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.

  1. linda.vrdoljak
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    linda.vrdoljak Junior Member

    HI guys, I need ISO scantling (12215-5) "report only" thicknes, from SCT or Hullscnat, will pay for it.

    simple monohul, motor yacht not sailng yaht

    boat total 17m (inlc. platform)
    15.18m hul length only (from transom up to nose tip)
    13.03 immersed waterline
    4.66 max beam
    4.5 max beem at waterline
    4.38 max beam at chine
    Hull angle 15*, at 0.4 waterline 19ish*
    displacement no less than 15ton dry, no more than 20ton (max design) for speed
    max speed 35 and 50
    max deept or immersed waterlane, 1m
    D at front 2m, (waterlevel to hull nose)

    design is simmilar to Beneteau 49 GT only 1m longer

    it will be B catergy (offshore)
    I need 2 reports
    1. for 3g (up to 35miles) (2x500hp)
    2. for 6g (up to 50 miles) (2x900hp)

    thanks let me know,


    so I need scantling report,
    1st report for 35mph
    2nd for 50 mph

    thanks
    linda.vrdoljak@gmail.com
     
  2. Alik
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    Alik Senior Member

    One would need to look at structural drawings and laminates of this boat first. There is no point to ask 'scantlings' without this information.
     
  3. gonzo
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    gonzo Senior Member

    What material and method is it going to be built with?
     
  4. linda.vrdoljak
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    linda.vrdoljak Junior Member

    I have cad drawings, side, bottom, elevations with dimensions, even 3d model, but its basic monohul, with longitudinal stiffeners, transverse stiffeners, bulkheads may or may not be the part of transverse stiffener, as Ignacio from SCT said, if stiffeners satisfty the preshure requirement, bulkheads can be all around as needed (walls), if no water tightnes is needed.

    I know for basic engine type (up to 2x500hp) bottom will go in 11.5, sides, 9.5, deck 7.5... since we are going to use better laminates (tested), 300g mat 500-600g roving and so on to satisfy required thickness. I have played with Veritas material and scantling software and know material is important in any of scantling software. It doesn't have to be carbon or crazy bi, tri-ax, just plain report for mat+roving combo, something easy to get.

    its all visible in ISO Hartz report at the end of the document.
    thickness vs hull length

    also, scantling under Lloyd (8666) is done hull length+water length/2, so its calculated for 14.3 on 15.6m monohul, correct me if I'm wrong.

    Thanks for input!
     
  5. linda.vrdoljak
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    linda.vrdoljak Junior Member

    Most of class rules, are calculated in mat and polyester only, I may be wrong... but in ISO report vs other Class Rules they say so.

    I know guys at shipyard (Croatia) did use combo, 300g mat + 500g roving, 18mm hull thickness, 10m working catamaran, pilot-like vessel.


    Let me attach pictures of my boat mold and drawings
     
  6. TANSL
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    TANSL Senior Member

    Although you can use the rules of Classification Societies (I like Lloyd's SSC Rules, it is simple and practical), but I think you'll find advantages using the ISO standard.
    A thickness of 18 mm in the hull of a ship 10 m length seems high unless the speed is great. Determining the scantlings not always done rigorously, which leads to put much extra thickness. Worth calculate the scantlings in detail because a lot of material and labor saving.
    If you think I can help you with anything, email me to exchange information with sufficient confidence.
    Assuming that this is a GRP hull, according to what Alik says, you must know the scheme of laminates you prefer to use, the method of construction (projection, manual, infusion) and the evaluation level of mechanical properties.
     
  7. linda.vrdoljak
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    linda.vrdoljak Junior Member

    Re..

    Fiberglass hul, and fiberglass stiffeners.

    I found hull thickness in 12215 spreadsheet program

    20t @ 35knots = 11.7mm at bottom
    20t @ 50knots = 15mm at bottom

    And materijal plays role 13.3mm in mat, in mat roving combo 11.7mm
    For family type (3.25g) 35knots

    Performance type 50 knots, 16.6mm in mat, and 15mm in mat+roving.

    I have to do more calc,

    Someone told me 11mm less than 1/2" for same boat for 50knots, under Iso, with stiffeners 45x65 apart, I think its to thin... Any ideas?
     
  8. TANSL
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    TANSL Senior Member

    The impression I have, without doing any calculations, there is something wrong. It is illogical to obtain 13.3 mm for mat and 11.7 mm with mat + roving. The difference should be greater. The second variant (50 knots)16.6mm in mat , and 15mm in mat + roving, is even more surprising. On the other hand, is required to study the stress distribution by layers. If you do that study, it is likely that some layers not meet regulatory efforts.
    Have you taken into account the evaluation level for mechanical properties of the material?
    The ISO standard is valid up to 50 knots.
    Forget what people tell you, if it is not based on rigorous calculations. The CE mark, you're likely to get for your ships, depends on compliance with ISO, does not depend on the thickness in your friend's boat. My impression is that 11 mm for 50 knots, is very thin, depending on which areas.
     
  9. Alik
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    Alik Senior Member

    Thickness of bottom will depend on size of panel, i.e. unsupported dimensions of every bottom plate, and its longitudinal location. Thus, structural drawings are needed. Without this, all the discussion is bla-bla-bla nonsense.
     
