Dividing hull for frame spacing

Discussion in 'Boat Design' started by rxcomposite, Apr 18, 2023.

  1. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    This was originally developed for dividing the hull into equal parts for Simpsons rule, generating half stations for hull sections, locating a parallel mid body and for a quick check if the frame spacings meet the minimum set by the Rules. This is tedious and repetitive.

    Later, I used it for locating the centroids of each panel to plot the pressure points along the hull length generated by hull pressure formulas. There are different methods available to determine panel pressures/points along the length of the hull. You just use whatever you are comfortable with. I use LR.

    My latest application is using it to plot the pressure points in high speed cored hulls to determine the shear derived to find an appropriate core material. Core shear is determined primarily by pressure, panel geometry, and thickness. With core shear derived, I could pick an appropriate core material. In “Planing Hulls” sheet, I showed the pressure points generated superimposed on a typical chined hull. Pressure is most critical at bow because of Hs wave impact+slamming. It rises almost to the deck level. It is now an aid to hull scantlings.

    The spreadsheet is not sophisticated because it uses the old Excel version for generating sequential numbers/termination/rollover. The newer version has the “sequence” function for generating dynamic arrays. The instructions for tweaking the spreadsheet are included in the “basic + application” page (sheet). Included are the exercises I created to force the spreadsheet to fail. None so far.

    It took a lot of time to make it user friendly and add self explanatory images so that others may benefit.
     

    Attached Files:

    bajansailor and fallguy like this.
  2. bajansailor
    Joined: Oct 2007
    Posts: 3,614
    Likes: 1,574, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    This is baffling - I have Excel on my computer, as part of Microsoft office, so I should be able to open this file.
    But when I click on it, it tells me "This action is only valid for products currently installed".
    But I do have Excel installed.....
    It tells me the same for Excel programs that I already have on the computer - I can't just click on them, rather I have to open them with Excel. And that works ok.
    But I can't do this when it won't allow me to download the file in the first place.
     
  3. wet feet
    Joined: Nov 2004
    Posts: 1,399
    Likes: 435, Points: 83, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    It might be from a more recent version of Excel as Microsoft use the increasingly common tactic of altering file types so that victims customers are obliged to buy or subscribe to the latest flavour.For rather a lot of file types the free Open Office suite will function very well and might be worth investigating.
     
    bajansailor likes this.
  4. bajansailor
    Joined: Oct 2007
    Posts: 3,614
    Likes: 1,574, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    This is strange - even though it told me "This action is only valid for products currently installed", it later changed it's mind, and I found two different versions of RX's spreadsheet downloaded and saved under different names (as I had tried twice, but each time it told me this).
    I still can't just click on an Excel link though - I have to download it first, and then ask Excel to open it.
     
  5. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    Strange also with my file. It says it is not registered but I paid for it. I am using it for 3 years and Microsoft keeps updating. My son had the same source and no problem. He was even able to upgrade to Windows 11 free.

    PM me your email address and I will send the file.
     
  6. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    I have the old version of Excel. I found this out when I could not find the sequence function. I have doubts about upgrading until I find out if I was scammed or not. "The SEQUENCE function is only available with Microsoft 365 subscriptions and Excel 2021. In Excel 2019, Excel 2016 and earlier versions, it does not work since those versions do not support dynamic arrays."

    I have Office 365 an it says "product activated"
     
    Last edited: Apr 18, 2023
  7. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    Stranger still. I viewed my own file in the forum and it says I have to enable it to edit. I was able to download even my own file.
     
  8. Ad Hoc
    Joined: Oct 2008
    Posts: 7,788
    Likes: 1,688, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    There are no minimum spacings per se.
    There are rules where you no longer gain any benefit by reduction of spacings....these are rule limitation (of the parametric based equations) to prevent very thin members or very low moduli results occurring.
    So, it is just a "cut-off" to provide minimum acceptance scantlings.

    Make sure you don't conflate the two separate issues.

    I can see that.
    But too complex for a dumby like me ... :confused:o_O:(
     
  9. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    AH- In the old LR rules for composite construction, the rule states that longitudinals must be supported by bulkheads not more than 2 meters apart and there is a table for stiffener spacings based on length. Now obsolete because the new rule just state that bulkheads must not be more 6 meters apart.

    ISO has a similar rule. The length (l) or span (s) is "l need be taken as >330 x LH, in mm"

    Assuming that the length has been subdivided properly and the span has been determined, the aspect ratio comes in, With AR of 2 or greater, there is no adjustment factor but less than 2 and AR adjustment factor kicks in. This appears both in LR and ISO rule, In cored construction, the AR factor greatly influence the core shear. 2 or greater, no effect (except deflection) but reducing AR reduces core shear stress. A quick and easy way to reduce core shear stress is just to close in the spacing. The skin thickness does not even influence the core shear.

