WATERFARING CRAFT DESIGN SYSTEM
George William Herbert 3-27-91 thru 4-1-91
[note: this entire work is copyright to it's author and may not be used except
for personal use or reproduction. As it eventually is intended for
publication, please don't abuse this early look...thanks]
***notes***
I need to fix table numbering (speed moved to Rating/Evaluation section)
The length table is only partially filled in...
***unix notes***
Some of the tables (and a few lines) are misformatted due to transfer problems.
If you have any questions, ask. (they should be obvious, even if not lined up)
INTRODUCTION
Humaniti's progress in transportation technology has reached a
number of plateaus over the millenia. Currently, the highest reaches of
Imperial technology are found in its starfaring vessels. But these are often
overshadowed in importance by other craft: small craft, atmospheric
vehicles, and sometimes waterfaring craft. As a Naval Architect, I'm proud
to present these rules for designing waterfaring craft in MegaTraveller.
They cover designing displacement-based watercraft, surface and
submersible, including Hydrofoils. For hovercraft and grav vehicles, refer
to the basic design charts.
Waterfaring craft (Ships and Submarines) have a number of
advantages in low (and even mid and high) tech societies: reliability, cost,
and size. While ships may be sunk, much less effort is required to crash an
airplane or grav vehicle. Also, ships with broken engines usually have
plenty of time to fix them. Aircraft tend to just crash... Even the lure of the
sea still remains a pull to some.
These rules are a variation on the Referee's Manual basic
vehicle design system. As a variation, they use the same form and many of
the same elements as the basic system. You must be familliar with the
vehicle design system to use the Waterfaring Vehicles rules.
Note that these rules can just as easily be used for vessels in
Liquid Methane seas, liquid Mercury, or whatever fluid you can find to
want to use. (Refereee's, here's your lead in for 'Methane Pirates of Planet
X...') In non-water seas, the changes for the rules are noted. As a handy
reference, the relative densities for some other possible/common liquids
are listed here (as well as if they are cryogenic):
TABLE 1: Liquid Densities/Specific Gravities
Liquid Hydrogen: 0.07 (Cryo)
Liquid Helium: 0.09 (Cryo)
Peterochemicals (Oils): 0.7 - 1.05
Liquid Methane: 0.28 (Cryo)
Water: 1.0
Mercury: 13.5
Liquid Nitrogen: 0.81 (Cryo)
Liquid Oxygen: 1.14 (Cryo)
Alcohol: 0.8
0. OVERALL DESIGN
Waterfaring ships are designed using a modified version of the
basic craft design rules from the Referee's Manual. The most significant
changes are in the Locomotion section, where the speed of the vessel is
determined, and in the importance of weight. Waterfaring vessels are
usually designed from a weight-critical and volume-secondary standpoint,
different from what most MegaTraveller vehicles emphasize (volume).
Keep this in mind when you're using these rules.
Surface Vessels must always way less than their volume in kL.
Submarines must weigh as much as their volume, when ballasted down.
Anything that weighs more than its volume for any reason sinks to the
bottom of the sea, wherever that sea may be. In non-water seas, multiply
this allowed weight by the specific gravity of the liquid. Archimedes
principle is hard on heavier-than-water vessels.
I hope you enjoy being able to add seafaring vessels to your craft
design reprotoire.
1. HULL DESIGN
Waterfaring vehicles are designed using the normal hull design rules.
The minimum armour rating guidelines are:
Table 2: Minimum Armour
UCP Minimum Armour
50,000+ 24
40,000 22
30,000 20
20,000 18
10,000 16
5,000-9,000 14
1000-4000 12
200-900 10
20-100 8
11-19 6
5-10 4
4- 2
Odd sizes are as usual treated as the next largest size. Hull
extensions (Turrets or Superstructure) are allowed,as are open topped
vehicles, but the stability and length calculations are based on the
unmodified volume.
Submarines use a different formula. A 'Operational Depth' is
chosen, representing the deepest that the submarine is capable of diving
safely. Divide the Operational Depth by 20, multiply this by the world's
surface gravity, and determine what the armour modifier (not rating) is for
that number. The armour rating corresponding to that modifier is the
required armour rating, unless the Surface Ship minimum armour is
greater, in which case the higher value is needed.
(Depth/20) x g = req'd. armour multiplier
Submarines also use different rules for hull extensions.
Submarines are not allowed to be open-topped. They are required to have a
hull extension in the form of ballast tanks, and usually have one for a Sail
(fin sticking up). The ballast tanks percentage must be between 5% and 35%
of the hull volume. This extra volume is unavailable for other purposes.
