# Need scantling for 17m motor yacht in ISO SCT or Hullscant will pay for it

Discussion in 'Class Societies' started by linda.vrdoljak, Feb 2, 2015.

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### TANSLSenior Member

See attached two files with the results I get for 35 and 50 knots. But I want you to understand that they are calculations for which I had to assume several things I do not know. I hope they will serve as a guide.

#### Attached Files:

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• ###### linda_vrdoljak (50 knots).doc
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110 KB
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### linda.vrdoljakJunior Member

re

so, we have same thickness for both speeds?
I didn't expect that.

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### TANSLSenior Member

You must take my results with much prevention. It is necessary to analyze the boat and building system in detail.
The same thickness is obtained, I guess, because there is a formula, (35), which requires a minimum thickness to the side, no matter how calculated. It is very likely that this is what happens, I have not studied. If the side has a certain thickness, the bottom can not have less. (also possible an error on my part)
Again, do not take my figures as definitive. Furthermore, it should make the layer by layer analysis and I have not done. This analysis may lead to new changes in the composition of the layers.

Last edited: Feb 9, 2015
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### TANSLSenior Member

See laminates with a new layers distribution. Although the thickness may be suitable, the stress distribution in the thickness is not correct.

#### Attached Files:

• ###### Bottom Panel Ply analisys.doc
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### linda.vrdoljakJunior Member

And what is correct schedule of laminates?
What should I tell to architect.

Also if this is so, than pilot boats have same problem, they stuffed 300csm600roving to get the tickness.

How would correct schedule look like?

I dont know any better other than fine mat outside 300-500-500 and fill the rest with roving more and csm less to bond it.

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### TANSLSenior Member

And what is correct schedule of laminates?: That is precisely what needs to be calculated
What should I tell to architect : to calculate laminates schedule

Also if this is so, than pilot boats have same problem, they stuffed 300csm600roving to get the tickness : the pilot boat, I'm sure, has not been calculated in accordance with ISO. The structure of reinforcements is surely stronger than to be applied to your boat. Therefore, you can not deduct their scantlings are not correct.

How would correct schedule look like? : at this time we can not know. You have to calculate it.

I dont know any better other than fine mat outside 300-500-500 and fill the rest with roving more and csm less to bond it. : the same as before. Like I said, I´d put 2 or 3 layers of mat, various tissues and ending with mats.

Perhaps the answers that others have given you in this thread and on the other you started, have made you think that the issue is very simple, but it is not. I tried to tell you and show you that it is not a simple issue and, moreover, Alik explained very well why calculations are different according to ISO or a Classification Society.
There is a very good book by Glen Larson with simple formulas to define the scantlings. 10 or 15 years ago, as there was nothing else, it was a book a must see for all yacht designers. Perhaps you can use it but if your boat must obtain the "CE" marking that book is worthless.

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### linda.vrdoljakJunior Member

It sounds more complicated than it is with selfcertifing spreadsheet and iso 12115 manual we did calculations, and from book similar to yours, iso spreadsheet clearly shows you passed iso requirement or you didn't.

Wasnt iso made up to simplify class rules into express cookbook? For <24m
GL has less reduction 5% vs iso 20% per range of operation but, dont do it in C cat if is iso.

after all, iso vs class rulles is comparable from chart I left at the begining. All I asked was Sct or Hullscant report, to see what is going on vs my calcs.

Same stories I had for cnc mold cutting, and turn out more correct was my way than what expert said, also half of his cnc cut molds was useless to work with. So I would rather stick to what gives me results, and move to next thing.

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### TANSLSenior Member

In my view, the ISO 12215 has not tried to simplify nothing but to give formulas for calculating scantlings of boats that before its publication, it was unclear what had to meet. The ISO 12215-5 has introduced aspects as the type of molding or the "evaluation level" that before were not necessary considering. He has also made obligatory stress analysis layer by layer, which is not a simplification, but quite the opposite. The ISO 12215-5 has introduced more rigor in the calculations which led to many ship designers now do not know where to go. The ISO 12215-5 greatly increases the quality of ships, rigor in the design, and that is not achieved by simplifying things.
I do not know on what basis you say "It sounds more complicated than it is", because I can assure you, it is more complicated, much more, than you think. Just reading the rule, and its understanding requires considerable effort.
Cheers.

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### linda.vrdoljakJunior Member

Re

When iso was represented to the court to become official (brainwashing) they said" less formulas to deal with, is safe, compared to rest 7 class soc, result are close and comparable, model is similar to abs offshore, its closed type you cant miss, it was designed to speed up small craft certification"

Now more complex - even less understandable, this part was hit&miss. (Germans you read? you are familiar with this model overcomplicating things up to the point where its own usability becomes problem)

Einstein said "if you dont know to expain it simple, you dont understand it either" and "make things as simple as possible but not simpler".

Functionaly of it hit&miss.
In general I dont like "european" readings, for fact above.

On contrary I do enjoy Abs, Rina books, esp. Rina guidelines, despite more pages, I wish there is more.

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### merenJunior Member

It´s a work of a couple of days or a week if structrure needs to be optimized for ISO, but stability and other issues like powering walk hand in hand with this, so it´s best that You order this work as whole from some naval architect or institution which can save Your project and give You some more real value and save You financially. What is more depressing than some poor manufacturer "saving" some thousands of or even hondreds of euros in design and fail most fatal way in a some houndreds of thousands worth a project?

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### merenJunior Member

It´s a work of a couple of days or a week if structrure needs to be optimized for ISO, but stability and other issues like powering walk hand in hand with this, so it´s best that You order this work as a whole from some naval architect or institution which can save Your project and give You some more real value. What is more depressing than some poor manufacturer "saving" some thousands of even houdreds of euros in design and fail most fatal way in a some houndreds of thousands worth a project?

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### linda.vrdoljakJunior Member

This is first our first boat, and it should be registred as prototype to test it first... I dont wanna cut material, I even prefear Lloyd High Speed Craft or ABS HSC, or ISO A rank...

This why we included high acceleration 6-10g's into calculation, to cope with high speeds and loads.

Its going to be anything but weak yacht, we dont even bother with ISO inshore type of scantling, 0.6?
Also, for rough see, Pilot boats are the most experienced ones, And this is what I refer as good model.

Some Nordheaven boats have A clasificstion in ISO, with bulkheads and longitudinal stiffeners only, this is what I'm planing to do.

There will be 2 boats "family" type with accelerations at 3Gs this can go under ISO, and 2nd undes RC, high speed craft, 60nm +, 6+ G's just as iso is classifing it, but not under iso.

I found architects, we must work fast to finish "base" model first.

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### TANSLSenior Member

Here is a study a bit more elaborate, for a bottom-bow panel (50 knots). Note that, without knowing details of the structure, one may not take these results as correct.

#### Attached Files:

• ###### RV-50.doc
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### AlikSenior Member

6-10g? Are You kidding? Not common for motor yachts and not even for fast patrol boats. These values are OK for small RIBs with shock absorbing seats.

I think about 3.5g is the upper realistic limit; more than that one has to slow down.

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### SkuaSenior Member

6-10g's is what an F-16 pulls in a 600mph turn!

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