# Optimize Hull Form with Constant Displacement and Cb

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Greetings.

Hye, i'm new with this software and I'm currently doing final year task on optimizing hull form of fishing vessel. Can anyone give me some guidance to optimize hull form of fishing vessel towards reducing ship resistance with constant displacement and constant center of buoyancy? And which tutorial you prefer me to refer for completing my task?

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Hi Atiyah,

I would recommend that you take a look at the Lackenby (there is also a tutorial "Lackenby Hull Variation"). It is a partially parametric modelling technique that allows you to set both, longitudinal center of buoyancy and prismatic coefficient (and thereby displacement) at the same time.

Best regards,
Heinrich

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Greetings Mr. Heinrich,

I have been discovering several samples and tutorials for ship hull optimization. I'm a little bit confused about the use of delta shift and lackenby. I hope you dont mind to give a little bit explaination about the differences of this two features.

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Hi Atiyah,

the working mechanism ist the same for both (actually, the Lackenby is also a Delta Shift). A function is defined along the ship which defines by how much the geometry is shifted at the respective longitudinal position. As you can imagine, this easily allows to shift the longitudinal center of buoyancy and adjust the displacement. Since this is such a common task in hull design, we offer the Lackenby which allows you to manipulate prismatic coefficient (CP) and longitudinal center of buoyancy (LCB) simultaneously.

So basically, there is no difference except that you can use the Lackenby if this is what you need, or alternatively set up the geometry variation all by yourself through a standard Delta Shift... E.g. you could also use a delta shift to move the design waterline up and down without changing the height of the hull...

A typical scenario of the Lackenby being used in an optimization would be to fix LCB and CP all the while the geometry is modified. This way, you can better compare the different geometry variants on a "fair" level (Otherwise you would often just find that the geometry variant with lowest displacement has lowest resistance, which is usually not what you where looking for...). Also, often times these two measures are fixed constraints, anyways...

Like said, there is a Tutorial that covers the complete setup.

Cheers,
Heinrich

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Thankyou so much for your great explaination Sir.

By the way, do have this files (*picture attach) or any related files regarding hull variation other than in the tutorial ? I only have the manual but not have the files. If you have the files, can you share with me?

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Dear Atiyah,

you are very welcome. About the file you might want to get in touch with my colleague Daehwan Park -- his mail is shown in the screenshot you sent.

Best regards,
Heinrich

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Okay noted, thankyou so much Sir.

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