By now you may have found the online articles about tank failures and 0.090"
walls, right? Big improvement if you go to 0.125". Number one reason for
failure on thin tanks is metal fatigue, especially at or near weldments.
Number one reason for failure on heavier tanks is corrosion. Number one
reason for corrosion is tank immersion (in water) or standing water on the
tank. If the tank is kept dry, ventilated, and built with 0.125" or thicker
walls and lid, then you've nixed 99% of the tank failure problems. Add
baffles, I think 20" to 30" apart? Stephen? What's the spec here? A
friend that builds tanks drills holes in the lid and sides, makes baffles
(lots of holes and limbers) with a bent over tab on top and both ends. He
welds the bent tabs to the tank through the holes, then fills the holes with
fill material. Grinds flush. Having baffles welded to lid and sides means
that regardless of tank mounting, that the lid-to-tank weldment is prevented
from fatigue failures since the baffles are doing double duty and
transferring load to the tank sides. He either glass beads or etches (can't
remember which) the whole tank, primers and paints. He doesn't use a
special anti-corrosion primer such as zinc chromate, but you could if you
want. The paint is some kind of epoxy paint. Ameron Devoe 229h I think
....industrial grade epoxy paint.

He puts the pick-up at the aft end, an inspection plate above that point,
sometimes a well (water and sludge collection) below that point. He uses
1-1/2" filler and a vent ...what was it? 5/8" or so? Can't remember. He
doesn't put sending units in the tank...FloScan instead. When my boat is
nearer being ready, I'll probably let him build me a tank ...

Brian

--
My boat project: http://www.advantagecomposites.com/tongass


"Glenn Ashmore" wrote in message
news:jcnjb.77205$sp2.22847@lakeread04...
That sounds more reasonable. #12 MSG is .1046" thick so that puts me a
little over the minimum.

Stephen Baker wrote:
Glenn,
ABYC states a min. thickness for alu diesel tanks (5052, 5083, or 5086
alloy)
of 0.090", and all fittings should be 6061-T6 or 300-series stainless.
There is a lot more to the "recommendation", let me know if you want it.
Steve

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

I picked up on most of that already. It was the thickness that had me
flustered. You are right that .125" would be much better. Easier to
get good welds on too. Baffels are required every 30" and rosette welds
are what those filled holes are called. Fillers must be a minimum of 1
1/2" and vents 5/8". Those things I expected.

Other things I found that I was not expecting: 46 CFR 183.518 for small
passenter vessels says ALL fittings must be on top. 46 CFR 58.10-10(a4)
allows cleanout plugs and supply outlets on the bottom of the tank.

What has me really confused is the relationship between 33 CFR 181 - 183
and 46 CFR. They are not easy to figure out in the first place and the
way they are presented on the web makes it a lot worse.

SAFETY STANDARDS FOR BACKYARD BOAT BUILDERS has nothing in it that
applies to diesel powered vessels over 20'. I guess I will have to
spring for the ABYC guides but from what I have seen so far they don't
track exactly with the CFRs either.

Brian D wrote:
By now you may have found the online articles about tank failures and 0.090"
walls, right? Big improvement if you go to 0.125". Number one reason for
failure on thin tanks is metal fatigue, especially at or near weldments.
Number one reason for failure on heavier tanks is corrosion. Number one
reason for corrosion is tank immersion (in water) or standing water on the
tank. If the tank is kept dry, ventilated, and built with 0.125" or thicker
walls and lid, then you've nixed 99% of the tank failure problems. Add
baffles, I think 20" to 30" apart? Stephen? What's the spec here? A
friend that builds tanks drills holes in the lid and sides, makes baffles
(lots of holes and limbers) with a bent over tab on top and both ends. He
welds the bent tabs to the tank through the holes, then fills the holes with
fill material. Grinds flush. Having baffles welded to lid and sides means
that regardless of tank mounting, that the lid-to-tank weldment is prevented
from fatigue failures since the baffles are doing double duty and
transferring load to the tank sides. He either glass beads or etches (can't
remember which) the whole tank, primers and paints. He doesn't use a
special anti-corrosion primer such as zinc chromate, but you could if you
want. The paint is some kind of epoxy paint. Ameron Devoe 229h I think
...industrial grade epoxy paint.

