steveb wrote:

http://www.tek-tanks.com/

Would probably be my choice.

Tek-Tank will make welded HDPE water and holding tanks but their line of
fuel tanks is very limited. Fuel tanks have to be cross linked
polyethylene and you can't weld XLPE. It has to be rotomolded so you
are stuck with the tooling cost.

--
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

boatdreams wrote:
Guys, Dave Gerr (Elements of Boat Strength, pg.186) and others have
written volumes about 5000 vs. 6000 series aluminum alloys. They all
recommend 5000 series for marine applications, but caution that it's NOT
taboo to substitute 6000 series for use other than hull plate--including
non-intregal fuel tanks.

6000 series can be used but with limitations. First it does not weld
anything like as well as 5052 or 5086 and second it is much more
susceptible to corrosion than the 5000 series.

Welded aluminum sounds horribly weak from the drift of this discussion.

Nobody has said welded aluminum is "horribly weak" but it will loose
about 20% of its strength in the area of the weld which has to be taken
into consideration when designing the structure.

I guess that's why aluminum tankers supply the fuel to our local gas
stations? Think about it. That tanker you passed on the freeway this
morning held 5000 gallons of gasoline enclosed inside an aluminum
skin--0.180" sides/top and 0.220" belly--and it bridged 30' kingpin to
center of axles. The girth weld, 15' from the nearest bearing support is
a simple butt joint and was probably hand mig welded by a kid who didn't
finish high school.

Only about 20% of those shiny tankers are aluminum. Most are stainless.
Aluminum tankers must meet DOT406-AL standards. They have a
longitudinal structure, either chassis rails and cross members or
internal webbing to prevent excess flexing of the tank. They are also
built with 5000 series material. The design is fairly standardized and
carefully refined and that kid that welded it has 2 or 3 years of
training, uses a $5K TIG welder and lays the same bead 8 hours a day 5
days a week. The guy I am working with can hardly write his name but he
lays a beautiful full penetration bead. :-)

Forget the semi trailer, the 50 gallon round or rectangular saddle tanks
hung off brackets bolted outboard from the truck chassis were most
likely welded aluminum and at 0.161" to 0.250" plate thickness--thicker
than they need to be--for added protection against puncture. And they
are hung--suspended by fabricated straps and/or U-brackets.
So please don't malign welded aluminum tanks. They've been the fuel tank
of choice for 50 years where light weight, low maintenance and cost
effectiveness are appreciated.

It is very hard to compare automotive tanks to marine tanks. While
automotive tanks have to deal with vibration they don't get the constant
cyclical loading of marine tanks. They also don't have to contend with
a constant exposure to a highly corrosive environment.

Again, nothing wrong with aluminum tanks but they are not the ideal tank
for all situations. They do weigh between 20% and 50% less than mild
steel but they are more than twice as expensive. They are also more
susceptible to stress cracking than mild steel. Removing weight from
consideration I would rank the material for diesel tanks under about 40
gallons like this:
#1 Mild steel
#2 5086 aluminum
#3 5052 aluminum
#4 Cross linked polyethylene (XLPE)
#5 stainless steel (either 304 or 316)
#6 FRP.

Over 40 gallons XLPE drops to fifth place because of the difficulty in
adding baffles and the limited selection of stock shapes.

Now, before Lew gets to upset, ;-) because fiberglass can be molded on
site to the required space it is the most efficient for the use of
volume but it is almost impossible to keep diesel from permeating site
fabricated FRP. (duck'n and run'n) :-)

--
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

Glenn Ashmore wrote in message news:Gytkb.80009$sp2.24474@lakeread04...
steveb wrote:

http://www.tek-tanks.com/

Would probably be my choice.

Tek-Tank will make welded HDPE water and holding tanks but their line of
fuel tanks is very limited. Fuel tanks have to be cross linked
polyethylene and you can't weld XLPE. It has to be rotomolded so you
are stuck with the tooling cost.

I know this will not solve your problem, but on the twenty footer I
will be building, I planned areas such as fuel storage areas to use
common size readily available marine fuel tanks. Easily replaceable in
any marine store.
I don't need to carry as much as you, but I have two 6 gallon tanks
(mains) in the rear of the boat, with a third stored in the bow. I can
just plug them in as I need them. Just thought I would note that to
anyone else is in my situation and watching this thread.
Scotty

Sorry if this is off topic.
A few NOTs from someone with 15 years hands-on experience building
welded tanks--aluminum, steel and stainless:

First it {6061) does not weld anything like as well as 5052 or 5086

NOT. Welders don't even notice when they're moving from 5000 to 6000
unless one or the other is extrusion instead of plate. They're apt to
wire brush the extrusion a little more whichever alloy it is. They
don't change gas or rod/wire and don't even adjust their current if the
thickness and position are similar.

second it is much more susceptible to corrosion than the 5000 series.

