# Calculations stability

DELFTship forum Hydrostatics and stability Calculations stability

• Author
Posts
• #38309
Tran Van Cua
Participant

Hello Everybody, I have a Ship with length = 21.0 meters, Beam = 5.9 metes, Height = 3.0 meters. Almost of all is normal, but when I calculations stability for it, Heel angle only is 0, 10, 20, it not larger.
Example: Displacement = 120, Hell angle is 0, 10, 20, it not larger.
Displacement = 60, Hell angle is 0, 10, 20, 30, 40, it not larger.
Displacement = 10, Hell angle is 0, 10, 20…..80, 90.
Is there anybody who can help???
CuaNTU

• #38319
Robert Holme
Participant

GM of 1.727m? are you sure this is not KM?

IIRC GM should vary with displacement and where in a vertical plane the weight is added or subtracted.

HTH

Regards
Bob

• #38320
Tran Van Cua
Participant

I mean, Heeling angle only full 0 – 90 when I calculator with Displacement is very small compare to Ship. if I calculator with right Displacement is heeling angle only 0 – 20.

• #38321
Tran Van Cua
Participant

• #38336
Sharat Jami
Participant

I think its a classic mix up which everybody experiences for the first time when they execute stability on any software.

The major idea of stability depends on buoyant hull which is considered, if there are any openings on the hull, the stablity GZ curve stops at that particular angle where the point gets immersed.

I am showing a case study for better explanation which was executed in Freeship GPL software. which is primitive version of Delftship.

A Box of dimensions L=21 m,B=5.9 m,D=1.5 m is submerged for a draft T = 0.5 which corresponds to Disp = 63.499 T,
stability is assessed for 2 cases. for constant draft/disp.

Case-1: Deck Surface closed.

GZ curve comes as follows:

Case-2: Deck Surface Open

GZ curve comes as follows: you can actually see a sudden collapse in GZ, that is because at that angle the water starts flooding inside thus changing the displacement, hence here a much advanced concept of dynamic stability including ingress of water is applied to predict stability.

Normally when performing intact stability check the body which is floating needs to be completely enclosed, a complete enclosure can be checked by an option called check model in delft ship. if leak points are observed your hull is open to flooding.

I hope i have solved the issue.

• #38337
Tim Stewart
Participant

Thank you jsharatchand, for taking the time to explain this.

Regards Tim