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

    re

    Lets do comparison

    Persing 54 vs this
    pershing 54 does 45knots at 26 tons
    I have pershing lines, deadrise and stepps gave some adjustments,

    So lets do weight reduction down to 20 tons (this is max disp, actual is less), same boat will go 52-54knots

    there is more, Alik said deadrise, well this pershing has 15deg, we angle it few deg more, only for stepps to catch air for propper ventilation this is why chine is how it is for venting problem wider = vent opening goes higher, rear part chine less important - stepped, still is high rise angle, this is stepped 3,5m3 less drag per 1m of movment, stepped hull is faster, see PT boats 70 years ago

    Pershing specs,
    Specifications. METRIC Length / overall, : 17.73 m Beam, : 4.65 m, Draft, : 1.25 m, Displacement, : 29.5 t, .

    Displacement is brutal 26-29 tons compared to this one, 30% less weight and stepped hull,

    length and tonage is the same, only with 2x650 gave 40knots, I plan on installing 2-3 Mercruisers 800-1300hp with surface drives, or equivalent diesel, so 1m wider make no difference
     

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  2. rxcomposite
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    rxcomposite Senior Member

    To compare Class Rule against ISO method, this is how I do it. I feed the relevant principal data of linda into LR SSC software and ISO onto a spreadsheet.

    Comparatively, LR shows a higher derived value of bottom pressure 409.6 kN/m2 against 337.8 kN/m2 of ISO. LR defaults to minimum single skin plating thickness of 6.1 mm. while ISO requires 5.41 mm (derived from 2.98 kg/m2 of mass,@ 0.30 Glass content).

    Since the strength of a panel is dictated by its thickness and the boundary of the frames and stiffeners, the panel dimensions that will satisfy the required pressure is chosen.

    Using a 6.4 mm thick of mat and roving combination and a panel size of 220 mm. x 180mm., panel showed no failure at any layer using the classic lamination theory of LR. Though it passes the criteria, scantlings are too impractical.

    To come up with a workable panel size, the LWL (13.0m) was divided evenly into 17 stations and the half breadth into 4 parts giving roughly 650 x 340 mm. panel size after deducting thickness of frame and stiffeners. About 2:1 panel aspect ratio which is ideal.

    LR SSC assigns a slightly higher value to the laminate compared to ISO. It also uses a factor of safety of 3 compared to ISO. This very conservative ratings required a thicker panel of 23.3 mm, 640mm long side, 340 mm. short side, to satisfy a pressure of 408.6 kN/m2.

    ISO computes bottom pressure of 337.8 kN/m2. This is the maximum as ISO requires to limit the dynamic load factor (an input to bottom pressure) to less than 7. As constrained in equation 1 and equation 2, 180.43 kN.m2 is to be used but let us stick to maximum (337.8) in the meantime.

    By feeding the data required into table H1 of ISO (format provided courtesy of Tansl), we obtain the laminate performance. Table H1 is also a form of classic lamination theory and is very similar to LR method. With the same panel size, bottom pressure of 337.8 kN/m2, the required panel thickness is 17.02 mm. The optimum panel size calculated by ISO according to data is 14.0-14.7 mm. By judicious arrangement/placement of each layer, the laminate can be optimized. This is a trick commonly employed by composite designers.

    Thus if you build in accordance with ISO rules, the scantlings will be lighter but with a safety factor of only 2 against LR SSC of 3. You have to be very careful in the analysis.

    If you want to build light, consider using Eglass with Vinyl Ester or epoxy as the rated material properties will increase tremendously. Sandwich construction on sides and deck will also save some weight. Add some local carbon reinforcement but not as skins because you will limit the strain allowed which might require you to increase panel thickness.
     

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  3. linda.vrdoljak
    Joined: Jan 2015
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    linda.vrdoljak Junior Member

    re

    Lady who is doing laminate, gave me this
    ---------------------------------------
    1. csm300 x5 (podwered cloth with iso resin)
    2. quadriaksial 900-300combo, ortho resin
    3. csm300
    4. 2-3
    5. 2-3
    PVC foam ?
    6. 2

    12.8mm, 38% of fiber

    --------------------------------------
    I dont like it to much, to many thin layers to lay, and quadriaksial combo is hard to find and expencive, also nothing better than regular roving laminate I made, I'm not fan on foam either.

