Method 3 alternative 1.The extracted factor can be used directly to determine a correction in tones to apply to the final displacement.
Correction (tone) = factor x TPC x hog/sag (cm)
Where: hog/sag (cm) = (DMAMD) x 100
Method 3 alternative 2.
The graph or table itself may be adapted to give a correction table directly in tones (i.e. factor X TPC) for each centimeter of hog or sag. This would give a correction to apply to the final displacement by entering the table with the AMD and the hog/sag in CMS.
Other alternative methods.
These require additional draught/freeboard measurements at points other than perpendiculars and midships, along the vessels length. This is very difficult to establish.
CORRECTION FOR TRIM
There may be a total trim correction table included in the stability information book. This will normally combine the following 1^{st}.and 2^{nd}.corrections. Find out what it includes, and examine the ships stability data carefully before conducting a survey.
First trim correction (Correction for Layer)
The displacement scale is normally calculated on the assumption that the vessel is lying on an even keel. The first trim correction is to correct the draught midships to the true mean draught, at the center of flotation. This correction is known as the correction for layer (or layer correction).
AP Midship FP
W1
LCF
W L
Layer Correction Trim
TMD
TMD
L1
LBP
AP aft perpendicular FP forward perpendicular
TMD true mean draught AMD arithmetical mean draught corrected for hog or sag
LCF longitudinal center of flotation LBP length between perpendiculars
Layer correction (metros) = (distance LCF to midships) x trim/ LBP
Then TMD = AMD +/ layer correction
1^{st} trim correction (tones) = layer correction x TPC x 100
Metric: 1^{st} trim correction (distance LCF to midships) x TPC x trim (cm)
LBP
Imperial: 1^{st} trim correction (distance LCF to midships) x TPI x trim (inches)
LBP
Actual displacement = tabulated displacement +/ 1^{st} trim correction
Sign convention: Trim LCF forward of midships LCF aft of midships
Aft negative () positive (+)
Forward positive (+) negative ()
Date: 20160103; view: 613
