Metal Marine Tanks (mainly welded aluminum)

Steel and aluminum boatbuilding. See: "Boatbuilding Methods", in left-hand column of the Home page, for information about alloys.

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Kevin Morin
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Re: Metal Marine Tanks (mainly welded aluminum)

Postby Kevin Morin » Tue Jan 12, 2016 4:02 pm

To follow on the introduction of metal forming shown in a few of the previous post's images of tank building joint design considerations; we need a brief review, not an in depth examine of the machines and how they need to be understood as you manage your tank build.

First Shears: while you layout mark and cut your sheet or plate into the sizes and dimensional criteria needed for your tanks; mechanical shears (sometimes called guillotines) are very common in metal sales businesses of any size and more often present in welding fab shops that don't even work in aluminum regularly. These shears can cut many straight line cuts in a few minutes, so... #1 if your tank is mainly rectangular/cubic without an 'indents' on an give side then having the material, including baffles sheared could be very economical since all the straigth cuts can be made for what is usually a minimum shop charge.

Now and L has and indent and this machine cannot cut those inner two edges, but square has no indents in the outline nor does a rectangle so both of these shapes could be cut by a shear.

2nd Notchers: a notcher is a kind of shear that cuts square corners out of larger shapes. For example if you wanted to bend (we'll get to forming) a 'pan' like those shown in the previous post, you could layout the square of the corner to be removed with a jig saw but ... there is an industrial grade tool designed and built for that exact purpose. They are common in welding shops, and it only takes seconds to cut all the corners out of a small tank's end panels that are planed to be pan formed with flanges for lap joints- as shown in the post above on corner design.

this link has several sizes of both machine types for further explanation. http://www.americanmachinetools.com/hydraulic_shear.htm

Why consider these services? Depending on tank design and your tool or skill set- you may elect to 'farm out' - 'sub-out' some of the build tasks and these two machines can be very helpful.

NOTE; because a tiny tank job will often be set aside for days before some shops will pay attention even with a work order; mark your materials with tape, and magic marker with your name and phone, and each piece to be sheared or notched should also be shown clearly and its THE best practice to put the tape along all cut/sheared lines! this serious shortens the machine operator's time to get set of any cut- he's usually using a very bright overhead light that shadows the blade, if you use blue painter's tape on silvery aluminum and put the edges on accurately- you will save your self lots of money in time and reduce the confrontation in the office "Welll...I THOUGHT that's what he wanted cut!""" so to avoid confusion, do the layout correctly and mark the pieces exactly.

To do this in some instance is may be best practice to find this service vendor and meet with them with a drawing, and a plan for the cuts- showing the material sizes you're bringing, and what you want to take home... let them fill you in if you're off the best practices path?

3rd Bending: Bending in aluminum is done by two main types of mechanical advantage (machines) the first is to push down on the sheet metal with a very tall/thick bar that has a narrow edge on the bottom AS the sheet metal to be bent is held up by two parrallel bars. The upper 'bar' or tool pushing the metal down into the gap and below the surface of the two supporting pieces under the aluminum to bend. Using this action pressing is called press braking, and it puts a uniform permanent bend in sheet or plate.

The second generally used method is to hold the metal in a long vise, and lift one end of the metal up some the metal bends around the lip of the big vise- there are call sheet folds, leaf folds and pan brakes, several other names. The bending action is to bend like a strip of metal between your hands- bend a strip by holding one side and pulling/pushing the other end around.

So if the machine puts a giant slow motion karate chop on the metal- that's a press brake and if machine holds the sheet and bends the end sticking out by a folding or wrapping action- that's not a press brake- call 'em what your shop people do.

The first two machines can and will damage your metal in one main way, they are designed to cut steel so the surface treatment of handling and laying your metal into the shear's deck is not as clean and scratch free as would be seen in an all aluminum shop. The edges of sheared cuts can be Vixen filed to remove a tiny layer of torn metal that doesn't weld as well as cut metal surface.

The 3rd machine set can ruin your entire pile of metal if you do not understand and have a full, complete and exact agreement with your shop and their machine operators. Bending aluminum in forming machines is not as simple as bending steel; steel is widely used and well known and its requirements are also widely known and practiced by machine operators all over. Those conditions of common use, wide understanding and wide acceptance of requirements are not true of aluminum.

Aluminum strain hardens when it is cold formed. If you take a piece of 1/8" 5052 and bend it 90 degrees the bent area has increased in tensile strength nearly 25-3-% depending on its original work treatment grade. But that comes with a price- was the metal gets stronger it goes through a phase wear it will 'tear' or fail. The stronger the tensile of the original grade and alloy of aluminum the more this event has to be observed to keep from damaging aluminum sheet or plate when bend forming.

Steel bending, both press and leaf/wrapped bending can be done with a 'knife' edge or a hardened steel edge that has no rounding. This piece of metal called the "nose bar" has to be discussed with your potential metal forming shop's people. Different thickness, alloys and 'tempers' or grades of milling worked into different alloys require different radius nose bars to avoid the tearing/cracking/splitting result I've briefly described.

There are online table of 'minimum bend radius' nose bar sizes, the manufacturers of these machines also have references, the various manufacturing and engineering associations related to this type of machine work all have various references available to guide machine operators buttttt...

To change the nose bar on a big press for a little 7 minute job is just not real world. If you discuss this with some shops - you'll be told- "Don't worry about it... we do this all the time with no problems" .. and then your materials come back cracked- because you didn't listen to your friend Kevin in Alaska who already bought thousands of dollars worth of tank material and boat framing more than one time... well then join the club! I believed more than a few "no problem we do this all the time..." and spent plenty to learn what was true. You too can pay for Metal Bending 101 education; or get it here Free at Glen-L Forum, unfortunately there are not T-shirts available for this topic.

Incidentally if you design a lapped corner tank, make sure to confirm the pan size (both X&Y dim.) with your shop. A pan-shaped brakes require a 'finger brake' or cut lengths dies on press brakes and those need to be confirmed, otherwise when bending the 2nd set of four edges- the press will not 'fit into' the pan or he leaf type will not be able to move the nose bar pieces/fingers aside as the first two bends raise up against the nose bar.

