[PSUBS-MAILIST] Fiberglass

Mon May 4 16:33:32 EDT 2015

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, thencopy around it on to the corresponding sheet of the mirror imageballast tank, to get two tanks that are identical.When I did mine I marked the hull with a felt pen as to where theballast tank was going to fit against it. I covered this area with plasticfood 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 problemon vertical walls & there may be a similar appoach that works better.You need to embed this shape in to the polystyrene section by wire brushingout 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 overthe 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 designedto be laminated in one shot. It is air inhibited & remains tacky on the outersurface unless it has a wax additive.I once made a 1/4 size ambulance out of polystyrene using mainly achain 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 saw2) 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+Blade3) 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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