    original cad drawing was like this, her laminate didnt pass (, than I made smaller plates 40x60, 45x65, with 5cm or 10cm stiffeners, thas was better, even gave me .13 over minimum at high preshure area mid and bow,

    best plates are 35x xxx it can go 30% less in thickness

    Tansl told me to same some material I could do If at stern I do 10mm, and than next layers I start from mid or any plate asking for thicker

    Also there is 4-5 main bulkheads, with oversizes engine beds going along the hull so mediocare hull and stiffeners is not a problem,

    I would like to add futniture from mid to bow in high preshure area (from 8 to 15m), also collision bulkhead at bow

    I would like to have longitudinal engine beds like sketch and this military boat, along the hull, engines are 1ton each, also it may help overall bending, jumping at rough water I know its overkill but half size would do it.
    My mold 15.6m 4.66wide 20deg at 0.4, my boat model, and laminate this lady made,

    Engine sits right over stepps and is iffy area, so I would "lock" engine beds and stepps area with bulkheads B1 B2 and span longitudinals acorss the hull, half size of the sketch.
     

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  4. rxcomposite
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    rxcomposite Senior Member

    I don't like using quad with ortho resin. Ortho is brittle and has the lowest tensile strength. What is it doing in a high performance boat?

    You need about 1,000 gr/m2 of CSM in the outer layer as a water barrier and print through, so after the initial CSM300 you can jump to 2 xCSM 450. No need to add more.

    Are you using 0/90, +-45 quads? Important to use strength reduction on +-45 fabric as outlined in ISO, DNV, LR, and all CR instructions. If hand laminated, light CSM is needed in between layers of quads. You have it right.

    No problem about steps as long as you keep it single skin area and reinforced 1.5 times panel thickness at bend/corners. Does your steps have ventilating channels? Important for stepped boats. Need internal bulkheads for main longitudinals or engine bed stiffeners whenever it is bisected by steps.
     
  5. linda.vrdoljak
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    linda.vrdoljak Junior Member

    re

    I dont like ortho resin, she mention for stiffeners in ortho (arent stiffeners bending?=cracks), here is her laminate, she didnt tell if is single 90 or 90+45 quadrialksial, I know its combo stiched with csm300, and also she mention powdered csm300 for better bonding, this part is good. Also iso resin in first 5 ply's., and heavy fabrics in ortho, she mention to use only 300 powdered csm in between layers.

    her laminate, and my substitube chart, I may remove wr600 out of mine, and 1000g roving lower to 900g I have read if over 1000g is used - heavy fabrics its hard to impregnate with resin and you end up with airgaps and dry cloth and crakcs, and its possible to separate laminate with scredriver and have dry unweted cloth onlys, so I'm not going over 1000g's in fabric, transl did his with 1700, so I dont think this is smart idea. Also this lady didnt go over 1000g and most important UK pilot boats (safeheaven, here is laminate configuration) all are under 1000g, 900g specific. They even cut roving down to 600g and add 900g on csm, also they opose to use cored hulls. They had iso in first layers, and than I guess orhto afterwards.
    I did go heavy with csm(450) in between layers, just to avoid delamination of dry fiber.

    First boat we are doing by hand with laminate rollers and so on.
    she told to use foam 80kgm before last quadriaks, but lets disrigard it.

    I cut her 16 layers down to 11-12 so faster buildup.

    See how Safeheaven Marine Pilot boats start at 300csm and they hit right up to 900 at 2nd and 3rd ply.

    Is there particular rule for csm thickness in between roving?
    Roving to roving is bad practice if no infusion used. Air gaps. So if yo have 900g rooving is 300g csm good to bond it, or 450g 1/2 of rooving or even more 600g ?
    This lady had 600g 2 plys if 300, for 900g of quadriaksials.

    Safeheaven Marine goes hevay on csm 600-300 combi rov csm, and heav 900g csm.

    Croatian Ship Register, requires certified person to lay laminates, its over 12m. And one told me to use 300csm with 500 roving, so csm to rooving over half in ratio, sam with thus girls laminate.

    But I'm going safeheaven route, fast layup and
    thicker plys.

    What you thick for csm in between layers? Too much is bad, too less is even worse.
     

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  6. rxcomposite
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    rxcomposite Senior Member

    Do not omit laminate from the designed schedule. Remember that with ISO, the safety factor is only 2. You may substitute heavier fiber as long as the total designed thickness is met and you are within the 50% CSM-50% Roving rule, which is the basis for ISO laminate strength.

    The CSM rule is that it is used in the outermost layer first as a water barrier, second to prevent print through. As I have stated, CSM 300 first with 0.3 Glass content, 2X CSM 450 with 0.33 Glass content, then the WR or biax or quad series. If your quad comes with the CSM, you can eliminate the CSM300 in between but you must add extra ply to compensate for lost thickness.