What you're looking for is a shop that says - "We'll change the nose bar if you'll pay the shop time"- and gives a figure- OR some purely aluminum working shop where the understand your point of view OR someone that has a brake that regularly provides 4T (four thickness) now bar bends (!- that's rare). But you may not find good results with steel-only shops who find your work an interruption in their work and really preferred you to go way- your requested die/nose bar change if they even have one? is a pain- not a profit. Look elsewhere.

If your tank is 5052 H32 (for example) then some brakes' nose bar for steel will work - to learn if that is true of your service vendor; take them a piece of the tank material 2' long and have it bend to 90, and "see" what comes of the knife edge in your material? ["Trust; But Verify"- Ronald Reagan].

The purpose here was to give the metal tank builder an option to hand cutting all the pieces, to introduce the pro's avoid the most common con's to machine shop forming tool use and to give an overview focused on the issues of this type of service in designing and building welded aluminum tanks.

Remember; you can use the inside edge fit, cut it all your self and only have to find a welder to 'glue it together', machine tool shops may be a help but for the uninformed those services could prove to more trouble than they're worth? I hope to have introduced the matters that will require your attention if you plan to engage outside machine forming services of the types mentioned above?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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Re: Metal Marine Tanks (mainly welded aluminum)

Postby Kevin Morin » Fri Jan 15, 2016 12:19 am

Part of tank design is the mounts that hold the tank in place within the structure of the boat's framing. If a tank is small, say less than 15 gallons @ 6.2 lb/gal. ; tank and gas will probably be less than 120 lb. filled. Not something that is really "portable" but not something that can't be chocked on deck or under the stern lockers? Therefore mounting can be as simple as putting a cleat/chock/retainer on deck and let it go?

However if you're building larger volume tanks? say a 75 gallon tank mounted on the centerline in your boat, under the deck? Then you need to treat the tank just like an engine- in terms of providing mounts, support and structural elements that can withstand this 500-600lb item's loads in a seaway.

Engine mount type tank mounts need to be used, longitudinal or 'engine timber' types of hull framing should be built in, and the same types of hardware (not isolation mounts) you'd use for an engine will be appropriate for larger tanks. Just figure the wt of the tank plus fuel and if the wt is over a 130-150lb.s? plan to use some serious engine mount type structures for this tank.

Image
Here is a sketch, in some wild colors! of the minimum structural elements needed for the longitudinal (all the purple colors) and the tank side blue, with its orange hardware flange and mount.

The blue patch or doubler should be welded to the tank side, this spreads the loading stresses into a wider area than the flat bars welded on edge- so the load on the tank side is dispersed and the rounded corners of the blue doubler insure the welds don't create any hard spots where stress cracking could begin.

Image
In this image, above, of a large tank with the top off to show the baffles, there are several mounts along the sides- in the foreground is an 'engine timber' type of longitudinal and UNDER this tank are some (green) longs that were called for in the plans as hull stiffeners interlocking with the frames.

The purpose of this set of images is to explain that if you have 'engine like' wt.s involved with your fuel- the loads need to be carried by deep hull longitudinals, the tanks need to have side plate doublers to distribute the mount's load to the tank plates in a distributed area, and the tank should be joined by bolting to the boat's structural elements so it is removable if at all possible.

Tanks that are welded into the boat, will be discussed in a future post; here (above) we're exploring best practices for tanks that need to located on the centerline below decks on stringers, because the wt is similar to an inboard engine.

Next, lets look at a pair of skiff tanks of about 25 gallons each. They were designed to be mounted under the guard deck in a metal skiff forward of the console so the skiff's natural balance when fueled was heavier by the bow- due to the location of the engine on an extended bracket -aft.

The tanks were made by folding to symmetrical pieces of sheet, and adding baffles that were the same shape as the ends, but the tanks had to conform to the skiff's topsides flam. Therefore they're designed to lean out with the side of the skiff at the location where they would be mounted.

Image
First skiff tank image, above, shows the pieces of the skin/shell/outside of the tank. The inner and outer sides were bent to reduce welding and stiffen those two corners, the baffles and ends were all sheared to width and then fit to their respective positions.

Image
Changing point of view of the previous sketch to increase clarity of the two images, the parts are shown again with labels.

Image
This sketch shows the relationship to the rest of the skiff and the interior piping included in these tanks. The tanks sit just a 1/2" above the deck so the wash down will flush any fishing by products out from under and the deck to tank fit's space keeps the tank walls from corrosion.

Image
Again, changing the view point to almost a full section of the tank an skiff side with its guard deck; the interior pipes are fairly clear. This skiff's draw is at the very tank bottom and the over large fuel filter takes care of tank bottoms, but since the tanks can be removed with a few easy to get to bolts... they are removed at the end of season and emptied and rinsed.

The two bent pieces were tacked along the top and toe of the tank. Then baffles were fit side and MIG welded to the two sides, then the ends were put on and TIG welded after the interior fittings and pipes were installed. Tested to 3 PSI for leaks, these tanks serve well to help balance the skiff by the bow, reduce roll motion because they're outboard not on the centerline and allow for 50 gallons of fuel to be carried with above deck tank that are not in the way.

Image
This photo may be hard to correlate to the previous sketches? This was taken while the tank top doubler for the fittings base was installed and the vent and draw half couplers are welded on. The down comer for the fill is welded to the doubler plate- larger diameter pipe to the left but the coupler for the tank cap is not welded on in this pic.

Image
This photo may be confusing as well! sorry its all I've got handy. This view of the tank installed, painted (Zolatone) and bolted in to the boat, shows the direct mount cap- like is on the top of off the shelf steel cans. This fitting is available from various suppliers and allows the tank to use a standard twist on cap with vent.

The upper right hand thread fitting is the same 1/2 coupler from the previous bench welding photo, but now the SS street El fitting is installed with the tubing (draw and tank isolation valve) to the right in the OFF position) From behind the black cap another SS tube runs forward- left in this photo of the Starboard tank from inside the skiff. This is the vent tubing but the vent tube tank top adapter fitting is behind the cap (you're right the builder isn't the best photographer around....)