Sails may be any size up to 10% of the basic hull volume, and add half of
their volume to the interior hull. Both ballast tanks and sails simply
multiply the base hull cost and weight by the added percentage. Ballast
tanks are necessary to allow the submarine to submerge. When surfaced,
the tanks are filled with air to keep the sub at the surface. This added
bouyancy is released when the sub dives. Note that the ballast tank volume
is also the percentage of the pressure hull that may flood without rendering
the submarine unable to surface.
Length for submarines is calculated for the volume of the hull
plus the ballast tanks. Weight for submarines while submerged should be
multiplied by 1 + the ballast tank percentage to account for the added water
in the tanks. In non-water seas, divide the ballast tank volume
requirements by the density.
Waterfaring vehicles may use any hull configuration except
open frame (Config 0) or Irregular (Config 7) or Planetoid (Config 8 and 9).
Immobile bouyant structures may be Irregular configuration if desired, but
are not self-mobile (must be towed). Larger waterfaring vehicles are usually
Box or Needle configuration. Submarines are usually Cylinder or Needle
configurations. Smaller vehicles can also be found that are Wedge and
Cone configurations. Sphere and Dome/Disk configurations are very rare.
A waterfaring vehicle's loaded weight must be smaller than its
volume in kL (exception: submarines). For normal vessels, the mass
should be within the range shown below, for safety and stability. Heavier
vessels have too little freeboard (distance from water level to deck), lighter
ones are too unstable (tend to be top-heavy). For seas that are not water,
divide the fraction shown by the local specific gravity of the fluid being
designed for.
Table 3: Safe Weight to Volume ratios
Min and Max safe loaded weights
UCP (as fraction of volume in kL)
5000+ 0.15 - 0.75
1000+ 0.15 - 0.66
100-999 0.15 - 0.50
25-99 0.15 - 0.45
24- 0.10 - 0.35
In addition, when the hull is selected, the Hull Length and the
Length Speed Factor are determined also.
Hull length (Referred to as 'L') also must be determined. The basic
length is given below for all UCP values. If you want to interpolate, the
basic formula is that hull length is the length of a box with relative
dimentions 8L*1W*1H and a volume of 4/3 the hull displacement.
Configuration and Streamlining modify the length as shown:
Table 4: Streamlinging Length Modifier
Streamlining Length Modifier
Unstreamlined x 0.75
Streamlined x 1.0
Airframe x 1.25
Table 5: Configuration Length Modifier
Configuration Length Modifier
1 Needle/Wedge x 1.25
2 Cone x 0.75
3 Cylinder x 1.0
4 Box x 1.0
5 Sphere x 0.33
6 Dome/Disk x 0.5
Table 6: Volume/Length Table
UCP Length
0.007
0.019
0.037 3.2
0.056
0.074
0.093
0.111 5.0
0.130
0.185
0.25 6.6
0.5
0.75
1.0 10.5
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0 22.5
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0 28.5
25
30
35
40
45
50 38.5
55
60
65
70
75
80
85
90
95
100 48.5
200
300
400
500 83.0
600
700
800
900
1000 105
2000
3000
4000
5000
6000
7000
8000
9000
10000 225
20000
30000
40000
50000 384
60000
70000
80000
90000
100000 484
200000
300000
400000
500000
600000
700000
800000
900000
100000 1,040
2. POWER SUPPLY
Choose any power supply available from the design charts in the
Referee's manual. Note that, as in land-based installations, there is often a
tradeoff bewteen output and reliability made: If you lower the output power
of a powerplant by some factor, the maintenance requirements (and
probability of breakdown) and fuel requirements also decrease by the same
factor. At TL7 and below, powerplants often are seen with effeciencies 10%
or lower than the book values, soley to decrease maintenance costs and
increase safety.
In addition, the Solar Cells system has to take into account that
on planetary surfaces, Night cuts the solar power down to zero. An
alternate source must be provided, or the vessel will drift at night (not
always safe).
A new type of engine is available, the Steam Engine, at TL 3 and
4.
Table 7: New Powerplants
Fuel
TL Description Power Out Price Kl/Hr
3 Basic Steam 0.05 500 0.015
4 Steam Engine 0.10 750 0.015
All steam powerplants weigh 1 ton per Kl and burn hydrocarbon
fuels. At TL3 this is usually coal or wood (solid), requiring 1 crewmember
(stoker) per 10 Kl powerplant (per shift) over and above other crew needs.
Submarines are a special case. While submerged, they may not
in general operate a airbreathing powerplant. At lower tech levels,
Submarines normally install batteries (giving limited endurance
underwater). Fission power sources solve this problem (as do fusion, and
fuel cells, which also require Oxygen as per airless worlds rules).
