ISO Natrual Stiffener Definition

[willfox]

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

[ABoatGuy]

ISO 12215-5 9.1.6 defines natural stiffeners

[willfox]

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

[Ad Hoc]

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.

[willfox]

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

Will