Reefs in program Maxsurf Resistance

Discussion in 'Hydrodynamics and Aerodynamics' started by Rabah, Jan 15, 2018.

  1. Rabah
    Joined: Mar 2014
    Posts: 247
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    Location: Bulgaria

    Rabah Senior Member

    Reefs in program Maxsurf Resistance


    I hail everyone,

    We shall try to make calculation of a catamaran with program Maxsurf Resistance. Model with length 32,3m is made from Alexander Alexanov from Norway /see jpeg files/ also is published with his consent. Here it is necessary to pay attention to the following reefs:

    Before to test parameters of model with Maxsurf Resistance, in Maxsurf Modeler it is necessary to make the following:

    1. To be convinced that we have in cash only surfaces generating the shell plating of the hull of the starboard. Then we make surfaces symmetrical for the port side.

    2. We test Frame of Reference and Design Grid /see screens /.

    3. It is necessary to fill snug in the table for the Vessel Type in Maxsurf Modeler /see the screen /.

    When we test the model on Maxsurf Resistance it is possible to mark all surfaces. But when it is necessary to mark surfaces participating in calculation on method Slender Body then it is necessary to mark only those surfaces which participate in wetted surfaces of hull, i.e. without the surface of the upper and lower deck and pairing them among themselves.

    It is extremely important to test integrity of the curve of the immersed areas of frames. If in it defects are visible to signify model abnormally is imported to program Maxsurf Resistance /see screen/.

    Let's make some preliminary calculations:

    At LWL = 31,646m and V/2 = 349,99 / 2 = 174,995 m^3 we have slenderness ratio for one hull = 31,646 / (174,995 ^ 1/3) = 5,66 > 4

    If to take slenderness ratio concerning general displacement we shall receive: 31,646 / (349,99^1/3) = 4,49 > 4.

    Outcome of calculation on Maxsurf Resistance:

    For velocity 12kn at FnL = 0,35 and Fnv = 0,743 we shall receive towing resistance 58,1 kN and general nominal /specification/ power = 597,841 kW at efficiency for engine installations of 60 %.

    Let's round on 600 kW. I.e. the power necessary for one engine is not less than 300 kW that the catamaran to reach 12 kn.

    The total power necessary for velocity 16kn at FnL = 0,467 and Fnv = 0,99 at R=272kN is 3732 kW/2x1866~2x1900kW/.

    Wave making is shown for velocity 12kn at vertical exaggeration = 1.


    NA Razmik Baharyan
     

    Attached Files:

  2. Rabah
    Joined: Mar 2014
    Posts: 247
    Likes: 7, Points: 18, Legacy Rep: 50
    Location: Bulgaria

    Rabah Senior Member

    I hail all,

    We go on the subject about the catamaran. It is the second version of the model with a length of 32,3 m, but this time with a bulb. The author of the model too is NA Alexander Alexanov from Norway.

    Let's make preliminary calculations:

    At LWL = 30,497m and V/2 = 348,15 / 2 = 174,075 m^3 we have slenderness ratio for one case = 30,497 / (174,075 ^ 1/3) = 5,46 > 4

    If to take slenderness concerning general displacement we shall receive: 30,497 / (348,15^1/3) = 4,33 > 4.

    Outcome of the calculation on Maxsurf Resistance:

    For velocity 12kn at FnL = 0,357 and FnV = 0,743 we shall receive towing resistance 63,3 kN and general nominal /specification/ power = 650,836 kW at efficiency of engine installations of 60 %.

    Let's round on 650 kW. I.e. the power which is necessary for one engine not less than 325 kW that the catamaran to reach 12kn.

    The total power necessary for velocity 16kn at FnL = 0,476 and FnV = 0,991 at R=276,6kN is 3794,289 kW / ~2x1900kW/.

    The Wave making is shown for velocity 12kn at vertical exaggeration = 1.

    NA Razmik Baharyan
     
  3. Rabah
    Joined: Mar 2014
    Posts: 247
    Likes: 7, Points: 18, Legacy Rep: 50
    Location: Bulgaria

    Rabah Senior Member

    At the preparation for this publication I have noted some inaccuracies and vagueness in the manual of program Maxsurf Resistance. On 26.02.2018 I published them at the forum Bentley Maxsurf:

    <https: // communities.bentley.com/products/offshore/f/maxsurf-moses-sacs-forum/147420/remarked--program-maxsurf-resistance>


    But unfortunately regardless of the fact that it was already 272 times read, nobody has wanted to make what that comments.