Submarines also may not operate a Solar Power system while submerged.
3. LOCOMOTION
Surface water vehicles may or may not have a suspension
(hydrofoil), and all water vehicles must have a Transmission (Propellor or
similar system). Using a Hydrofoil suspension changes the nature of the
final Speed calculation and makes the vessel more vulnerable to
catastrophic damage from groundings etc.
Table 8: Contact Based Hydrofoil Suspension
(all values per kL of suspension)
Type Power Weight Price (MCr)
Hyd 0.04 1.5 0.05
Minimum volume of suspension is 5% of vehicle volume. A
hydrofoil syspension is optional.
Table 9: Contact Based Water Transmissions
(all values per Mw of powerplant output)
TL Type Vol. Weight Price(MCr)
3 Paddlewheel 3.0 5.0 0.25
4 Propellor 2.5 2.0 0.25
5 Propellor 2.0 1.0 0.25
6 Propellor 1.5 0.5 0.25
7 Propellor + Elec. 1.0 0.5 0.2
8+ MHD Drive 1.0 0.25 0.15
The TL 3-6 Transmissions are directly connected to the
powerplant. At TL7 and above, the system is an electrical
generation/electric motor system, and the power can be utilized for other
purpses if the craft is not moving at full speed.
This transmission is in one or more units (propellor/shaft or
equiv.). The maximum power per shaft/propellor unit is the square of the
Tech Level in MW. If total installed power is more than this, there must be
as many shafts as the installed propulsive power divided by the TL squared
(round up).
4. COMMUNICATIONS
Communications systems are installed as per the Referee's
Manual. The range required depends on the intended range of the vessel
and the size of the planetary oceans. A good rule of thumb is that a vessel
should be able to communicate all the way across the largest ocean it's
intended to cross.
5. SENSORS AND ELECTRONICS
Sensors are the same as in the Referee's Manual, with the
addition of the Sonar sensor system. Sonar comes in two types,
Active/Passive (pingers and passive sensors) and Passive only (passive
sensors). Active Sonar has the same characteristics as a Radar system, but
with one range band less range. Passive Sonar ***
Table 12: Active/Passive Sonar
Weight in tons by TL
Range 6 7 8 9
Long 0.5 0.01 0.005 0.001
Very Long 2.0 1.0 0.1 0.05
Distant 5.0 2.0 1.0 0.1
V. Distant - 10.0 5.0 1.0
Regional - 25.0 15.0 5.0
Table 13: Passive Sonar
Weight in tons by TL
Range 6 7 8 9
Very Long 0.1 0.05 0.01 0.005
Distant 0.5 0.1 0.05 0.01
V. Distant 1.0 0.5 0.1 0.05
Regional - 10 5 1
Continental- 20 10 5
Table 12&13 notes: Sonars have a power requirement of their
weight in tons. They cost MCr 1.0 x their weight in tons. Volume is the
weight in tons x 2.
In addition, a simple depth sounder or fishfinding sonar
(minimal imaging ability or directionality) is available for one-tenth the
size and cost of a Very Long range sonar of the same TL.
6. WEAPONS
Waterfaring vessels may have any listed weapons installed. In
addition, a new weapon (Torpedoes) are available. At low TL, Guns are
favored, with the emphasis changing to Missiles at TL 7, and somewhat to
Beam Weapons (Lasers) by TL 8 to 9. Waterfaring Craft may mount any
starship (hardpoint) weapons, with the same restrictions as other craft.
***torpedoes***
Note that underwater explosions are naturally tamped by the
surrounding water.
7. SCREENS
All standard screens may be installed. In addition, three new
screening devices are available for sound screening.
Anaechroic Coatings are a passive hull coating available for any
size hull. They reduce the sound signature by x 0.5, and weigh 0.01 ton per
KL of vehicle. They cost MCr 1.0 per ton. Anaechroic Coatings are
available at TL 8; early coatings ( only reduce signature by x 0.75) can be
found at TL 7 for the same size and cost.
Bubble Screens are active equivalents of Anaechroic coatings.
They also reduce the sound signature by x 0.5, and weigh 0.025 ton per KL
of vehicle. They take 0.1 MW power per ton and cost MCr 1.0 per ton. They
are available for any surface ship except hydrofoils at TL7.
Noisemakers are decoy bouys, at lower TL's simply bubble and
sound generators, by TL9 they include sonar jamming electronics. A
noisemaker launcher costs MCr 0.05, takes 0.1 KL volume, and weighs 0.1
ton. Noisemakers are MCr 0.05 each, and require 0.05 KL and weigh 0.05
ton. Noisemaker effectiveness is dependent on TL.