Just to the right of the tank, below the top is a section of 3"x 3" x 3/8" angle extrusion that is used to bolt the tank to the structural frame element under the vertical pipe. ( I did mention this was not a very clear photo but it was all I had to hand.) Again, a bare outline of the bolt head shows to the left of the vertical support pipe but the mounts are seen slightly better in the next photo.

Image
This photo, of Mr Oran Morin as a younger fellow, caught the port tank's lower edges and deck mount- but not very close up! The angle section is welded to the tank side, there is a tapped block welded to the deck and a passivated SS, socket recess cap screw threaded into the tapped block, holding the tank in all four corners. To the left of the tank is the angle section and the bolt into the deck welded tap block, this fastener is removed annually, the tank removed and cleaned, and the fastener replaced with Teflon Pipe 'dope' as lubricant and isolation.

Who said tanks have to be hidden? or tucked under the deck? or in a cabinet in the stern? Welded tanks can be designed to fit where they're needed, to the shape that is required and as long as the main fuel flow in and out is accommodated; they can be very serviceable and useful to help balance small boats.

Image
This last SketchUp image is included to show the section of this skiff's construction- the vertical pipe we see blocking the mount, and appearing to the right of the photo above is equivalent the struts or triangulation legs in this type of skiff side construction.

Summary; if the tank is to heavy is shouldn't be 'sitting' in the boat, it should be mounted (at least) like an engine because if that much weight gets to move freely in a boat it could cause damage or even sink the boat. Tank mounts for heavy tanks should be attached with side wall doublers in order to distribute the stress or load forces wider and that is true of the hull as well, if the tanks will be heavier than 150lb longitudinal stringers and mount reinforcement for the tanks mounts should be planned.

Metal tanks can be shaped almost any shape that is needed to fit in a specific location in your boat. By planning the shape - metal forming equipment service may be used to reduce the labor to shape and fit the parts for your tanks. At least these machines can be considered and their cost estimates obtained by showing your local fabrication shops your tank plans, and getting work cost estimates allowing you to understand if the external services for cutting and forming are worth the time they'd save you in your tank project.

Tanks fittings, especially on thinner wall tanks should be mounted to plate doublers to avoid pluming fittings or fill fittings from flexing thinner material resulting in potential fitting weld cracking.

Cheers,
Kevin Morin
Kenai, AK
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Re: Metal Marine Tanks (mainly welded aluminum)

Postby Kevin Morin » Sat Jan 16, 2016 2:06 pm

A quick review of the last few posts shows I've forgotten to mention some items not shown but present in these tanks. Pipes, fill downcomers, draw or water bottoms/sump draws- are all anchored inside the tanks. A flat piece of scrap off-cut 1" to 2" wide and long enough to reach a side of the tank will work fine to keep the pipe from the three types of wobble that might break the weld at their tops' to tank joint.

Fuel sloshing or wave motion is reduced or eliminated by baffles that allow the fuel level itself a liquid will, but if there is a path for wave action that could put side forces on the pipes. If the boat has an engine and that is why we'd have a fuel tank; then at some (hard to predict) RPM that engine creates vibrations within the boat and that includes handrails, pipes in tanks and various other parts of the boat- so welded tabs attaching the downcomer 's inside tank work to eliminate this vibration's expression on the pipes.

Last, the weight of any given piece of metal suspended from the top of the tank acts like a pendulum inside the tank. Not that the pipes are free to move- but that normal movement in water tends to put momentum forces on the pipes- these forces are countered/eliminated by the welded on brackets/tabs/struts described here.

These items are not shown in the illustrations or photos shown above, but needed to be mentioned as they're critical to well built tanks.

Image
This photo shows the type of struts explained in this post. There are two downcomers in this tank, to the right foreground is the fill pipe with a 1/2 coupler already welded to the pipe. In the background right side is a miniature downcomers of 1/2" pipe and its top welded coupler. Both pipes are fully mounted inside the tanks with welded struts or tabs, before the top panel is put on.

NOTE: This tank will be mounted like an engine on hull stringers with side mounted, cantilevered strut supported flanges where the bottoms of the tanks do not touch the boat, the tanks are not supported by a flat platform underneath. So the honeycomb/egg-crate/baffle system is very heavy and welded fully to the bottom of these tanks (3/16" 5086) so the fuel wt can be carried by the tank as an internally reinforced box beam. Baffles, inner supports, structural elements of tanks that carry fuel on the sides as longs, bolted to hull stringers need a bit more internal stiffening than tanks that might be mounted on longs or platforms underneath.

I hope, in this post, to make it clear you must be sure the pipes inside any tanks you consider are well supported to the sides with MIG welded tabs so they cannot move in any direction for any reason.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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Re: Metal Marine Tanks (mainly welded aluminum)

Postby tcough » Sat Jan 16, 2016 3:34 pm

Just a note to let you know we're all following your thread. I have enough going on just building the Flyer and all my extra time and money are going into it, so I don't think I'll tackle building my own tank, this time. Thanks for all the effort you're putting into this thread, I know many are learning something from it.
Happy Boating,
Tracy

Building a 19'-9" Flats Flyer

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Re: Metal Marine Tanks (mainly welded aluminum)

Postby gap998 » Sat Jan 16, 2016 5:09 pm

Another brilliant post - They should give out certificates for anyone who reads them! I wont be building my own tanks, (a fabricator in work will do that for me), but I am planning to design them; there were lots of points I hadn't thought about. Thanks for all your time & effort.
Gary

Planning a whole fleet, but starting with a Zip...I think.

"Just when you think you've made something idiot-proof, someone builds a better idiot!"

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Re: Metal Marine Tanks (mainly welded aluminum)

Postby gap998 » Sat Jan 16, 2016 5:10 pm

Another brilliant post - They should give out certificates for anyone who reads them! I wont be building my own tanks, (a fabricator in work will do that for me), but I am planning to design them; there were lots of points I hadn't thought about. Thanks for all your time & effort.
Gary

Planning a whole fleet, but starting with a Zip...I think.

