Iron fuel tanks, in general
Good perspective from Bob on iron/steel tanks. Very often these tanks rust
from the inside, due to water in the fuel, condensation,etc, so even when the
entire exterior can be inspected, it's inadequate. Water naturally sinks to
the bottom of any fuel tank as it's denser. As we have discussed before, the
major expense is usually preparation for removal, tank removal,
cutting,disposal, and rebuilding all the structure after new installation. The
cost of a new tank is not the major expense...I guess I'd have a fiberglass
replacement tank made if I ever had to go thru all that.
The only preventive measures I can think of would be a drain at a low point to
remove water periodically, a fuel polishing system with pick up at the low
point, or chemical additives that would disperse water in the fuel.. Dipstick
testing for water via an acess hole is better than nothing, but once water is
detected, it needs to be pumped from the low spot, not always feasible due to
location and baffles.
I don't think its "legal" to cut access holes low in a tank side for access
cleaning and then resealing with a gasket and larger plate. Cutting a hole,
cleaning, inspecting, then welding the patch back to the tank may be
satisfactory to insurance and other inspectors...anybody know??
Rob Brueckner
Hatteras YF
I think my story is in the archives. Last year, I had my Starboard tank
repaired. It's mild steel ( I don't think anybody really has "iron" tanks).
We cut four new inspection ports in it, cleaned it out, coated the inside
with a sealer made for the inside of aircraft fuel tanks and sealed it back
up. The inspection ports are now there in each baffled compartment, ready to
use again if needed.
As far as where the ports are put... they were put at the same level and the
single original one, maybe 2/3 the way up the tank. No real reason to put
them lower, but I don't see why you couldn't. They either seal or don't...
these worked fine. The main hole was cut, then a ring of smaller bolt holes.
Two half rings with bolts were put on the inside, with the threaded parts of
the bolts sticking out, then the cover plate bolted to those with gasket and
sealer. These seem to be stock items, although I don't know where the guy
who did the work purchased them. Since finishing, no leaks, either where the
tank was originally seeping or the new inspection ports, and the boat has
been surveyed. No problems noted by the surveyor.
There are alternatives to just replacing the tanks. Still, the best advice
is to keep the water out as much as possible. A lot of the crud in the
bottom of mine appeared to be rust particles falling off the top of the
tank, where water condensed and diesel fuel doesn't coat the steel unless
you're totally full and sloshing around.
Keith
If at first you don't succeed, try management.
----- Original Message -----
From: "Robin" gymkidd405@netzero.com
I don't think its "legal" to cut access holes low in a tank side for
access
cleaning and then resealing with a gasket and larger plate. Cutting a
hole,
cleaning, inspecting, then welding the patch back to the tank may be
satisfactory to insurance and other inspectors...anybody know??
Keith's adventure tracks with my discussion with Don Miller of Marine
Trading Intl.. He said the only tank problems they had were the tops
rusting off on the 44s and turned me on to Elk River Marine where they send
their tank work. It's up by the C&D canal and they do the work for half the
"normal" price of 10-12BU. Fortunately my repair is still holding so I
haven't talked with them as yet.
Regards....
Phil Rosch
Old Harbor Consulting
M/V "Curmudgeon" MT44 TC
Currently lying Bond Creek, NC
<<I don't think its "legal" to cut access holes low in a tank side for
access
cleaning and then resealing with a gasket and larger plate>>
Actually, many larger ocean-crossing trawlers are built with such tank
access plates. Assuming that you don't charter your vessel with over 6
passengers, there's very little that's not legal for you to do on your
personal boat. Other than having the required safety gear aboard, and
proper lights, we have incredible freedom compared with aircraft and
automobiles. Fuel tanks are one area where the "Industry Standard" is very
much below standard. Most tanks in trawlers are defective in design in
several ways, making it almost inevitable that they will have to be replaced
at great expense at some time in the future.
Most tanks are welded from flat plate, either aluminum or mild steel. Tops
and bottoms of the tanks are usually flat, and mounted horizontally. This
allows the water inside to cover a wide area to a very tiny depth, and
allows the water which inevitably drips onto the outside tank top to puddle
there and maximize corrosion. Pumping the tank bottom is ineffective at
removing water and sludge, since these are dispersed over a wide flat
bottom.
What's needed is a tank with a curved or sloped bottom, so that even a quart
of water/sludge will collect in a very small area so that a drain or dip
tube located at this low spot can effectively get rid of all the
contaminants. Every small aircraft fuel tank is designed this way, with easy
to access valves so that the tank can be checked for water before every
flight. How much more effective would polishing systems be if they could
draw from a tube in this deep sump.
Tank tops would also be more corrosion resistant if sloped or curved to shed
water. Many trawlers' tanks are corroded from the top because of small deck
leaks through the fuel fill or other deck hardware. With sound insulation
built around the tanks in the engine room, there's often little the owner
can do to detect or remedy this source of corrosion.
Mark Richter, M.E.
M/V Winnie the Pooh, Ortona, FL on the Okeechobee Waterway