    The CSM in your quad should be laid down face down. This acts as the interface by having a reinforced bond line instead of a pure resin bondline. This integrated CSM is normally 200-230 grams/m2. If there is none, you need to use CSM300 in between.

    I do it a little differently. If you look at the calculated stress in the mid portion in the laminate, you can see that it is very low. I stuff the mid portion of the laminate with the "soft" CSM. Plenty of it to build up bulk quickly. Foam would be best as the forces acting in the middle of the laminate is shear with the upper layer trying to slide past with the lower layer. I do not see the logic of adding foam after the base laminate as your designer adviced. There is no sense to it, The sandwich laminate has to be balanced.

    I have no problem laminating WR against WR as when I do it, it is a continous process,3 shifts/day, about an hour for each layer (tacky dry). If you work on 8 hour shifts with overnight breaks, then a light CSM interface is a must (plus sanding in between coats).

    For the stiffeners, your quad might be too stiff to handle. I start having problem with biax at 450 grams. Hard to bend on corners. Is your stiffeners foam filled or just hollow form?
     
  7. linda.vrdoljak
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    linda.vrdoljak Junior Member

    re

    I'm not going going to omit any layers, only supstitute with wr in same thickness. and substitute numerous 300csm with 450-600, for faster buildup. I have roving for 1.5eura per kg, and qvadriaks cost 6eura per kg. I dont see point of using it at this price point, also like you said 900 is heavy to bend. 1m2 of laminate she made cost to $100, 12.8mm fiberglass thickness, foam price included. I can do better. I need stiffeneres, deck, interior, so I cant pay 400% for "same" cloth.

    And I plan on 300, 2x450, and than wr 900 lets say combined with 450csm, as many is needed to pass.

    if I lower panel size (35 I hope by 70-75, to mach to bulkheads above) I can easy get 30% over minimum required. Would this add to safety factor of 3X if 2x is shown as minimum? its 30% over... it looks like 14mm is with SF 3.0 vs 12 we had before with SF 2.0

    Tansl said to save on thicknes so in aft portion I could satisfy minimum with 8 ply's (of my laminate 12 total vs her 16) and for middle I could start with 9-10-12 layer toward front, to follow calculated thickenss for mid and bow sencion, I left shpreadsheed above and its shows min thickess vs panel size per ISO B 20t, 5o knots.

    I may think about adding more csm mid portion of laminat...

    She added foam I qoute her "EXP PVC can be installed after 3rd quadriax" so she is telling to finish 5 plys in 300 csm, finish 3 with quadriax 300csm inbetween, and add foam before last quadriax?

    If I do this than engine beds would lay on 1 layer or 900+300 qvadriax, and foam uneder? 1 engine is 700-1000kg, I have 2, also bulkheads would crush 1 ply of qvadri over foam...

    I need installer friendy material, stiffeners are together and its going to be real hard to wrap with heavy cloth. I'm thinking 450csm, and 600 rooving, or even 600 roving is overkill for corners you think?, I think is more "loose" than quadri, buit again it depends on how is stiched together some are heavy and lines are 'loose" and I could be bended over egg shaped panel. Hollow or full foam we dont know yet but foam looks attractive to build nice engine beds thorugh the hull, like sketch above. Even for A category iso is showing 15mm min thicknes, and one 20m boat per LLoyd had 25mm and that was wather tight I assume, what is rule for wather tight bulkheads and in this case under the floor, also is any restriction in proportions if bulkheads are cut into rings like on this speed catamaran.

    Stepps are vented and geometry is "correct" as it could be, abount the same as Mercedes AMG hull, taken from Cigarette racing boats, also I looked close on fountains boats, but in aft there will be "virtual keel" to prevent drift, I also used straight spray-stability ralis vs "lifting" ones, this hull has enough lift, and I didnt like how saling boats behave left-right-left right it makes it slower..., so longitudinal course must be line not drifting left&right. I angled venting opening bit toward front to higher above water area when planing to catch air even faster, opening is bit larger so proper ventiling is ensured.

    deadrise Alik, is 4.18m, not much more (1m) from thin speed boats since this full layout, 4.38m that was draft at full 20ton, but planing is 4.18 plus the stepps so 4.18 becomes nothing soon, 3.5m3 less water vs regular monohul for each 1m passed.


