# Scantling Calculations for high speed light craft

Discussion in 'Boat Design' started by Bhaumik, May 22, 2013.

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### BhaumikNew Member

I am trying to do to Scantling calculations for a 7m high speed catamaran as per the DNV classification society.
Primary aim is to find thickness, spacing of various structural member, Have an autocad design ready.
I went through the classification society rules and only thing i could get out of it were the loads that are actually acting on the catamaran. The material being used for the catamaran are fiber composites.
I could also find out the maximum loads the composite can bear at different places in the ship.
The only problem is I am not able to co-relate both of them as the equations for maximum load is an equation of any variable which are unknown.

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You first go to Part 3. Ch.1 the “design principles, design loads”. There according to your area or operation you select the appropriate “R” notation. Then you go to section.3, B, Twin Hull Loads. Here you establish the bending moments for the global structure.

Then in section 2.C Pressure and Forces you calculate the slamming pressure using the design vertical acceleration values you calculate from section 2 B. Accelerations.

Then loads loads/moments you sue in Pt.3 Ch.4 section5, to calculate the structure for sandwich panels, section 6 of single skins and section 7, for frames/stiffeners. The design pressure values used are those you have calculated in Pt.3 Ch.1

Good luck

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### daiquiriEngineering and Design

AH,

Is there a minimum craft length for the applicability of DNV HSLC Rules? I can't find any reference to an eventual lower limit, but rules of some other Classification Societies' are valid for vessels bigger than a certain length or which carry more than a certain number of passengers, requiring compliance with ISO for smaller craft (for example, RINA RES6 valid for vessels >=16 m, Rules for High-Speed Craft valid for vessels with >=12 passengers)...

By the way, can you please tell me what are the limits of applicability (in a sense of Length, or pax. No.) of the IMO HSC? Thanks.

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Not as far as I am aware. But I generally don't design vessels that small, so never really bothered about a min length applicability.

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### daiquiriEngineering and Design

Ok, thanks. I have appended another question while you were replying, please see my previous post if you don't mind.

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### AlikSenior Member

For 7m craft take ISO12215-5 and use simplified method of scantlings from Annex. Calculations for such craft to DNV cost more than hull structure itself.

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### BhaumikNew Member

Sir but ISO12215-5 rules are not available for free can you provide some links where they can be found

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### daiquiriEngineering and Design

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### T0x1cJunior Member

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### TANSLSenior Member

#### Attached Files:

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Last edited: May 22, 2013
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### tomasSenior Member

That requirement list is overwhelming and understandably, adds cost.

What factors does a boat-builder use to decide whether or not to use the DNV guidelines?
How much discretion if any, is left to the boat-builder?

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### BhaumikNew Member

I tried out your method but the slamming pressure is a function of x and so how do i utilize it, do i need to integrate over the entire hull?
I am second year undergrad naval architecture student so do guide me

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### daiquiriEngineering and Design

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The HSC Code limits are:

1.3.5 This Code, unless expressly provided otherwise, does not apply to:
1 craft of war and troopcraft;
2 craft not propelled by mechanical means;
3 wooden craft of primitive build;
4 pleasure craft not engaged in trade; and
5 fishing craft.

Length has no minimum criterion.

Depends upon your scope. You can have just the midship section and Deck & Profiles only, or you can the whole shooting match. You decide.

Again, the scope is up to you….but if a client expressly wants a fully compliant DNV notation vessel…then yes, it is a lot of work. I tell this to clients everyday and that it shall add approximately 20% to the weight and cost from a”normal” workboat code.

As noted above, it depends what has been “sold” to the client in the vessel’s specification or if a client explicitly expresses to have a fully compliant DNV Classed vessel as part of their SOR.

Please quote rule reference number so I know which formulae you are using. Since so far, you have been far too succinct (but vague) in your postings to know what is being referenced.

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### T0x1cJunior Member

DNV certification is for commercial vessels going 25 knts. No point using it for a 7m. leisure craft.

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