tank wall thickness

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I've got a big old WWII tug boat-style boat that I am restoring, called a Sea Mule.  Didn't have any fuel tanks in it when I got it, unfortunately.  From the literature, I know they were 250 gallon tanks each (there's two of them, one in each front hull compartment.  This boat runs on gasoline, also unfortunately, powering 2 chrystler straight 8's.I'm trying to decide whether to buy or build replacement tanks.  I'd like  them to be about 6' wide and say, 2' square, or there abouts.  This way they'd be down low in the hull to keep my center of gravity low, and also would maximize useable space in those front compartments (which are about 7' wide by 7' high by 12' long.)  There is a pedastal already in place for the tanks, so no need to discuss total tank weight or how the tanks attach to the hull.  See pic of boat and of front compartment (looking to the bow in the compartment).My questions for you guys are:If I were to fabricate the tanks, what gauge/or thickness metal would you use?  I'm thinking I want to use steel as to minimize any dissimilar metal electrolysis action and also to keep costs as low as possible since the budget's pretty darn tight.I'm a pretty good stick welder.  Would that be an acceptable way to make sure all seams are tight?  Don't have TIG/MIG experience, but could gas weld it, too, if that would produce a less likely to leak product.If I were to hire someone local to build these, what kind of bucks would be reasonable?  There isn't many businesses to choose from out whre I live so it'd be hard to get competitive bids.Since money is so tight, what would be some creative salvage tank possibilities?  Round tanks would be my last choice due to the way they take up so much space, but the old style home-heating oil tanks would be a possibility (you know, those old retagularish tanks with the mounting feet on the bottom).  What do you think about those?  Or other ideas? Problem is with using these kinds of tanks is there isn't a baffle in them.I'm really open to any suggestions and different ideas about how to go about this.thanks for any help.  I'm brand new to this forum but am very impressed with the extent of knowledge and the helpful spirit I see here.~martin Attached Images
Reply:First hurdle you need to consider is the issue of using 'approved' tanks, via USCG, etc. certification.Presumably some agency will be inspecting this craft.       If safety and serviceable life are concerns; that precludes using tanks designed for non-marine use.Suitable tank wall thickness is determined after the basics of the tank design have been created,not before.The method of mounting and securing the tanks to the hull is part of the tank design. This 250 gallon fuel load weighs 1500#, by itself.Any design details you could get from original craft tank, mounting and plumbing would really help you. What you're asking about, isn't exactly a quick and dirty, weekend project.Then there's all those quirky little details about: filling, venting, vapor/head/expansion space allowance inside the tank, low point drains, fuel pickup points, overfill prevention fill neck extensions, sending units and mounting, tank electrical ground-bonding, tank corrosion protection, placing flanged bafffles opposite the outer tank mounting points for strength, etc.Blackbird
Reply:Thanks for the good info, Dave.  Lots of food for thought there. Fortunately, inspection won't be an issue and, since money IS an issue, I gotta do this on the cheap for right now.So, I'm still looking for creative ideas about how to approach this.  200 gallon or so tanks for my boat.  Any other thoughts from you all?~martin
Reply:I can think of several posibilities.Home heating oil tanks come to mind. You can get the 275 gal ones both in the upright modles and in the "sideways" models that are short and wide, (like the std ones tipped over). If new open up the top and add your baffles. If they are used you would have to clean them well to get good welds as well as being safe. I got my 275 for diesel from a heating/AC repair guy. They took out the tank and it was almost new (3 years old) when they replaced the furnace and switched to gas. I paid like $25 for it. Might check with local installers and have them keep you in mind.You can some times find surplus fuel bladders. All the ones that I have quick links for are for large bladders right now. Here's a company that make them I believe.http://www.interstateproducts.com/pillow_tanks.htmYou can also get the 100-200 gal transfer tanks tanks that go in pickups. You would have to figure out how the fills/ pickups gauges etc would have to work on all these.
