Calculation of the stability of a sailing yacht by ISO 12217-2
Calculation of the stability of a sailing yacht by ISO 12217-2 with the program Maxsurf Stability Enterprise v.20
We look through model of a plastic sailing yacht with one mast and centerboard in CL, with the following principal dimensions and characteristics:
Maximum length of the hull Lmax = 6,3 m
Maximum beam of the hull Bmax = 2,456 m
Maximum depth in the bow Hmax = 1,188 m
Amidships depth Hmiddle = 1,084 m
Depth on the transom Htransom = 1,045 m
Draft in fresh water T = 0,3 m
Full Displacement in fresh water D = 1219 kg
Crew 4 persons
Navigation area for class "C" - internal waterways and coastal marine floating at designed speed of the wind 17 m/s (up to 6 balls on Beaufort), height of the design wave - 2 m
Sails - mainsail and staysail
Declination of the raked stem from the vertical - 15 deg
Design of the present model was made of young engineer Alexander Ermolenko from city Kiev - Ukraine. From me only some particulars - the view /rake/of the stem, check and flattening the curvature of the water-lines in the fore, adding the bulbkeel and ruder blade and the present calculation of the stability.
The publication is made by the A.Ermolenko's consent.
|. All over again it is necessary to update what cases of load it is necessary to look according to requests of ISO 12217-2.
1. The first and most important case of load this is the Full displacement of the yacht in operating conditions. It will consist of the weight "Light craft" plus deadweight /weights of the crew, the store, the fresh water and the reserve of fuel for the suspended motor /.
We still do not have data for "Light craft". Precise value will be received at „ Experimental definition of the weight and CG of the Light craft”. For this purpose it is selectable the draft and the displacement relevant to it on prototypes data.
For CG of full displacement the reasoning is the following:
As overall dimensions of the yacht and the geometric shape are already fixed /on the ground of some prototypes / then at already adopted draft we can receive LCB of the computer model. That the vessel was maintained on an even keel it is necessary LCB = LCG. As it is possible to achieve it is by means of different versions of the location of the mast with sails, the bulbkeel and the crew. At designing usually receive all crew it is arranged in the cockpit, less often two persons in the cabin and two in the cockpit or three in the cabin and one steering in the cockpit. So that it is possible to influence on the trim on the axis "X" most likely only by means of successful arrangement of the mast and the centerboard or dry ballast under the bottom ceiling.
On height we receive CG of full displacement on 60% of an amidships depth.
At full displacement it is received that the centerboard is in the lower position.
2. In ISO there is a testing on “Wind Stiffness test”.
It is made at „Minimum operating mass” which it is necessary to correspond to following conditions:
a.) The weight will consist from "Light craft" plus one person steering standing on the cockpit, on CL.
b.) Sails shall be stowed ready for hoisting.
c.) The centerboard is in the upper position / keel is hidden in the hull, and the bulb is under the bottom of the yacht / if it is impossible to fix it in the lower position and if there is a relevant instruction in the manual for the owner.
We look also both two versions - centerboard in upper and centerboard in lower position.
As "Experimental definition of the weight and CG” is not made yet instead of "Light craft" we shall accept in calculation the weight of the yacht ready for trip, but crewless.
Thus we shall receive “Minimum operating mass” it is equal:
[1219 kg - (4чел. x 75kg)] + (1чел. x 75kg) = 994kg
ISO 12217-2 supposes specific performance “Wind Stiffness test” to exchange with computational version.
NA Razmik Baharyan
Rousse – Bulgaria
||. Improvement of the critical points of downflooding.
The cut-out for an entrance in the cabin should have coaming in lower edge agrees ISO apart > 0,2 m from the floor of the cockpit.
To stability criteria it agrees ISO 12217-2 specified in Maxsurf Stability are satisfied if this coaming will defend a minimum on 0,456m > 0,2m from the floor or 0,652 + 0,456 = 1,108 m from BL where 0,652 m it is height of the floor of cockpit from BL on 2 m from the transom.
At breadth of the cut-out 600mm, critical points of downflooding have the following coordinates:
X=2,0m Y = (+/-) 0,3m Z=1,108m |||. Input data in the tables of the criteria
In Maxsurf Stability six different kinds of criteria on ISO 12217-2 are specified. First five of them concern to the case of load “Full Displacement”, and the sixth “Wind Stiffness test” concerns to the case of load “Minimum operating mass”.
From five criteria concerning to “Full Displacement” only criterion "STIX" on p.6.4 from ISO requires explanation what data is necessary to introduce in the table of criterion /see the attached file / .
Data for the Silhouette at Full displacement are received by program Delftship Professional /see the attached file /.
First from five criteria - “Downflooding height at equilibrium”/p.6.2.2 by ISO/, is more special case.