NOT. 5083 and 5054 create a slight electrical potential and with 6061
you have slightly more. Don't use it in direct contact with salt water.
Bill Gates could afford to specify 5083 throughout a boat, but even he
could not guarantee that every piece of alloy on his boat is exactly
what he specified and probably paid for.

Only about 20% of those shiny tankers are aluminum. Most are
stainless.

NOT. ALL the shiny tankers you see dropping off fuel at the gas station
are aluminum.

They have a longitudinal structure, either chassis rails and cross
members or internal webbing to prevent excess flexing of the tank.

NOT. Truck tanks like semis and pull trailers are supported front and
back on bearing pads or short subframes. There is no longitudinal
stiffening other than the shell, rings, baffles and bulkheads that form
a structural tube. By excess flexing, you probably mean 'failure'. Any
aluminum semi tanker driver will tell you his 5000 gallon balloon flexes
with a period equal to the period of his suspension...And the first 50
years he drove the damn thing it scared the hell out of him.

The design is fairly standardized and carefully refined

NOT. There are off-the-shelf tanks and off-the-shelf boats. Every time
the customer buys a new tanker he recalculates the proportions of
regular, midrange and premium or diesel--always moving the baffles,
bulkheads and piping and often demaning a custom tube shape. Kind of
sounds like boaters. Everyone wants a 40' boat, but there are a lot of
interpretations of what goes in a 40' boat.

kand that kid that welded it has 2 or 3 years of training,

NOT. He completed a 60-day welding course at the county ROP training
site and the rest of his training was on-the-job training working with a
lead welder, definitely doing his share of weld-offs on the girth seams
of the semi-tankers we're talking about.

uses a $5K TIG welder and lays the same bead 8 hours a day 5
days a week.

NOT. All welded aluminum production tankers are mig welded. Period.
And nobody in a tank fabrication shop welds off every day. Your
aluminum hull might be a 90-day building project followed by 5 days of
weldoff. Tanker fabrication has a similar ratio of building : welding.

The guy I am working with can hardly write his name but he
lays a beautiful full penetration bead. :-)

NOT. One pass full penetration in butt welds is a myth. Your guy does
it the same way everybody else does. 1st he tacks it all together. 2nd
he runs a solid weld around the inside of the seam. 3rd he runs a
portable skill saw around the outside of the seam to remove
contamination and increase penetration. 4th the welds off the outside.

It is very hard to compare automotive tanks to marine tanks. While
automotive tanks have to deal with vibration they don't get the constant
cyclical loading of marine tanks. They also don't have to contend with
a constant exposure to a highly corrosive environment.

NOT. The Principle of Uniformitarianism assures us that the
mathematics, physics and chemistry on the 3rd rock from the Sun is the
same as on the 3rd rock from Polaris or anywhere else. Granted, the
period of waves is going to be different from the period of any given
set of trailer springs. The bending moments will differ. The number
and placement of anodes will differ. But we're talking about different
numbers, not different sciences.

Cheers,
Boat Dreams

Brian Whatcott wrote:

On Sat, 18 Oct 2003 12:39:43 -0700, w kensit
wrote:



In a sailboat, maximizing tank size is going to result in an irregular shape
with the fuel pick up at the deepest point. A sump is an unnecessary
embelishment. Water is going to be of concern only with contaminated
supply in a well designed system. If water in the fuel causes sleepless
nights tee into the fuel pump discharge so a liter or so can be pumped
into a container for disposal.


Disagree. Tanks that are less than completely full condense water
during thermal cycles, and water being heavier than gas or diesel, it
collects at the low point. This really ought to be a small sump, need
not be more than a tea cup - where it can be checked via a sampler.
Nothing stops an engine better than water in the fuel.

Brian Whatcott Altus OK

Which all the more reason to end the season with full tanks. The only
time I experienced problems was from a load of contaminated fuel in mid
summer. My point is that unless your tank has a large flat bottom you
are in fact adding a sump to a sump.

Brian Whatcott wrote in message . ..
On Sat, 18 Oct 2003 12:39:43 -0700, w kensit
wrote:
....
Nothing stops an engine better than water in the fuel.