Reply:martinf,Sounds like this project needs a lot more thought.  Several questions come to my mind, and I do a lot of work in the marine industry.Why do you feel you need that much fuel capacity in a boat that size?  Looking at the photos, the boat isn't "that large".  My only experience with the straight 8's was in a 45' Chesapeake Bay deadrise, built in 1938 and commandeered by the Navy as an offshore crash boat (patroled off N. Carolina picking up downed pilots (training)).  The Navy had installed 2-1000gal fuel tanks, but that was because the boat had to stay on station for a week/10 days at a time.  My experience with those straight 8's is that the pair @1750 RPM will only burn about 20-22 gph.  Any higher RPM and the cooling system will not handle it.Welding up "GAS" fuel tanks is not a backyard, hobby project.  The questions asked regarding material, thickness, etc. would lead me to question whether this is something you should be taking on.  If properly designed, fabricated, and tested fuel tanks are not in the budget, maybe the project shouldn't proceed.  The discussion of using 275gal used fuel tanks is not even worthy of comment.  BAD IDEA.  500 gallons of gasoline is not something to be messed with.Another factor to consider is that fuel tanks too large for the intended purpose will mean that there is a lot of fuel just "sitting around".  Todays fuel (with all the addititives) does not store well.  In fact, marina's in this area are seeing the fuel go bad in less than 90 days.  The alcohol additives in the fuel cause it to absorb water from the air.If the tanks in question (non-approved/non-inspected) caused a fire/explosion in your local marina, you can be assured the marina owner and other boatowners will be coming to you for restitiution.This whole discussion sounds like an accident looking for a place to happen.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Amen to what SundownIII sez.To expand further on DSW's comments (and probably some more to follow):1-surplus fuel bladders---These need a properly sized/designed metal containment, plus custom made fill/vent/drain fittings bonded in. More cost effective to have custom bladders and containers made--andthat runs as much or more than a custom, USCG certified, marine tank.2-Home heating oil tanks come to mind.      100-200 gal transfer tanks tanks that go in pickupsThe heating oil tanks have no baffling and thin wall construction.The bogus, 16 ga. truck transfer tanks have minimum baffling.Neither of these 2 options have a chance of surviving the stress ofmarine application--from fuel slamming around, hull flexing, etc. (The Northern, etc.; branded tanks can and do crack thru the baffling--just in the use they're intended for.)Large blow-molded or rotational molded, engineered plastic tanks-don't have internalbaffling, or reinforced mounting to withstand the hammering of fuel inside the tank.****Additionally, the placement of these tanks in the hull, relative to fore/aft CG is a factor you needto determine--or you will wish you had, after the fact. Following the original design on the above,would help--presuming that your restoration is re-creating the original.'Your's Truly', has designed, built and tested- marine, on-road/off road, CARB, USCG, Corps of Engineers, DOT--tanks and structures in aluminum, stainless, steel, and aluminum-coated steel.I don't build 'cheap' tanks.I've had to repair numerous, manufactured 'USCG-approved' tanks (usually for fresh water boats) that exhibited failures from flimsy, minimal designs. very poor tank mounting systems, zip corrosion control protection.         A tank structure that absorbs and distributes its stresses thru the tank shell, heads, and baffling, then thru the tank mounts to the hull mounts, is critical to tank integrity.      A tank can be built  'stout', yet promptly fatigue crack and fail, due to the mounting system.Marine tanks require a  robust design and construction.Blackbird
Reply:Originally Posted by SundownIIImartinf,Sounds like this project needs a lot more thought.  Several questions come to my mind, and I do a lot of work in the marine industry.Why do you feel you need that much fuel capacity in a boat that size?  Looking at the photos, the boat isn't "that large".  My only experience with the straight 8's was in a 45' Chesapeake Bay deadrise, built in 1938 and commandeered by the Navy as an offshore crash boat (patroled off N. Carolina picking up downed pilots (training)).  The Navy had installed 2-1000gal fuel tanks, but that was because the boat had to stay on station for a week/10 days at a time.  My experience with those straight 8's is that the pair @1750 RPM will only burn about 20-22 gph.  Any higher RPM and the cooling system will not handle it.Welding up "GAS" fuel tanks is not a backyard, hobby project.  The questions asked regarding material, thickness, etc. would lead me to question whether this is something you should be taking on.  If properly designed, fabricated, and tested fuel tanks are not in the budget, maybe the project shouldn't proceed.  The discussion of using 275gal used fuel tanks is not even worthy of comment.  BAD IDEA.  500 gallons of gasoline is not something to be messed with.Another factor to consider is that fuel tanks too large for the intended purpose will mean that there is a lot of fuel just "sitting around".  Todays fuel (with all the addititives) does not store well.  In fact, marina's in this area are seeing the fuel go bad in less than 90 days.  The alcohol additives in the fuel cause it to absorb water from the air.If the tanks in question (non-approved/non-inspected) caused a fire/explosion in your local marina, you can be assured the marina owner and other boatowners will be coming to you for restitiution.This whole discussion sounds like an accident looking for a place to happen.
