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stability curves, understanding
- Thread starter tranmkp
- Start date
mistral
Senior Member
just few words on a very wide argument:
considering the "about sinusoidal" curve:
-the initial slope will tell how stiff is your boat; the steeper the curve the stiffer is your boat on little angle of heeling
-the Y-axis value on 30 degrees of heeling RM30 is traditionally considered as the projecting value to dimension the mast section
-the peak of the curve is the maximum righting moment of your boat
-the angle (approx 115 degrees, i guess) at wich curve came back to y=0 represent the angle of vanishing stability. Assume that your boat is knocked down by a wave, this would be the widest angle at wich you may hope that your boat recover to unheeled position by herself; at wider angle your boat will capsize.
-the area under the curve from 0° to 115° is the amount of energy required to capsize your boat, or, on the other side, your reserve of total stability
-the area from x-axis and lower part of the curves (from 115° to 180°) is the amount of energy required to restore your boat from a capsize.
A great book to understand this argument is "seaworthiness: a forgotten factor", by Tony Marchaj, very good and wide explanation of phenomenon but somehow anti-historical conclusion (just in my opinion of course
).
To spent some words on specific boat, generally speaking (i don't know the boat) I would expect a wider angle of vanishing stability for a 36' offoshore racer, 115° is not a huge value, and even most disappointing is the maximum negative value (at 155° heeling), this means than this boat is quite stable when capsized, it means that it's difficult that a wave can recover her after a capsize
fair wind
mistral
considering the "about sinusoidal" curve:
-the initial slope will tell how stiff is your boat; the steeper the curve the stiffer is your boat on little angle of heeling
-the Y-axis value on 30 degrees of heeling RM30 is traditionally considered as the projecting value to dimension the mast section
-the peak of the curve is the maximum righting moment of your boat
-the angle (approx 115 degrees, i guess) at wich curve came back to y=0 represent the angle of vanishing stability. Assume that your boat is knocked down by a wave, this would be the widest angle at wich you may hope that your boat recover to unheeled position by herself; at wider angle your boat will capsize.
-the area under the curve from 0° to 115° is the amount of energy required to capsize your boat, or, on the other side, your reserve of total stability
-the area from x-axis and lower part of the curves (from 115° to 180°) is the amount of energy required to restore your boat from a capsize.
A great book to understand this argument is "seaworthiness: a forgotten factor", by Tony Marchaj, very good and wide explanation of phenomenon but somehow anti-historical conclusion (just in my opinion of course
). To spent some words on specific boat, generally speaking (i don't know the boat) I would expect a wider angle of vanishing stability for a 36' offoshore racer, 115° is not a huge value, and even most disappointing is the maximum negative value (at 155° heeling), this means than this boat is quite stable when capsized, it means that it's difficult that a wave can recover her after a capsize
fair wind
mistral
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