ISO 12215-7 Global Loads Case 5

Did you mean "Since kg is a mass, it can be converted to Newtons or kN force."

 

Not exactly. It is ISO that referred it to a mass expressed in kg. Reading the ISO rule further they referred to "displacement volume VD volume of displacement of the boat that corresponds to the appropriate loading condition, taking the density of water as 1 025 kg/m3 NOTE Displacement volume is expressed in cubic metres."

 

But can be. As explained thru Wiki "In other words, an object with a mass of 1.0 kilogram weighs approximately 9.81 newtons on the surface of the Earth, which is its mass multiplied by the gravitational field strength.|

 

That is, a 1 kg mass weighs 1 kg. Is that correct?

 

In common use, the mass is referred to as its weight. ISO refers to the mLDC as the mass of the boat in loaded condition expressed in kilograms.

Where I am confused is that it is asking it to be expressed in Newtons (or kN) not kGf. Since as stated above, "a mass of 1.0 kilogram weighs approximately 9.81 newtons on the surface of the Earth" and the mass is multiplied by a number, is ISO looking for inertial property (longitudinal force)?

 

I use mLDC in kN and the results obtained seem correct. What worries me now is why it is necessary to select the lesser of two forces, one of which is always less than the other.

 

Because in the example it is a cat so two hulls not one. 1 of the 2 hulls is the lesser assuming it is a symmetrical hull.

I do not know what the formula is used but I have a clue since the boundaries are in g's and is denoted as deceleration. Must be the opposite of vertical acceleration which is also measured in g's.

 

In the case of a trimaran, the mass (or weight) mLDC is compared with the mass (or weight) of a float (see picture in post #1) :

FLT = min (5 mLDC; 5 mFLOAT) (kN)
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But I think it is better to leave it for the moment because we are thinking about the same thing. If at some point I find the explanation for this comparison, I will tell it right away (in case someone, other than me, is interested).

 

Just pick the smaller of the two or three.

 

mLDC is the full load boat mass (or weight) that is always greater than one hull or one float mass (or weight). Hence my doubt.

 

TANSL, for sure this is a mistake in the standard.
But acutally, we have never calculated this case yet. It is only applicable to craft with shord bridgedeck, so we don't care.

Regarding the case itself, I doubt if it is useful, as it does not count acceleration of impact which will depend on speed.

 

Hi,

Officially, there is indeed 2 main questions :
- what is the purpose of this case ? there is no clear indication of speed, which would be a minimum when considering the question of impact.
- what are these numbers & funny formulas...
I have no idea. I ask the question to our national representant on the subject : 3 words.

"No one knows. (But there should be a mistake)"

 

Overview of the current status of the ISO 12215-7

As the European Union has released a new update of the harmonized standards, to be used in application of the Directive 2013/53/UE for small craft, It may be of some use to recall the current status of the part 7, dedicated to multihulls.

ISO 12215:2019 Small craft — Hull construction and scantlings —, Part 7:2020 Scantlings determination of multihulls, chapters 12 & 13, provide load cases and requirements for multihulls to be assessed. Although being absent from the harmonized standard list in application of the Directive 2013/53/UE for Recreational Craft, the part 7 is fully applicable, as an international standard. Yet, the great variety of structural arrangements of multihulls could hardly be covered by a standard whose declared purpose is “to keep structural analysis and scantling as simple as possible”. Although well intentioned, this approach, together with important typos, and a lack of technical background, does not satisfy users, including Notified Body or control officials. As a consequence, this part 7 is officially not being considered by the European Union as a preferred proof of conformity. How long will last this situation ? Probably some times after an official revision of this part, whose schedule is not knows, by now. In the meantime, we keep questionning our national representatives about how to deal with the present situation. Still, no practical answer has been given, but all agree to declare that it is a lack of funding that stopped any early revision process. Considering the continued increase of multihull sales around the globe, could a lack of competence be also hidden behing such an excuse ?


In gold, harmonized standards in application of the Directive 2013/53/UE. In white, obsolete versions. Every craft or craft model, put on the market, should demonstrate their compliance with the requirements of the active standards, or equivalent.. Source : Recreational craft https://single-market-economy.ec.europa.eu/single-market/european-standards/harmonised-standards/recreational-craft_en

 

No surprises there then!!
Utter waste of time and money...especially given the fact there are many other far more suitable options available.
Classic case of ISO extending beyond its reach...and its MO.

 

It would be too much to ask, and it would be somewhat strange, for Directive 2013/53/EU to refer to a regulation that was published in 2019.