8. BRIDGE
As Referee's Manual. Until TL 8, waterfaring vessels don't
usually use a computer for controlling more than Sensors, Screens, and
Weapons. Also, most vessels don't need more than basic environment,
and never (except Chemical/Biologically sealed) need more life support
than the world's environment demands. Lights and heat usually suffice,
and except for passenger vessels, are usually fitted only to operations areas
(not cargo areas).
9. ACCOMIDATIONS
Waterfaring Craft use the standard accomidations rules.
Subordinate craft may be carried as shown below.
Carrying subordinate craft requires three elements: hangars,
elevators, and a flight deck.
First, there must be hangar space for the vehicles. For grav or
other Referee's manual designs, use the listed subordinate craft volume
requirements. For COACC aircraft, fixed-wing aircraft require 60 KL per ton
of design weight, and folding wing aircraft (and helocopters) require 40 KL
per ton. Other watercraft require the same as Referee's manual listings
(dependent on size), and don't need elevators or a flight deck. Land
Vehicles aldo don't require a flight deck or elevators, but do need some way
of being landed.
Second, there must be elevators to move the vehicles from the
hangar to the flight deck. They are not required for vessels with a less-
than-total flight deck.
A flight deck is where actual flight operations take place. It may
have any area up to (maximum) 0.15 x L^2 (one sixth L squared).
Minimum area is the largest of 20 % of hangar volume (in meters square
per Kiloliter) for the largest helocopter aboard, 15% of hangar volume of
the largest VTOL aircraft aboard, 10% of the hangar volume of the largest
grav vehicle aboard, 100% of the volume of the largest STOL aircraft aboard,
or 200% of the hangar volume of the largest normal takeoff aircraft aboard.
STOL and normal aircraft need that much space to take off and to land. A
single deck area may do both, but not at the same time. Dedicated carrier
ships often have seperate launch and landing facilities for aircraft.
10. FUEL
Evaluate the fuel needs and cargo as per the Referee's Manual.
Normal fuel needs are determined by determining speed at 0.75 max power,
dividing required range by this speed, and multiplying by fuel usage. A
safety factor of 25% is normally added. Some military vessels will have an
endurance requirement in days or weeks rather than required range.
WATERFARING VEHICLE DESIGN EVALUATION
After going over the design carefully, the vehicle Universal Craft
Profile is generated from the design. The UCP for watercraft is slightly
different than for other vehicles, the exceptions being noted below.
CraftID
Watercraft type codes are preceded by 'SW' for Surface
Watercraft or 'SS' for Surface Submersible or submarines.
Hull
List the normal hull data, and additionally include the hull
length.
Power
As normal vehicles
Locomotion
List the power-to-weight ratio and the loaded and unloaded
cruise and maximum speeds. Cruise speed is speed at 0.75 maximum
powerplant output. Speed is determined as shown below.
The speed of a ship depends on its hull length, it's power to weight
ratio, and a factor of how 'fat' (bulky or wide) the vehicle is. The speeds
listed below work for all speeds that watercraft are practical.
The formula for determining speed is:
Speed(kph) = (LF/g) + PWR - (W/L)/50g
For Hydrofoil vehicles, this is
Speed = 2 x PWR - (W/L)/50g
with a minimum resulting speed of twice the hull's LF. Hydrofoils slower
than this cannot get 'foilborne' and lift out of the water.
For submerged Submarines, the formula is
Speed = 2 x (LF/g) + PWR - (W/L)/50g
Definitions:
L=hull length in m
LF=hull Length Speed Factor of the ship (see below)
P=ships' power, in kW (power in MW x 1000)
W=ships' weight in metric tons
PWR=Power Factor, depends on power to weight ratio (see below)
g=local gravity in G's
The Length Speed Factor ('LF') depends on the hull length. It is
tabulated below:
Table 10: Length Speed Factor
Hull Length LF
50+ m L/10
25-49 m 0
15-25 m -3
8-14 m -6
7- m -10
The Power Factor ('PWR') is a direct function of the power to weight
ratio. Multiply its powerplant output (in megawatts) by 1000 to find power
in kW. Divide this by the loaded weight of the ship in metric tons to find
the
power to weight ratio. Look up the corresponding PWR factor on the chart
below.
Table 11: Power Factor
P/W PWR
0.033 2
0.066 4
0.15 6
0.30 8
0.45 10
0.55 12
0.67 14
0.85 16
1.20 18
1.75 20
2.40 22
4.50 24
7.50 26
11.0 28
14.5 30
18.0 32
21.5 34
24.0 36
27.5 38
31.0 40
35.0 42
40.0 44
50.0 50
70.0 60
90.0 70
110.0 80
130.0 90
150.0 100
175.0 110
200.0 120
225.0 130
250.0 140
275.0 150
300.0 160
325.0 170
350.0 180
375.0 190
425.0 200
higher speeds are impossible with floating ships.
