Presentation Transcript
STABILITY :STABILITY
FIRST PRINCIPLES :FIRST PRINCIPLES BUOYANCY
CENTRE OF GRAVITY
RIGHTING FORCE
FACTORS WHICH CAN CAUSE CAPSIZE
CBCentre Of Buoyancy :CBCentre Of Buoyancy Force generated by boat displacing water
CB is point of concentration of this force
Changes with HEEL ANGLE, TRIM and LOADING CB
CG Centre of Gravity :CG Centre of Gravity Determined by structure and weight distribution of boat
Best when it is low down
GZ The Righting Lever :GZ The Righting Lever Force that combination of CG and CB make, to return boat to the upright. CG CB GZ
RM Righting Moment :RM Righting Moment Mass (Weight and volume) of boat affects stability
When multiplied with GZ it gives RM CB GZ X mass = RM
ANGLE of HEEL :ANGLE of HEEL As boat heels more, RM becomes greater RM
POINT OF VANISHING STABILITY :POINT OF VANISHING STABILITY RM is ZERO
BOAT INVERTS CB
RIGHTING MOMENT CURVE(Flat Water) :RIGHTING MOMENT CURVE(Flat Water)
DIFFERENT TYPES OF CURVE :DIFFERENT TYPES OF CURVE
DESIGN CATEGORIES :DESIGN CATEGORIES CATEGORY TYPE WIND FORCE WAVE HEIGHT A OCEAN >F8 >4M B OFFSHORE F8 4M C INSHORE F6 2M D SHELTERED WATERS F4 0.5M
CATEGORIES :CATEGORIES
RE-RIGHTING :RE-RIGHTING A = Re-righting factor
B
If it is large then
re-righting is good
RE-RIGHTING FACTORS :RE-RIGHTING FACTORS Type A will be harder to re-right than type B
A’s re-righting factor is lower than B’s
FACTORS THAT CAN CAUSE CAPSIZE :FACTORS THAT CAN CAUSE CAPSIZE SWAMPING OR FLOODING
FREE- SURFACE EFFECT
LARGE BREAKING WAVES
CG MOVED UPWARDS
RESONANT ROLLING
BROACHING
FACTORS WHICH CAN IMPROVE STABILITY (1) :FACTORS WHICH CAN IMPROVE STABILITY (1) INCREASED LENGTH
HEAVY DISPLACEMENT FOR SIZE
HIGH PROPORTION OF OVERALL WEIGHT AS BALLAST
HIGH ANGLE OF VANISHING STABILITY
HIGH RE-RIGHTING FACTOR
GOOD RM AT 90° OF HEEL
MODEST BEAM IN RELATION TO LENGTH
FACTORS WHICH CAN IMPROVE STABILITY (2) :FACTORS WHICH CAN IMPROVE STABILITY (2) GOOD BUT NOT EXCESSIVE FREEBOARD
MINIMAL TOPSIDE FLARE
ABSENCE OF LARGE NEARLY FLAT AREAS OF DECK
LARGE ANGLE OF HEEL BEFORE FLOODING CAN OCCUR
INCREASED KEEL PROFILE AREA
ABSENCE OF BULWARKS
IN ROUGH WEATHERDO :IN ROUGH WEATHERDO CLOSE HATCHES, WASH BOARDS ETC.
PUMP OUT BILGE REGULARLY
WATCH OUT FOR GUSTY CONDITIONS
AVOID BEING CAUGHT BEAM ON TO LARGE, BREAKING WAVES
BE AWARE OF CATEGORY AND CAPABILITY OF YOUR BOAT
IN ROUGH WEATHER DO NOT :IN ROUGH WEATHER DO NOT SAIL IN CONDITIONS THAT ARE OUTSIDE THE CAPABILITY AND CATEGORY FOR WHICH YOUR BOAT WAS DESIGNED
DELIBERATELY SAIL THROUGH KNOWN TIDAL RIPS, RACES, OVERFALLS OR WHERE THE BOTTOM SHOALS RAPIDLY