Instructions:
1.
The first part of this lab consists of a prelab that covers the theory that will be examined experimentally during the lab.
2.
3.
The prelab is to be completed and handed in to your instructor at the beginning of the lab period.
If you can, answer the questions without referring to your notes. Only refer to your notes if you are confused or fail to understand a concept. This will greatly improve your understanding of the concepts this lab is designed to reinforce. Remember you will have no notes during quizzes, tests, and exams.
4.
5.
By conscientiously completing this prelab, you will have a thorough understanding of what the lab is trying to show. Your lab performance will be maximized.
For full credit, all work must be shown on your lab. This means that you must show generalized equations, substitution of numbers, units, and final answers. Engineering is communication. Work that is neat and shows logical progression is much easier to grade.
Student Information:
Name: ___________________________
Section: __________
Date: ____________
EN400 Lab 5 1 Lab #5

Apparatus:
1.
The apparatus used in this lab is exactly the same as for Labs 3 and 4. In this lab the curve of intact static stability will be constructed for three conditions:

A single compartment free surface tank held within the model’s central compartment.

A double compartment free surface tank held within the model’s central compartment.

A single compartment free surface tank combined with a transverse weight shift.
2.
In this lab a free surface will be produced using half-full tanks of dyed water. The effect that the free surface has on the curve of intact static stability will be measured and compared with the normal loading condition. It is possible to predict this effect by an analysis of the heeling ship shown in Figure 1.
M

M

S
G
0
Z
0
B g
0 g
1
F
B
WL

S

G
0
F
B
3.
a.
b.
Figure 1 – Ship heeling with partially filled tank
On the enlarged view of the heeling diagram in Figure 1, sketch the following:
The approximate location of the center of gravity of the ship created by the movement of fluid in the tank from
The new righting arm G
1
Z
1
.
g
0 to g
1
. Label this centroid G
1
.
Z
0
B
EN400 Lab 5 2 Lab #5

4.
5.
6.
With reference to Figure 1: a.
What would happen to the location of amount to port?
G
1 if the ship were heeling by an equal
______________________________________________________________ b.
Would the overall stability be the same or different for starboard or port heeling?
______________________________________________________________
From Figure 1, free surface can also be seen as virtual rise of the ship’s center of gravity,
G
V
, although the free surface actually causes a transverse shift in the center of gravity.
Label the virtual center of gravity, G
V
, corresponding to the transverse weight shift caused by the free surface.
The distance G
0
G
V is the virtual rise in the center of gravity and is called the “free surface correction” (FSC), give the equation for the free surface correction.
7.
Most ship tanks have rectangular cross sections, find the equation for the 2 nd area about the tank centerline, ( i t
).
moment of
8.
The distance G
V
M is called the “effective metacentric height” (GM eff
), and the ship will exhibit stability characteristics as if this were its real metacentric height.
Write the expression for the effective metacentric height (GM eff
) in terms of KM
T
, KG, and FSC in the box below.
11.
If the tank in Figure 1 were divided longitudinally into two tanks, how would this affect the effect of the free surface?
________________________________________________________________________
________________________________________________________________________
EN400 Lab 5 3 Lab #5

12.
In the box below, write an expression for the effective metacentric height if the single tank in Figure 1 were divided longitudinally into two separate tanks ( tank 1 and tank 2 ).
13.
In Lab 5 you saw the effect that a transverse shift in the center of gravity had on the model’s stability characteristics. What effect would a transverse shift in the center of gravity combined with a free surface have on the stability of a ship?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Remember that you should use the same 27-B-1 model for all your labs.
a.
b.
c.
d.
From Lab 4 (step 4) obtain the values for
 normal in step 4 of this lab.
and KG normal and insert this data
From Lab 4 (step 6) obtain the righting arm for 0, 15, 30, and 45 degree heeling angles and insert this data in step 6 of this lab.
From Lab 4 (step 14) obtain the listing angle produced by the transverse shift of the 1.5 lb weight. This data will be used in step 19 of this lab.
You will need to plot the curve of intact static stability for the model in its normally loaded condition for this lab. This data was calculated in Lab 4. This plot is required to compare the stability characteristics of the model in its normally loaded condition and its characteristics with a free surface.
EN400 Lab 5 4 Lab #5

3.
4.
Instructions:
1.
This lab is conducted in the Hydromechanics Lab on the ground floor of Rickover Hall.
2.
Prior to arriving in the Hydro Lab, read through the lab procedure so that you are familiar with the steps necessary to complete the lab.
You will need to bring this handout and a calculator to the lab.
The lab is to be performed in small groups of 2 or 3. Your instructor will specify whether the group or each individual must submit the completed lab.
5.
6.
7.
Follow the stages of the lab in consecutive order. The lab follows a logical thought pattern and jumping ahead without completing the intervening theory questions will limit your understanding of the concepts covered.
For full credit, all work must be shown on the lab. This means that you must show generalized equations, substitution of numbers, units, and final answers.
Keep your workstation (including the floor) clean and dry. Ensure all equipment and the models are returned to their original location when you complete the lab.
Student Information:
Name: _________________________________
1 st
Partner: ______________________________
2 nd
Partner: ______________________________
Date: ___________
EN400 Lab 5 5 Lab #5