Reply:If the OP wishes not to listen to the sage advise given by Black... and Sun... Shame on him. I have no experience with marine application tanks. I do have several years designing, fabricating and welding aluminum, steel and stainless steel tanks for rough service (arctic circle North Slope), truck mounted for off road use. In these conditions a poorly designed tank starts leaking within days of use. You reinforce one area and you just move the stress to another. Common mistake is the mounting. I have seen many attempts to isolate the tank from the movement of the chassis, and seen them fail. I have replaced tank heads that have blown out due to the force of the product repeatedly hammering on it. Major difference between a dynamically loaded structure and that of the statically loaded one.  Using a tank designed for static use is asking for fuel in the bilge, and a fire.As to one part of the OP question can SMAW be used in the construction of a tank, sure why would you think otherwise? If you can build a ship with this process why not a tank? If you can build a pipe line from the North Slope of Alaska to the port in Valdez Alaska, 48" diameter and 800 miles long, why not a 200 gallon tank. Should the OP undertake this from opinions received from an anonymous forum, well sure why not I don't like small boats any way, so Ill never be on it.
Reply:8 miles per hour is 6.95181 Knots.It appears you are as new to boating as to welding (tanks). I suggest you get a copy ofChapman Piloting & Seamanship, 64th Edition.My boys have been boating with me since they could walk.  I still gave each of them one when they bought their first boats. It's the boaters bible.A butterfly without wings, is just an ugly bug
Reply:Martin, my responses are in blue, below: Originally Posted by martinfThanks for the info about the N. Carolina Navy boat.  I've had a hard time getting estimates as to the fuel consumption for these engines.  My specific situation is this: a 55 mile long lake that's mostly in a Nat park (no opportunities to re-fuel except down at the end where town is).  My boat weighs 60,000 lbs and has a blunt bow.  The boat cruises at a fast 8 mph (the screws are really built for major pushing).  So, if I had to go to the end of the lake and back, that'd be 14 hours.  14 hours at 20 gph would be 280 gallons of fuel.  Additionally, the original gas tanks were 225 gallons in size.  So this is why I'm looking at tanks between 2 and 3 hundred gallons.1-Since this is operated at least partially within a National Park, I'd really suspect that this vessel, will be subject to some form of inspection and marine survey--for that reason, let alone its size. Is this a 'For Hire', commercial use?Or can you afford 500 gallons of gas for a day trip?I' m hearing you that the used fuel oil tanks are a bad idea...and it's getting thru my thick skull!  But, just so I can completely put that idea to rest (as I look out and see these tanks for free around me) tell me a bit more why these would not work.  Is it that they're too thin gauge?  Or couldn't handle the sloshing movement repeated over time?  Or the lack of a solid mounting system?  (You'll probably say "all of these"!) 2-Correct! "All of the above" and more reasons--some of which I've already given.I realize that I'm new to this site and that you folks probably get a fair amount of guys just dreaming about stuff with no real-world experience to back them up.  I own lots of heavy equipment and tired iron and have been in a shop my whole life, pretty much.  What I lack is marine fuel tank experience and I really appreciate your and Dave's insight here.Dave,Okay,a couple of points I'd like you to expand on, if you don't mind.I get it about the fuel oil tanks and pick-up tanks.My tank location is right where the other tanks were and will be about the same size so my c of g will be similar.  In fact the mounting pedastal is still present so the plan is to put the new tanks right there (which is at the aft bulhead of the forward compartments).  The pedastal is about 4' square made out of 1/4" steel.These boat hulls are made entirely out of 1/4" steel with lots of reinforcing.  In fact, this boat is so heavy, it's really a pain to lift/move it even with the boat seperated into it's 4 smaller sections.Lets say that the tank is a 4 ft cube sitting on the tank pad and it is attached well so that there's no worry about it moving off.  