# Iso 12215 stiffener calculation.

Discussion in 'Boat Design' started by Vaboat29, Dec 6, 2023.

1. Joined: Dec 2023
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Location: France

### Vaboat29Junior Member

Hello Everyone,

I am new here and I am working on tre project of designing a plywood motorboat of 6.5m long.

I am trying to go trough the iso 12215-5 (2008) and I am facing difficulties in calculation.

What should I consider for Fd and Md for the stiffener calculation ? I consider that the hull and the stiffener are the same material.

Could some one help ? Maybe it is obvious but to me it's not.

Thanks.

Best regards !

2. Joined: Sep 2011
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### TANSLSenior Member

Welcome to the forum.
The first thing you should do is get the 2019 version of ISO 12215-5 since the 2008 version has been replaced by that other one.
If you insist on using the old version (which is no longer allowed to be used), you will find that chapter 11.5 answers your questions. Fd is calculated by formula (51) and Md by formula (52)

3. Joined: Dec 2023
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### Vaboat29Junior Member

Yes I know, currently I just have the 2008 version but it's planned to get the latest one from 2019.

Okay, to me in the 11.5 it was necessary to have materials which are different to apply formulas (51) and (52). If the stiffener is made from the same material I can use them ? It was not clear to me.

Another problem I am facing is the difficulty to understand where is difference made between longitudinal stiffeners (stringers) and transversal ones (web frames). In my case it's a longitudinally framed boat.

Is it just with the KE0-90 ?

Does the Web frame has to be divided in multiples stiffeners ? (like lu1, lu2, lu3 in figure 11 ?)

4. Joined: Sep 2011
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### TANSLSenior Member

Your doubt regarding different materials is reasonable since normally the layers of a laminate do not differ in their properties by 25%. However, the method proposed for "different" materials is applicable to any type of material, if it consists of several layers, even if all of them have the same properties.
If you only place longitudinal reinforcements, the span between supports of each longitudinal may be too large. On the other hand, transverse reinforcements help give the hull its shape better than longitudinal ones.
I don't know what KE0-90 is, I can't answer.
You can divide the web frame into parts or put it in one piece. In the latter case, you must calculate everything with the maximum pressure at the bottom which will cause the frame in the side areas to be, probably, very oversized.

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