Free Surface Effect

Please Help. I Want Just To Clarify On How To Calculate The Free Surface Effect Of Liquid (s.w.) In A Certain Tank That Has Swash Bulkhead?

Say For Example The The Tank Dimensions, Length= 5m ; Breadth=3m
I Solve The Free Surface Moment Automatically By By Using (5)*(3^3)*(1/12)*(1.025). Not Considering The Factor Reduce By Swash Bulkhead.

Note: Swash Bhd Location - Mid. Long'l. Of The Tank


Your Kind Suggestion And Ideas Is Much Appreciated.

 

Are you looking for the moment shift (ultimate stability) or GM reduction (initial stability)?

For moment shift, you need to work up a set tank curves for all your stability angles (which will include heeled free surface at large angles of heel).

For initial GM reduction, the corrected inertia of the tank is (LB^3/12) divided by the specific volume (tonnes/m^3). The GM reduction for an individual tank is then the corrected inertia divided by the vessels volumetric displacement.

Generally, swash bulkheads are ignored. While they do have some effect on initial statbility at certian roll frequencies, those effects are tank capacity dependent. Swash bulkheads have on effect on ultimate stability. See Principles of Naval Architecture, Chapter 2, section 5, Effect of Free Liquids and Special Cargos.

 

Thank You So Much. Your Reply Helps A Lot To Answer My Doubt. Actually I Am Making Stability For A Floating Dock. As A Newly Grad. Naval Architect,,,i've Still To Learn More.

 

A floating Dry Dock? Or just a floating pontoon? FWIW, water balasting a floating pontoon that will have a live load (i.e. mooring loads, people or cargo handling) is a bad idea. Use solid ballast for that.

 

Yes a floating dry dock (100m x 32m) with 4 towers on its corner (fwd and aft). Although it's very tiring to my brain,,,i just consider it a challenge.

 

Jehardiman (post #2) is right.

 

Do not worry, a floating dock is like any other boat, with the advantage that their tanks are usually rectangular and it is much easier to define and calibrate. The hydrostatic curves and KN have discontinuity when the dock submerges its deck, but no calculation (to my knowledge) different or more difficult than, for example, a dredger when opens its bottom to discharge.
Cheer up, it's easy. If you have a program of naval architecture, the calculation is as fast as a traditional boat.

 

Yep, the hardest and most critical thing with a wing wall floating drydock is making sure the Tank Level Indicators (TLIs) work correctly. If they don't you can break the dock...or topple the docked ship...(and so in there hangs a tale...that I can't tell, LoL...) Just make sure they are working correctly and monitor their actual soundings ALL THE TIME!

 

Thank you so much for your ideas. I'm already done with my calculations.