If the hull is really stout, is there still major issues with what you say here? "A tank structure that absorbs and distributes its stresses thru the tank shell, heads, and baffling, then thru the tank mounts to the hull mounts, is critical to tank integrity. "And regarding mounting, is a flat bottom tank sitting on a pedastal a good way to do this, as opposed to mounting feet or some other strategy?3-The flat plate pad is good. Mounting feet is not good, depending upon design. A tank with the shell resting on this wouldstill need some form of perimeter framing/bracing to serve as strong mounting attachments to the pad.This framing is integral to the tank and is tied into the same planes as the lapped tank head-to-shell joints and flanged internal baffles.       The mounting pad and the mating tank surfaces resting on it, and the edge gapping--need to be sealed, painted,powdercoated, etc. to prevent corrosion. Never use carpet or foam rubber padding under a tank.                 Urethane-based sealants are gas resistant, Silicone based--are not.Real, low-point drains, need to be incorporated. This is normally ignored by most manufacturers (especially in heavy equipment), since itadds a bit of time and cost, but goes a long ways towards stopping problems.[An HR (hot-rolled) steel tank, can rust through, very quickly or take decades, depending how full it is, how often the low point drains are drained, fuel quality, etc. Aluminum coated steel doesn't exhibit the same problems-at all.]Are baffles and "sloshing" as critical for a boat that moves so slow and in a lake rather than ocean (smaller swells)?4-Baffles not only control sloshing and hammering forces, they strengthen the tank. (Presuming that the baffles are fullyflanged, fully welded, etc.) The first test of baffles is in the leak pressure testing--which is the most severe stress testingthat the tank normally sees. Correct baffling counteracts fatigue cracking. Any fuel movement creates stresses.While open water use can be really hammering, who's to say, this boat will never see anything but gentle swells? The tanks need baffles. If the baffles aren't stout, then they tear cracks in the tank wall. 5-Headspace/expansion space--for gasoline that's 10% of the tank fuel volume       250 gallons =25 gallons air space.Hey, I appreciate your taking the time to pound the keys with all of this.~martin
Reply:Dave,I haven't provided a followup comment to this thread, because to do so, may lead the OP to believe he's gained enough information to proceed with the build of said tanks.  He hasn't.  He should get in touch with a qualified tank builder and discuss the issue with them.I agree with all your comments except the one about drains.  The regulations changed years ago and no longer allow for drains in marine fuel tanks.  Sounds crazy, but I guess there were several problems with fittings leaking.  All openings (fill, pickup, vent, inspection plate, sending units, etc) must be in the top of the tank.  All fuel has to be removed by extraction.  The only exception to this rule, that I have seen, is when saddle tanks, located above the main fuel tank, are used and then it is permissible to have them gravity feed the main tank.On the 65' Viking Convertible, for instance, the boat carries 2000 gal of diesel fuel.  1350 gals is in the aft main fuel tank.  There is an additional 650 gals located in a forward tank.  The only way to get the fuel from the aux. tank (which is higher than the main tank) is with a high volume transfer pump.  All fittings are located on the top of both tanks.OP has received good information.  The reasons are obvious why he should contact a qualified tank builder.Last edited by SundownIII; 02-22-2009 at 10:14 PM.Reason: additionSyncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Dave,All of your suggestions have helped lots.  Thanks for taking the time to do that.  I'll keep you all posted as to progress on this great old boat.~martin
Reply:Originally Posted by martinfDave,All of your suggestions have helped lots.  Thanks for taking the time to do that.  I'll keep you all posted as to progress on this great old boat.~martin
