Stability of motor- sailing yacht MS 16 m by ISO 12217-2:2013, design category "A"

Stability of motor- sailing yacht MS 16 m by ISO 12217-2:2013, design category "A"
I. Introduction
Mr. Feodor Vyachin from Saint Petersburg -The Russian Federation, has dispatched me computer model of his future yacht /see the attached files/ with request to test its stability. The present publication is made with his sanction.
Principal dimensions and characteristics of the yacht:
1. Maximum length of the hull Lmax = 16 m
2. Maximum hull beam Bmax = 4,909 m
3. Maximum depth of the hull in the bow - without keel, from BL
/i.e. from the bottom plate in CL/ Hmax = 2,85 m
4. Depth on transom from BL HTr = 2,248 m
5. Features of the hull
- Hard-chine outlines with double bilge
- Stem - vertical
- Transom – with slope from vertical
- The lower point of the ballast keel Z = - 1,138 m from BL
- Weight of the ballast keel ~ 9 t
6. Material of the hull and the superstructure - ship steel
7. Sail - mast arrangement
Single-masted Bermudan sloop with mainsail and staysail
8. Engine - stationary in CL, 150 hp + reductor
9. Propeller - one, shaft – with slope to BL
10. Velocity of the yacht with engine – 9 -12 kts
11. Light displacement D light = 31,87 t
12. Coordinates of CG of the Light ship: X=7,309m; Y=0m; Z = 1,174 m from BL
13. Full displacement D = 35,194 t
14. Coordinates of CG of the Full displacement: Xg=7,378m; Yg=0m; Zg = 1,143 m from BL
15. Drafts at-sea at Full displacement, from BL
- Mean in the midship Tm = 1,111 m
- Bow draft in FP Tf= 1,157 m
- Stern draft in AP Ta = 1,064 m
16. Length of the water-line at Full displacement LWL = 16 m
17. Maximum breadth of the water-line at Full
displacement BWL max = 4,483 m
18. Navigation area for design category "A"- unlimited

II. Choice of Rules for calculation of stability
First of all it is necessary to test whether the vessel is sailing.
The yacht is determined as sailing, if:
As > or = 0,07 * (mLDC) ^ (2/3)
Where As - gross area of sails in m^2
mLDC -Full displacement of the yacht in kg
Or 0,07 * (35194) ^ (2/3) = 75,17 m^2
From the calculation of the Silhouette on Delftship Professional /see the attached file/ we have:
As = 108,93 m^2 > 75,17 m^2
I.e. the yacht is sailing and it is necessary to fulfill all requests on ISO 12217-2 for sailing yachts with length from 6 up to 24 m.
III. Program for calculation of stability
Calculation is carried out at program Maxsurf Stability Enterprise - v.20 in which stability criteria on ISO 12217-2:2002 are incorporated.
Except for that must check and hand-operated account on ISO 12217-2:2013 criterion STIX because of change in the formulas of two of the factors participating in its definition is made.
IV. Improvement of critical points of downflooding
In the cut-out of the entrance door in the superstructure the coordinates of the critical points of downflooding are the following:
X = 3,2 m Y = |-0,8m; -0,2m| Z = 2,36 m
V. Load cases
1. The first and most important case of loads this is the Full displacement of the yacht in operating conditions. It will consist of the weight „ Light ship” + deadweight /weights of crew with baggage, provisions, fresh water, reserves of fuel and oils /.
2. In ISO 12217-2 it is defined and the case “Minimum operating mass” - mMO.. For design category "A" he will consist of the weight „Light ship” + 150 kg /weight of two person / arranged in CL up to the control position of the yacht, i.e. mMO = 31,87 + 0,15 = 32,02 t.
VI. Requirements ISO 12217-2 on stability for monohull sailing yachts of design category "A"
Five criteria are specified in issuing 2013 for category "A" on which it is necessary to make calculations:
1. Downflooding height
2. Downflooding angle
3. Angle of vanishing stability
4. STIX-Stability Index
5. Minimum Righting Energy
The first three criteria coincide with issuing 2002. See the outcome in the attached file for calculation of stability of the yacht.
On the fourth criterion - STIX, calculations are made two times:
- With program Maxsurf Stability on issuing 2002 - it was received STIX = 66 > 32 /see the file /
- In hand-operated on issuing 2013:
There is a variance in the formulas for factors FDS and FDF.
FDS it is received 0,98 instead of 0,935.
FDF it is received 1,27 instead of 1,527, but also in two cases it is necessary to accept no more than 1,25.
For the Index of stability of the yacht on issuing 2013 it is received STIX = 67,5 > 32.

The fifth criterion on issuing 2013 is concerns to “Minimum operating mass”. From program Maxsurf Stability it is calculated and received to schedule of the righting lever curve, whence we receive the angle of vanishing stability 111,68 deg and AGZ-the positive area under the righting lever curve encased between 0 deg and angle of vanishing stability:
AGZ = 57,27 m.deg
Minimum Righting Energy = mMO* AGZ = 32,02 * 57,27 = 1833,8 t.m.deg > 172 t.m.deg

In the issue it is received that the stability of the yacht meets the requirements
ISO 12217-2: 2013 design category "A" for unlimited navigation area, i.e.:
Maximum wave height- approx. 7 m significant
Typical Beaufort wind force<= 10 balls
Calculation wind speed - 28 m/s

You can see calculation of the stability at program Maxsurf Stability in the attached file.

NA Razmik Baharyan
Rousse - Bulgaria
04.04.2017

 

Hello Razmik.
I must be missing the point of your post - is there something you wanted to ask the members of this forum?

 

Only with the noble intention of improving this thorough study I would like to point out that ISO 12217-2's definition of full load displacement, mLDC, is not exactly the same as Rabah does.
On the other hand, if the aim is to verify compliance with this standard, the most appropriate would be to present the results as indicated by that standard.
The attached figure shows how ISO defines the "mLDC". It is necessary to be rigorous in these things because, if the data entered are not correct, the study is of no use.