Oil Tank Barge - from existing single hull to double hull conversion

Good PM.

Just wanted ask some few advice.

from the attached pic, you can see i intend to convert a single hull barge to a double hull. (tank barge).

concerning the Inner Bottom Longitudinal (existing member)

from ABS rules. attached file

under requirement of "h"

- distance in meters (feet) from the inner bottom to the following point....

* as defined in 5-2-1/3 for cargo or ballast tank...

***since the inner bottom long'l (existing part) will be inside the cargo tank.

now the question is what if the existing would-be inner bottom long does not comply with the abs requirement of with use scantling head as "h".

from scantling calc of the "inner bottom long" showing:

SM top = 5.585 cu. inch
SM Bottom = 26.474 cu. inch

while using the scantling head from the requirement giving me a
5.963 cu. inch

well just asking and its obvious i cant use the other requirement for "h"
which is ... ***deck at sides amidship for "void space". though it will give me a shorter "h" compare to the scantling head.

what are thoughts?

thanks.

 

According to the ABS Rules, you can't assume h is measured from the longitudinal to the deck at sides amidships, because presumably, the cargo tanks are fitted with some sort of vent or a system which catches any cargo overflows. The tank scantlings must be strong enough to withstand the additional load if the cargo level goes above the top of the tank.

However, since the longitudinals almost meet the SM requirements of the Rules, you have two choices here. You can either:

1. fit additional longitudinals, in order to reduce the transverse spacing, or

2. you can add brackets to the longitudinals at each transverse frame and tank bulkhead.

If brackets are already fitted, they may have to be increased in size, so that the length of the unsupported span of the longitudinals is reduced. Since the Rule SM varies as the span squared, only a small reduction in span may be necessary to bring the existing longitudinals into compliance with the ABS scantling Rule SM.

 

Thnks NavalSArtichoke.

it never came to my mind that just simply adding a bracket can do the trick.

though from bhd to bhd there are already existing brackets installed, will add some on the transverse to transverse to reduce unsupported span.

thanks sir will keep you updated once i finish the additional bkts.

 

Just keep in mind that the length of the unsupported span extends about 25% of the length of the bracket from the toe end.

You can take the actual SM of your longitudinal and use the Rule formula to work back and find out what the maximum unsupported length can be, and design your brackets accordingly.

 

Good AM.

ive added a 8x7x3/8 thk BKT. per transverse frame.

at tank bhds existing brackets are already installed.

ive also attached some pic as reference from your advice.

SM requirement has gone down to 4.44 cu. inch after adding of brackets
versus the SM of the exist long'l of 5.585 cu. inch.

Many thanks!

ps. more likely on the existing side long'l, same situation may come up, anyway the proper approach for this one has been cleared. :idea:

 

I'm glad things worked out for you. Good Luck with the rest of the barge.

 

Just a brief comment, if it helps: when the console is too big, should have a flange. The regulations indicate when the flange must be placed and its dimensions.

 

TANSL, it's not clear what you mean by "console" here, unless you mean "bracket".

 

Sorry, you are right, I mean bracket.

 

Good AM.

point taken sir's,

I've re-sized the bracket to 8.5" x 7" x 5/16" - it gives a face length of 7"+

with respect to the regulations since it does not exceed the 12" face length it is not required for a bended or attached flange.