Commo
List all installed communications systems.
Sensors
As Referee's Manual, but add Active Sonar Scan, Active Sonar
Pin, and Passive Sonar Scan and Pin (if Sonars are installed).
Active Sonar Scan: Active sonar scan difficulty is listed below:
Table ??: Active Sonar Difficulty
Range of Sonar Difficulty
Long Formidable
V. Long Difficult
Distant Difficult
V. Distant Routine
Regional Routine
Active Sonar Pin: Same difficulty as Active Sonar Scan
Passive Sonar Scan: The difficulty level for locating vehicles
passively with sonar is listed below:
Table xx: Passive Sonar Scan
Sonar Range Difficulty
Long Formidable
V. Long Difficult
Distant Difficult
V. Distant Routine
Regional Routine
Continental Simple
Passive Sonar Pin: Passive Sonar Pin is one level more difficult
than Passive Sonar Scan.
Off
List all weapons as normal, including any Torpedo launchers.
Def
List all defenses, including anaechroic coatings, bubble screens,
and noisemakers (if installed). For computing Defensive DM, Agility is
effectively the top speed in KPH divided by 35 (round up) minus the Target
Size DM (minimum Agility=0).
Control
As normal
Accomm
As normal
Other
Add the AcousticSig signature value to the ratings. The
Acoustic Signature is determined as follows:
Table yy: Acoustic Signature
Power Plant Output AcousticSig
Over 10 MW Strong
1 to 10 MW Moderate
0.1 to 1 MW Minimal
Under 0.1 MW Faint
Anaechroic coatings and bubble screens reduce the effective
Power Plant output for purposes of determining the Acoustic Signature.
SPACECRAFT IN THE WATER
There are several references to using spaceships as submarines
and other watercraft in various places in MegaTraveller. Most importantly,
the safe operational depth must be determined for subsurface operations.
To find this, multiply the armour modifier corresponding to the vehicles'
armour rating by 15, and divide by the local surface gravity. This is the safe
operating depth in meters. A normal starship hull (armour 40) is thus safe
at up to 495 meters depth. (This is slightly less than purpose-built hulls.
Spacecraft, while strong enough, tend to have weakpoints in airlocks and
sensors and turret connections that lessen the safe depth.)
Second most important is determining the operating speed. Due
to excessivly bad hydrodynamic properties, spacecraft use the following
formula to determine in-water speed:
Speed = PWR * 0.5 (surfaced and underwater equal),
with PWR in this case being determined by using the gravitic
power (Grav modules or Thrusters) or Rocket thrust in tons. Other
propulsive systems are nonfunctional underwater.
Note that it's quite possible to exceed the high end of the PWR
system. You may either treat this as a hard limit or extrapolate the table. In
either case, the vehicle has become very, very noisy, and is automatically
detected on every available sonar system (and may be tracked visually on
the surface if submerged). Running at these speeds is usually less subtle
than running on the surface, and to be avoided unless, for instance, there's
a MK 48 torpedo about to test your hull armour's manufacturers guarantee.
(Note that heavyweight torpedoes at TL7, with a 1 ton warhead, will breach
armour 40 and leave a 1-meter plus hole, a fact not lost of several of my
players who tested the high end of this speed range for exactly that reason
once...)
Entering the water is safely done at speeds under 50 KPH. If you
touch down faster than this, the pilot must make a difficult piloting roll
with a negative DM of the speed divided by 50 or suffer damage to the
vehicle.
NOTES
A few random comments about these rules and about
waterfaring vehicles and activities.
Remember that a submarine must weigh as much as its hull
volume in KL to be able to submerge. Several previous forays into
watercraft in MegaTraveller have forgotten this basic fact and designed
unsinkable submarines.
How mush deeper than Operational Depth may a submarine
actually go before it implodes? I've used the US Navy 66% criterion
(Operational Depth is 66% of the calculated crush depth), so theoretically
you can go 50% deeper than operational. Submarines are normally test
dived to 20% deeper than operational. Any further than this and the
referee can start rolling their favorite accident system rolls for hull collapse.
Damaged hulls often will fail at much shallower depths.
SAMPLE WATERCRAFT DESIGNS
TL 8 Guided Missile Destroyer 'Admiral' class
TL 7 Peteroleum Tanker 'Valdez' class
TL 7 Aircraft Carrier 'Gulf' class
.