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Redefining Hull Characteristics for Traveller: The New Era

Something that has bothered me for a while is the treatment of hulls on the Hull Size table (Fire, Fusion & Steel p.11). The assumptions made in the descriptive text do not tally with the figures shown on the table.

The relationship between Rate (tons of displaced liquid hydrogen) and Volume (cubic meters, or kiloliters) is obviously correct, for it assumes a simple equation (Rate × the volume of 1 ton of liquid hydrogen). But beyond this, the table fails.

For example, taking a Rate of 1. Where 1 ton of liquid hydrogen occupies 14 cubic meters gives a total internal volume of, obviously, 14 cubic meters. All of the calculations for material use and so forth are based around a default shell 1cm thick. Thus the length (diameter) of a spherical hull should be equal to the diameter required to produce 14 cubic meters in volume, plus 2cm. The following formulae are required:

V = (4 × pi × r^3)/3, or

r = ((3 × V)/(4 × pi))^(1/3)

where

r is the radius of the sphere (half the diameter)
V is the volume of the sphere
pi is a constant equaling approximately 3.142

Thus the diameter (length) of a sphere required to enclose 14 cubic meters is 2.99m. Adding on the 1cm shell gives a grand total for the length of a spherical hull of 3.01m (rounded).

Therein lies the first problem: the value of L listed for a hull rate of 1 is 3.2m, which would require a hull thickness of 10cm to achieve.

To calculate MV, the diameter of the hull (inclusive of the shell) is fed back into the spherical volume formula, and the enclosed volume is subtracted from the result. Using a diameter of 3.01, MV is thus calculated to be 0.28 cubic meters. If the initial calculation for the diameter of the enclosed hull is rounded from 2.99m to 3m (thus giving an overall value of L of 3.02m), then the value of MV would be 0.4 cubic meters (rounding to one decimal place) - providing the value indicated on the table.

If the given value of L is used, MV comes to 3.16m - a far cry from that listed for MV.

MegaTraveller Compatibility

The MegaTraveller design sequences assume that one ton of liquid hydrogen occupies not 14 cubic meters, but 13.5 cubic meters (a vessel with a UCP hull rating of 100 has an internal volume of 1,350 cubic meters - see the Referee's Manual). For those looking to engender better design compatibility between T:TNE and MT (particularly useful when re-engineering MT equipment under T:NE rules), I suggest using this value of 13.5 cubic meters in place of 14 cubic meters when dealing with FF&S volumes. For simplicity's sake, multiply all volume calculations expressed in terms of liquid hydrogen (including the volume of hydrogen fuel etc.) by 0.96 before applying it to your design.

The Formulaic Approach

Two approaches to the design of hulls can be used: the formulaic approach, providing more accurate results, or the table approach (coupled with interpolation) for a more easily referenced angle.

For the formulaic approach, start with the desired rate of the hull, then apply the following formulae:

Vol = rate × 14 (13.5 if using the MegaTraveller Compatibility suggestion)

L (Hull length) = (2 × ((3 × V)/(4 × pi))^(1/3)) + 0.02

MV = ((4 × pi × (L/2)^3)/3) - V

VehicleMV = MV × 1.7

The Table Approach

This approach follows the same manner as the published FF&S rules, but replace the standard table with that shown below.

Two tables are provided. The first uses 14m T:NE compatibility, the second 13.5m MT compatibility. Vehicle MV is provided as an alternative to the Chassis Size table, FF&S p.17.

HULL SIZE
(1 ton = 14 cubic meters LHYD)
Rate Vol MV L VehicleMV
1 14 0.28 3.01 0.48
2 28 0.45 3.79 0.76
3 42 0.59 4.33 1.00
4 56 0.71 4.77 1.21
5 70 0.82 5.13 1.40
6 84 0.93 5.45 1.58
7 98 1.03 5.74 1.75
8 112 1.13 6.00 1.92
9 126 1.22 6.24 2.07
10 140 1.31 6.46 2.22
15 210 1.71 7.39 2.91
20 280 2.08 8.14 3.53
25 350 2.41 8.76 4.09
30 420 2.72 9.31 4.62
35 490 3.01 9.80 5.12
40 560 3.29 10.25 5.60
45 630 3.56 10.65 6.05
50 700 3.82 11.03 6.49
55 770 4.07 11.39 6.92
60 840 4.31 11.72 7.33
65 910 4.55 12.04 7.73
70 980 4.78 12.34 8.13
75 1,050 5.00 12.63 8.51
80 1,120 5.22 12.90 8.88
85 1,190 5.44 13.17 9.25
90 1,260 5.65 13.42 9.61
95 1,330 5.86 13.66 9.96
100 1,400 6.06 13.90 10.30
200 2,800 9.62 17.50 16.35
300 4,200 12.60 20.04 21.43
400 5,600 15.27 22.05 25.95
500 7,000 17.71 23.75 30.11
600 8,400 20.00 25.24 34.00
700 9,800 22.17 26.57 37.68
800 11,200 24.23 27.78 41.19
900 12,600 26.21 28.89 44.55
1,000 14,000 28.11 29.92 47.79
2,000 28,000 44.62 37.69 75.86
3,000 42,000 58.47 43.14 99.39
4,000 56,000 70.82 47.48 120.40
5,000 70,000 82.18 51.15 139.71
6,000 84,000 92.80 54.35 157.76
7,000 98,000 102.84 57.21 174.83
8,000 112,000 112.42 59.82 191.11
9,000 126,000 121.60 62.21 206.72
10,000 140,000 130.45 64.43 221.76
20,000 280,000 207.06 81.18 352.00
30,000 420,000 271.31 92.92 461.23
40,000 560,000 328.66 102.27 558.73
50,000 700,000 381.38 110.17 648.34
60,000 840,000 430.66 117.07 732.12
70,000 980,000 477.27 123.24 811.36
80,000 1,120,000 521.70 128.85 886.89
90,000 1,260,000 564.31 134.01 959.33
100,000 1,400,000 605.37 138.80 1,029.14
200,000 2,800,000 960.94 174.87 1,633.60
300,000 4,200,000 1,259.17 200.17 2,140.59
400,000 5,600,000 1,525.37 220.32 2,593.12
500,000 7,000,000 1,770.02 237.33 3,009.03
600,000 8,400,000 1,998.77 252.19 3,397.91
700,000 9,800,000 2,215.10 265.49 3,765.66
800,000 11,200,000 2,421.32 277.57 4,116.25
900,000 12,600,000 2,619.10 288.69 4,452.48
1,000,000 14,000,000 2,809.68 299.01 4,776.46