    Bulkheads if stepped, here I found something of racing cat. I'm not shure where to put it, engine sits in the middle of stepps, and engine beds shuld be locked with bulkheads-walls in my case.
     

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  8. rxcomposite
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    rxcomposite Senior Member

    Read the volume of "Construction Details" by LR, I think it can be downloaded. There are plenty of design details there that ISO do not cover.
     

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  9. TANSL
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    TANSL Senior Member

    Engineering the structure of a ship is not just calculate the thickness of the panels and modules of inertia of the reinforcements. That is, we can say, the easy part of the process. The first thing to do is define the structure, transverse and longitudinal elements, how are the connections between them, know how to work each of these elements and the type of stresses acting on them. According to all that, the structure will have a "look" or another. Only after knowing all that you can start calculating panels and reinforcements. IMO.
     
  10. rxcomposite
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    rxcomposite Senior Member

    I agree Tansl. That is the easy part. The scantling arrangement has to be defined first, then the dimensions and proportions.

    For example, the engine bed/primary longitudinals aligns with the vertical stiffeners/pillars of the bulkheads that aligns with the primary stiffeners of deck whick forms a "ring" like structure. Then the transverses that will define the panel size. Everything works together like a symphony, everything falling into place.
     
  11. TANSL
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    TANSL Senior Member

    For those who love the design of structures the simile of the "symphony" seems very successful.
     
  12. linda.vrdoljak
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    linda.vrdoljak Junior Member

    re

    here is laminate configuration they gave me,

    I made same laminate in 12215 spreadsheet and it can pass at 45x75 panel size

    but,
    1. why to use foam after 3rd layer?
    2. why to use quadriax material at all, 4x more money over wr in same weight I can get

    and my substitute (or any similar version, we said 2x450 or more), its about the same but half the cost
     

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  13. rxcomposite
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    rxcomposite Senior Member

    With the laminate schedule given by your designer, here is my comment.

    1. The outer layer (the one with 5X CSM) is too thick. Only 5 mm. required. The inner layer needs to be finished with a light CSM. Promotes adhesion when bonding secondary structures (stiffeners, bulkheads, frames).

    2. You need at least 100 kg/m3, 50 mm thick foam core with shear strength greater than 1.1 N/mm2 to pass the shear requirement of core.

    3. Given a panel size of 45 x 75 cm., Pbm of 110 kN.m2, the panel is an excess and is very lightly loaded (almost no stress on skins) even with LR safety factor of 3.

    I am a little uncomfortable with your bottom pressure of 110 @ 50 knots. I am getting 180 kN/m2.

    Personally, I will only use Quadaxial only in catamarans and or square panels configuration. It is very good in twisting of a square or nearly square configuration. At 1:2 panel aspect ratio, the +45-45 fibers are not very efficient. +30-30 would do a better job.

    Also consider that you have a monohull with a rectangular proportion. Most likely, longitudinal bending will dominate rather than torsion. In this case, there will be more 0 degree laminate than 90's and some +45-45 will be there only to absorb some twisting. ISO does not require this computations but Class Rules requires bending/twisting load to be satisfied,
     

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  14. linda.vrdoljak
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    linda.vrdoljak Junior Member

    Q

    Do you think 900csm is to heavy for stiffeners?

    Or should I rather use 450 weight? For easy instalation?

    as you mention biax 600 weight may be hard to bend, and bottom is full of grilage,

    Many times they suggest biax at 45deg in stiffeners.

    But 12215 spreadsheet do well with csm 450 in 4-6 layers, total thicknes of 4-6mm, and I get 1.5 cf so not to bad, 75-50@100

    Higher stiffener the better, also crown should be wide as possible, not overdo larger than base.
     

  15. linda.vrdoljak
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    linda.vrdoljak Junior Member

    Q

    here is pic of the hull, it was hard to install water spray openings but we did it, and I think its considered as "natural stiffener" becouse each spray rail has 135deg corner touching the sides of bottom and openings are 3", 4 rails gives you 8 "naturals stiffeners" @ 1/2" thickness this is rigid stiffener, they say 130-150 is good angle.

    green lines are representing longitudinal stiffeners and sides, and are places between spray-guide railes so they act in harmony, to stiffen the structure even more

    purple lines are natural stiffeners, and what should I do with chine edge?, do I expand last plate all the way up up chine edge black or red arrow?

    now I did up to red, chine - side panel corner,

    panels are 2:1 for the most part,
    with 3 longitudinals stiffeners per half, I couldn't pass at 12mm bottom, now 4 per side can go low as 9mm, the this gives me 1.3 CF
     

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