He puts the pick-up at the aft end, an inspection plate above that point,
sometimes a well (water and sludge collection) below that point. He uses
1-1/2" filler and a vent ...what was it? 5/8" or so? Can't remember. He
doesn't put sending units in the tank...FloScan instead. When my boat is
nearer being ready, I'll probably let him build me a tank ...

Brian


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Don't forget that Subchapter K (the 46CFR passages) are for vessels
carrying passengers for hire. Their rules are much stricter than
those for rec. vessels, presumably because recreational vessels are
used more "voluntarily." Subchapater K covers vessels up to 100 tons,
so they are not really thinking of 40-gal fuel tanks.

ABYC publishes a book that puts together in one place all the federal
regs for recreational boats -- a good thing to have.

Cheers,
Michael Porter




Glenn Ashmore wrote:

snip

What has me really confused is the relationship between 33 CFR 181 - 183
and 46 CFR. They are not easy to figure out in the first place and the
way they are presented on the web makes it a lot worse.

SAFETY STANDARDS FOR BACKYARD BOAT BUILDERS has nothing in it that
applies to diesel powered vessels over 20'. I guess I will have to
spring for the ABYC guides but from what I have seen so far they don't
track exactly with the CFRs either.


Michael Porter Naval Architect / Boatbuilder
mporter at mp-marine dot com
www.mp-marine.com

Brian D says:

Add
baffles, I think 20" to 30" apart? Stephen? What's the spec here?

No spec listed, but 30" or so is reasonable. The other thing to make sure of
with baffles is that the size of the holes does not exceed 25-30% of the
cross-section area.
On alu tanks, I would recommend as little plug-welding as possible, say limited
to the top surface. (i.e. build the tank without the top, then insert baffles,
then close) Each plug becomes a hard point, albeit small.

Steve

Steve,

I've seen tanks made the way you suggested, but with the tank top oversize
so it extended an additional inch-plus on either side. This was for
suspending the tank by the lip. With all the pounding that a boat goes
through, I feel concern that the top weldment would be prone to fatigue and
cracking. OTOH, I do know lots of people do it this way (1/8" sides/bottom,
3/16" top). What do you think?

Brian


"Stephen Baker" wrote in message
...
Brian D says:

Add
baffles, I think 20" to 30" apart? Stephen? What's the spec here?

No spec listed, but 30" or so is reasonable. The other thing to make sure
of
with baffles is that the size of the holes does not exceed 25-30% of the
cross-section area.
On alu tanks, I would recommend as little plug-welding as possible, say
limited
to the top surface. (i.e. build the tank without the top, then insert
baffles,
then close) Each plug becomes a hard point, albeit small.

Steve

Brian says:

I've seen tanks made the way you suggested, but with the tank top oversize
so it extended an additional inch-plus on either side. This was for
suspending the tank by the lip. With all the pounding that a boat goes
through, I feel concern that the top weldment would be prone to fatigue and
cracking.
OTOH, I do know lots of people do it this way (1/8" sides/bottom,
3/16" top). What do you think?


I'm not exactly fond of that method. As you say, too risky. If you want to
hang something make up a bracket properly sized, and then all you have to
replace is the bracket if it fails. THat's the same reason why my stereo
system is component rather than "boom-box" style. I don't have to replace
everything coz the turntable dies (yes, I'm that old ;-))

I love things that work, and can be depended on. That includes gravity. If
gravity will hold something in place when static, then a simple strap to take
care of the dynamic situation is all you need. And it's cheap!

Steve

Steve, or an aluminum expert:

In general bends are better than welds (in aluminum) since you don't have
the heat treatment hardening of the tank in the area of bends, but do in the
area of welds. What if the aforementioned lips on the side, the sides, and
bottom, were all made from one sheet that was bent to make the shape. The
end caps would be welded on, as would the lid, but the welded-on lid would
not be carrying the weight. Is there any issue with bends becoming weak?

