aviation fuel storage - cofferdams

[expedition]

Rules from both Germanischer Lloyd and MCA require cofferdams around aviation fuel tanks.

We have a conversion project on our hand and it would be relatively easy to convert an existing fuel tank into a aviation-fuel capable tank, provided the cofferdam space is between 15-30 cm. We'd simply add an extra wall to the tank (in- and outside)

Would that be OK?

Thorwald Westmaas

[yipster]

for dams i was thinking wall's like around explosive storage's but dont know what cofferdams are

did read up recently on glare and arall (http://www.boatdesign.net/forums/showthread.php?t=2629&page=3&highlight=glare), witch are explosion resisting new materials

here some more reading and adresses
http://en.wikipedia.org/wiki/Glare_(material)
http://www.tudelft.nl/live/pagina.js...63671d&lang=en
http://www.nlr.nl/id~4418/lang~en.pdf

had to know what a cofferdam is and made this edit
http://en.wikipedia.org/wiki/Cofferdam

[TeddyDiver]

Cofferdam doesn't ring any bells, but bladder tanks are quite common in aviation, so maybe the "hard tank" around the blader could fit in the description?
Anyways it's one though I've had reasently, I mean having bladder tanks for diesel and water. That would make it possible to use appropriate tank departments to desired purpose just with chancing the bladder...

[yipster]

trying to get to grips with the rules i just recieved new abs updates
reading scantlings for river and intracoastal waterway's i read bout cofferdams
guess the offshore papers cover the big stuff, its a big search tho


19 Bulkheads

19.1 Arrangement

19.1.1 Subdivision
It is assumed that those responsible for the design of the vessels have assured themselves that
the subdivision is such as to ensure sufficient stability in service when the tanks are being
filled or emptied. The length of the tanks and the positions of longitudinal bulkheads are to be
such as to avoid excessive stresses in the hull structure.

19.1.2 Cofferdams
In vessels intended for the carriage of flammable or combustible liquids having flash points at
or below 60°C (140°F) (closed-cup test), bulkheads are to be arranged to provide cofferdams
between the cargo tanks and any spaces used for living quarters, general cargo, or containing
machinery where sources of vapor ignition are normally present. Spaces containing cargo
pumps, steam pumping engines or which are used as tanks for products having flash points
not less than 60°C (140°F) (closed-cup test) may be considered as cofferdams for the purpose
of this requirement, but in the latter case the piping and pumping arrangements for the high
flash point liquid are to be entirely separate from and have no means for connection with the
arrangements for handling the low flash point products.

19.1.3 Pump Rooms
Spaces containing pumps, piping and valves for handling flammable or combustible liquids
having flash points below 60°C (140°F) (closed-cup test) are to be completely separated from
all sources of vapor ignition by gastight bulkheads. Steam driven engines are not considered
sources of vapor ignition for the purposes of this requirement. The gastight bulkheads may be
pierced by fixed lights for lighting from outside sources and by pumping engine shafts and
control rods, provided the shafts and rods are fitted with efficient stuffing boxes where they
pass through the bulkhead.

[jehardiman]

Rules from both Germanischer Lloyd and MCA require cofferdams around aviation fuel tanks.

We have a conversion project on our hand and it would be relatively easy to convert an existing fuel tank into a aviation-fuel capable tank, provided the cofferdam space is between 15-30 cm. We'd simply add an extra wall to the tank (in- and outside)

Would that be OK?

Thorwald Westmaas

As long as you can get the clearences and the accesses, then I believe yes. There must be access for inspection, leak detection, and external ventlation. This may not work with some smaller or odd shaped tanks. Most military ship that carry AvGas and some of the lighter jet fuels had thier tanks converted decades ago when I was just starting out.

[Guillermo]

30 cm is not enough to allow for inspection through all the cofferdam as it doesn't allow a man to crawl into it. You have to take into account the man-pass holes in the internal structure of the cofferdam need to be adequately sized.
If the cofferdam is a very small one, or one of its dimensions is short enough to allow for inspections without going into it, and enough provision of registering accesses has been provided, then 30 cm can be enough, if the statutory authority accepts it.
Usually cofferdams' walls are made to coincide with the main reinforcement elements of the vessel. As an example, if we are talking about double bottom tanks, transverse cofferdams use to have the length of one frames' clearance, in many cases around 500 mm.

Cheers.

[DanishBagger]

Wow, at first I was somewhat "proud" to know straight off what a cofferdam was (since I am not a native english speaker, as you know), but then it struck me, I only knew because I had been readong about the Dashews FPB 64 in detail. Turns out it was pure luck, haha.

[expedition]

Hi Guillermo,

Yes, I see your point of course. My concern was how to assure corrosion protection in a space that's unaccessible but the solution to that can be VpCI's (vapor phase corrosion inhibitors).

I actually spoke with a G/L surveyor yesterday and he said I should call it some thing different than cofferdam and then I would be OK. At any case, I'll wait for the final word on that from Hamburg...