Rate is the displacement of the enclosed volume of the hull, in tons of liquid hydrogen
Vol is the volume of enclosed hull, useable for installation of equipment, in cubic meters
MV is the material volume of the hull's shell, assuming a shell thickness of 1cm, in cubic meters
L is the length of the hull (diameter for spheres), in m
VehicleMV is the material volume of a vehicle's chassis, assuming a MVM of 1.7

HULL SIZE
(1 ton = 13.5 cubic meters LHYD)
Rate Vol MV L VehicleMV
1 13.50 0.28 2.97 0.47
2 27.00 0.44 3.74 0.74
3 40.50 0.57 4.28 0.97
4 54.00 0.69 4.71 1.18
5 67.50 0.81 5.07 1.37
6 81.00 0.91 5.39 1.55
7 94.50 1.01 5.67 1.71
8 108.00 1.10 5.93 1.87
9 121.50 1.19 6.16 2.02
10 135.00 1.28 6.38 2.17
15 202.50 1.67 7.30 2.84
20 270.00 2.03 8.04 3.44
25 337.50 2.35 8.66 3.99
30 405.00 2.65 9.20 4.51
35 472.50 2.94 9.68 5.00
40 540.00 3.21 10.12 5.46
45 607.50 3.48 10.53 5.91
50 675.00 3.73 10.90 6.34
55 742.50 3.97 11.25 6.75
60 810.00 4.21 11.58 7.16
65 877.50 4.44 11.90 7.55
70 945.00 4.67 12.19 7.93
75 1,012.50 4.88 12.48 8.30
80 1,080.00 5.10 12.75 8.67
85 1,147.50 5.31 13.01 9.03
90 1,215.00 5.52 13.26 9.38
95 1,282.50 5.72 13.50 9.72
100 1,350.00 5.92 13.73 10.06
200 2,700.00 9.39 17.29 15.96
300 4,050.00 12.30 19.79 20.91
400 5,400.00 14.90 21.78 25.33
500 6,750.00 17.29 23.46 29.39
600 8,100.00 19.52 24.93 33.19
700 9,450.00 21.64 26.25 36.78
800 10,800.00 23.65 27.44 40.20
900 12,150.00 25.58 28.54 43.49
1,000 13,500.00 27.44 29.56 46.65
2,000 27,000.00 43.55 37.24 74.04
3,000 40,500.00 57.07 42.62 97.01
4,000 54,000.00 69.13 46.91 117.52
5,000 67,500.00 80.21 50.53 136.36
6,000 81,000.00 90.58 53.69 153.98
7,000 94,500.00 100.38 56.52 170.65
8,000 108,000.00 109.72 59.10 186.53
9,000 121,500.00 118.69 61.46 201.77
10,000 135,000.00 127.32 63.66 216.45
20,000 270,000.00 202.10 80.20 343.56
30,000 405,000.00 264.81 91.80 450.18
40,000 540,000.00 320.79 101.04 545.35
50,000 675,000.00 372.24 108.84 632.81
60,000 810,000.00 420.35 115.66 714.59
70,000 945,000.00 465.84 121.76 791.92
80,000 1,080,000.00 509.21 127.30 865.65
90,000 1,215,000.00 550.80 132.39 936.36
100,000 1,350,000.00 590.87 137.13 1,004.49
200,000 2,700,000.00 937.93 172.76 1,594.47
300,000 4,050,000.00 1,229.01 197.76 2,089.32
400,000 5,400,000.00 1,488.83 217.66 2,531.01
500,000 6,750,000.00 1,727.62 234.47 2,936.96
600,000 8,100,000.00 1,950.90 249.16 3,316.52
700,000 9,450,000.00 2,162.04 262.29 3,675.47
800,000 10,800,000.00 2,363.32 274.23 4,017.65
900,000 12,150,000.00 2,556.37 285.21 4,345.83
1,000,000 13,500,000.00 2,742.38 295.40 4,662.05

Rate is the displacement of the enclosed volume of the hull, in tons of liquid hydrogen
Vol is the volume of enclosed hull, useable for installation of equipment, in cubic meters
MV is the material volume of the hull's shell, assuming a shell thickness of 1cm, in cubic meters
L is the length of the hull (diameter for spheres), in m
VehicleMV is the material volume of a vehicle's chassis, assuming a MVM of 1.7

Material Volume & Hull Volume Usage

Because a hull thickness of 1cm has already been taken into consideration, through the formulae and the values on the tables, do not subtract total hull volume from the useable volume of the vessel if the hull has a thickness of 1cm.

Because additional hull plating does not affect a vessel's length, plating is assumed to be added inside the useable volume of the vessel. Calculate the volume occupied by additional plating by working out the total volume of the hull as per the standard FF&S rules, then subtract from this the volume of material required to plate the hull in a 1cm shell (basically, MV hull configuration MVM).