Calculations of resistance of water and towrope power capacity of a motor yacht of project B20-R

Discussion in 'Hydrodynamics and Aerodynamics' started by Rabah, May 10, 2019.

  1. Rabah
    Joined: Mar 2014
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    Location: Bulgaria

    Rabah Senior Member

    Hello dear readers of the forum „ Boat Design.net”,

    I bring to your attention a new theme: « Calculations of resistance of water and towrope power capacity of a motor yacht of project B20-R »

    I devote this publication to my grandson Stanislav М. with the hope that he will be a very good and very skilled engineer!

    Contents

    1 Introduction

    1.1 Purpose of the present publication

    1.2 Used methods under existing programs and bibliography

    2 Reduction of the quantity of the surfaces included in the Shell Plating of the hull model on project B20-R

    3 Characteristics of the used model of project B20-R

    4 Features of calculation in program Orca3D

    5 Features of calculation in program NavCad

    6 Features of calculation in program FreeShip +

    7 Features of calculation in program Maxsurf Resistance

    8 Comparative diagrams by the results of the calculation of the power capacity

    9 Conclusions



    1. Introduction


    1.1 Purpose of the present publication

    To show hydrodynamic calculations for motor displacement yachts executed by various methods on four different programs, and to compare the received results to the data on trial runs of the constructed vessel.

    The General Director of company SeaTech in Nizhni Novgorod-Russia - NA Peter Ezhov, has given me for this purpose computer model of a yacht - project B20-R, as a file of program Rhinoceros, some photos from launch of the vessel, calculation of resistance of water and power capacity of the propulsion installation, executed by company SeaTech, and the data received as a result of sea trials of the vessel. Not each company makes such noble gesture. Usually such results do not reach broad masses of experts on hydrodynamics of small motor boats.

    Such statistical data are the invaluable manual for the young experts engaged small motor ships.


    1.2 Used methods under existing programs and bibliography

    1.2.1 Methods for displacement ships under program Maxsurf Resistance v.21.14 from 2018.

    - Method Holtrop - under 5 publications:

    Holtrop, J., “A Statistical Analysis of Performance Test Results”

    International Shipbuilding Progress, February 1977.

    Holtrop, J., “Statistical Data for the Extrapolation of Model Performance Tests”

    Netherlands Ship Model Basin (NSMB) Paper 588, May 1978.

    Holtrop, J. and G.J. Mennen., “A Statistical Power Prediction Method”

    NSMB Paper 603, October 1978.

    Holtrop, J. and G.J. Mennen., “An Approximate Power Prediction Method”

    NSMB Paper 689, July 1982.

    Holtrop J., “A Statistical Re-analysis of Resistance and Propulsion Data”

    International Shipbuilding Progress, Volume 31, No. 363, November 1984.

    - Method Compton - by publication Compton, R., “Resistance of a Systematic Series of Semi-Planing Transom-Stern Hulls” Marine Technology, v23, No.4, October 1986.

    - Method Fung - by publication Fung, S.C. and Leibman, L., “Revised Speed-Dependent Powering Predictions for High Speed Transom Stern Hull Forms” FAST ' 95: Third International Conference on Fast Sea Transportation, Lubeck Travemunde, September 1995

    - Method Van Oortmerssen - under publications:

    Oortmerssen, G., “A Power Prediction Method and its Application to Small Ships” International Shipbuilding Progress, vol 18, No.207 1971

    Helmore, P.J., “Update on van Oortmerssen's resistance prediction” RINA - International Maritime Conference, Pacific 2008, pp. 437 - 448


    1.2.2 Methods for displacement ships under program HydroComp NavCad 2005 /2011 Edition/

    - Method CRTS - by publication Fung, S., "Resistance and Powering Prediction for Transom Stern Hull Forms During Early Stage Ship Design", SNAME Transactions, Vol. 99, 1991.

    - Method HSTS - by publication Fung, S.C. and Leibman, L., "Revised Speed-Dependent Powering Predictions for High-Speed Transom Stern Hull Forms", Proceedings Third International Conference of Fast Sea Transportation (FAST ' 95), Germany, 1995.