Reply:Don't worry--you've convinced me!  I won't be constructing my own tank.  But, knowledge about the "why's" behind all this is important to me, whether I employ someone to fabricate a custom tank and have a way of making sure that good work is done, or whether I shop for a pre-made tank.  It's too bad that the other responses to my post mistook my wanting to know "why" as my not believing what you all were telling me.  I've never been the kind of guy to just let it be and not know the what and why's.    Having a good tank made is going to really set me back, budget wise, and I'll need to be involved as much as possible in the installation, so the more I know about this, the better. best,~martin
Reply:martinf,I've built many marine fuel cells over the years.  In fact, my first experience with tig, back in the mid-60's was, building aluminum fuel cells for the race boats we were campaigning.  I never had a failure, but some of the tanks did get beat up pretty bad when the boats went over.Rules and regulations regarding marine fuel components (tanks, fittings, and hoses) have changed drastically over the years.  You need to be in touch with someone who has kept up to speed.The changing makeup of the gasoline itself is still causing all sorts of problems in fuel tanks.  For years, some of the better yacht builders (Bertram & Hatteras) build fuel tanks out of fiberglass.  These tanks were marketed as being lifetime tanks, not subject to the rust and corrosion found with metal tanks.  Great.  That is until ethanol was added to the fuels.  Now we have fiberglass tanks failing and fuel hoses deteriorating much faster than anticipated.  Bottom line, fuel with ethanol is a bad idea for marine use.  It plays heck with the delivery systems on boats and it's storage life (even with additives such as Sta-Bil) is very short.  It's not so bad in the automobiles where the fuel is cycled more frequently, but for marine use, it sucks.Another thing to consider with those old straight 8's is the valve seats.  If you've had the heads worked, I hope they replaced the valve seats with the hardened ones.  If not, the newer fuels (with no lead), will destroy the seats in pretty short order.  Those old straight 8's were a horse of an engine.  The ones I was familar with were in a boat I ran for my cousin, back in the mid 50's.  I remember seeing those blocks with the heads off.  Now that was a set of jugs to behold.  Seemed like the bore was about 6".  Slow turning suckers too, but plenty of torque.  Seems they were rated at something like 160 HP.  Basically a diesel engine (strength wise) burning gasoline.That should be a real classic when you get her back operational.  Pictures of the build would be great.  Don't be a stranger.PS. I grew up in a little town (Deltaville) which, years ago, was known as the boatbuilding capital of the Chesapeake Bay.  When I was a kid, we had 46 boatbuilders, all within a 10 mile radius.  Started running a crab boat for an old waterman here when I was 6 yrs old.  Ran a haul/buy boat, hauling oysters from Hampton to Baltimore when I was a young teenager.  Been pretty close to the boating scene about my whole life (except for a 22 yr stint in the army--and even then I didn't get too far from boating--haha-13 mos in the Mekong Delta).  Let us know if there's anything we can help you with.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Hey SundownerIII,That's some great info.  You know, I hadn't gotten to the part of thinking about the valve seats yet.  I haven't even heard the engines run (just a compression test when I bought the boat).  I rescued this old relic, called a Sea Mule, from the cutting torch for 3 grand, figuring that, at worst, at 30 ton, I could recoup my cost in scrap.  But, she's way to cool to even talk like that.  The engines are Chrystler Royals with trannys geared at 11:1 reduction and after I bought it, the guy said, "oh yeah, I've got a few parts for you" and came back with a pallet on a fork lift FULL of engine parts, all in the original Mopar boxes.  We're talking vavle sets, gaskets, bearing, extra starters, water pumps...pretty unbelievable.Since it coming home on a low boy with 3 pilot cars (narrow highway the whole way) and me off-loading it with my 1955 NW crawler crane, I've been researching the history and looking for anybody who has piloted these things or knows anything about them.  