After input in the table of criterion of the Minimal freeboard - 0,37m on requests ISO, the outcome for the real freeboard - 0,808m /on levels of the downflooding point/ at Full displacement is received by means of Start Analysis /Equilibrium/ or Batch Analysis /Large Angle Stability/, at elimination of all remaining criteria.
The sixth criterion “Minimum operating test” requires explanation for input precise value "A" in the table of criterion.
The formula in Maxsurf Stability is following:
Heeling arm = A * cos^n (phi)
Where “A” - amplitude of the heeling levers from the operation of the wind in [m]. How much it is necessary to receive the value "A"?
It agrees ISO 12217-2, p.6.6.6 the heeling moment from the wind is calculated by formula:
Mw = Mwo * (cos ϕ) ^ 1,3
Where Mwo - amplitude of the heeling moment from the wind in [N.m]
Mwo = 0,75*Vw^2*As' * (hCE + hLP) [N.m]
For category "C" the maximum designed speed of the wind is Vw = 17 m/s
(hCE + hLP) = distance between CG of the area subject to the operation of the wind and CG of the sunk area of the yacht.
Data for Silhouette at the Minimum operating mass for cases „Centerboard in upper position” and „Centerboard in lower position” are received by program Delftship Professional. a.) Centerboard in upper position - see attached file for Silhouette
As' = 6,908 m^2 /without areas of the sails /
(hCE + hLP) = 1,222 - 0,069 = 1,153 m
Mwo = 0,75*17^2*6,908*1,153 = 1726,4 [N.m]
In the intersection point of the two curves of the moments, relevant to the unknown quantity of the heel angle, we have equality of the heeling moment Mw and the righting moment Mr /or RM/.
Mw = Mwo * (cos ϕ) ^ n
Mr = ℓr * D
At Mw = Mr follows Mwo* cos^n (ϕ) = ℓr * D
Where ℓr = GZ for angle ϕ [m] and D=Displacement [N]
Or Mwo [N.m] / D [N] = ℓr [m] / cos^n (ϕ);
If to exchange Mwo / D = A [m] that we shall receive A*cos^n (ϕ) = ℓr
But in the intersection point of the two curves except for equality of the two moments there is also an equality the arms of the moments in [m], i.e. ℓr = ℓw
Here ℓw is the heeling lever from wind at the heel angle ϕ
Then ℓw = A*cos^n (ϕ); At ϕ = 0 ℓw = ℓwo = A [m]
I.e. "A" is the amplitude of the heeling levers from the operation of the wind in [m].
If to converse D in [N] we shall receive D=1219kg = 9751N
Then A = Mwo / D = 1726,4 [N.m] / 9751 [N] = 0,177m A = 0,177m - this value should be introduced to the table of criterion!
b.) Centerboard in lower position
Data for Wind area are too most:
Area 6,908 m^2 X = 3,208 m Z = 1,222 m
But for Lateral area /sunk area/ the data are changed for the sake of the centerboard:
Area 2,144 m^2 X = 2,559 m Z = - 0,179 m
(hCE + hLP) = 1,222 + 0,179 = 1,4 m
Mwo = 0,75*Vw^2*As' * (hCE + hLP) = 0,75*17^2*6,908*1,4 = 2096,23 [N.m]
A = Mwo / D = 2096,23 / 9751 = 0,215 m A = 0,215 m - this value should be introduced to the table of criterion!
The final output of calculation on stability criteria by ISO 12217-2 is shown in the attached file “Stability Calculation”.
NA Razmik Baharyan
Rousse - Bulgaria
It seems very interesting although it is difficult to evaluate because of the blandness of your text. It would be very important, if not essential, to present the results in the format required by ISO 12217-2.
Certainly if to find new issuing ISO 12217-2 from 2015 it is possible to make calculation of stability by hand-operated method, but I had purpose to show as it is made at the help by computer program Maxsurf Stability and I has particularly indicated version 20. Apparently from the attached file for criteria, issuing from 2002 there is specified. I hope that in new 21 Maxsurf Stability versions it is specified ISO 12217-2 from 2015, but I yet do not allocate with it.
After all this calculation is not ultimate, but only preliminary!
NA Razmik Baharyan
Rabah, ISO 12217 states nowhere that stability calculations should be done by hand. They can, of course, be done with a computer and apply the results to the formats required by ISO 12217-2.
By the way, should I deduce that ISO 12217-2 of 2013 no longer serves ?, has been replaced by a version of 2015?. Maybe I misinterpreted you. In any case, although MaxSurf is not updated, which is really strange, we can always do the calculations with another tool of the many that exist.
Just one opinion, exposing to the public preliminary calculations is not advisable. There may be bugs, and it is very common for them to be, that will devalue the work done.
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