# FREEship and Terminology

Discussion in 'Software' started by AstroTux, Jul 20, 2006.

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### AstroTuxJunior Member

Hi,

(I'm off to the library today to get some books on this kind of thing, so hopefully these kinds of questions will get answered by myself soon!)

In FREEship there is a utility "Lackenby hullform transformation". In there rae terms such as:

Displacement (OK, I got this one! ), however it has current and desired. I'm OK so far...... but I noticed at the bottom there is another calculation: Maximum Displacement. Would the difference between these two values (Max displacement - displacement) be the maximum payload capacity of the hull before the entire hull was submerged and the limit before it is overloaded and the whole lot sinks??

Block coefficient: No idea. Should I be trying to increase or decrease this figure? What is it in reference to?

Prismatic coefficient: No idea. Should I be trying to increase or decrease this figure? What is it in reference to?

Long center of bouyancy: I think I understand what this is, but again, what should I be doing with this to get the best out of the design?

Prismatic coefficient aftship: ???

Prismatic coefficient foreship: ???

Again, I know these are probably questions I should already know the answers to if I want to design my own hull, but right now I need all the help I can get. Thanks!

Best regards,
Robin.

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### yipsterdesigner

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### lewisboatsObsessed Member

Prismatic coefficient is described as how fine the ends are as compared to the midsection... the Cp of a destroyer is say .64 while the Cp of a Barge is .95. 1.00 would be a block.

The foreship and aftship simply give further detail as to how fine the respective ends are. If you have a wide transom and a fine entry, the coeffs will be high and low respectively.

Suggestion: Break out the credit card and hit Amazon for some books...most likely you won't find the ones you need at the library.

Steve

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### terhohalmeBEng Boat Technology

Google "prismatic coefficient" and enjoy! There are plenty of excellent information especially at canoe and kayak sites.

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### bhnautikaSenior Member

AstroTux The Utility “Lackenby hullform transformation” enables you to change your hull shape using this program to do it for you rather than manually. Take for example you have a hull shape with a Cp of .53 and you wont to change it to .56 but leave the displacement, LCB etc the same. You change the Cp to the desired figure and the programme does the rest.

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### petlilyJunior Member

You should consider to give yourself a look on how this Lackenby hullform transformation method was applied for as being shown with many examples in H. Lackenby's paper entitled "On the Systematic Geometrical Variation of Ship Forms", 1950, Transactions, RINA. These hull transofrmation method are very useful for the conceptual design stage since they are based on an existing parent hull shape and a few basic form factors.

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### jrossNew Member

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### marshmatSenior Member

Astrotux- Most of those parameters you ask about don't have "ideal" ranges, per se. Rather, they are clues to the designer as to how a boat will compare against other boats. Cp, for instance, is closely linked with the target cruising speed. LCB has an effect on both speed and seakindliness. Once you know what a vessel is expected to do, how fast it has to go, how much it has to carry, in what conditions- then, with appropriate research, you can define your ideal ranges for the hydrostatic parameters.

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