    - Method Holtrop 1984 - under publications:

    Holtrop, J., "A Statistical Resistance Prediction Method with a Speed Dependent Form Factor ", Proceedings SMSSH ' 88, Varna, Oct 1988.

    Holtrop, J., "A Statistical Re-Analysis of Resistance and Propulsion Data", International Shipbuilding Progress, Vol. 31, No. 363 Nov 1984.

    Holtrop, J. and Mennen, G.G.J., "An Approximate Power Prediction Method", International Shipbuilding Progress, Vol. 29, No. 335, Jul 1982.

    - Method De Groot RB - by publication De Groot, D., "Resistance and Propulsion of Motor-Boats", International Shipbuilding Progress, Vol. 2, No. 6, 1955.

    1.2.3 Method Holtrop 1984/mod/-under program Orca3D v.1.4 WIP from 2018, plug-in for Rhinoceros v.5

    The method is created under publications:

    Holtrop, J., "A Statistical Re-Analysis of Resistance and Propulsion Data", International Shipbuilding Progress, Vol. 31, No. 363, November 1984.

    Holtrop, J. and Mennen, G.G.J., "An Approximate Power Prediction Method", International Shipbuilding Progress, Vol. 29, No. 335, July 1982.

    ITTC, Proceedings of the 15th ITTC, The Hague, The Netherlands, published by the Netherlands Ship Model Basin, Wageningen, 1978.

    1.2.4 Methods under program FreeShip+, v.3.50 from 2015 - Author NA Victor Timoshenko

    - Method Holtrop 1988 (84) - under publication Holtrop from 1984 and Holtrop, Mennen from 1982.

    - Method Fung-Leibman 1995 under publication Fung, Leibman from 1995 for round bilge military ships

    - Method De Groot - under the publication from 1951 for high-speed round bilge boats

    - Method according to modelling experiment - OST 5.0181-75 - for anyone displacement ships


    2. Reduction of the quantity of the surfaces included in the Shell Plating of the hull model on project B20-R


    2.1 To receive model for calculation of the Resistance and Power capacity with program Orca3D it is enough to remove the superstructure from the Rhinoceros file. Therefore, we shall receive model of the hull of the vessel from the bottom up to the main deck and from the transom in the stern up to the bulbous nose (see the enclosed file with frames, buttocks and waterlines).


    2.2 More difficult is reception of model without deviations from the valid contours of the vessel, suitable for work with program Maxsurf Resistance.

    The problem arises because of that that all cut off surfaces in the Rhino file at import from Rhino in Maxsurf Modeler by means of the file format IGES, or at direct use Rhino file in Maxsurf Modeler, turn out not cut off.

    Here to help there has come program Delftship Pro v.4.03. From existing Rhino file has removed all superfluous, has left only surfaces of one board (the bottom, the side and the reverse chine flats) and by means of the IGES file imported in Delftship Pro. At once the unpleasant problem is visible - not cut off surfaces of the bottom and the side go in parallel each other as "bottom - side", and not cut off surface of the reverse chine flats crosses them. They are not accepted finally cut off neither in Delftship Pro, nor in Maxsurf Modeler.

    The problem can be solved as follows:

    To receive traces of contour lines, using function of crossing of surfaces in Delftship Pro.

    To remove superfluous parts of the bottom and the side under and above these lines (for the side to remove the lower part, and for the bottom to remove the top part).

    To create a new surface of the reverse chine flats on control points of the received contour lines of the bottom and the side, and the old not cut off - to remove.

    Having contours of the bottom, the reverse chine flats and the side, it is necessary to measure only in the Rhino file height of the transom from BL and to create a point in CL at the level of height of transom in program Delftship Pro. It is already easy to make the surface of the transom which in the top part reaches the horizontal stern platform.

    All « leak points », shown by green color in program Delftship Pro (at a choice are shown by yellow color in the program FreeShip +), are above the level of the waterline determined at full displacement (draft aft Taft = 1,25m). They can be seen in the enclosed file.

    It is enough four received surfaces for performance of calculations on hydrodynamics of the vessel. We import surfaces of the bottom, the side, the transom and the reverse chine flats with help of the IGES file from Delftship Pro in Maxsurf Modeler.