Brian


"Stephen Baker" wrote in message
...
Brian says:

I've seen tanks made the way you suggested, but with the tank top
oversize
so it extended an additional inch-plus on either side. This was for
suspending the tank by the lip. With all the pounding that a boat goes
through, I feel concern that the top weldment would be prone to fatigue
and
cracking.
OTOH, I do know lots of people do it this way (1/8" sides/bottom,
3/16" top). What do you think?


I'm not exactly fond of that method. As you say, too risky. If you want
to
hang something make up a bracket properly sized, and then all you have to
replace is the bracket if it fails. THat's the same reason why my stereo
system is component rather than "boom-box" style. I don't have to replace
everything coz the turntable dies (yes, I'm that old ;-))

I love things that work, and can be depended on. That includes gravity.
If
gravity will hold something in place when static, then a simple strap to
take
care of the dynamic situation is all you need. And it's cheap!

Steve

My theory is that the least amount of welding the better. It weakens
the material much less and is a whole lot less expensive.

Brian D wrote:
Steve, or an aluminum expert:

In general bends are better than welds (in aluminum) since you don't have
the heat treatment hardening of the tank in the area of bends, but do in the
area of welds. What if the aforementioned lips on the side, the sides, and
bottom, were all made from one sheet that was bent to make the shape. The
end caps would be welded on, as would the lid, but the welded-on lid would
not be carrying the weight. Is there any issue with bends becoming weak?

Brian


"Stephen Baker" wrote in message
...

Brian says:


I've seen tanks made the way you suggested, but with the tank top

oversize

so it extended an additional inch-plus on either side. This was for
suspending the tank by the lip. With all the pounding that a boat goes
through, I feel concern that the top weldment would be prone to fatigue

and

cracking.
OTOH, I do know lots of people do it this way (1/8" sides/bottom,
3/16" top). What do you think?


I'm not exactly fond of that method. As you say, too risky. If you want

to

hang something make up a bracket properly sized, and then all you have to
replace is the bracket if it fails. THat's the same reason why my stereo
system is component rather than "boom-box" style. I don't have to replace
everything coz the turntable dies (yes, I'm that old ;-))

I love things that work, and can be depended on. That includes gravity.

If

gravity will hold something in place when static, then a simple strap to

take

care of the dynamic situation is all you need. And it's cheap!

Steve




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Brian says:

Is there any issue with bends becoming weak?


No, there is an issue with bends BEING weak. ;-)
Take a sheet of aluminum, bend it 90 degrees, then bend it straight. Now try
to rip it.
See what I mean?
Welding will lose you a lot of strength, yes, but it is a well-documented loss,
and folks will generally use only strength figures for the welded condition.
If you use bent plate, and calculate for the un-welded strength, you _will_
suffer for it.

Steve "not an aluminum expert...."

I must disagree. Especially with non-heat treatable alloys like 5052
and 5086 used in marine applications. These alloys are work hardened.
You are confusing bent strength with fatigue cracking. If you bend any
metal back and forth it will crack but if you bend aluminum once it gets
stronger. Aluminum can be bent and stretched more than almost any
metal. A beer can starts of as a flat disk.

Aluminum sheet usually comes hardened to some degree. The hardness
comes primarily from the rolling process. The amount is indicated by
the H number that follows the alloy number. For example H0 is anealed,
the softest and weakest. H1 is hardened only. H2 is hardened and
partially anealed. H3 is hardened and then stabalized. The second
number is the amount of hardening and the third number defines hardnes a
little colser. H116 is between 1/8 and 1/4 hard only. H34 is half hard
and stabalized. When you bend them the hardness and therefore the
strenght goes up slightly. When you weld any of them they drop back to
the anealed H0 condition and are up to 20% weaker.

Also if the weld is not done exactly right or it is a little windy when
it is done blowing the shield gas away you run the risk of hydrogen
enbrittlement which results in cracking.

Stephen Baker wrote:

Brian says:


Is there any issue with bends becoming weak?



No, there is an issue with bends BEING weak. ;-)
Take a sheet of aluminum, bend it 90 degrees, then bend it straight. Now try
to rip it.
See what I mean?
Welding will lose you a lot of strength, yes, but it is a well-documented loss,
and folks will generally use only strength figures for the welded condition.
If you use bent plate, and calculate for the un-welded strength, you _will_
suffer for it.

Steve "not an aluminum expert...."

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com