Question about scale weight calculation

Discussion in 'IRCWCC' started by acomputerdog, Dec 8, 2019.

  1. acomputerdog

    acomputerdog Member

    Joined:
    May 28, 2016
    Posts:
    12
    Location:
    Chattanooga, TN
    Hello all,
    I have a question about the scale weight data in the IRCWCC shiplist. Is there an equation for calculating the scale weight and max weight from a ships standard and full displacement? I've been working with the data file from the shiplist and I can't seem to figure out how the scale weights are derived. I checked in the rules but there is nothing about how the scale weight is calculated / chosen.

    I tried to work out the ratio with math, but I don't get consistent results. For example, here is the computed ratio of standard displacement to scale weight for a few common ship classes:
    • Bayern: 28000 / 24.160 = 1158.94
    • Bismarck: 40600 / 37.280 = 1089.06
    • Courbet: 23100 / 19.500 = 1184.62
    • North Carolina: 35000 / 35.110 = 996.87
    • Q. Elizabeth: 27470 / 25.540 = 1075.57
    This inconsistency extends to most classes in the shiplist so I assume that the scale weight must be derived in some other way.

    Any help will be greatly appreciated!

    Thanks,
    Chris Koehler
     
  2. absolutek

    absolutek -->> C T D <<--

    Joined:
    Sep 6, 2009
    Posts:
    1,806
    Location:
    Ontario, Canada
    I think John Hunt put together the current list. You may want to ask on the ircwcc mailing list.
     
    acomputerdog likes this.
  3. acomputerdog

    acomputerdog Member

    Joined:
    May 28, 2016
    Posts:
    12
    Location:
    Chattanooga, TN
    Thanks, I'll ask there if I don't get an answer here.
     
  4. Anvil_x

    Anvil_x Well-Known Member

    Joined:
    Nov 4, 2017
    Posts:
    1,222
    Location:
    Park Falls, WI
    The question's been asked a few times pondside while I've been present.

    the shoulder-shrug-while-waiting-for-"BATTLE!!"-to-be-called answer I have heard is that it's a shotgun blast estimate to get the boats to sit at waterline.

    I build wooden boats, so I can't 'float test' my boats beforehand.
    I use the weight on that chart to estimate about how much ballast I need to make room for in my hull. then when she floats the first time with a full combat load, I ballast her out with spare .308 WIN bullets I have laying around (Hard to lose, easy to handle, consistent weight), take notes, and go back to the workshop to epoxy them in place.

    It's by no means a rule that you have to be up to such and such weight for such and such boat. but you cannot exceed the max weight.

    Texas has a weight of 25 pounds with a max of like 27 pounds.
    my Texas floats on the scale waterline at 22 pounds.
    If I had to make TX 25 pounds, she'd be a few hits from sinking. At max weight, she'd be decks awash.

    Definitely ask John if you need something more definitive. Kevin, Tyler, or Bob could also give eloquent answers.
    But unless you have a DD, CL, or SS, float your boat at waterline and you won't really worry about weight.
     
  5. Kevin P.

    Kevin P. Well-Known Member

    Joined:
    Mar 29, 2015
    Posts:
    1,306
    Location:
    Alexandria, VA
    You need to go off full displacement, not standard. The ratio between full displacement and scale weight is 1330 +/- 5. To go from scale to max you add either 10% for class 3 and up, or the greater of 25% or 1 lb for class 2 and below
     
    acomputerdog likes this.
  6. acomputerdog

    acomputerdog Member

    Joined:
    May 28, 2016
    Posts:
    12
    Location:
    Chattanooga, TN
    Thanks so much, this is what I was looking for!
     
  7. Anvil_x

    Anvil_x Well-Known Member

    Joined:
    Nov 4, 2017
    Posts:
    1,222
    Location:
    Park Falls, WI
    Oh good, you're here. excellent.

    Out of curiosity, how was the 1330 +/- 5 ratio derived?
     
  8. Iunnrais

    Iunnrais Active Member

    Joined:
    Jul 11, 2009
    Posts:
    149
    Location:
    Texas
    IRRC, it's long tons divided by the cube of the scale * 2250 (for tons to lbs conversion) and then there's an additional factor to translate the figure from saltwater -> freshwater. It's been almost 20 years since I looked into the exact math and it predates my gmail account. Long tons divided by 1333 is what I was given back in the depths of time and it works quite well.

    Usually takes a bit of research into a specific ship to find the scale weight that the hull prefers. Especially when looking at WWII US battleships vs most Europeans (Italians in particular) due to fuel & feed water not being included in Std. disp*. NC/Sodak had Pacific size tanks where Roma was really only setup for Mediterranean Ops.

    *post 1920 Washington Naval Treaty which standardized how std disp was to be measured. For earlier ships, you really have to dig into the measurement
     
    Last edited: Dec 8, 2019
  9. Anvil_x

    Anvil_x Well-Known Member

    Joined:
    Nov 4, 2017
    Posts:
    1,222
    Location:
    Park Falls, WI
    Thanks for the explanation.