    On the received model it is determined the Forward and the Aft perpendiculars. The Forward Perpendicular (FP) passes through the point of crossing DWL (in case with a trim) with the line of the stem in CL on levels Tforw = 1,1m from BL. The Aft perpendicular (AP) coincides from the aft edge of the horizontal platform in CL, on 0,25m aft from the transom.

    We fix average draft 1,19m (equal keel) for full displacement 54,8t and we determine quantity of frames, buttocks and waterlines.

    We keep the file of model in program Maxsurf Modeler.

    We open this model in Maxsurf Stability and hydrostatic calculation of initial stability with a trim 0,15m and displacement 54,8t is made.

    We keep results of calculation with a trim then to use them for specification of entrance parameters in program Maxsurf Resistance.


    2.3 In program FreeShip +, v.3.50, there is an opportunity of direct opening of model, and also, separate entering of necessary entrance parameters.

    If the model is already made in Delftship Pro, we keep it in version 2.6 of program Delftship Pro and directly is opened in FreeShip +, then we keep in last version 3.50 and we carry out calculations of resistance and capacity.

    Method Holtrop of program FreeShip+ supposes introduction of the entrance data about DWL with a trim.

    In other methods the program demands input of parameters from initial stability the vessel to equal keel, with average draft 1,19m, at preservation of size of displacement 54,8t.


    2.4 In program NavCad 2005 there is no opportunity to take ready model that then to execute calculations of resistance and power capacity as it was possible in programs Orca3D, Maxsurf Resistance and FreeShip+.

    Such opportunity is only in the new version NavCad Premium 2018, with use of the model made in program Rhinoceros.

    Therefore, for work we shall use entrance data given programs Maxsurf Resistance which coincide with the required entrance data for program NavCad 2005 (behind small exception).

    As well as in Maxsurf Resistance, in NavCad 2005 there is an opportunity to use the data on DWL with a trim.


    Continuation follows!


    Has developed: NA Razmik Baharyan

    Rousse-Bulgaria
     

    Attached Files:

    Last edited: May 13, 2019
    valber, Dejay and Alexanov like this.
  2. Rabah
    Joined: Mar 2014
    Posts: 246
    Likes: 7, Points: 18, Legacy Rep: 50
    Location: Bulgaria

    Rabah Senior Member

    Calculations of resistance of water and towrope power capacity of a motor yacht of project B20-R
    / continuation /


    3. Characteristics of the used model of project B20-R

    Full displacement of the vessel in fresh water, agrees to the data of sea trials 54,8t at drafts Tforw=1,1m and Taft=1,25m.

    Coordinates of CG:

    Xg = 8,59m (from AP, taking place on 0,25m in aft from the transom);

    Yg = 0,00m;

    Zg = 2,24m from BL.

    Operational speed - 9 kts, maximal - 12 kts.

    Class of the vessel on River Register of Russia: М-СПмс 3,5 (лед 20) A;

    Class of the vessel on GIMS EMERCOM-Russia - Кс III, area of navigation – III category of complexity.

    The maximal power capacity of engines =2 x 155 hp = 2 x 114 kW.

    Other data can be seen in the hydrostatics calculations executed on programs Orca3D and Maxsurf Stability enclosed to the publication (see the enclosed files). The given calculations are executed in case with a trim 0,15m (0,432deg) at D=54,8t.

    As for the account of the influence of the head wind which speed for class М-СПмс is accepted equal 13,4 m/s (26,05 kts), it is necessary to know the transverse and longitudinal wind areas.

    The transverse wind area easily calculate on the usual way manually.

    The longitudinal wind area is designed by means of program Delftship Pro v.4.03 (see the enclosed file of the silhouette of the yacht).

    Design altitude of the wave for this class - h3%= 3,5m.

    If careful to look on the transom of the model in the Rhino file, we shall see, that the breaking in the plan transom represent a combination from three flat surfaces: one central - in CL, and two lateral - on sides.

