HT Stability

 

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)

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)

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)

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%)

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.
Our thanks to Bruce Trott for the use of his copyright material. 

 

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