"Just when you think you've made something idiot-proof, someone builds a better idiot!"

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Re: Metal Marine Tanks (mainly welded aluminum)

Postby Kevin Morin » Sat Jan 16, 2016 8:23 pm

tcough, gap998, thanks for the encouragement, I appreciate you reading the posts and remarking.

Hopefully, even designing your tanks, you'll be more informed about what to avoid, and what to plan to include for the best job you can get for your boat? That's where we're headed.

We've got a few posts to go, so hopefully by the time you're ready to design and plan- we'll have enough up here to make that plan the best you can do?

Cheers,
Kevin Morin
Kenai,AK
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Re: Metal Marine Tanks (mainly welded aluminum)

Postby specialk » Sun Jan 17, 2016 11:13 am

Kevin ..I too have been following... this is good info...I found out I need to take my brass fittings out of my fuel tank...thank you for the time you spend education us... I do have a few belt buckles I need to send you to be finished... yes I worked a couple of Fluor, Becon and BE&K jobs...
Kelly...1st Boat...Flats Flyer
2nd Boat.....?

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Re: Metal Marine Tanks (mainly welded aluminum)

Postby mrintense » Sun Jan 17, 2016 1:31 pm

Kevin,

Again, I would like to thank you for all your effort here. This series of posts is outstanding and I dare say, should be considered as part of an update to the boatbuilding books offered by Glen L. Like many here, I will probably not be fabricating my tanks, but I may have to design them (I won't know this until later in the build). Regardless, there is useful information for owners of aluminum tanks as well as builders/designers. Thanks again.
Carl
a.k.a. Clipper

Crafting a classically styled Vera Cruise named "Some Other Time"

Clipper's Vera Cruise Build

Kevin Morin
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Re: Metal Marine Tanks (mainly welded aluminum)

Postby Kevin Morin » Sun Jan 17, 2016 3:19 pm

Specialk, if the brass fittings are installed with good layer of thread goop often the threads will last a good while, most fuel/gasoline will solvent the goop out of the fittings' threads over time... so that can be a problem. Those problems would be inside the threaded tank fittings.

But exposed brass/copper alloys of all types can have another problem. Dew. Water condenses in humid atmospheric conditions when the day cools, that moisture collects on the fittings and some it will drip on the tank/metal below. That dew dripping evidently has copper ions in it (?) because I've repaired lots of small boat (manufactured boats in this instance) tanks where the damage was on the tops of the tanks! That's right the top with fittings and the damage or corrosion patches were very often immediately below the fittings- expecially true of Street 90's where the male thread of the fitting is vertically threaded into the tanks' 1/2 couplers or thread blocks- and the hose is fitting to a horizontal barb OR, worse, there is small fuel shut off valve that is brass threaded to the 90 El and the hose barb fitting to the valve.

This instance reminds me another post to bring up... to follow.

mrintense, thanks for the words of encouragement, I'm glad you're learning about something to help your project's planning. A word of our communications about this series, I would say if you design your tanks and then supervise a group of vendors/suppliers/tradesmen doing your tanks: I would day that is you building the tanks. So while I realize many non-welding members won't rush out to buy welding power supplies- I consider it "building your own tanks" when you're the guy that controls the project. We may not do all the different trades in a house but if you select the plans, supervise the subs, and even work day to day with the general contractor..... I see that as a house you "built". So, I wanted to make sure other readers didn't think I meant for everyone to learn to weld aluminum for a 18 gallon day tank!!!

Mod.s, Ms Gayle, Glen-L.com is welcome to do whatever they'd like with the posts, use them in any way that will help the Glen-L book of plans become more useful to a wider audience and more 'build-able' by helping to detail some of the aluminum working techniques, practices and potential pit falls involved with welded fuel tanks made of marine series aluminum alloys. I'd have thought the posts would be enough? but a "metal_tank.pdf" could be offered along with plans packages- free to new plans purchasers. No copyright is involved, intended, implied or expected on my part- with a public release of the information online.

I'd best backtrack a bit to talk tank tops and standing water, should have recalled this before; but better late than forgotten.

Cheers,
Kevin Morin
Kevin, Morin
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Re: Metal Marine Tanks (mainly welded aluminum)

Postby jim8014 » Sun Jan 17, 2016 11:21 pm

Kevin,
I have followed as many of your posts in various Forums, that I can find. Thank you so much for what your giving back. You have a PHD In not only welding, but in just being a great guy and superb teacher.

Jim Collins

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Re: Metal Marine Tanks (mainly welded aluminum)

Postby Kevin Morin » Mon Jan 18, 2016 3:50 pm

jm8014, thank you for the kind words, glad you're enjoying reading the posts. Hopefully my long list of mistakes will allow someone to skip a few of my mistakes so they can concentrate on mistakes of their own! Someday, welded aluminum work will have been around long enough that the work methods will more widely known?

Tank tops shouldn't be a place to stand water but I'd neglected to mention that as a focused topic, however its important enough that it should be explored a bit.

I realize that most boats' motion on the water and lots of angles of trailer parking will drain tank tops, so this may be a non-issue? The reason to focus on this if from previous discussions about standing water on aluminum, corrosion can come from several aspects of water- especially stagnant water. There are three main ways to keep water off the top of tanks, one is tank shape, the next is mounting position, and the last is tank installation. Coating may be considered a 4th method, but even coated tanks shouldn't be designed or installed so that water will stand on the tank.

Image
This sketch shows the two main tank design methods used to shed water. The cambered end panel's tiny arc is not all that clearly shown- however I think if you look at the right end of the tank (above the cutaway) section you'd see small camber of curved top edge on that panel. Short arc depth, curved tops on fuel tanks will usually shed all the water or even dew condensate droplets that collect on any tank- the curvature is not enough to make the tank build difficult- the baffles' tops or key holes may have to be carefully formed so they push up the entire top to match the end panels- but with a little attention to his detail the cylindrical section of the top can be put onto the top panel with little or now loss of fit along the two sides that remain straight.

