ISO Natrual Stiffener Definition

Hi there,

Just wondered if anyone knew what the definition of a natrual stiffener was according to ISO rules? I have been looking through 12215-5 and cant see where this is defined. I am designing a yacht with a round bilge but there will obviously be a place where the centerline of the yacht becomes too rounded to be counted as a natrual stiffener. Please help

 

ISO 12215-5 9.1.6 defines natural stiffeners

 

I saw this but is this not just for chined hulls?

 

Will

You need to read it in conjunction with Fig.9 in 9.1.4.3.

Basically a "natural" stiffener is a major change in the transverse section of the hull. If, looking at fig.9, if you extended span "b4" down to the baseline and extended "b1" so they meet, to create a "chine"...is this subtended angle less than 130-150 degrees.

The angle created would be very different from that of the angle between "b1" and "b2".

A natural stiffener in this sense is that where the angle of the two members that are butting together is enough to consider the two members discontinuous. So, if 2 members butted together the angle is just 10 degrees, this is NOT considered discontinuous, therefore the span is the total length of the 2. If the same 2 members butted together and the angle is say 110 degrees, this is sufficient to consider the 2 member discontinuous, i.e. not part of each other. Thus, this would be your span.

That is what fig.10 in 9.1.5 is trying to show.

 

That's great. Thanks so much for your answer and for making it so clear!

Will