Slowly, I've been able to get original manuals, find one of the previous owners (after WWII it did 30 yearsof service working on the Ft. Peck resevoir in Montana..still a mystery where it was in the 1990's and how it came to the Columbia river in Washington, where I got it thru a bankrupcy sale).The basic plan is to sandblast, prime and paint, place new fuel tanks, put the four sections back together (they used steel bolts with 1 3/4 BRASS nuts), build a wheel house, install a large winch for the anchor (1500 lb stockless navy anchor), a pretty sizeable capsain winch and, lastly a Prentice knuckle boom loader(24 ft reach) that I'll rob off my Mack log loader truck.As you can easily see this is a large project and I'll be asking you guys for lots of advice and suggestions, if you don't mind.  Every website forum has got people with opinions; the knowledge and expertise is here, in my opinion.More queries later!  ~martin
Reply:You appear to have made an excellent deal on the boat.  I don’t know the dimensions of your boat but if I were you I'd do some research before installing a 24' boom.  You’re going to need a lot of beam to keep from capsizingA butterfly without wings, is just an ugly bug
Reply:Martin just one questionWHY? How will you use this boat?
Reply:We have some people down here who collect and restore old military equipment; I heard one was working on a Tiger tank pulled from the bottom of a river in Germany, where it had been since our troops 'bulged it's sides a bit' with explosives before dumping it. If I can get an address for him, I'll PM it to you. Your boat isn't exactly in the same category, but these fellows may still know something about it or have friends who do. Don't hold your breath waiting though; I'm a good procrastinator so it may take some time if I even succeed.
Reply:Originally Posted by Magnetic MechanicYou appear to have made an excellent deal on the boat.  I don’t know the dimensions of your boat but if I were you I'd do some research before installing a 24' boom.  You’re going to need a lot of beam to keep from capsizing
Reply:You know, one of these days someone is going to take all the miss-information he "learns" on a forum, do something he shouldn't and kill himself.  The authorities will vacuum out his hardrive and see where the ideas came from . . . Lawyers are hungry these days too ya know Gordie -- "I believe you understand what you think I said, but I'm not sure you realize that what you heard is not what I meant."
Reply:Originally Posted by NiteskyYou know, one of these days someone is going to take all the miss-information he "learns" on a forum, do something he shouldn't and kill himself.  The authorities will vacuum out his hardrive and see where the ideas came from . . . Lawyers are hungry these days too ya know
Reply:Well Gordie,I agree that there is a problem with miss-information disseminated on the internet forums, however I'm not sure this is the case here.Maybe you'd like to elaborate on what you feel is the "incorrect information" that has been posted in this particular thread.  To me, that's the benefit of an internet forum.  If you have specific knowledge about a particular subject,  feel free to fire away.Martinf,In pursuing your information on this particular vessel, I may suggest you also contact the US Army Transportation School at Ft. Eustis, VA.  Many of these smaller inland vessels were used by both services during the war.  A little known fact is the Army has a larger fleet (in numbers) of vessels than does the Navy.  Just a little tidbit of info.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by SundownIIIMartinf,In pursuing your information on this particular vessel, I may suggest you also contact the US Army Transportation School at Ft. Eustis, VA.  Many of these smaller inland vessels were used by both services during the war.  A little known fact is the Army has a larger fleet (in numbers) of vessels than does the Navy.  Just a little tidbit of info.
Reply:Originally Posted by SundownIIIWell Gordie,I agree that there is a problem with miss-information disseminated on the internet forums, however I'm not sure this is the case here.Maybe you'd like to elaborate on what you feel is the "incorrect information" that has been posted in this particular thread.