  10. linda.vrdoljak
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    linda.vrdoljak Junior Member

    For 20t and 35knots, I have calculated 11.7mm minimum bottom thickness, if using 225g mat and 600g roving, same dispacement 20t at 50knots gave me 15mm minimum thickness with same material, planning preshure goes up from from 136 kP to 180 kP if speed is rased 35 - 50knots.

    They use Loyd over here in Croatia (they say so...), and I could not find adequate ISO expert, one told me 11mm is minimum and he will use 45x65 stiffener spacing, not mentioning material composition, not mentioning displacement, and not mentioning most important factor 50knots speed.

    His calculation is even worse since I found more speed needs more hull thickness from 11.7mm 136kP (35knots) to 15mm for 180kP (50knots), this was done in IMCI ICOMA spreadsheet 12215 I found one here on forum I don't have ISO rule book yet, they say to 12m only but its same formula as SCT or hullscant, and up to 24m even in manual they say not over 24m, and 12m and over see your boat register to control building process...

    Is possible to use 11mm if you you have more 45x65cm grillage? I think it maybe ok for regular uner 30 knots, but not for high speed 50knots, I don't understand stiffeners so much...

    but in Loyd handbook up to 24m they told "panel thickness reduction is not allowed".

    Also loyd scantling dimension for pleasure vessel is under (L hul + Lwl)/2 wich for my boat 15.6m hul only goes down to 14.3m "scantling size" (middle of (waterline length + hull length))

    does same measuring regime stands for ISO? if yes than guy who told 11mm with 45x65 may be right

    Becouse, I found ISO vs other Rules (registers) for pleasure crafts and 11mm with stiffer grillage could make sense up to 6G's (with my 20ton boat will be at 65knots).

    I got 4.6G at 20t and 50 knots, so ISO report with 6G's is more than enough.
     

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  11. linda.vrdoljak
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    linda.vrdoljak Junior Member

    left side of rectangle = 14.3 (Lloyd scangling size middle of waterlane and hull length)
    right side of rectangle = 15.6 hull length no platform
    or green line = 17, hull with platform

    left chart, loads at 2,3G for my boat 24knots
    right chart, loads at 6G for my boat at 65knots

    I know 65 is over 50, but arm over heart, Savitsy calculation is not adequate for high speed offshore racing, speeds are way over and still is used as only one to calculate it. So much for speed calculation. ABS offshore racing is done with Savitsky and they hit 200MPH mark, 2x or 2.5X over.
     

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  12. TANSL
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    TANSL Senior Member

    The ISO standards are similar but not the same nor equivalent to the standards of CS. My impression is that the CS lead to greater thicknesses than the ISO, but I can not prove it for all cases (I have only one example in which ISO thickness was 7% less than average thickness). As Alik says, speaking without knowing the boat, is just talk.
    There are two very important things that are required by the ISO standards:
    - Study the stress distribution through the thickness.
    - Take into account the evaluation level for the material.
    Without this, the results of the ISO are not valid. That is, for example:
    - You can have a very large thickness and be invalid.
    - The mechanical properties of the material enters the designer can be reduced to 20%.
    In short, I agree with Alik, we need more data. But even without data, we can provide explanations for you to understand that you must use the ISO standard and, in my opinion, does not take into account what others do with other boats and other regulations.
    As for the values of G or calculations Savitsky, I'm not sure why you need them (speaking about scantlings)
     
  13. Alik
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    Alik Senior Member

    There are differences between CS and ISO.
    - ISO is using lower safety factors, say 2.0 for normal stresses vs 3.33 for bottom in most of CS;
    - design pressure distribution under ISO is different, say higher pressure at FP. Also in ISO design pressure depends on acceleration nCG, so at higher nCG design pressure at stern is taken same as at bow, assuming craft can
    become airborne.This is different from CS.
    - ISO is using different set of strength criteria for composites, say there is no obvious deformation criteria, and also min skin thickness criteria is much lower compared to LR or DNV.
    - there are other issues; it might be close but will not comply 100%. Usually CS results heavier schillings, but...
     
  14. linda.vrdoljak
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    linda.vrdoljak Junior Member

    re

    here is semi-fihisned hull mold we are building, more sanding has to be done, than resurface it with VE and tooling getcoat.

    I understand ISO is "light version" of CS, and 11mm for 50knots at 20t sounds phony to me after I got 16mm for mat and 14.9mm roving mat combo in 12215 spreadshet calc.

    I managed to get under 11mm for 35knots, if more roving is "stuffed in" with 12215 spreadsheet program and it passed the required thicknes for 35knots, 130kP bottom preshure. But again can't go with csm100g and roving1000g either, it need some 300-450 csm to stick roving together.

    I'm trying to do basic info calculation just to see where I stand.
     

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  15. linda.vrdoljak
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    linda.vrdoljak Junior Member

    TANSL, I'm comparing 2 similar boats Benetau 49gt and Pershing 50.1

    both,
    waterlength 12m
    beam 4.3m
    18* deadrise

    Beneteau is 15t, 32knots max (2x400hp)
    Pershing is 19t, 45 knots max (2x900HP)

    ISO 12215 gave me minimum 11.3mm for beneteau @ 130kP bottom preshure
    while Pershing is asking 15.5mm to support 190kP due to 4t more and higher speed.

    The one with 7% less thickness than average was less power or lighter in weight. My guess.

    If I use 15t and 20knots on my, there is no planing presure, it is same as displacement 80kP, and min hull thickness shows 8.7mm? even for B offshore. If swordfish hits us we go down...
     

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