Slide1: DYNAMIC STABILITY LT Tom DeNucci (860) 444-8672


Slide2: G Station Coos Bay 47’ MLB training Nov 1999


Dynamic Stability Objectives: Dynamic Stability Objectives Understand heeling moments Determine dynamic stability Determine max roll from righting and heeling moment curves Understand the Navy Criteria for dynamic stability


Heeling Moments: Heeling Moments Moments of forces are what cause a ship to heel, list, return to equilibrium or capsize. A righting moment tends to rotate a vessel towards its initial position A heeling moment tends to rotate a vessel away from its initial (stable) position. Causes of heeling moments Off-Center Weights Beam Winds Off Center Weights (Weights over the side) High Speed Turns Crowding of passengers Icing


Heeling Moment Curve: Heeling Moment Curve Plot of the Heeling Moment versus angle of heel, for any externally applied force. Heeling Moment curves usually start at a maximum value, and then decrease to zero at 90 degrees of heel.


Slide6: Angle of Heel Heeling Moment Curve (From - wind, turns, etc.) Moment


Static Stability Curve: Static Stability Curve Area under the curve represents work performed to heel the ship and stored energy available to return the ship to 0.


Righting Moment Curve: Angle of Heel Righting Moment Curve Righting Moment Curve Moment


Slide9: Angle of Heel Heeling Moment Curve Moment Righting Moment Curve


Slide10: Angle of Heel Moment Excess Heeling Energy


Slide11: Angle of Heel Moment Excess Heeling Energy Excess Righting Energy


Slide12: Angle of Heel Moment Excess Heeling Energy Excess Righting Energy Max Angle of Roll The ship will roll until excess heeling energy equals excess righting energy


Slide13: Angle of Heel Moment Excess Heeling Energy Excess Righting Energy Max Angle of Roll Static Angle of Heel If everything stays constant, the ship will settle out to a constant angle of heel


Slide14: Angle of Heel Moment Excess Heeling Energy Excess Righting Energy Excess heeling energy greater than excess righting energy Ship will capsize


CGC JARVIS - November 15, 1972: CGC JARVIS - November 15, 1972 Prior to damage Added weight only Added weight & Free Surface Effect Dynamic Stability curve


CGC JARVIS - November 15, 1972: CGC JARVIS - November 15, 1972 Prior to damage Added weight only Added weight & Free Surface Effect Max roll Dynamic Stability curve Heel


U.S. Navy Criteria: U.S. Navy Criteria In 1960’s, U.S. Navy developed dynamic stability design criteria for their ships Compares energy used to heel the ship to energy available to right the ship Applies a safety factor to ensure positive dynamic stability Similar criteria used by shipbuilders worldwide


U.S. Navy Criteria: U.S. Navy Criteria Navy criteria addresses specific hazards We’ll briefly look at criteria for: Beam winds with rolling Operating with a weight over the side High speed turns Crowding of Passengers to one side


Beam Winds With Rolling: Beam Winds With Rolling DRAFT H - LEVER ARM (feet) - From Center of SAIL AREA to 1/2 DRAFT A - SAIL AREA (square feet) [cross-hatched area] Vw - VELOCITY of WIND in knots H HEELING ARM created by WIND = 0.004 V A H 2 w 2240 ² cos ø 2


Beam Winds With Rolling: Beam Winds With Rolling


Weight Over the Side: D D Weight Over the Side


Weight Over the Side: Weight Over the Side Stability Criteria: 1 (Angle of Heel at Point C)  15 A1 (Excess Righting Energy)  40% A2 (Total Righting Energy) c) Righting Arm at Point C (RA 1)  60% of Maximum Righting Arm (RA 2)


High Speed Turn: High Speed Turn


High Speed Turn: High Speed Turn Stability Criteria: a) 1 (Angle of Heel at Point C)  10 for Newly constructed ships 1 (Angle of Heel at Point C)  15 for Existing ships b) A1 (Excess Righting Energy)  40% A2 (Total Righting Energy) c) Righting Arm at Point C (RA 1)  60% of Maximum Righting Arm (RA 2) A1


Crowding of Passengers: Crowding of Passengers D


Crowding of Passengers: Crowding of Passengers Stability Criteria: 1 (Angle of Heel at Point C)  15 A1 (Excess Righting Energy)  40% A2 (Total Righting Energy) c) Righting Arm at Point C (RA 1)  60% of Maximum Righting Arm (RA 2)


87’ WPB addition: 87’ WPB addition Does this meet Navy Criteria? Not all the time!