.  Besides, syntactic foam inside the hull gains you nothing.

You keep returning to the Bionic dolphin but it is designed and built to a different set of operating parameters than would be optimum for a PSUB.
R/Jay


Respectfully,
Jay K. Jeffries
Andros Is., Bahamas

A skimmer afloat is but a submarine, so poorly built it will not plunge.


From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent HartwigSent: Saturday, August 04, 2007 12:10 AMTo: personal_submersibles@psubs.orgSubject: [PSUBS-MAILIST] Syntactic Foam Attached to a Metal Hull


Jay,


You make a very good point, about using syntactic foam as much as possible in a way you can work on, or reconfigure the sub in the future. I've had that in mind for some time now.  Some designs can be done in such a way the the syntactic foam is apart of the strength of a pressure hull, like the beautiful R300. In that case I would make sure the metal is carefully treated before it is encased in foam and forget about trying to do a major reconfiguration later.
With regards to my design of filling the spaces between the ribbing of a K-250 internally, to insulate, sound deadening, and some extra strength that could be needed in a emergency like a collision with something or forced deeper then 250'. I could attach the foam solid to the hull for maximum strength, or wax and then spray a mold releasing agent on the steel hull surfaces, and then cast the foam. This way the foam can be removed much more easily.
I still don't know how much difference there is in the expansion and contraction of the foam to a metal hull, wether the foam completely covers the inside, the outside, or both, as well as if it's just on part of the hull, like on the Idabel? Will the foam want to pop loose, or will they move together? I'm aware that it would also depend on the hull size and thickness, as well at the foam type and thickness. Doc is using a urethane binder in the new two seater Bionic dolphin. The urethane will flex allot more then a most resins used to cast syntactic composites and so it will not have as high of depth rating as most other types.
Regards,
Brent




From: "Jay K. Jeffries" <bottomgun@mindspring.com>Reply-To: personal_submersibles@psubs.orgTo: <personal_submersibles@psubs.org>Subject: RE: [PSUBS-MAILIST] MIG Welding a SubDate: Tue, 31 Jul 2007 20:31:05 -0400
Sorry for the late reply.  You need to be careful with syntactic foam.  The old Asherah (STAR I) had its main battery foamed in with syntactic foam which resulted in a major stumbling block for refurbishment as it was very difficult to remove.  This submersible and a custom built saucer submersible were stored in a warehouse next to where we docked in Boston.  Took forever to rebuild Asherah due to the syntactic foam and the saucer had major stability and power issues.
R/Jay


Respectfully,
Jay K. Jeffries
Andros Is., Bahamas

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