Acrylic vs Polycarbonate

[Bob S]

I will be cutting an access hole into my diesel tank for cleaning. I want to fabricate a cover that I will be able to see inside the tank with. I plan on doing something similar to the SeaBilt cover using (8) 5/16-18 bolts. I also have access to some 1/16 neoprene rubber to make the gaskets from. I want to cut the top cover from either clear Acrylic or Polycarbonate. A question for all you engineers out there. Is there a difference and will one stand up better than the other when exposed to diesel?

 

[BobM]

http://www.coleparmer.com/techinfo/chemcompresults.asp

They didn't have acrylic, but polycarbonate rated excellent. This site works for many chemicals and plastics and is a great resource. I put the initial link below.

http://www.coleparmer.com/techinfo/chemcomp.asp

 

[Maine Sail]

Bob,

Personally, for that application, I would use aluminum. If you have an engine fire, and that polycarb melts, your insurance company won't be very happy with you. You also likely won't see much looking into a dark tank filled with red fuel. If you are going to do it anyway, which I suspect you will, polycarb is the correct tool for the job is it is less prone to splitting where the bolts go through it.

ABYC 2.5 Minute:

"All individual components of the fuel system, as installed in the boat, shall be capable of withstanding a 2-1/2 minute exposure to free burning fuel (N-Heptane), or No. 2 diesel fuel without leakage, when tested in accordance with Title 33 CFR, Section 183.590, Fire Test."


P.S. The vast majority of boats DO NOT comply with this standard.

 

[Bob S]

Thanks BobM, great site.

Maine, Thanks for the heads up. I thought I might be able to see inside using a flash light. I have a 1/4" thick piece big enough to do it but now I am reconsidering it. I also have some 3/16 6061-T6 aluminum. Unfortunately my biggest hole saw is Ø4-3/4. I priced a 6" @ $36.00 ouch!

 

[Allan12210]

Do you think you could find a round piece of tempered glass? You could hold it in place with an aluminum ring and gaskets. If you are only using it as a sight glass and not for access, there might be some tempered glass gauge faces out there up to 2-3 inches. You can drill a ring out of your aluminum with a couple of hole saws.

 

[Richard Bryer]

Bob- I used polycarbonate (1/8 inch) and it has been fine for 4 years now. The tank is poly so the fire hazard is no greater.

 

[MoonSailer]

http://www.coleparmer.com/techinfo/chemcompresults.asp

 

[dscribner]

Polycarbonate (AKA Lexan) would be your better choice. Acrylic will find a crack or grove along the edge and chase it across the face over time. Polycarbonate can actually be brake formed like metal withought fracturing. If you drill it, hit the holes with a torch to smooth the edges. Check the gasket material for compatability with the poly. Incompatable sealants or gaskets WILL cause plastic to craze and compromise its strength. NEVER clean it with amonia (Windex). Just use dish water. Amonia will cause it to craze also.

I'm a designer for a skylight company in Maine. One of our product lines uses millions of square feet of sheet plastic per year. Go to Walmart, Hannaford, Stop & Shop, Lowe's, Home Depot or any other number of stores and look up. If they're not ours they're just like 'em.

If you decided to go aluminum, you can cut that on a band saw easily, or use a jig saw. If you countersink the underside just t touch, you can use the depression as a pivot point and get a real nice circle. Just keep the guides close to the surface.

I bought my boat in Mattapoisette.

 

[Bob S]

Decided to go with an aluminum cover as Mainesail suggested. Cut the access hole and fabricated the cover. I am waiting on Buna N gasket material from McMaster Carr. The tank was cleaner than I expected considering she sat for so many years. The tank was probably empty as RichH recommends.

 

[Hermit Scott]

Bob-you could always have a polycarbonate window with a aluminum hatch over it.