SailNet Community - View Single Post - Interesting Sailboats
 Thread: Interesting Sailboats View Single Post
PCP
Senior Member

Join Date: Dec 2004
Location: Portugal, West Coast
Posts: 16,505
Thanks: 21
Thanked 113 Times in 96 Posts
Rep Power: 13

Quote:
Originally Posted by slap View Post
Paulo -

In a recent post, you gave two different definitions of prismatic coefficient - one was not correct.

This one is incorrect - this one is the definition of block coefficient.

Quote:
Prismatic Coefficient is a mathematical measurement of the relative shape of the bow and stern of the boat. It displays the ratio of the underwater volume of the hull relative to a rectangular block.

And this is the correct one:

Quote:
We express the "full hull" property by the prismatic coefficient, which is the ratio of volume displaced to the product of waterline length and maximum cross-sectional area.

Slap, I was quoting, not giving definitions and both quotes seems correct to me. The problem here is that is difficult to translate mathematical definitions to words.

In fact both the Prismatic coefficient and the block coefficient are ratios to a box or a prismatic figure as you want to put it.

Block Coefficient... If you draw a box around the submerged part of the ship, it is the ratio of the box volume occupied by the ship.

Prismatic Coefficient... It displays the ratio of the immersed volume of the hull to a volume of a prism with equal length to the ship and cross-sectional area equal to the largest underwater section of the hull (midship section).

http://en.wikipedia.org/wiki/Hull_(watercraft)

These drawings explain it clearly:

http://www.marinetechs.com/Definitions,27

The guy you have said that had given an incorrect definition explains it more detailed (and correctly) on the linked text with this figure an comments:

From the diagram, the longitudinal Cp = Volume / (Am x Lpp) Volume = volume of hull at draft T Am = midship section area (at given draft T, in figure) Lpp = length between perpendiculars.

http://nasailor.com/2011/06/05/boat-...c-coefficient/

Regards

Paulo

Last edited by PCP; 10-20-2011 at 09:12 AM.
PCP is offline