Hydrostatic Report
CHAPTER 10
LONGITUDINAL STABILITY AND TRIM
A ship floating at equal draught all along is said to be on an even keel, or to have zero trim. If the fraughts are not the same from bow to stern, the ship is floting with a trim. Deeper draughts aft than forward result in trim by the stern. If the draught forward exceeds the draught aft, the condition is called trim by the head or bu the bow. The measure of the amount of trim is simply the difference between the after and forward draughts.
Figure 10.1.
Two waterlines (or waterplanes) are shown on the ship in Figure 10.1; a trimmed waterline (W1L1) and the even keel waterline (WL) corresponding to the same displacement. They are shown intersecting at the centre of flotation of the even keel waterplane. The quantities shown in the figure are defined as follows
Centre of Flotation (F): Geometric center of the ship's waterline plane. The ship trims about this point. May be forward or aft of the midships depending on the ship's hull shape at the waterline.
Longitudinal Centre of Flotation (LCF) : Distance from the centre of flotation (F) to the midships. Used to distribute changes of trim between the fwd and aft draughts.
Trim (t) : The difference between the forward and after draughts
Parallel Rise/Sinkage (PR/PS): When weight is removed/added from/to a ship at LCF, the forward and aft drafts will change by the same amount.
Change in Trim (CT): The sum total of the absolute values of the change in forward and after drafts.
Trimming Arm (TA): The distance from the center of gravity of the weight to the LCF. If the weight is shifted, TA is the distance shifted.
Trimming Moment (TM): Moment about the LCF produced by weight additions, removals, or shifts (wd), where w is the amount of weight added, removed, or shifted.
Moment to Trim One cm (MT1cm): The moment necessary to produce a change in trim (CT) of one cm. Found using the hydrostatic curves.
Tons Per cm
LONGITUDINAL STABILITY AND TRIM
A ship floating at equal draught all along is said to be on an even keel, or to have zero trim. If the fraughts are not the same from bow to stern, the ship is floting with a trim. Deeper draughts aft than forward result in trim by the stern. If the draught forward exceeds the draught aft, the condition is called trim by the head or bu the bow. The measure of the amount of trim is simply the difference between the after and forward draughts.
Figure 10.1.
Two waterlines (or waterplanes) are shown on the ship in Figure 10.1; a trimmed waterline (W1L1) and the even keel waterline (WL) corresponding to the same displacement. They are shown intersecting at the centre of flotation of the even keel waterplane. The quantities shown in the figure are defined as follows
Centre of Flotation (F): Geometric center of the ship's waterline plane. The ship trims about this point. May be forward or aft of the midships depending on the ship's hull shape at the waterline.
Longitudinal Centre of Flotation (LCF) : Distance from the centre of flotation (F) to the midships. Used to distribute changes of trim between the fwd and aft draughts.
Trim (t) : The difference between the forward and after draughts
Parallel Rise/Sinkage (PR/PS): When weight is removed/added from/to a ship at LCF, the forward and aft drafts will change by the same amount.
Change in Trim (CT): The sum total of the absolute values of the change in forward and after drafts.
Trimming Arm (TA): The distance from the center of gravity of the weight to the LCF. If the weight is shifted, TA is the distance shifted.
Trimming Moment (TM): Moment about the LCF produced by weight additions, removals, or shifts (wd), where w is the amount of weight added, removed, or shifted.
Moment to Trim One cm (MT1cm): The moment necessary to produce a change in trim (CT) of one cm. Found using the hydrostatic curves.
Tons Per cm