[PSUBS-MAILIST] Fiberglass

Mon May 4 17:11:07 EDT 2015

Hi Alan,

Interesting comment about the polyester being designed for one shot. The
polyester resin I used is from 3M and the instructions say that it you
restart the job on a cured layer you should sand it lightly first - so
that's what I did, since it took about a month to get the desired number of
layers on. It didn't seem to have any bonding issues with layers applied on
cured material. This particular 3M polyester cures fully in 2 hours, and
didn't feel tacky after that, so perhaps this is brand specific.

Good point about the sections helping make the mirror versions of the MBTs.
I made templates out of thin particle board to cut out the foam sections,
and by flipping the templates was able to make mirror image tanks.

Best,

Alec

On Mon, May 4, 2015 at 4:33 PM, Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Hi Scott,
> some great ideas from Alec there.
> I like his idea of using sandwiches of thinner sheets of polystyrene.
> You should be able to trace a shape on one sheet, cut it out, then
> copy around it on to the corresponding sheet of the mirror image
> ballast tank, to get two tanks that are identical.
> When I did mine I marked the hull with a felt pen as to where the
> ballast tank was going to fit against it. I covered this area with plastic
> food wrap. I then draped glass mat over it & epoxied about 3 layers over
> this.
> Polyester resin will disolve the plastic food wrap. This approach may be a
> problem
> on vertical walls & there may be a similar appoach that works better.
> You need to embed this shape in to the polystyrene section by wire brushing
> out the polystyrene untill it's a good fit. Because of shrinkage of the
> fiberglass
> & warping it won't nessecarily be a perfect match & may require additional
> work.
> Once you have the polystyrene shape done you cover it with fiberglass & go
> over
> the area you formed against the hull.
> I used epoxy because it can go straight on to the polystyrene (test it
> first) &
> you can spend a month slowly building it up, whereas polyester resin is
> designed
> to be laminated in one shot. It is air inhibited & remains tacky on the
> outer
> surface unless it has a wax additive.
> I once made a 1/4 size ambulance out of polystyrene using mainly a
> chain saw. Great fun but one hell of a mess.
> Alan
>
>   ------------------------------
>  *From:* Alec Smyth via Personal_Submersibles <
> personal_submersibles at psubs.org>
> *To:* Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> *Sent:* Tuesday, May 5, 2015 3:33 AM
> *Subject:* Re: [PSUBS-MAILIST] Fiberglass
>
> Hi Scott,
>
> Coincidentally your timing is really good, because I just finished four
> rather complex-shaped MBTs for the new sub. Since my sub is a one-off
> rather than a series production item, I used the method of glassing foam
> plugs that are then dissolved, rather than making molds. To summarize:
>
> - The plugs are a sandwich of many layers of pink home insulation foam
> from HomeDepot. When I did Snoopy's saddle tanks I cut out the sections
> with a hot wire, but this time I realized my jig saw does the job in about
> a tenth the time. Step one is to cut a whole bunch of sections and glue
> them together. If I weren't so tight-fisted, the ideal solution here would
> be to mill a single block of foam using CNC equipment, but I get by with
> what I have on hand if it'll save money - and a milling job would probably
> take quite a lot of it.
>
> - The glued sections are only a rough draft of the final form. Next you
> have to shape them until the steps between sections are gone and everything
> is nice and smooth. I use three tools to go from the draft to the final
> product, in this order:
> 1) A plain old wood saw
> 2) A Stanley Surform shaver, with flat and or rounded blade fitted
> depending on the surface. This thing is absolutely essential and I use it
> for 99% of the job. See
> http://www.stanleytools.com/default.asp?CATEGORY=SURFORM+TOOLS+AND+BLADES&TYPE=PRODUCT&PARTNUMBER=21-296&SDesc=Surform%26%23174%3B+Plane+Type+%96+Regular+Cut+Blade
> 3) Sand paper
>
> I'm afraid I have no scientific answer to ensuring symmetry. I just put
> the plugs side by side and do a bunch walking in circles, taking
> measurements, and using a level. The plugs won't come out identical, but
> close enough to be functional. This part is more sculpture than science.
>
> - Next, paint the plugs with several coats of water-based paint. This is
> to prevent the resin from dissolving them. Water-based because if not you
> run the risk of the paint dissolving the foam.
>
> - Now apply layer after layer of wetted fiberglass cloth. I don't mean all
> in one sitting, I mean iteratively for about a month. There are two main
> considerations then, cloth and resin.
>
> I can't give you a specific recipe for cloth or the cost for cloth,
> because I used a combination of material I already had on hand and new
> stuff. I have purchased from http://www.fibreglast.com in the past, but
> this time found lower prices on eBay for what turned out to be perfectly
> good material. Mostly I used 6.5 oz (quite light) cloth so that it would
> drape better, but that depends on the shape of your tanks. For instance, on
> the inside face that goes against the hull, you can get away with much
> heavier material since its a gentle curve in just one plane, and the same
> goes for any flat surfaces. But if you have compound curves or tight curves
> its way more challenging to drape cloth without forming air bubbles. I make
> the walls that go against the hull thinner, since they aren't going to be
> banging against things like the outer or upper faces will. On average I
> probably put down ten to fifteen layers of cloth. The pros use vacuum
> bagging to prevent bubbles. With my caveman fiberglass skills I just try to
> avoid them in the first place by selecting better-draping cloth, and when I
> get a bubble I remove it with a flap wheel before putting down the next
> layer. In the middle of my layup I put down several layers of Kevlar. This
> material is trickier to work with than fiberglass, it can't be sanded and
> once cured you can only really go through it with carbide tools. The idea
> is to increase survivability by making the MBTs puncture resistant. If I
> hit a rock or a dock I still expect the resin might crack, but it should be
> quite hard to put a hole in the Kevlar. You might think this hard layer
> should go on the outside, but I put it mid-schedule so I could sand
> imperfections out of the fiberglass layers above it.
>
> This job (new sub, not Snoopy's tanks) took ten gallons of resin. Everyone
> will tell you epoxy is stronger than polyester resin. However, epoxy is $76
> per gallon vs. $34 for polyester, and Snoopy's polyester tanks have held up
> perfectly well for years. So, for me, this is a case of
> cheaper-is-sufficient and I went with polyester.
>
> - Iteratively sand and fix imperfections with a fairing compound. I used
> West Marine's #410 fairing filler (
> http://www.westmarine.com/buy/west-system---410-microlight-filler--P004_120_004_016).
> You can do this with Bondo as well, but #410 is easier to sand.
>
> - Dissolve the plugs. When I made Snoopy's saddle tanks the pink foam
> dissolved instantly with gasoline. This time, despite being the same brand
> foam it was somehow gasoline resistant, but acetone did the job.
>
>
> Best,
>
> Alec
>
> On Mon, May 4, 2015 at 9:22 AM, via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>
>
> Alec,
>
> I was curious if you could go into details about the making of your saddle
> tanks?
>
> *Where did you get the foam and fiberglass and what types did you use
> *How did you shape the foam to ensure symmetry
> *Was there any difficulty or anything you would do differently
>
>
> Thanks,
> Scott Waters
>
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