    Unfortunately, at use of the model in Maxsurf Resistance, the program perceives in quality of transom only the central surface, therefore erroneous sizes for Transom area (the immersed area of transom) and TransomWLbeam (the width of the transom on the waterline) in entrance parameters for the further calculations was received.

    It was necessary to calculate them manually. It was turned out:

    - The immersed area of transom= 1,14m^2

    - The width of the transom on the waterline at full displacement = 4,26m

    One more of sizes which is easier for calculating manually, is immersion of the transom: 1,25 - 0,96 = 0,29m,

    Where 1,25m = Taft,

    0,96m - distance from the bottom point of the transom in CL to BL.

    Fortunately program Maxsurf Resistance allows to correct or add in addition some sizes and after that renews final calculation on the corrected data.

    The area of transverse section of the bulb on Forward Perpendicular /Bulbtransversearea/= 0,018m^2; coordinate on axis Z of CG of section of the bulb /ZBulb/= 0,899m from BL and half angle of entrance of WL in the bow (½ angleofentrance) = 14,073 deg, was used from received at calculation of resistance and towing capacity on method Holtrop on program Orca3D.

    Dead rise of the bottom on 50 % LWL at a trim it is accepted in Maxsurf Resistance identical with size at WL without a trim = 6,7deg.



    Continuation follows!


    Has developed: NA Razmik Baharyan

    Rousse-Bulgaria
     
    Last edited: May 12, 2019
  3. Rabah
    Joined: Mar 2014
    Posts: 246
    Likes: 7, Points: 18, Legacy Rep: 50
    Location: Bulgaria

    Rabah Senior Member

    Calculations of resistance of water and towrope power capacity of a motor yacht of project B20-R
    / continuation /



    4. Features of calculation in program Orca3D

    In program Orca3D the unique method for calculation of resistance and power capacity for a displacement ships - Holtrop, is submitted.

    To the received size of resistance of the naked hull 10 % reserve are added.

    To receive the maximal propulsion power capacity specified in specifications and certificates of firms - manufacturers of engines on which further the designer chooses engines, it is necessary to accept the general propulsion efficiency from 50 up to 70 %. For project B20-R this efficiency is accepted 50 %.

    The program makes calculation of resistance and power capacity, only if design hydrostatic calculation of the vessel on DWL is preliminary designed. If the normals to some surfaces are directed in inside vessel, the program corrects them.

    The ready model in Rhino is then used.

    The program itself checks model and fixes all parameters necessary for calculation.

    Final results of calculation and graphs it is kept in general pdf file.

    See the final file in attachment.


    5. Features of calculation in program NavCad

    As already it was spoken earlier in program NavCad 2005, as against other three programs, there is no opportunity to use ready model.

    All entrance data are necessary for bringing manually.

    Almost all data it is possible to use from the table of the entrance data of the program Maxsurf Resistance.

    First of all, it is necessary to choose metric system.

    Then, in the first dialogue window kinematic viscosity and density of water in specified, under the task, area of navigation - fresh water are filled.

    After that the range of speeds - from 5 up to 16 kts is filled.

    In the second dialogue window the data on the hull are brought, and the program at once calculate ratio between them.

    The trim is taken into account by filling of the following sizes: maximal design draft 1,25m and a trim in aft 0,15m.

    In the third dialogue window it is filled nothing, as there is no information on the areas of appendage.

    In the fourth dialogue window it is necessary to bring in the data on the wind-wave mode of the specified area of navigation:

    - Design speed of the wind;

    - Angle of direction of the rate of the vessel in relation to the direction of the wind and wave. The angle = 0 deg - the heaviest case (counter wave and wind) is accepted;

    - The areas and the CG of the transverse and longitudinal wind area;

    - Type of the vessel - passenger;

    - Height of the wave of security 3 % = 3,5m;

    - The maximal period of the rough sea = 7,7 s;

    - Design depth of water = 10m.

    In fifth (last) dialogue window the percent for a reserve, attached to size of resistance of the naked hull is filled. For the stage of final designing in program NavCad 2005 it is accepted 4 %.

    After filling the entrance data, we press button "Bare-hull" in the left part of the screen with an inscription "vessel drag" and it is chosen "calc" (calculation).