    The practice followed is that in the bow area, it is almost always closely spaced. I haven't compared but maybe reducing AR is a quick fix VS scantling "efficiency". Not familiar also when it comes to steel or alloy design which has a higher modulus than composites.
     
  10. Ad Hoc
    Joined: Oct 2008
    Posts: 7,788
    Likes: 1,688, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Ahh...need to be 100% clear here.
    It is not obsolete, it is referring to different longitudinal structural members.

    LR Pt.8 Ch.3 Sec.4:
    "4.4 Bottom longitudinal stiffeners
    4.4.1 The bottom longitudinals are to be supported by bottom transverse web frames, floors, bulkheads, or other primary structure, generally spaced not more than 2 m apart

    and
    4.5 Bottom longitudinal primary stiffeners
    4.5.1 Bottom longitudinal primary stiffeners are to be supported by bottom deep transverse web frames, floors, bulkheads, or other primary structure, generally spaced not more than 6 m apart"

    You need to clarify whether a basic stiffener, i.e a longitudinal panel stiffer, or a main longitudinal structure, like ER girder.
     
  11. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    It was meant for a broader audience. Not everybody has the experience or the depth of knowledge like you.
     
  12. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    There it is. the spreadsheet does not indicate the specifics, It just guides you where to place the bulkheads(s), primaries, or longis. It is beyond the scope or practicality of the spreadsheet as this is already design. What supports what is up to the designer to arrange. Users must be cautioned. This is not design, just a guide to make intellegient decision and make things easy.
     
  13. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    Let us take specifics for the sake of discussion. In "planing hull" sheet, If I decide to place a collision bulkhead at 6.25 m from the transom, I will be violating the 6 meter LR rule. But since this just a small boat, I will disregard the rule since this is just a fraction of infraction. I need to connect the two "bulkheads" with a primary. A central girder is a primary but too impractical for such a small boat. That means I have a remaining option. Two primary longitudinals that will suppport also the bottom plate. With such a span, the primary longi would show it needs too much depth if the scantling is calculated. To reduce depth, I need to halve the span of the longi. Looking at the spreadsheet, it can be at 3.76 or 4.38 meter. Since this is a small boat, it cannot be a bulkhead or even a partial bulkhead. Needs to be a primary transverse to support the longi. The other subdivisions are just there to guide me where to place the remaining stiffeners (secondaries).

    But this is already design. The spreadsheet just tells me what is available. That is until I decide to rearrange it again to meet the design goal.
     
  14. IngLaTorre
    Joined: May 2023
    Posts: 11
    Likes: 0, Points: 1
    Location: Venezuela

    IngLaTorre Junior Member

    Hello Mr. rxcomposite, warm greetings. The reason for my message is firstly to comment that the Excel material you have published looks very good and useful. I will review it and compare it with my calculations to see if I can start using it from now on to determine bottom pressures. Now, I have a question to see if you (or someone from the community) can help me. I am determining the scantlings for a 13.84m long vessel and I am calculating the transverse section of the longitudinals (Stringer) according to Lloyd's Part 8. Sec 3. 1.16, but I find it very confusing. So, I wonder if you have any simpler and effective method for performing these calculations? Or if there is another simpler regulation to obtain the results (Lloyd's is not mandatory). I have seen that ISO also has its own calculations, but I only find the regulations for vessels under 6m. I would greatly appreciate your insights.

    P.S.: Oh, the vessel is already under construction for the first time, and I want to ensure that its framing is correct.
     

  15. rxcomposite
    Joined: Jan 2005
    Posts: 2,754
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    The first subdivision(s) is for the bulkheads (=<6 m for LR), the second set is for the frames (<=2 m) apart. ISO 12215-6 may have a different rule. Most would just divide evenly from the transom to the first bulkhead in the bow just to make things easy for identifying stations, then half sections in the bow area.

    Now that you have bulkhead/frame spacing you subdivide longitudinally to arrive at the proper Aspect Ratio for the panel. I work around 2:1 or less for composites. Steel or alloy, I see 3:1 or 4:1 ratio.

    The rest of the spreadsheet just shows you the AR ratio and the centroid of the panel just to make things easy to look at a glance.

    Sorry it won't show bottom/side pressures. You need a software or do long hand calculations for that. The pressure I gave are derived examples of a particular craft.

    I also made this for cored composites as it is the more difficult thing to do repeatedly. Works for single skin though.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.