Stability Figures

MKIII Stability (Full Working Sail)

Displacement (lbs) - unladen displacement
Payload (lbs)
Displacement (lbs) - cruising displacement
Hull centreline to centreline beam (ft)
Sail Area - Main (sq ft)
Sail Area - Genoa (sq ft)
Sail Area - Staysail (sq ft)
Sail Area - Total (sq ft)
Height of centre of effort above the centre of lateral
resistance (ft)

Formula used = 14*(SQRT((Wu*(0.5*CC))/(SA*Ht)))

Stability - unladen displacement
Windspeed (knots)
Dynamic Stability Windspeed (knots)

Stability - cruising displacement
Windspeed (knots)
Dynamic Stability Windspeed (knots)

7840 (3.5 Tons)
1568 (20%)
9408
9.58 (9'-7")
140
250
43
433
16

32.59
19.56

35.71
21.42

MKIII Stability (1 Reef)

Sail Area - Main (sq ft)
Sail Area - Genoa (sq ft)
Sail Area - Staysail (sq ft)
Sail Area - Total (sq ft)
Height of centre of effort above the centre of lateral
resistance (ft)

Stability - unladen displacement
Windspeed (knots)
Dynamic Stability Windspeed (knots)

Stability - cruising displacement
Windspeed (knots)
Dynamic Stability Windspeed (knots)

105 (75%)
188 (75%)
43
336
14

39.59
23.75

43.36
26.02

MKIII: Interpreting the Stability Figures

The figures simply indicate the windspeed at which the weather hull will begin to lift. From the calculations it can be seen that if nothing is allowed for wind gusts and the fact that the craft is passing through water, the Heavenly Twins 26, under full working sail will begin to lift a hull at 32.59 knots of wind when unladen and 35.71 knots when fully loaded. To calculate the dynamic stability which takes account of wind gusts and wave action, multiply by a factor of 0.6 to give the safe working windspeed. The results are 19.56 knots and 21.42 knots respectively.

27 Stability (Full Working Sail)

6272 (2.8 Tons)
3136 (50%)
9408
9.58 (9'-7")
140
250
32
422
17 (16'+4"+8")

28.64
17.18

35.08
21.05

27 Stability (1 Reef)

105 (75%)
188 (75%)
32
325
15

34.75
20.85

42.56
25.53

27: Interpreting the Stability Figures

The figures simply indicate the windspeed at which the weather hull will begin to lift. From the calculations it can be seen that if nothing is allowed for wind gusts and the fact that the craft is passing through water, the HT 27, under full working sail will begin to lift a hull at 28.64 knots of wind when unladen and 35.08 knots when fully loaded. To calculate the dynamic stability which takes account of wind gusts and wave action, multiply by a factor of 0.6 to give the safe working windspeed. The results are 17.18 knots and 21.05 knots respectively.

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