    Then it is already possible to press the button for a choice of methods for calculation.

    By pressing this button there is a dialogue window. In it with dark blue color, shows four recommended methods - Holtrop 1984, CRTS, HSTS and De Groot RB, as the most suitable for application.

    If color is pink - is considered method good, if it is black - the method is considered comprehensible with a clause and if red - the method is unacceptable.

    Preservation of results is better for making in format Word and then to transform docx file in pdf.

    Graphs of resistance and power capacity are initially kept in bmp file then they should be transferred in pdf.

    After final calculations on all methods in program NavCad all received pdf files are united in one general.

    See the final file in attachment.



    Continuation follows!


    Has developed: NA Razmik Baharyan

    Rousse-Bulgaria
     

    Attached Files:

    Last edited: May 12, 2019
  4. Rabah
    Joined: Mar 2014
    Posts: 246
    Likes: 7, Points: 18, Legacy Rep: 50
    Location: Bulgaria

    Rabah Senior Member

    Calculations of resistance of water and towrope power capacity of a motor yacht of project B20-R
    / continuation /



    6. Features of calculation in program FreeShip+
    The entrance data are entered in two dialogue windows.
    In the first the specification data are input:
    а) The general data: the minimal, design and maximal speed; density and viscosity of fresh water.
    b) The data on the hull - are possible two variants:
    - To take the data of the current model on the project;
    - To enter the data manually.
    As against program NavCad, here it is required not maximal design draft, but only draft on midship 1,19m.
    The trim should be specified only at calculation on method Holtrop, but with negative it is familiar, as in the program the positive trim in the bow is accepted.
    The immersed area of the transom - as in Maxsurf Resistance.
    Absolute roughness-150 microns for a new vessel.
    The factor of the stern form is equal (-24) at method Holtrop (from help).
    Quantity of screws equally to two, exception of method De Groot; diameter of the screw is equal 0,56m from the data on sea trials, with exception of method De Groot at which it is necessary to accept only 1 screw with diameter 0,812m.
    We select « Extract half entrance angle from model».
    c) The additional data in the second dialogue window:
    - Time of stay in water of 0 months for the new hull
    - Height of the wave of security 3 % - 3,5m
    - Course angle of moving wave and wind - 0 deg
    - Speed of the wind - 13,4m/s
    - Height of the free board - 1,525m
    - Density of air - 1,226 kg / m^3
    - Middle height of superstructure above DWL- 4,22m
    - Design depth of water - 10m
    - The immersed area of the middle section- 4,57m^2 (according to model)
    - Type of the vessel - 1 (passenger)
    - For appendage- there is no information on the areas

    Then in the main window we press the button « To begin calculation ». After calculation the size for the factor which is taking into account operational conditions as follows is automatically filled:
    - For method Holtrop Ке = 1,32
    - For method De Groot Ке = 1,44
    - For method Fung-Leibman Ке = 1,762
    - For a method of modelling experiment Ке = 1,44
    This factor /Sea margin coefficient/ show as far as it is necessary to increase size of the resistance and towing power capacity to take into account operational conditions.
    To take into account data Ке in calculation, it is necessary to make a mark (to put a tick).
    Then results turn out:
    - Graphs of curves of resistance and power capacity in the basic window
    - Results of calculation and the entrance data in the third dialogue window
    The entrance data and results of calculation are save in one pdf file, and graphs - in other pdf file. Two files it is united in one for each of four methods. At last all files on four methods it is united in one and it is save.
    See the final file in attachment.