Also showing here is a long green wedge of the long sides that would be removed when the panel outline is cut. Simply providing an incline to the top of the tank will also allow water to run off an not puddle. Either method will 'dry out' your tank tops and allow any free standing water to drain, as it should.

Now a note about welding tank tops- this relates very strongly to the topic, but I don't have an illustrations or photos to support the text. This relates to welding tanks and the results. If and tank top is welded to the rest of the tank last, as is often the case; then keyhole or pocket welds are very commonly used to allow the welds along the outside seam (one sided weld) to be joined with 'field welds' or welds out in the middle of the panel- not along its edges.

This term (Field Welds) may be used to describe welds done by truck mounted welders- away from the boat shop, OR; in the field of the panel. Where repairing a weld on a hull at the marina is "in the field" and welding the side ribs inside a topsides hull panel but not the chine or sheer- is a 'weld in the field ' in relation to that weld's location on the panel/sheet/topsides- not the weld's geographic location in relation to the boat shop. (sometimes confusing terms)

These keyhole or pocket welds are welded with a back up, that is a baffle edge or frame bar or extrusion is below the weld opening in the top panel. So the weld is kind of a cup, the bottom being what holds the hot molten puddle up from falling into the tank and the sides of the sides of the 'cup' are the edges of a hole (a keyhole) cut in the sheet or plate of the tank top panel.

Keyhole welding, pocket welding (other names are used too) are like screws in plywood onto a frame- they hold the plywood at points along the frame. However unlike ply wood the metal can contract - that is; the tank top panel (or deck) can contract from this weld, depending on weld preparation and joint design and the weld method and skill of application. When a top contracts like this we could compare it to an upholstered couch or chair back.

The buttons down in the recesses of upholstered furniture hold the padding onto the frame and make the chair comfortable but the upholstered tank top just holds water. It would be worth while to avoid this type of design and weld problem so we'll try to explore that subject later in this series - for now let's leave this with a caution that tank top welding can leave an other wise flat to 'quilted' so it will have puddles of water that could stand and promote corrosion.

The cambered (small pink arc on the top edge of the end plate) sheet of metal will have to be clamped down to the two long edges. What happens is that long edge #1 (either side) is clamped or held for tacks, then the 2nd side (remaining side #2 ) is clamped to pull the sheet/plate over the cambered frame with the set of baffles 'proud of the top plane' and while under tension- the second side would be tacked.

This will tension the top plate and a plate in tension while its welded will resist the quilting contraction distortion mentioned above. So not a bad practice to consider adding some tension to flat panels in boats by bulging those shapes slightly in the design.

Next method; Tilt the tank at installation. We've touched on a few methods of installing tanks, mounts of a few types; all these could be level just out of level, if the boat is level on its at rest waterline, the tanks could be pitched for an aft or rolled side to side, both of these positioning or mounting methods could drain the tops. Also tanks mounted out of plumb don't need as much work to camber the tops, or have to be considered for painting to help reduce corrosion.


Tanks can be installed so they're not washed by the deck wash, rain, spray or any other water source but that may leave them subject to condensate anyway. The fuel is cooled overnight sitting in the harbor or on the trailer so if the morning air is moist and has some humidity then just that amount of water will form dew on the tanks - where the sides may drip dry as the day warms- the top may not dry up completely? IN this case installing the tanks in locations where they're not exposed to much external water is only one way to defend from water - what to do about avoiding condensate?

Depending on the boat's design and tank locations, using engine heat or cabin heat to warm the tanks will usually dry them off- I've built more than a few day boats with large capacity tanks used as seating in the cabin. This allowed the cabin heater(s) to keep the tanks room temp, and that in turn reduced any condensate formation so installation location is also a consideration.

Here is a detailed last location design consideration- it only apply to boats that have inboards as they have bilge blowers to exhaust the engine room or tank spaces vapors prior to ignition as precaution to having explosive or ignition conditions in the bilge. Tanks can also be located in the air flow path of the bilge exhaust flow intake- this stream of air will also work to dry out the tank tops. If the bilge blowers are ducted then the tanks or the intake ducting (supply flow) can be used to help create and air flow over the tanks and that also applies to an engine free air intakes. All of items in this paragraph apply to inboard boats where the variables like engine air or bilge exhaust apply.

Last is coating (4th method) and that is a good item to consider if the tank will be part of the interior or even deck furniture? Also coatings, paint (all methods), powder coating, and anodizing are all valid methods of creating a water resistant film on tanks that will improve their longevity if they're constantly subject to water standing or forming on their tops.

The last two coating methods are probably only happening by outside services who regularly do this type of work? Both instances of those services will governed by their respective oven sizes and their immersion vats' sizes. However, both these coatings are worth exploring if you happen to have service vendors in your area that offer either process?

I did skip this aspect of a tank design in the posts above, that is; standing water on tank tops wasn't mentioned. But I hope to have addressed that specifically in this post? As always, if there is any aspect of what is shown or alleged to be true- that raises questions or confusion, please show what part of the wording or images we need to clarify and I'll give that some attention.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Ozzieboat
Posts: 232
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Location: Logan, Queensland, Australia

Re: Metal Marine Tanks (mainly welded aluminum)

Postby Ozzieboat » Wed Jan 20, 2016 5:17 am

Kevin
Thank you very much for sharing such valuable information. We all got a lot out of this. One question I have that you can put some light on is USCG Regulation 33 CFR 183.510 Fuel Tanks. In particular regulations, 183.584 Shock test, 183.586 Pressure Impulse Test, 183.588 Slosh Test and 183.590 Fire Test. How do you go about performing these? I have intentionally omitted 183.580 Static Pressure Test as it is straight forward to perform and one test you would perform regardless of where the tank is to be used.
ozzieboat

Kevin Morin
Posts: 697
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Re: Metal Marine Tanks (mainly welded aluminum)

Postby Kevin Morin » Wed Jan 20, 2016 10:34 am

Ozzieboat, I'm not an expert in CG regs, and even the newer vent and fill reg.s I'll try to cover in this thread all came into effect after I quit building full time so my knowledge of them are also vague. It is my understanding those reg.s/tests you're mentioning are tests for commercial tank vendors or manufacturers, and for various classifications of inspected vessels- and don't apply to the home built, one-off boat or its tanks.