Setup
1.
Before beginning the experiment, ensure you are using the same model hull number as in
Labs 3 and 4.
2.
3.
27-B-1 model number = ________________________
You should have three different tanks at your work station: the solid floored tank, a single compartment free surface tank, and a double compartment free surface tank.
For accurate comparisons to be made between the normally loaded condition and these three conditions (single, double, and damaged), the model must have approximately the same displacement and same KG at zero degrees of heel as the model in its normally loaded condition. Using the scale find the weight of the 3 tanks and complete the table below.
Tank
Weight (lb)
Solid Floor Single Compartment Double Compartment
From the geometry of the three tanks would you estimate their centers of gravity to be in the same location or in different locations?
________________________________________________________________________
4.
Before beginning the series of measurements, the displacement and KG of the normally loaded model as determined in Lab 4 should be recorded below:
Normally Loaded
Condition
 normal
(lb) KG normal
(in)
Single Compartment Free Surface Condition
5.
Calculate the free surface correction (FSC) with the single tank compartment.
EN400 Lab 5 6 Lab #5

6.
Calculate the effective metacentric height, GM eff
, with the single tank compartment.
7.
Calculate the expected righting arm using the free surface correction for the single compartment.
Angle of Heel

(Degrees)
0
15
30
45
Normally Loaded
Righting Arm
(in)
Free Surface
Correction
[FSC*sin(

)]
(in)
Corrected Righting
Arm
(in)
8.
Configure the model in its single compartment condition as follows: a.
b.
c.
Single compartment free surface tank in the model’s center compartment. Ensure the compartment’s hatch cover is securely fastened.
4 x 0.2 lb weights on the aft centerline post.
Inclinometer mounted on the weather deck.
9.
Place the model in the tank so that the pins are inserted into the tracks at each end of the tank. Set up the heeling apparatus.
10.
Data collection can now begin.
a.
b.
With the wire slacked, adjust the transverse weights to ensure zero list angle.
Heel the model to starboard in 5 degree increments until capsize, and record the force in the wire. Ensure you note the angle at which the model capsizes.
EN400 Lab 5 7 Lab #5

Starboard Measurements
Angle of
Heel
(degrees)
Force in the Wire
(lb)
Righting
Arm
(inches)
Starboard Measurements Continued
Angle of
Heel
(degrees)
Force in the Wire
(lb)
Righting
Arm
(inches)
11.
How has the presence of a free surface affected the model’s stability?
________________________________________________________________________
12.
What happened to the center of gravity to cause this decrease in stability?
________________________________________________________________________
13.
Do your calculated righting arms agree with your experimental results? Why or why not?
______________________________________________________________________
______________________________________________________________________
Double Compartment Condition
14.
Calculate the Free Surface Correction (FSC) with the double tank compartment.
EN400 Lab 5 8 Lab #5

15.
Load the double tank compartment in the model. Now calculate the effective metacentric height, GM eff
, with the double tank compartment.
16.
With the double compartment tank installed in the model’s center compartment and deck weights on the centerline post, heel the model to starboard and record heeling data in the table below. Ensure you record the capsize angle.
Starboard Measurements
Angle of
Heel
(deg)
Force in the Wire
(lb)
Righting
Arm
(in)
Starboard Measurements Continued
Angle of
Heel
(deg)
Force in the Wire
(lb)
Righting
Arm
(in)
17.
Compare the stability for the model in the normally loaded, single compartment, and double compartment conditions.
Condition
Starboard Heel Stability Comparison
Normally Loaded Single
Compartment
Double
Compartment
Range of Stability
(degrees)
Maximum Righting
Arm (inches)
Maximum Righting
Moment (in-lb)
Angle of Maximum
Righting Arm (deg)
18.
In which condition is the model most stable? ___________________________________
Why? __________________________________________________________________
EN400 Lab 5 9 Lab #5

19.
In which free surface condition is the model more stable? _________________________
Why? __________________________________________________________________
DAMAGE STABILTY
One of the worst scenarios for ship damage with respect to stability is the presence of a partially flooded compartment off centerline. The combined effect of a transverse weight addition and the free surface effect results in an exaggerated list angle and a dramatic decrease in overall stability.
20.
To model an off-centerline free surface, configure the 27-B-1 model as follows: a.
b.
Place the single compartment free surface tank in the model’s center compartment.
Place the 4 x 0.2 lb weights on the starboard weight post.
21.
Record the model’s initial angle of list in the damaged condition: _____ How does this compare to the angle of list in Lab 4? _________________________________
________________________________________________________________________
22.
Heel the model through its range of stability to find its curve of intact static stability in the damaged condition and record heeling data in the table on the following page. Do only starboard heeling angles.
Starboard Measurements
Angle of Force in Righting
Heel

(degrees) the Wire
F wire
(lb)
Arm
GZ
(inches)
Starboard Measurements Continued
Angle of Force in Righting
Heel

(degrees) the Wire
F wire
(lb)
Arm
GZ
(inches)
EN400 Lab 5 10 Lab #5

23.
From your data, complete the following table.
Condition
Range of Stability
(degrees)
Maximum Righting
Arm (inches)
Maximum Righting
Moment (in-lb)
Angle of Maximum
Righting Arm (deg)
Starboard Heel Stability Comparison
Normally
Loaded
Single
Compartment
Damaged
Condition
24.
How has the off-center damaged condition affected the model’s stability?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Counterflooding, the intentional flooding of a tank or compartment, is occasionally used in response to damage; however, counterflooding can render the ship even less stable.
Based on your knowledge of hydrostatics and ship stability, describe the possible positive and negative effects of counterflooding on ship survivability?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
25.
Plot your righting arm data for the normal, single (calculated and experimental), double, and damaged compartment using Excel.
Label your title, axes and data correctly .
EN400 Lab 5 11 Lab #5