    7. Features of calculation in program Maxsurf Resistance
    After input of the entrance data, in programs Orca3D, NavCad and FreeShip+ calculation of final results is carried out simultaneously for definition of the resistance of the naked hull and towing power capacity, and also the maximal resistance and maximal propulsion power capacities.
    But in program Maxsurf Resistance calculations are carried out separately:
    - Once - without taking into account the head wind - for definition of the resistance of the naked hull on calm water and towing power capacity (propulsion efficiency 100 %);
    - Second time - in case with speed of the head wind and the transverse wind area at propulsion efficiency 50 % - for definition of the maximal size of the resistance and maximal propulsion power capacities.
    To speed of the head wind and the transverse wind area, stipulated in point 3 of the given publication, we shall add factor of air resistance which in the manual of the program varies from 0,8 up to 1,2. We accept 0,8 for passenger ships from book « Designing of sea going ships » - L.M. Nogid, 1976, page 91.
    By results of calculation are created two separate pdf files which can look in the attachment.
    At input of the entrance data for the width it is necessary to accept the maximal width on WL, and for the draft it is necessary to accept maximal design draft on AP equal 1,25m, as in program NavCad. In addition it is required also the draft on FP equal 1,10m that there was a full information on the trim.
    In program NavCad to be entered size LCB [m] from FP, or from AP, but in program Maxsurf Resistance it is necessary to enter LCG [m] from midship (the middle of length Lpp).
    Sizes for transom and bulb coincide in both programs-NavCad and Maxsurf Resistance.
    In Maxsurf Resistance there is also a new size - deadrise of the bottom on 50 % LWL = 6,7 deg.
    The factor of correlation for methods Van Oortmerssen and Compton is accepted under the formulation of 19th ITTC; for method Fung it has a fixed size and is equal 0,0005, and for method Holtrop-according to calculation on method Holtrop.


    Continuation follows!


    Has developed: NA Razmik Baharyan

    Rousse-Bulgaria
     
    Last edited: May 13, 2019
  5. Rabah
    Joined: Mar 2014
    Posts: 246
    Likes: 7, Points: 18, Legacy Rep: 50
    Location: Bulgaria

    Rabah Senior Member

    Calculations of resistance of water and towrope power capacity of a motor yacht of project B20-R
    / continuation /


    8. Comparative diagrams by the results of calculation of the power capacity

    By means of program Advanced Grapher v.2.2 three comparative diagrams /see the added files / are constructed:

    - The comparative diagram for the results of the calculation of the towing power capacity on method Holtrop;

    - The comparative diagram for the results of the calculation of the towing power capacity on other methods;

    - The comparative diagram for the results of the calculation of the maximal propulsion power capacity.

    For comparison in the diagram on method Holtrop the curve of the towing capacity by results of calculation B20-R-020-030 « Calculation of the propulsion characteristics of the vessel » executed by company SeaTech, and also the curve of the towing power capacity received as a result of the sea trials of the vessel on project B-20R, carried out by company SeaTech in June 2018 is shown.

    In the diagram on other methods, for comparison, the curve of the towing power capacity is resulted according to sea trials.

    In the diagram for maximal propulsion power capacities are shown all results on the specified methods, received with the four programs. For comparison the curve of the maximal power capacity under the Fuel Consumption, received is shown also as a result of sea trials.


    9. Conclusions

    Comparing results under three diagrams it is possible to make follow conclusions:

    Calculation on Method Holtrop in program Orca3D completely coincides with the data of sea trials for the maximal power capacity under the Fuel Consumption within the limits of the test range of speeds of the given vessel.

    The data on sea trials for the towing power capacity are very close to curve of the towing power capacity on Method Holtrop in program Orca3D.

    If further the project will undergo modernizations with necessity of maintenance of speed of the vessel for 13 kts, in this case it will be necessary to increase the power capacity of the Main Engines up to 370 kW and if the customer will want speed not less than 16 kts, it is necessary the power capacity to be 650 kW.

    In that case the much big power capacity of the engine will result in increase in weight of the propulsion installation that it will be necessary to compensate for preservation of the current displacement and draft. But in case of essential changes, it is necessary to repeat the calculation with the new parameters. Fortunately, program Orca3D operates very quickly in hands of the one who knows as with it to work.


    At the end of calculations I want to thank all which have helped me to realize them, including all who was made this project and which have carried out the manufacture of this remarkable and beautiful vessel. With special gratitude to NA Peter Ezhov for given an opportunity, also many thanks to eng. Alexander Obidin for the rendered help during calculations and for editing of the text of the publication.

    Once again thank all!