It is my understanding, and subject being ill informed- the key word in the regulations is "manufacturer" (not sure where that is defined?) where the tanks we see in the marine catalogs are a regular product or a manufacturer and not 'home-builders' as defined by the regs. I think the definition is worded " an individual who builds less than (x) boats a year for their own use"? So manufacturing is a business with ongoing operations and products (boats included) that would regularly be for sale to the general public, but not the person who builds one or two for themselves- regardless if the boat is resold.

Therefore; I don't think these regulations are applicable unless you go into the tank building business-(manufacturing) and then; they are a series of tests that are run on sample products, and likely by an independent testing service. I've never heard of any CG boarding inspection look at our 'homemade' tanks for even "nomenclature labels"? Of course, living in Alaska, where routine boardings or CG inspections are rare as hen's teeth, perhaps home built boats are inspected more closely in the contiguous states where there's many more boats and people?

Fire testing, to my knowledge would be confined to manufacturer's fuels system parts, might include tanks but... that fire test is for ferry boats, charter boats, hire boats of different types that have licensing to haul passengers, not for a one off boat.

However; What do I do about these tests? I don't do them, as I'm not building tanks as a product to sell. However, they do give a good indication of how important quality welding would be - not as much in the double sides welds of the lower 3/4 of a box tank where MIG is used inside and TIG or MIG is used outside but the top where only one side of the tank's seam can be accessed.

The pulse pressure or pressure surge test consists of (thousands of) cycles of pressure than relieving that pressure, adding pressure again and relieving again in a constant cycle. This is designed to test the weld's mechanical (flexibility) integrity where the top panel could be 'pushed up and down'. The pressure inside the tank even a small pressure will try to flex the top of the tank upward. When the pressure is relieved, and flexure of the top would return to an "at rest" position.

This cycle is intended to insure #1 the tank top weld will not fail if there were weld stresses that acted like a bend and break test; #2 that the top is not truly 'flexible' in the sense that the entire top could be deformed enough to back break the welds; & #3 the entire tank, fittings and all are welded with sufficient integrity to withstand the momentum surges of wave motion of the boat expressed on the fuel as forces that could degrade the tank.

This series of tests is also designed to confirm the panel size deflection effects on the tanks. We have not addressed panel size/baffles/stiffeners yet but we will.

NOTE of Reference: boats that are 20'LOA (or designated commercial use) don't have to have foam blocks inside various voids so the boat will float level when flooded/swamped. However, those level flotation requirement regulations do apply to boats less than 20' LOA- so a 19' skiff would be subject to the level flotation regulations but the 20' boat would not be. For this reason, many builders will not build in the smaller sizes to avoid the effects of this regulation. What I'm pointing out is there are regulated and unregulated tanks based on being in business or building for your self.

So, it is my understanding, but I'm not familiar with the regulations enough to say for a fact #1 we're not manufacturing, #2 home building your own tanks don't come under these regulations & #3 therefore while good guidelines for design and construction these reg.s don't apply to 'our' tanks.

Thanks Ozzieoboat, we'll move into the tank top weld information to explore this detail more.

If anyone reading here, has a friend in the boating safety office near you- that knows the CG/Homeland/CFR well enough to list the different details we'd need to read through to understand what making our own tanks imply- according to the current regulations??? Please post up!

Cheers,
Kevin Morin
Kevin Morin

Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
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Re: Metal Marine Tanks (mainly welded aluminum)

Postby Kevin Morin » Wed Jan 20, 2016 1:39 pm

Welding Aluminum Tanks

Ozzieboat's question lead to discussing welding as part of planning your own tank build, or just supervising your own tanks. This is not an exhaustive exploration or a tutorial, this post is here to help the wood or glass worker to know some basics, and to be able to judge your prospective welders' views, equipment, and methods of work.

Aluminum is mainly welded with two weld processes- MIG and TIG where the abbreviations are Metal Inert Gas and Tungsten Inert Gas but are more recently called GMAW (Gas, Metal Arc Welding) instead of MIG and GTAW (Gas Tungsten Arc Welding) for TIG. I will use the older abbreviations of MIG or TIG for simplicity.

MIG involve a very long mechanically fed (electric motors) wire that is vaporized (melted to droplets of molten aluminum) in an electric arc to melt the metal being welded, and to add a filler of aluminum alloy that will bond the two original pieces of metal when the weld puddle cools.

TIG welding involves hand feeding (there are motorized, wire feed TIG systems) a filler rod into a molten puddle formed by an electric arc created by a non-consumable tungsten electrode in a hand held "torch".

Aluminum can be stick welded, using a consumable, rod of metal coated with a chemical flux, however the results are very poor quality and not suitable for tank welding in any instance of which I'm aware. Generally there are only two methods of aluminum welding; MIG and TIG.

MIG welding, and especially of aluminum is very fast; travel rates of welding in this method are inches per second, while welding with TIG normal travel rates are in inches per minute. MIG is fast but as a function of speed the welds can be less pure because gas bubbles in the root of the weld may be trapped due to cooling (resulting from fast travel) before they completely float to the surface of the weld and are washed away by the hot argon gas most often used to shield these welds.

TIG welding is generally slower paced welding and therefore the gas bubbles formed in the bottom/root of the molten puddle have longer to float to the top of the liquid metal and be released into the inert (non reactive) cover gas; argon. Hot argon, washing over the molten puddle keeps the Oxygen in the atmosphere from forming aluminum oxide while the metal is liquid/molten and makes this type of welding possible.

