Principles of naval engineering - Historic Naval Ships Association

; onChapter S-STABILITY AND BUOYANCYMaximum righting arm AB.Angle of maximum righting arm at A.Range of stability 20° to 50°.Total dynamic stability is representedby the lined area.The ship will have a permanent list at 20 °ch is the angle where B is under G, inclining1 equals original righting arm, cosine curvesses original GZ curve, and residual rightarmis zero. In a seaway the ship will rollut this angle of list. If it rolls farther to theed side, a righting moment develops whichis to return it toward the angle of list. If•oils back towards the upright, an upsettingnent develops which tends to return it todthe angle of list. The upsetting moment;ween ° and the angle of list) is the differebetween the inclining and righting moments.GONAL WEIGHT SHIFTA weight may beshifted diagonally, so thatnoves up or down and athwartship at thele time, or by moving one weight up or downanother athwartship. A diagonal shift shouldtreated in two steps; first by finding the ef-GM and stability of the vertical shift,second, by finding the effect of the horitalmovement. The corrections are appliedjreviously described.EFFECTS OF WEIGHT CHANGESThe additional removal of any weight in aD may affect list, trim, draft, displacement,and stability. Regardless of where the weightis added (or removed), when determining thevarious effects it should be considered firstto be placed in the center of the ship, thenmoved up (or down) to its final height, nextmoved outboard to its final off-center location,and finally shifted to its fore or aft position.Assume that a weight is added to a ship sothat the list or trim is not changed, and G willnot shift. The first thing to do is find the newdisplacement, which is the old displacementplus the added weight:whereNew displacement = W +w tonsW = old displacement (tons)w = added weight (tons)With the new value of displacement, enter thecurves of form and on the displacement curvefind the corresponding draft, which is the newmean draft. Figure 3-25 shows typical displacementand other curves generally referred toas curves of form.If the change in draft is not over 1 foot, theprocedure can be reversed. Find the tons-perinchimmersion for the old mean draft fromthe curves of form, divide the added weight(in tons) by the tons-per-inch immersion inorder to get the bodily sinkage in inches, andadd this bodily sinkage to the old mean draftto get the new mean draft. Using the new meandraft, enter the curves of form and find thenew displacement.2