    Has developed: NA Razmik Baharyan

    Rousse-Bulgaria

    14.05.2019
     
    Last edited: May 14, 2019

  6. Rabah
    Joined: Mar 2014
    Posts: 246
    Likes: 7, Points: 18, Legacy Rep: 50
    Location: Bulgaria

    Rabah Senior Member

    Greetings dear readers of the forum of the "Boat Design.net",

    I suggest to continue the theme of calculation of resistance and power capacity of a small motor yachts. This time we shall consider the motor yacht of project AY-15 of the company SeaTech from Nizhni Novgorod-Russia.

    The General Director of the company Sea Tech-NA Peter Ezhov, has given me a Rhino file of the model of project AY-15 for performance of calculations on resistance and power capacities -see the attached png files from Rhino.

    The purpose of the present publication is not that was in the publication about calculations of resistance under project B20-R.

    Vessel it is not constructed yet - at the present is on a design stage.

    The purpose of the development - to choose the most suitable method for calculation of resistance for the given hull and to define the most suitable curve of towing power capacity for the further choice of the total rated power of the main engines.

    As against project B20-R, this time we shall use only two programs:

    - Maxsurf Resistance x64 v.20 from 2013

    - HydroComp NavCad 2005 /2011Edition/

    Let's carry out calculations for definition of the resistance and the towing power capacity of the naked hull on calm water without any additives.

    This time we shall not carry out calculations the transverse and longitudinal wind areas as all additives to resistance will be take into account with change of the general propulsive efficiency of the propulsion installations from 100 % on 50 % /see the Remark below/.

    To obtain the entrance data for program Maxsurf Resistance, it is necessary to use model of project AY-15 executed in Rhino.

    It is necessary to solve the same problem which arose in project B20-R - cut off in Rhino surfaces are perceived in Maxsurf Modeler as not cut off.

    NA Alexander Andreev-Director of Design office A4 in Irkutsk, has offered a simple way - make export / import the NURBS surfaces not through IGES file, and stl file in a text code ascii of the Trimesh surfaces.

    NA A.Andreev has offered me a file without a superstructure, with a fictitious deck. But as already know from the publication about calculations of project B20-R, program Maxsurf Resistance makes calculations irrespective of presence or absence of the deck. More likely it was necessary for CFD- Analysis.

    I have agreed to use model in Irkutsk variant as contours of the bottom, transom, sides and reverse chine flats have remained without change.

    According to company Sea Tech full displacement of the yacht in fresh water corresponds to draft in bow Tf = 0,9m and in AP Ta = 1,0m; coordinates CG Xg = 6,42m, Yg=0,00 m, Zg =1,34 m.

    Operational speed - 8-9 kts, the maximal speed - 12-13kts.

    Calculation of the initial stability on DWL is made three times - see attached files:

    - In program Orca3D, in the existing Rhino file for half hull of the vessel, we add frames, buttocks and WL (see the enclosed file).

    Displacement of the vessel without a trim makes 22,6t.

    Displacement in fresh water 22,679t has receive at average draft on midship 0,957 m

    - After input of the model of Irkutsk variant in program Maxsurf Modeler, and then in program Maxsurf Stability, we make two calculations - once to equal keel at draft Т = 0,957 m (as in Orca3D) and displacement 22,38 t and second time with take into account a trim at a draft in bow- 0,9 m, in AP- 1,0 m and average draft on midship-0,95 m, again receive displacement 22,38 t.

    At input of the same model in program Maxsurf Resistance at a draft to equal keel T = 0,957 m full displacement has receive equal D = 22,647 t or volumetric displacement V = 22,647 m^3 at density of water of 1,0 t/m^3.

    The further calculations in program Maxsurf Resistance are made on mentioned above WL to equal keel.

    The methods accepted in program Maxsurf Resistance for calculation of towing resistance and necessary towing power capacity of the naked hull of project AY-15 on calm, deep water without taking into account appendage, wind and wave.


    The interval of speeds of 5-16 kts is chosen. Four are the chosen methods (i.e. on the statistical data of serial tests of models of ships in experimental pool) and one theoretical. The most suitable methods are:

    1. Fung-by publication of Fung, S.C. and Leibman, L., “Revised Speed-Dependent Powering Predictions for High Speed Transom Stern Hull Forms”-1995.

