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: 1st 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 (-)

Second trim correction

This is correction for the shift of the center of flotation (LCF), which occurs as the vessel changes its trim. The position of the LCF, as specified in the hydrostatic particulars, is normally for the even keel condition. The draught at the final position of LCF is required.

Metric: 2^nd trim correction (in meters) =trim (m) x (MCTC2 – MCTC1)

2 x TPC x LBP

Where : MCTC2 = MCTC for the draught at the AP

MCTC1 = MCTC for the draught at the FP,

Or vice versa when trimmed by the head.

However the 2^nd trim correction is normally calculated in tones as follows:

2^nd trim correction (in tones)=50 x trim2 (m) x MCTC2-MCTC1)

LBP

Where : MCTC2 = MCTC for mean adjusted draught +50cm

MCTC1 = MCTC for mean adjusted draught –50cm.

Imperial: 2^nd trim correction (in tons) =6 x trim2 (ft) x (MCTI2-MCTI1)

LBP

Where : MCTI2 = MCTI for mean adjusted draught +6in.

MCTI1 = MCTI for mean adjusted draught –6in.

Sign convention : always positive (+).