    For that I have decided them to publish in the forum Boat Design, hoping that we shall see a brisk controversy primarily from ship-building experts on hydrodynamics.


    I write concerning program Maxsurf Resistance v. 21.11/2017/ as has noted some errors and I want to straighten out some vague problems.

    The remarked errors and vagueness in the manual of the program are following:

    1. On page 55/see attached file/-instead of “DL ratio” it is necessary to write “SL ratio”.

    2. On page 57/see attached file/-for the series 60 and for Delft instead of "LCB" it is necessary to write “LCB / L”.

    3. There are no separately written parameters for method Delft I, II and for method Delft III.

    4. There is not in the program the series Delft IV - there are tests of 9 models.

    5. The series of models Delft from I up to IV concern for round-bilge yachts.

    How to make calculation of resistance and power of model of yachts from one or double chine if remaining parameters correspond to methods Delft?

    What other method can be applied to hard-chine yachts approximately in semi-planing mode?

    6. The program makes calculation on methods for yachts from series Delft only if the ballast keel is disregarded i.e. if to input the model without it, otherwise the program does not take into account the draft of canoe body and the maximum immersed draft and signals that parameters of the yacht are outside of allowable borders.

    7. For the method Savitsky pre-planing /see page 5 and attached file/ - to straighten out the text enclosed with a red line.

    For what outlines this method concerns - for every ones /including round-bilge/ or only for hard-chine /prismatic with bottom deadrise /?

    The problem has arisen as in the specified text is written “planing hull”- for me a hard chine and bottom deadrise is means, i.e. the model have potentials for operation in a gliding mode, but because of different reasons /for example changing of the engine / is necessary to make examination of the possibility to maintain the model in semi-planing or displacement mode.

    Except for that in publication Savitsky - Brown, 1976 the example for application of methods Savitsky pre-planing and Savitsky Planing for a gliding vessel with length LWL = 80ft with prismatic outlines /hard chine, spray rail and deadrise of the bottom/ is shown.

    At position that these two methods are applied for one model with gliding hard-chine outlines for me this example is acknowledgement of the conclusion that method Savitsky pre-planing cannot be applied to not gliding models that for me is equivalent on round-bilge.

    But if to edit the text in the manual on page 5 /enclosed with a red line/ and he looks approximately so:

    „ This algorithm is useful for estimating the resistance of a semi - planing hulls with a round bilge or hard chine and speed corresponding to FnV from 1 to 2 /see page 55/, i.e. its pre-planing resistance”.

    Then I agree that method Savitsky pre-planing can be applied to any outlines.

    But again there is a problem - how to make the resistance calculation of round-bilge vessels with FnV above 2? Likely the answer is only one - on method Lahtiharju /round bilge/ at which FnV = 1,5 - 3,8.

    And more one opinion for upper bound of FnV for high-speed round-bilge models:

    In the book of Russian scientists Egorov I.T., Bun'kov M.M., Sadovnikov Y.M. “Planing ship propulsion and seaworthiness of planning ships” 1978 –on page 106 there is a very important conclusion:

    „ The border of intelligent use of the round-bilge outlines for high-speed boats corresponds to Froude numbers FnV < or = 2,5. At major Froude numbers it is necessary to apply a hard-chine geometric shape. ”

    8. The borders of parameters for method Wyman are not written.

    9. It is not known when it is applied “Holtrop/monohull/” and “Molland/catamaran/” for Form factor.

    10. It is not known at what events what values it is necessary to accept for “vertical exaggeration”.

    11. What methods can be applied for multihull except for Slender Body?

    12. How /on what method / to calculate resistance for multihull in a gliding mode at position that method Slender Body valid only up to FnL ~ 1,0 i.e. if we have FnL> 1,25 or FnV > 3?

    13. On method Slender Body at calculation of slenderness ratio L / (V^1/3) for multihull what displacement should be taken - general or separately for each hull?

    14. How to receive wave making for a gliding vessel /monohull or multihull/, i.e. for FnV > 3 at position that method Slender Body concerns only to vessels with FnL up to ~1,0 or FnV < 2?

    Except for that at gliding we have running trim aft ward, i.e. the bow raised, and on method Slender Body the trim is not taken into account.


    NA Razmik Baharyan

    Rousse - Bulgaria
     

    Attached Files:

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