    2. Compton-in an interval of speeds only up to 13,8 kts, by publication of Compton, R., “Resistance of a Systematic Series of Semi-Planing Transom-Stern Hulls”

    Marine Technology, v23, No.4, October 1986

    3. Holtrop-under the publication of the author from 1977 and 1978 and the joint publication of authors Holtrop and Mennen - 1982 and 1984.

    4. Savitsky Pre-planing - only in an interval of speeds 10,5 - 16 kts, by publication of Savitsky, D. and Brown, W., “ Procedures for Hydrodynamic Evaluation of Planing Hulls in Smooth and Rough Water ” Marine Technology, October 1976

    In this publication the data from publication of Mercier, John A. andSavitsky, Daniel “Resistance of Transom Shear Craft in the Pre-Planing Range”-1973 are quoted

    5. Theoretical method Slender Body - under publication Couser, P., Wellicome J.F. and Molland, A.F., “ An improved method for the theoretical prediction of the wave resistance of transom-stern hulls using a slender body approach ” International Shipbuilding Progress, vol. 45, No. 444, 1998.

    Method Slender Body is applied to monohull and multihull ships in an interval of speeds from zero up to FnL ≈ 1,0. The given method is equally good both for Round bilge and for Hard chine hull.

    Necessary condition: Slenderness Ratio (relative length, i.e. "lengthening") = LWL / V^1/3 ≥ 5. Good results are receive at the Ratio 5-6.

    At project AY-15 at LWL = 14,779 m and V = 22,647m^3 Slenderness Ratio = 5,22> 5.

    At the maximal speed of 16 kts, FnL = 0,684 <1,0.


    At all the higher listed methods the efficiency of the propulsion installation it is accepted equal 1.0 (i.e. 100 %) to receive towing power capacity.

    If to accept the general propulsive efficiency = 0,5 (i.e. 50 %) then we shall receive the maximal power capacity (PE total), necessary for overcoming maximal resistance Rtotal (the naked hull on calm water in case with a wind, wave, shallow water and appendage). I.e. multiplication on 2 (or division on 0,5) results of towing power capacity (at efficiency = 100 %) we shall receive necessary maximal power capacity for the choice of engines /see the Remark below/.

    Example: If to look at the Diagram „Towing power capacity - Speed”, we shall see, that the smallest sizes are received on method Holtrop in red color, and the biggest - on theoretical method Slender Body too in red color - (see attached file). If to accept the average curve for this range it will be close to the curve received on method Fung and method Savitsky Pre-Planing. We allow to shall accept higher values - on method Fung (the curve with green color). Then if it is necessary to choose the engines, capable to provide of the vessel the maximal speed of 13 kts, the maximal total power capacity of engines should make:

    PEtotal = 152,96 x 2 = 306 kW

    Model of the vessel and wave formation behind the hull at movement of the vessel on calm water with speed of 9 kts it is shown in png files at the end of calculation.


    Remark:

    Let we shall pay attention as in program Orca3D suggest to choose power capacity of engines. We shall look the table in a manual of the program/see attached file/. There it is specified that mean OPC and Service Margin.

    OPC usually is in an interval of 50-70 %, and Service Margin - in an interval of 10-30 %.

    If we accept narrower interval - OPC = 55-60 % and Service Margin=10-20 % then it agrees the table we shall receive the Ratio of Engine power to Effective power = 1,83-2,18/see the marks in red color /.

    We accept average size of the Ratio = 2,0.

    In program Maxsurf Resistance I have accepted efficiency = 50 %, i.e. by multiplication to 2,0 the size of Effective power to receive the Engine power.

    I.e. in concept "efficiency" we include not only the maximal efficiency of the propulsion installations /OPC/, but also and the additives included in Service Margin-Appendage, Windage, Sea Wave and Shallow Water.

    Continuation follows!

    Has developed: NA Razmik Baharyan

    Rousse-Bulgaria
     

    Attached Files:

    Last edited: May 20, 2019 at 4:57 AM
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