Trim

Home
Flashing Light
Watch Training Workbook
Campus Life
The Joe Show
Deck Skills
Cruise
Navigation
Celestial Nav.
Radar
Meteorology
Ship Structure
Stability
GMDSS
Rules of the Road
Marlinespike
Ship and Cargo Ops.
Shipping Info
FAQs
Shanties and Sea Lore
Terms/Acronyms
World Port/Drink Guide
Forum

Because It's Not Only The Mates That Are A Bit Tipsy

Step 1: Calculate individual and total moments and total displacement using Sheet 7a.

Step 2: Find Mean SW Draft,  LCB, LCF-FP, and MT1 with Deadweight Scale and enter into Sheet 7a.

Step 3: Calculate LCG-FP by dividing total moments by total displacement; (moment/weight=distance). Enter into Sheet 7a

Step 4: Find the difference between LCG-FP and LCB and enter as Trim Lever in Sheet 7a. If LCG is greater than LCB, the trim will be down by the stern. If LCB is greater than LCG, the trim will be down by the head. If it helps, draw a picture along the outline of the ship. Both measurements are from the Forward Perpendicular; LCG is a downward force and LCB is an upward force. If the downward force is farther aft than the upward, the stern will be lower than the bow.

Step 5: To find change in trim, multiply Trim Lever by total Displacement and divide that by the Moment to Trim One Inch.

Step 6: To find your new drafts, apply half of the change in trim to the forward and after drafts. If you found in Step 4 that you are moving down by the head, add half the change in trim from the Mean SW Draft and enter as FWD Draft. If you are moving up by the head, subtract the change in trim from the Mean SW Draft and enter as FWD Draft. For whatever you do on the bow, do the opposite for the stern, (if bow goes up, stern goes down).

Moments
Weights x Distances (ft-tons)

LCG - FP
Distance to Longitudinal Center of Gravity, measure from the Forward Perpendicular aft. Equivalent to Total Moments / Total Displacement
LCB
Distance to Center of Buoyancy, measured from the Forward Perpendicular aft. Found on Deadweight Scale.
Trim Lever (fwd or aft)
Difference from LCG to LCB. If LCG is greater, change in trim is down by the stern. If LCB is greater, change in trim is down by the head.

Trim In Inches (fwd or aft)
Equivalent to (Trim Lever x Total Displacement)/MT1. Final units will be in inches of trim.

 
Initial FWD Draft (ex. 26-00)
Initial Midships Draft (ex. 26-00)

Initial AFT Draft (ex. 26-00)

1/2 Trim
Correction (ex. -06)
Correction; if no sink/rise, midship draft will not change.

Correction (ex. +06)

Final Drafts
Final FWD Draft (ex. 25-06)
Final Midship Draft (ex. 26-00)

Final Aft Draft
(ex. 26-06)