Inclining Experiment Flashcards
What is the purpose of the inclining experiment
To determine the GM of a vessel in its lightship condition. From this you can obtain the light KG. This value is then used as a point of reference when loading the ship, for establishing the ‘in-service’ stability.
Define Lightship Condition
What items are consider part of Lightship?
A ship complete in all respects, but without consumables, stores, cargo, crew and effects, and without any liquids on board except that machinery and piping fluids, such as lubricants and hydraulics, are at operating levels.
- Water in boilers (including FSM)
- Fluid in pipes
- ER spares attached to ship (e.g. spare piston) but NOT stores (e.g. nuts, bolts)
Where can I find the guidance for conducting a Inclining experiment?
Intact Stability Code Annex 1
How do you manage Free Surface for the test?
- Free Surface should be minimise as much as possible.
- Preferably all tanks are emptied and stripped dry.
- If they cannot be emptied then pressed up to 100% full, air pockets eliminated and weight/ centre of liquid accurately determined.
- If a tank has to be left slack then it should be a tank where FSM can be accurately measured.
- A slack tank should be between 20%-80% (if it’s a deep tank) or 40%-60% (DB tank). So, that the shifting of liquid is constant and there is no pocketing.
Important factors to consider in relation to the mooring arrangements for the experiment?
Depth of water
- Sufficient UKC, when vessel is listed max draft will increase
Tide
- If area is tidal then mooring lines could come under tension and influence the experiment
- If the lines are slack then the vessel could surge creating an external heeling moment and invalidate the results.
Lines
- Lines should be slack to allow free movement of the vessel
- Minimum lines required to safely hold the vessel alongside
Important information to know about test weights?
Describe there how they are used before, during and after the test?
- Weight of tests weights must be known and accurate.
- Onboard prior to test and placed evenly so vessel is upright and their initial position recorded.
- Shifted transversely to provide a list, distance from the Centreline must be measured.
- Weights are considered deadweight and should be included as an item to be discharged in the Inclining report.
How do you set up a pendulum for the Experiment?
- They can be placed anywhere around the ship.
- Length of pendulum should be long enough to give a measured deflection of 15cm. This will generally require a length of at least 3m.
- The length of pendulum must be known to calculate the GM
- A batten should be placed near the pendulum so the deflection can be clearly read.
- A winged pendulum weight should be connected to the bottom submerged in a trough of oil or water to help dampen the oscillations after each movement.
- There should be at least two pendulums to gain reliable data.
- U-Tube or Inclinometer could also be used used in but only in conjunction with a pendulum.
- Vessel with a small GM it may be difficult for a pendulum with a long length to settle
- Vessel with a high GM an extra long pendulum might be required to obtain the minimum deflection.
Describe the test procedure for the Inclining Experiment?
Initial Survey
- Ensure the vessel is complete enough to do the test.
- Inventory of all items that need to be loaded, discharged and shifted. There TCG, LCG and VCG should all be recorded.
- Ensure all loose items are secured
- Inventory of tanks and there condition (slack, empty, pressed up)
- Bilges are dry, to avoid the introduction of unknown FSM as this will give an inaccurate result.
- Number of people onboard for the test should remain constant
Draught Survey
- All six draughts should be taken or five freeboards evenly spaced
- Draught tube can used to accurately measure the draught in choppy water.
- Specific gravity of water taken
Test
- Eight distinct weight movements taken
- Weight should be able to provide a minimum of 1°and maximum of 4° of heel. ∴ M is considered constant
How do you estimate for unknown weights onboard or unknown weights that still need to be loaded?
Estimate on the safe side using these rules of thumb;
- when estimating weights to be added:
- estimate high for items to be added high in the ship
- estimate low for items to be added low in the ship - when estimating weights to be removed
- estimate low for items to be removed from high in the ship
- estimate high for items to be removed from low in the ship - when estimating weights to be relocated
- estimate high for items to be relocated to a higher point in the ship
- estimate low for items to be relocated to a lower point in the ship.
What is on the y-axis of the plot?
What is on the x-axis of the plot?
y: Weight of object (test weight) x distance from centreline
x: tangent of the heel angle.
tanΘ = deflection of pendulum / length of pendulum
What are the factors to consider with the inclining experiment graph?
- W(x)/tanΘ is constant so the plotted line should be straight. Deviations from the straight line is an indication that there are other moments acting on the ship during the inclining.
Who is required to have an inclining experiment?
- All pax ships.
- All cargo ships over 24m.
- All new builds.
- Any alterations made that materially affect the stability, the ship should be re-inclined.
Pax Ships Additional
- A lightship survey not exceeding 5 years.
- If the Light △ ± 2% or LCG ± 1% then the ship should be re-inclined.
How could the weather conditions affect the test?
- inability to accurately record freeboards and draughts
- excessive or irregular oscillations of the pendulums
- variations in unavoidable superimposed heeling moments.
- Surveyor may discontinue the experiment and reschedule the date
What factors could change a vessels lightweight and or LCG over its lifetime?
Weights being added to vessel by way of:
- Heavier / lighter anchors
- Changes in length of anchor cable
- Changes in deck equipment / ER equipment
- Extra Cranes / derricks
- LSA and FFA changes (L rafts, L boats, Foam tanks, CO₂ tanks)
- Structure added / removed
- Main Engine changed
- Propeller or rudder changed
- Stores and Spare parts
- Lengthening of hull
wastage of steelwork / accumulation of sediment in ballast tanks (particularly ends of vessel, peak tanks)
- Marine growth
- Removal of rust
What information should be provided the Master?
A report of the inclining experiment.