Other than me putting a wrench on it! Scotty

Brian,

Something a tank builder in RI suggested to me was mounting the tank on
something like UHMW material attached to the tank with 5200. That way no
water can get between the mounting device (UHMW pad) and the Al tank.
That would take care of keeping the tank from going any lower (gravity
again) and I guess straps across the top, but there you go again with a
water entrapment problem. Maybe more UHMW pads and a strap over them?

I'm leaning more and more toward a plastic tank, looking for a small one
but it has to fit under the cockpit and behind the mizzen step of o my
Kenner Privateer 26, a bit over 10 gals would keep me quite happy.

And I found out just the other day that Todd no longer makes the small
tanks, apparently only larger ones.

Do the makers (Tempo and who else) put baffles inside these plastic tanks?

Dave Cannell
--
In article %L4kb.805694$Ho3.219150@sccrnsc03, Brian D wrote:
We have a local guy here that teaches welding at the college and he's a
persnickety perfectionist and very very knowlegible about all types of
welding. I know another guy up in Homer, Alaska that is also extremely
top-notch and an excellent welder. I'll do my homework with both these guys
on the tank design, and then will spec it out. I'm hoping the local college
guy will weld it up for me ...he's such a perfectionist, not just with the
welding but all the structural issues. His students pass the certifications
at very near the 100% level, one of the highest rates of successful
certifications in the country. I don't know if he's willing to do custom
work but I sure hope so. I just want to get all the answers I can before I
go chase him down.

Having the tank suspended by the longitudinals means free open air under the
tank and prevents corrosion. I guess I could put a support stringer under
the tank and weld on a sacrificial strip of aluminum that'll rest on it.
Something like 1/4" thick...take a few lifetimes to corrode that away,
assuming you seal-weld the edges and don't trap water between it and the
tank via capillary action. Education is ongoing ...I'll keep looking into
this stuff. And I *do* own the full set of ABYC and USCG specs ...need to
go read the fuel tank stuff too.

Dave Gerr has a couple of articles, a 2 part series, in the current
Professional Boatbuilder and the last one (Number 84 and 85,
August/September issue and October/November issue, 2003).

Brian

Hey! Now we're talking. I can use SikaFlex 291 to put UHMW (thin) on the
bottom of the hull or whatever support stringers I put in (removable), then
use 3M 5200 to put UHMW strips on the bottom of the tank (permanent). No
water can gather between the tank and the support materials, nor between the
support materials and the epoxy/glass/wood either, and the UHMW will prevent
chafing forever...

Thanks for the inspiration ...I think I have a solution: custom tank, and
artful use of UHMW and supports!

Brian


"Dave Cannell" wrote in message
.. .
Brian,

Something a tank builder in RI suggested to me was mounting the tank on
something like UHMW material attached to the tank with 5200. That way no
water can get between the mounting device (UHMW pad) and the Al tank.
That would take care of keeping the tank from going any lower (gravity
again) and I guess straps across the top, but there you go again with a
water entrapment problem. Maybe more UHMW pads and a strap over them?

I'm leaning more and more toward a plastic tank, looking for a small one
but it has to fit under the cockpit and behind the mizzen step of o my
Kenner Privateer 26, a bit over 10 gals would keep me quite happy.

And I found out just the other day that Todd no longer makes the small
tanks, apparently only larger ones.

Do the makers (Tempo and who else) put baffles inside these plastic tanks?

Dave Cannell
--
In article %L4kb.805694$Ho3.219150@sccrnsc03, Brian D wrote:
We have a local guy here that teaches welding at the college and he's a
persnickety perfectionist and very very knowlegible about all types of
welding. I know another guy up in Homer, Alaska that is also extremely
top-notch and an excellent welder. I'll do my homework with both these
guys
on the tank design, and then will spec it out. I'm hoping the local
college
guy will weld it up for me ...he's such a perfectionist, not just with
the
welding but all the structural issues. His students pass the
certifications
at very near the 100% level, one of the highest rates of successful
certifications in the country. I don't know if he's willing to do
custom
work but I sure hope so. I just want to get all the answers I can
before I
go chase him down.

Having the tank suspended by the longitudinals means free open air under
the
tank and prevents corrosion. I guess I could put a support stringer
under
the tank and weld on a sacrificial strip of aluminum that'll rest on it.
Something like 1/4" thick...take a few lifetimes to corrode that away,
assuming you seal-weld the edges and don't trap water between it and the
tank via capillary action. Education is ongoing ...I'll keep looking
into
this stuff. And I *do* own the full set of ABYC and USCG specs ...need
to
go read the fuel tank stuff too.

Dave Gerr has a couple of articles, a 2 part series, in the current
Professional Boatbuilder and the last one (Number 84 and 85,
August/September issue and October/November issue, 2003).

Brian