MIG wire feeder 'guns' as they're most often called come in two basic configurations and this may be important to a tank builder- when interviewing a welding service since the design of equipment can effect tank building. The first type of gun has the wire mounted in a roll in the gun's body, usually over the forearm of the welder. This 'push only' wire feeder is called a "1lb. gun" because the original MIG feeders of this type held rolls of aluminum wire that weighed about 1 lb.

http://www.ebay.com/sch/items/?_nkw=spo ... rmvSB=true
link to a current page showing MIG guns of this type.
http://www.brweldingsupplies.com/miller ... un-130831/ and a vendor link to this type of MIG 'gun' or wire feeder. THe roll of wire is housed inside the gun's body and is held up by welder as they weld.

Another type of aluminum MIG wire feeder is the push-pull system where a much large roll of wire is mounted in a cabinet and the wire is fed (pushed) through a plastic lined flexible conduit (much like a marine control cable) and an electric motor in the guns' handle pulls the wire and feeds it though the gun's body to the gas cup and welding contact tip.

http://www.mkproducts.com/Prod_sub_CobramaticSys.htm link to a vendor of push pull MIG guns showing only the 'gun' or 'torch' end without the long 20-30' conduit with the weld power and control wiring bundle connecting the gun to the welding power supply and wire feed cabinet.

Image
This photo of a push pull type of MIG wire feeder being held inside a tank, above, shows one of the aspects of accessibility to a weld's location based solely on the shape of the gun used.

This photo allows readers who may be non-welders to see the implications of the different types of aluminum 'wire welders' (MIG guns) as regard tank building. The 1 lb. type, usually has a pistol or T grip where the hand holding the torch is at right angles to the wire with the motor inside the handle/grip. Then a wire spool is mounted somewhere behind the wrist and over the forearm meaning the gun takes more space to weld compared to the more streamlined design of the push pull type shown above.

If you are planning a tank build, and your local welding service only has the push only, 1 lb. type gun; you will need to plan the interior welds and the sequence of the baffles, down comers, an any other tank furniture so the gun's space access limits are taken into account- or your tank may not be welded as well as it could be?

ON the other hand, if the service has the push pull type of MIG torch, there are other implications. #1 Companies that have the push pull systems are usually more invested in aluminum work as this torch is most often justified by hundreds of hours of aluminum work- by comparison to the less expensive push only style torches. #2 The question of access to welding inside a tank is reduced by the smaller volume torch and hand orientation so more agility inside the tanks makes for better quality welding - angle of the gun, position in relation to the weld and visibility are all enhanced. & #3 the company that has the push pull aluminum MIG system have more invested in welding tools and that implies (to me) more reason to explore their services for aluminum work.

There is a Utube channel by Jody the Welder called "Welding Tips and Tricks dot com" where he demonstrates all sorts of welding in all metals. A this channel Jody shows both push pull and 1 lb. MIG torches in use welding aluminum so there's no need to do that here.

MIG welding consists of hold the gun with two hands, pulling the trigger (On switch) and feeding the arc/wire into the weld area. The power supply and wire feed speed adjustments require practice but the welding methods or 'puddle control' are not hard to learn- physically- by comparison to TIG welding. One of the main reasons is that you have two hands to hold the welding gun. In TIG, the welder usually holds filler wire in one hand and the torch in the other hand.... much more difficult a skill compared to two handed MIG.

TIG welding
I'll show a series of images about TIG welding, so that when you go to his video channel you have some appreciation of his skills as a welder.

Image
Above is a sketch of Tommie TIGhand where we're looking down over his hands- notice Tom has no PPE. The reason is we're trying to see his hands and gloves, welding hood and all the regular PPE would be in the way. Tom has the filler wire in his left hand and a TIG torch in his right hand. Grip on the two items varies and this set of sketches just shows a few- there are many other techniques of grip and movement from the one's shown here.

Tom's right hand is either touching the bench or work at the heel of his hand OR, one or more of his little and ring finger are 'propping' his torch hand to steady it to the work. Some 'free elbow- free cup' TIG welders exist (people who can weld without touching the work!) but they're rare and usually make space craft or extraordinarily expensive custom car parts!

Image
In this sketch, above, our point of view has moved down to Tom's right so we can focus on his left hand. Tom's thumb is extended back toward his wrist and while the tip of the filler rod (wire of aluminum alloy) so he can 'grasp' the filler between his thumb (that would be in a glove if he had ANY sense ) and the web of his palm between his thumb and first finger.

Image
This sketch of Tom's left or 'off hand' shows the his thumb moved back to get a 'dip' of wire/rod for the next 'puddle' of weld. Our point of view has moved to the table/bench top height and across Tom to his left side.

Image
Tom has begun to close his thumb on the wire and slide the wire down between his fingers and into the weld puddle, while holding his hand steady enough to keep the wire/rod aimed into the puddle location correct for this weld method. Our point of view is back above Tom's off hand, and Tom should really be wearing gloves.

Image
Last in this sequence of sketches Tom's thumb has closed to the back of his fingers and the rod has been fed into the puddle, which since its molten aluminum has caused the rod/filler to simply melt into the edge of the wet metal and add to the weld. IN MIG welding this process is very fast and continuous as the filler wire is BOTH the electric arc AND the filler metal, but in TIG the arc is from the torch and the filler is from the other hand's actions of feeding wire/rod into the puddle.

When you watch Jody's videos, he may or may not show you these basic ideas- as the videos are for welders they may not included these fundamentals, and Jody feeds his TIG wire in several different methods, all of which are just as valid as this one, but all require hours of practice to develop the skills needed for this type of welding.

Now lets get to a point about tank tops; Ozzieboat brought up the various tank tests required of manufacturers of tanks and I remarked that the welds, especially the top weld, would be tested because it was a 'one sided' weld.

Image
Our first tank top weld image, above, has aluminum with colored edges, and colored weld puddle but- unfortunately when viewed through a welding hoods' filter lens that is not the case- in fact sometimes that color scheme is very confusing - just watch some of the weld videos on Utube! I'm using the colors to give a sight picture that can be discussed.

Here, our tank top is the green edged material upper material edge and the tank side is pink , the puddle is blue where the metal has begun to melt. This image shows a tungsten and an arc (electric arc) cone but does not show a gas cover because we're not discussing that aspect of these welds. The gas cup is not shown, but the yellow filler rod, lower left of the sketch is shown.

