Fuel Tank for Sailboat

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Hi all,I'm starting a new tank project and while most of my questions are not specifically welding related, this site has a wealth of knowledge on tank fabrication.  So I thought I would try posting my questions here.My project is pretty similar to one posted here last year and I plan to use it as a model for my project:http://weldingweb.com/vbb/showthread.php?t=32091&page=2It'll hold diesel though and be approx 60 gal capacity; 60"x18"x18". It sits in the boat transversely and is curved on the bottom to sit down close to the hull (resting on fiberglass stringers that space it away from the hull by ~1/2").  So it's roughly twice the size of that other tank in every dimension and has four baffles.  My questions are mainly concerning connections:I'm planning to use 1-1/2" 6061 for the filler neck.  Is 1/8" wall tubing suitable?  It will be a short horizontal length for the hose connection and then turn 90 deg down into the tank with a 3/16 doubler for the fill penetration.  A 5/8 OD vent tube welded to the same doubler. I plan for a single 6" inspection port in the middle of the tank and put the fuel supply/return and level sensor in the inspection port.Everything I read says there "should" be an inspection port in every baffled chamber, but since the tank is curved on the bottom, anything I don't want to be in the tank should wind up in the middle compartment.  It wouldn't be a lot of trouble or expense to put a couple of smaller inspection ports in the outboard chambers, but do you think I should even bother?Any debris and/or water should wind up in the middle, so the other compartments should not need cleaning or be prone to corrosion.What do y'all think?Thanks!Walter
Reply:Don't worry about inspection ports.  Diesel problems are usually water related and will settle at the bottom of the tank where they can be simply rinsed out. Avoid 6061, it is prone to pitting in a marine environment.  Use  marine grade alloy like 5083 or 5086.
Reply:Thanks.  I didn't mention it earlier, but the tank skin/baffles will be 5052.  Fittings, bungs and doublers were planned to be 6061; is 1-1/2" tubing commonly available in 5053 or 5086?
Reply:Here's a sketch to get a better idea.  Fill and vent are in one end, and the fuel supply, return and pumpout will be in the middle. Attached Images
Reply:If you are doing stuff like this, and not normally in the boat business, best thing to do is go to the American Boat and Yacht Council (ABYC) website or the US Coast Guard website, find the books and pamplets that specifically spell out the REGULATIONS, not suggestions or recommendations, and follow the rules to the letter.The book pictured, happens to be the one dealing with fuel systems, several years ago I had to build, install, and plumb some tanks, I wanted to do it right.  I live just outside the California Delta, hear of boats catching fire or exploding all the time, it is mostly the fuel systems that are at fault. Attached ImagesLast edited by jsfab; 10-28-2010 at 03:07 PM.
Reply:Does the ABYC compliance guideline get into specific materials grades and wall thickness for filler necks?I was really hoping that someone experienced with building marine fuel tanks would chime in with specific recommendations on my project...I'm the boat owner by the way, I'm cutting the parts and then taking them to my welder for assembly.
Reply:I don't know, I'm not reading it for you, I only read stuff like this when I'm getting paid for it.  Buy your own book, and read it, there's information in there about subjects you haven't even thought of yet, including mounting, plumbing, venting, etc. etc.
Reply:BTW, I bought this one (and a couple others) back in 2002, possibly newer, updated editions available now?
Reply:Gee, everybody chipped in with specific useful recommendations in that post I referenced.  I was really hoping for that kind of input.  I'm not trying to start a fight, but "Go buy a textbook and read it" is not really what I'm looking for.
Reply:In any case, you convinced me to buy the book.  It's $35 BTW, after shipping.Still, if anybody would like to chime in on my plan to use 1/8" wall 1-1/2" OD tubing for a filler neck assy or any other specific recommendations, I'm all ears.
Reply:Fuel tank for sail boat = Cylinder of gas?
Reply:Try to do marine grade all around.  6061 will rot out inside of the hoses.  This is a slow process and will not likely cause problems within the lifetime of the tank, but...
Reply:No problem to do 5052 everywhere, but how about the filler neck tubing?My metals supplier doesn't stock it and the online sources I've found don't either.  6061 tubing is everywhere though.Is tubing commonly available in 5083 or 5086?
Reply:It looks like 5052-O is commonly used in aircraft fuel systems.  Would that be the best choice for the filler assy?  I had assumed that the annealed alloys might be too soft for an application like that?