Image
This sketch from a lower point of view compared to the previous image of the same stage of starting a TIG weld on an outside corner tank top weld, simply clarifies the various parts to the image being discussed. The welder has the the tungsten close but not touching the work, the arc has been started but the weld has not fully begun as there is no filler rod added yet and the weld puddle is not fully formed.

Tom TIG's hand are holding the torch to the right of this sketch but we're only showing the tungsten alloy electrode, and his off hand (left in Tom's case) is hold the filler rod which is only shown at the tip near the forming puddle.

Image
This is another view, just above, of the same state of beginning a TIG weld on the tank top from behind the welder's hands, again, the view changed to help make this set of variables clear to new welders; non-welders too.

Image
Now the weld is moving along. Remember Tom's left hand in previous images- do you recall how he used his thumb to feed some filler rod into the puddle? We only looked at one stroke or dip of wire/rod. Here we can see how this correlates to the welding process using TIG. The torch is 'aimed' back and forth along the weld track while the wire is fed into the leading edge of the puddle in time to both the forward movement of the torch and the slight front and back motion to help control the 'wetted metal' puddle.

Image
Just changing view point to show the same weld with the filler in the lower foreground, there are two tungsten electrodes shown to give the idea of the two angles for the arc, and the "stack dimes" of welded metal behind the active/wet/ current puddle.

Image
HOWEVER! there can be problems with this weld as its been shown so far. If you look at the previous images you'll notice that two blue area of melted (fused) parent metal do not touch one another? This could still leave a good looking TIG bead on the tank top but... it would be an inadequate weld for this location if this error were left in the weld technique.

In this weld sketch, we're looking down the weld seam from as near the metal's inside edges as we can get our 'eye' (camera?) and we see an exaggerated gap under the weld. I show the bead is actually suspended between the two pieces of the tank- that are supposed to be welded. This is not really the case, but is here to show the idea of 'root fusion' or a potential flaw in the tank top weld- one that is not rare if the welder is not regularly doing this type of work. Lack of fusion here is cured in the next few images.

Image
In this sketch of three types of weld corner preparation we're exploring the effects of joint preparation and welding results. The first, left instance, is what is shown in the previous weld corner images in this post. Next, or middle is the same type joint where the two 'shoulders' have been beveled to reduce the weld amperage/power required to weld the joint due to reduced amount of metal to melt. And last, to the right is a more fully beveled set of edges to further reduce the weld metal volume- these joints may be used to get better penetration on thicker materials when the welder is using a smaller size and capacity torch.

Image
Another view point change to introduce the inspection of the tank top welds. Notice the right hand weld is showing all the way inside the tank? That is generally referred to as penetration or backwelding, in all the other seams inside the tank, where a MIG gun could reach- the tank has been fully back welded by MIG. However on the top, which can only be welded from outside, the TIG weld has to penetrate enough to create this fully back welded seam OR>>>>> this is where a tank top weld would fail in a pressure surge test.

Image
IF you'll recall, just a few images above in this post we looked closely at a TIG weld being placed on the outside corner of two pieces of plate like a tank top weld? Here we're updating those images.. do you notice the blue areas of the weld, representing the arc's effected areas of melted metal, are wider, their inner edges are closer together? That is the result of #1 more amperage/wattage in the weld compared to our previous images # Less metal to melt in order to get a fully wetted edge so beveled or chamfered edges and #3 slower weld travel so the arc's heat is left longer in one place to more fully melt/fuse the edges.

But that's not the correct way to weld this joint- yet.

Image
HERE IT IS, the keyhole. The two parent metal edges are fully melted by the arc power (heat) and the travel speed is slow enough to allow those two edges to fully melt and there is a small hole or opening formed between the two edges of the parts being welded so a welder knows the back weld is happening since this keyhole, shown in this sketch, is the 'key' to that back weld condition.

Image
Above is a photo of a tank top edge weld- how do we know this weld is correctly being applied to this tank?

Image
Weld looks OK, farily uniform, not too bulged and not much surface contamination showing... so its OK - right?

Not so fast. What about the interior side of the weld?

Image
Here is what the weld should look like in progress, the size of keyhole will vary with material and welders' preferences but this is how to tell if the top weld (any single sided weld) is done correctly.

Image
A blow up of the previous weld photo so not very well focused image- however the keyhole shows up pretty well. The reason for being concerned about this level of inspection is: #1 if a welder doesn't agree to show this to you, as a test or part of your tank.. then the skills may not be as sound as you could hire? #2 if the welder says this isn't needed, you know some comparisons to his/her experience, #3 if you're paying for the work, shouldn't you be shopping for someone who can do the work at the levels of work you'd like to see?

Summary.
Tanks are welded with both MIG an TIG, and that includes inside and outside welds. TIG welds are very often used where singled sided welds are required since they're applied more slowly with more detailed control and are usually more 'pure' less porous than MIG welds in aluminum. TIG welds require a considerably increased amount practice to master a very complex skill set of dual handed coordination holding two mediums of the weld, (arc and filler) one in each hand to very close tolerances of movement while traveling along the weld seam.

Correct set up and execution of tank top (single sided) weld is critical to have the highest quality tanks. IT is unlikely that a substandard tank top weld would pass the various CG/CFR regulation tests for manufactured tanks, unless the welder were experienced and used the best techniques and weld joint preparation to apply the welds on an aluminum tank.

Will your tank top weld fall apart if you have the local welding service MIG on the top? I doubt it. Will you have to worry about the quality of your tank build if the welders near you are less experienced and don't make it a practice to insure keyhole welds on their tank tops? I doubt it. Why is all this detail here, if it's not critical to the tanks I may want to build.

The reason to show the correct way to design and plan your marine tanks of welded aluminum is so you have the goal of quality shown. If you shop around for welders, I hope to have given some background on what may help you make informed choices. If you're building your own tanks, I'd want you to know the way to build them the best they can be, and to do that I'm showing the exact weld details I've learned to use on tanks to build the best I can. Will all welding services take all these steps? Maybe not but you'll understand why each detail could have an effect on your tank project.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin


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